1. Basic principles of the theory of chemical structure A.M. Butlerov
1. Atoms in molecules are connected to each other in a certain sequence according to their valencies. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structure formula).
2. The chemical structure can be determined using chemical methods. (Modern physical methods are also currently used).
3. The properties of substances depend on their chemical structure.
4. Based on the properties of a given substance, one can determine the structure of its molecule, and based on the structure of the molecule, one can predict the properties.
5. Atoms and groups of atoms in a molecule have a mutual influence on each other.
A molecule of an organic compound is a collection of atoms linked in a certain order, usually by covalent bonds. In this case, bonded atoms can differ in electronegativity. Electronegativity values largely determine such important bond characteristics as polarity and strength (energy of formation). In turn, the polarity and strength of bonds in a molecule, to a large extent, determine the ability of the molecule to enter into certain chemical reactions.
The electronegativity of a carbon atom depends on its hybridization state. This is due to the fraction of the s orbital in the hybrid orbital: it is less for sp3 and more for sp2 and sp hybrid atoms.
All the atoms that make up a molecule are interconnected and mutually influenced. This influence is transmitted mainly through a system of covalent bonds, using the so-called electronic effects.
Electronic effects are called shifts in electron density in a molecule under the influence of substituents.
Atoms connected by a polar bond carry partial charges, denoted by the Greek letter delta (d). An atom that “pulls” the electron density of the s-bond in its direction acquires negative charge d-. When considering a pair of atoms linked by a covalent bond, the more electronegative atom is called the electron acceptor. Its s-bond partner will accordingly have an electron density deficit of equal magnitude, i.e. partial positive charge d+ will be called an electron donor.
The shift of electron density along a chain of s-bonds is called the inductive effect and is denoted I.
2. Isomerism- the existence of compounds (mainly organic), identical in elemental composition and molecular weight, but different in physical and chemical properties. Such compounds are called isomers.
Structural isomerism- the result of differences in chemical structure. This type includes:
Isomerism of the carbon skeleton, due to the different order of bonding of carbon atoms. The simplest example- butane CH3-CH2-CH2-CH3 and isobutane (CH3)3CH. Other examples: anthracene and phenanthrene (formulas I and II, respectively), cyclobutane and methylcyclopropane (III and IV).
Valence isomerism - special kind structural isomerism, in which isomers can be converted into each other only through the redistribution of bonds. For example, the valence isomers of benzene (V) are bicyclohexa-2,5-diene (VI, “Dewar benzene”), prismane (VII, “Ladenburg benzene”), and benzvalene (VIII).
Functional group isomerism - Differs in the nature of the functional group; for example, ethanol (CH3-CH2-OH) and dimethyl ether (CH3-O-CH3).
Position isomerism- A type of structural isomerism, characterized by a difference in the position of identical functional groups or double bonds with the same carbon skeleton. Example: 2-chlorobutanoic acid and 4-chlorobutanoic acid.
Enantiomers (optical isomers, mirror isomers) are pairs of optical antipodes - substances characterized by opposite in sign and equal in magnitude rotations of the plane of polarization of light with the identity of all other physical and chemical properties (except for reactions with other optically active substances and physical properties in the chiral environment). A necessary and sufficient reason for the appearance of optical antipodes is that the molecule belongs to one of the following point symmetry groups: Cn, Dn, T, O or I (chirality). Most often we are talking about an asymmetric carbon atom, that is, an atom connected to four different substituents.
3. sp³-hybridization - Occurs when one s and three p orbitals are mixed. Four identical orbitals appear, located relative to each other at tetrahedral angles of 109° 28' (109.47°), length 0.154 nm.
For the carbon atom and other elements of the 2nd period, this process occurs according to the following scheme:
2s + 2px + 2py + 2pz = 4 (2sp3)
Alkanes(saturated hydrocarbons, paraffins, aliphatic compounds) - acyclic hydrocarbons of linear or branched structure, containing only simple bonds and forming a homologous series with the general formula CnH2n+2 .Chemical structure of alkyne(the order of connection of atoms in molecules) of the simplest alkanes - methane, ethane and propane - is shown by their structural formulas given in section 2. From these formulas it is clear that there are two types of chemical bonds in alkanes:
S-S and S-N. Communication S-S is covalent non-polar. S-N connection- covalent weakly polar, because carbon and hydrogen are close in electronegativity
A p-orbital not involved in hybridization, located perpendicular to the plane σ bonds, is used to form π bonds with other atoms. This carbon geometry is characteristic of graphite, phenol, etc.
Bond angle- the angle formed by the directions of chemical bonds emanating from one atom. Knowledge of bond angles is necessary to determine the geometry of molecules. Bond angles depend both on the individual characteristics of the attached atoms and on the hybridization of the atomic orbitals of the central atom. For simple molecules, the bond angle, like other geometric parameters of the molecule, can be calculated using quantum chemistry methods. They are determined experimentally from the values of the moments of inertia of molecules obtained by analyzing their rotational spectra (see Infrared spectroscopy, Molecular spectra, Microwave spectroscopy). The bond angle of complex molecules is determined by diffraction structural analysis methods.
4. sp2-Hybridization (planar-trigonal) One s and two p orbitals mix to form three equivalent sp2 hybrid orbitals located in the same plane at an angle of 120° (highlighted in blue). They can form three σ bonds. The third p-orbital remains unhybridized and is oriented perpendicular to the plane of location of the hybrid orbitals. This p-AO is involved in the formation of a π bond . For elements of the 2nd period, the process of sp2 hybridization occurs according to the following scheme:
2s + 2px + 2py = 3 (2sp2)
The second valence state of the carbon atom. There are organic substances in which the carbon atom is bonded not to four, but to three neighboring atoms, while remaining tetravalent
5. sp-Hybridization (linear) One s and one p orbital mix to form two equal sp orbitals located at an angle of 180, i.e. on one axis. Hybrid sp orbitals are involved in the formation of two σ bonds. The two p-orbitals are not hybridized and are located in mutually perpendicular planes. -Orbitals form two π bonds in compounds.
For elements of the 2nd period, sp-hybridization occurs according to the following scheme:
2s + 2px= 2 (2sp)
2py- and 2pz-AO do not change.
Acetylene— unsaturated hydrocarbon C2H2. Has a triple bond between carbon atoms, belongs to the class of alkynes
The carbon atoms in acetylene are sp-hybridized. They are connected by one or two bonds, max. the densities of which are located in two mutually perpendicular areas, forming a cylindrical. electron density cloud; outside it there are H atoms.
METHYLACETYLENE(propyne, allylene) CH3C=CH. According to chemistry Holy M. is a typical representative of acetylene hydrocarbons. Easily enters into electroph., nucleoph. and radical addition at a triple bond, for example. when interacting with methanol forms methyl isopropenyl ether.
6. Communication types - Metal bond, Covalent bond, Ionic bond, Hydrogen bond
Ionic bond- a strong chemical bond formed between atoms with a large difference in electronegativity, in which the shared electron pair is completely transferred to the atom with a higher electronegativity. An example is the compound CsF, in which the “degree of ionicity” is 97%.
an extreme case of polarization of a polar covalent bond. Formed between a typical metal and non-metal. In this case, the electrons from the metal are completely transferred to the non-metal. Ions are formed.
If a chemical bond is formed between atoms that have a very large difference in electronegativity (EO > 1.7 according to Pauling), then the common electron pair is completely transferred to the atom with a higher EO. The result of this is the formation of a compound of oppositely charged ions.
Covalent bond(atomic bond, homeopolar bond) - a chemical bond formed by the overlap (sharing) of a pair of valence electron clouds. The electron clouds (electrons) that provide communication are called a common electron pair.
A simple covalent bond is formed from two unpaired valence electrons, one from each atom:
As a result of socialization, electrons form a filled energy level. A bond is formed if their total energy at this level is less than in the initial state (and the difference in energy will be nothing more than the bond energy).
Filling of atomic (at the edges) and molecular (in the center) orbitals in the H2 molecule with electrons. The vertical axis corresponds to the energy level, electrons are indicated by arrows reflecting their spins.
According to the theory of molecular orbitals, the overlap of two atomic orbitals leads, in the simplest case, to the formation of two molecular orbitals (MO): a bonding MO and an antibonding (antibonding) MO. The shared electrons are located on the lower energy bonding MO.
7. Alkanes- acyclic hydrocarbons of linear or branched structure, containing only simple bonds and forming a homologous series with the general formula CnH2n+2.
Alkanes are saturated hydrocarbons and contain the maximum possible number of hydrogen atoms. Each carbon atom in alkane molecules is in a state of sp³-hybridization - all 4 hybrid orbitals of the C atom are equal in shape and energy, 4 electron clouds are directed to the vertices of the tetrahedron at angles of 109°28". Due to single bonds between the C atoms, free rotation around carbon bond. The type of carbon bond is σ-bond, the bonds are low-polar and poorly polarizable. The length of the carbon bond is 0.154 nm.
The isomerism of saturated hydrocarbons is due to the simplest type of structural isomerism - isomerism of the carbon skeleton. Homologous difference - -CH2-. Alkanes with more than three carbon atoms have isomers. The number of these isomers increases at a tremendous rate as the number of carbon atoms increases. For alkanes with n = 1...12, the number of isomers is 1, 1, 1, 2, 3, 5, 9, 18, 35, 75, 159, 355.
Nomenclature - Rational. One of the atoms of the carbon chain is selected, it is considered substituted by methane, and the name alkyl1alkyl2alkyl3alkyl4methane is based on it
Receipt. Reduction of halogenated alkanes. Reduction of alcohols. Reduction of carbonyl compounds. Hydrogenation of unsaturated hydrocarbons. Kolbe synthesis. Gasification of solid fuel. Wurtz reaction. Fischer-Tropsch synthesis.
8. Alkanes have low chemical activity. This is explained by the fact that single C-H and C-C bonds are relatively strong and difficult to break.
Radical substitution reactions.
Halogenation of alkanes proceeds through a radical mechanism. To initiate the reaction, the mixture of alkane and halogen must be irradiated with UV light or heated. Methane chlorination does not stop at the stage of obtaining methyl chloride (if equimolar amounts of chlorine and methane are taken), but leads to the formation of all possible substitution products, from methyl chloride to carbon tetrachloride.
Nitration (Konovalov reaction)
Alkanes react with a 10% solution of nitric acid or nitrogen oxide N2O4 in the gas phase to form nitro derivatives:
RH + HNO3 = RNO2 + H2O
All available data point to a free radical mechanism. As a result of the reaction, mixtures of products are formed.
Oxidation reactions. Combustion
The main chemical property of saturated hydrocarbons, which determines their use as fuel, is the combustion reaction. Example:CH4 + 2O2 → CO2 + 2H2O + Q
In case of lack of oxygen, carbon dioxide is produced instead carbon monoxide or coal (depending on oxygen concentration).
In general, the combustion reaction equation for any hydrocarbon, CxHy, can be written as follows: CxHy + (x + 0.5y)O2 → xCO2 + 0.5yH2O
Catalytic oxidation
Alcohols, aldehydes, and carboxylic acids can be formed.
Thermal transformations of alkanes. Decomposition
Decomposition reactions occur only under the influence of high temperatures. An increase in temperature leads to the rupture of carbon bonds and the formation of free radicals.
Examples: CH4 → C + 2H2 (t > 1000 °C); C2H6 → 2C + 3H2
Cracking
When heated above 500 °C, alkanes undergo pyrolytic decomposition to form a complex mixture of products, the composition and ratio of which depend on the temperature and reaction time.
Dehydrogenation
Alkene formation and hydrogen evolution
Flow conditions: 400 - 600 °C, catalysts - Pt, Ni, Al2O3, Cr2O3;C2H6 → C2H4 + H2
Isomerization - Under the influence of a catalyst (for example, AlCl3), alkane isomerization occurs, for example:
butane (C4H10) interacting with aluminum chloride (AlCl3) is converted from n-butane to 2-methylpropane.
Methane conversion
CH4 + H2O → CO + H2 - Ni catalyst ("CO + H2" "syngas")
Alkanes do not interact with potassium permanganate (KMnO4) and bromine water (Br2).
9.Alkenes(otherwise olefins or ethylene hydrocarbons) are acyclic unsaturated hydrocarbons containing one double bond between carbon atoms, forming a homologous series with the general formula CnH2n. The carbon atoms at the double bond are in a state of sp² hybridization and have a bond angle of 120°. The simplest alkene is ethene (C2H4). According to the IUPAC nomenclature, the names of alkenes are formed from the names of the corresponding alkanes by replacing the suffix “-ane” with “-ene”; The position of the double bond is indicated by an Arabic numeral.
Alkenes with more than three carbon atoms have isomers. Alkenes are characterized by isomerism of the carbon skeleton, double bond positions, interclass and spatial. ethene (ethylene) C2H4, propene C3H6, butene C4H8, pentene C5H10, hexene C6H12,
Methods for obtaining alkenes - The main industrial method for producing alkenes is the catalytic and high-temperature cracking of oil and natural gas hydrocarbons. To produce lower alkenes, the dehydration reaction of the corresponding alcohols is also used.
In laboratory practice, the method of dehydration of alcohols in the presence of strong mineral acids, dehydrohalogenation and dehalogenation of the corresponding halogen derivatives is usually used; syntheses by Hoffmann, Chugaev, Wittig and Cope.
10. Chemical properties of alkenes Alkenes are chemically active. Their chemical properties are largely determined by the presence of a double bond. The most common reactions for alkenes are electrophilic addition and radical addition reactions. Nucleophilic addition reactions usually require the presence of a strong nucleophile and are not typical for alkenes.
Alkenes are also characterized by cycloaddition and metathesis reactions.
Alkenes easily undergo oxidation reactions, are hydrogenated by strong reducing agents or hydrogen under the action of catalysts to alkanes, and are also capable of allylic radical substitution.
Electrophilic addition reactions. In these reactions, the attacking particle is an electrophile. Main article: Electrophilic addition reactions
Halogenation of alkenes, taking place in the absence of radical reaction initiators, is a typical electrophilic addition reaction. It is carried out in an environment of non-polar inert solvents (for example: CCl4):
The halogenation reaction is stereospecific—addition occurs on opposite sides relative to the plane of the alkene molecule
Hydrohalogenation. Electrophilic addition of hydrogen halides to alkenes occurs according to Markovnikov’s rule:
Hydroboration. The addition occurs in multisteps with the formation of an intermediate cyclic activated complex, and the addition of boron occurs contrary to Markovnikov's rule - to the most hydrogenated carbon atom
Hydration. The addition of water to alkenes occurs in the presence of sulfuric acid
Alkylation. Addition of alkanes to alkenes in the presence of an acid catalyst (HF or H2SO4) at low temperatures results in the formation of a hydrocarbon with a higher molecular weight and is often used in industry
11. Alkynes(otherwise acetylene hydrocarbons) are hydrocarbons containing a triple bond between carbon atoms, with the general formula CnH2n-2. The carbon atoms at the triple bond are in a state of sp-hybridization.
Alkynes are characterized by addition reactions. Unlike alkenes, which undergo electrophilic addition reactions, alkynes can also undergo nucleophilic addition reactions. This is due to the significant s-character of the bond and, as a consequence, the increased electronegativity of the carbon atom. In addition, the high mobility of the hydrogen atom at the triple bond determines the acidic properties of alkynes in substitution reactions.
Main industrial method of obtaining acetylene is electro- or thermal cracking of methane, pyrolysis of natural gas and carbide method
12. DIENE HYDROCARBONS(dienes), unsaturated hydrocarbons with two double bonds. Alifatich. dienes СnН2n_2 called alkadienes, alicyclic СnН2n_4 - cycloalkadienes. The article discusses diene hydrocarbons with conjugated double bonds [conjugated dienes; see table]. Dienes with isolated double bonds according to chemistry. Holy to you in the main no different from olefins. About connection with cumulated double bonds, see Allens. In diene hydrocarbons, all four carbon atoms of the conjugated system have sp2 hybridization and lie in the same plane. Four p-electrons (one from each carbon atom) combine to form four p-molecular orbitals (two bonding - occupied and two antibonding - free), of which only the lowest is delocalized over all carbon atoms. Partial delocalization of p-electrons causes the conjugation effect, manifested in a decrease in the energy of the system (by 13-17 kJ/mol compared to a system of isolated double bonds), equalization of interatomic distances: double bonds are slightly longer (0.135 nm), and single bonds are shorter (0.146 nm) than in molecules without conjugation (0.133 and 0.154 nm, respectively), increased polarizability, exaltation of molecular refraction, etc. physical. effects. Diene hydrocarbons exist in two conformations that transform into each other, with the s-trans form being more stable
13. Alcohols are compounds containing one or more hydroxyl groups. According to their number, alcohols are divided into monohydric, diatomic, triatomic, etc. Bond lengths and bond angles in methyl alcohol.
For alcohols, there are several ways to name them. In modern IUPAC nomenclature, the ending "ol" is added to the name of the hydrocarbon for the name of alcohol. The longest chain containing the OH functional group is numbered from the end to which the hydroxyl group is closest, and the substituents are designated in a prefix.
Receipt. Hydration of alkenes. When alkenes react with dilute aqueous solutions of acids, the main product is alcohol.
Hydroxymercuration-demercuration of alkenes. This reaction is not accompanied by rearrangements and leads to the formation of individual alcohols. The direction of the reaction corresponds to Markovnikov's rule; the reaction is carried out under mild conditions with yields close to quantitative.
Hydroboration of alkenes and subsequent oxidation boranes with a solution of hydrogen peroxide in an alkaline medium ultimately leads to the anti-Markovnikov product of the addition of water to the double bond.
Reduction of aldehydes and ketones with lithium aluminum hydride or sodium borohydride
LiAlH4 and NaBH4 reduce aldehydes to primary alcohols, and ketones to secondary ones, and sodium borohydride is preferable due to its greater safety in handling: it can even be used in aqueous and alcohol solutions. Lithium aluminum hydride reacts explosively with water and alcohol and decomposes explosively when heated above 120° in a dry state.
Reduction of esters and carboxylic acids to primary alcohols. Primary alcohols are formed by the reduction of esters and carboxylic acids with lithium aluminum hydride in ether or THF. The method of reducing esters with lithium aluminum hydride is especially convenient from a preparative point of view. It should be noted that sodium borohydride does not reduce the ester and carboxyl groups. This allows selective reduction of the carbonyl group with NaBH4 in the presence of ester and carboxyl groups. Recovery product yields are rarely below 80%. Lithium borohydride, unlike NaBH4, reduces esters to primary alcohols.
14. Polyhydric alcohols. Glycerol- a chemical compound with the formula HOCH2CH(OH)-CH2OH or C3H5(OH)3. The simplest representative of trihydric alcohols. It is a viscous transparent liquid. Easily formed by the hydrolysis of natural (vegetable or animal) fats and oils (triglycerides), it was first obtained by Karl Scheele in 1779 during the saponification of fats.
Physical properties. Glycerol- a colorless, viscous, hygroscopic liquid, infinitely soluble in water. It tastes sweet, which is why it got its name (glycos - sweet). It dissolves many substances well.
Chemical properties glycerol are typical for polyhydric alcohols. The interaction of glycerol with hydrogen halides or phosphorus halides leads to the formation of mono- and dihalohydrins. Glycerin is esterified with carbonic and mineral acids with the formation of the corresponding esters. Thus, with nitric acid, glycerin forms trinitrate - nitroglycerin (obtained in 1847 by Ascanio Sobrero), which is currently used in the production of smokeless gunpowder.
When dehydrated it forms acrolein:
HOCH2CH(OH)-CH2OH H2C=CH-CHO + 2 H2O,
Ethylene glycol, HO—CH2—CH2—OH is the simplest representative of polyhydric alcohols. When purified, it is a clear, colorless liquid with a slightly oily consistency. It is odorless and has a sweetish taste. Toxic. Ingestion of ethylene glycol or its solutions can lead to irreversible changes in the body and death.
In industry, ethylene glycol obtained by hydration ethylene oxide at 10 atm and 190-200°C or at 1 atm and 50-100°C in the presence of 0.1-0.5% sulfuric (or phosphoric) acid, reaching 90% yield. The by-products are diethylene glycol, triethylene glycol and a small amount of higher polymer homologues of ethylene glycol.
15. Aldehydes- alcohol devoid of hydrogen; organic compounds containing a carbonyl group (C=O) with one substituent.
Aldehydes and ketones are very similar, the difference is that the latter have two substituents on the carbonyl group. Polarization of the carbon-oxygen double bond according to the principle of mesomeric conjugation allows us to write the following resonance structures:
This separation of charges is confirmed by physical methods research and largely determines the reactivity of aldehydes as pronounced electrophiles. In general, the chemical properties of aldehydes are similar to ketones, however, aldehydes exhibit greater activity, which is associated with greater bond polarization. In addition, aldehydes are characterized by reactions that are not characteristic of ketones, for example, hydration in an aqueous solution: in methanal, due to even greater polarization, the bond is complete, and in other aldehydes it is partial:
RC(O)H → RC(OH)2H, where R is H, any alkyl or aryl radical.
The simplest aldehydes have a sharp, characteristic odor (for example, benzaldehyde has the odor of almonds).
Under the influence of hydroxylamine they are converted into oximes: CH3CHO + NH2OH = CH3C(=NOH)H + H2O
Formaldehyde (from Latin formica - ant), formic aldehyde, CH2O, the first member of the homologous series of aliphatic aldehydes; colorless gas with a pungent odor, highly soluble in water and alcohol, boiling point - 19 °C. In industry, phosphorus is produced by the oxidation of methyl alcohol or methane with atmospheric oxygen. F. easily polymerizes (especially at temperatures up to 100 ° C), so it is stored, transported and used mainly in the form of formaldehyde and solid low-molecular polymers - trioxane (see Trioxymethylene) and paraform (see Paraformaldehyde).
F. is very reactive; many of its reactions underlie industrial methods for obtaining a number of important products. Thus, when interacting with ammonia, F. forms urotropine (see Hexamethylenetetramine), with urea - urea-formaldehyde resins, with melamine - melamine-formaldehyde resins, with phenols - phenol-formaldehyde resins (see Phenol-formaldehyde resins), with phenol - and naphthalene sulfonic acids - tanning agents, with ketene - b-propiolactone. F. is also used to produce polyvinylformal (see Polyvinyl acetals), isoprene, pentaerythritol, medicinal substances, dyes, for tanning leather, and as a disinfectant and deodorizing agent. By polymerizing polyformaldehyde, polyformaldehyde is obtained. F. is toxic; maximum permissible concentration in air is 0.001 mg/l.
Acetaldehyde, acetaldehyde, CH3CHO, an organic compound, colorless liquid with a pungent odor; boiling point 20.8°C. Melting point - 124 ° C, density 783 kg / m3 ", miscible in all respects with water, alcohol, ether. A. has all the typical properties of aldehydes. In the presence of mineral acids, it polymerizes into liquid trimeric paraldehyde (CH3CHO)3 and crystalline tetrameric metaldehyde (CH3CHO) 4. When both polymers are heated in the presence of sulfuric acid, A is released.
One of the main long-known ways to get A. consists of adding water to acetylene in the presence of mercury salts at a temperature of about 95°C
16. Ketones- these are organic substances in the molecules of which the carbonyl group is associated with two hydrocarbon radicals.
The general formula of ketones is R1-CO-R2. Among other carbonyl compounds, the presence in ketones of precisely two carbon atoms directly bonded to the carbonyl group distinguishes them from carboxylic acids and their derivatives, as well as aldehydes.
Physical properties. Ketones are volatile liquids or fusible solids that mix well with water. The impossibility of forming intermolecular hydrogen bonds causes their volatility to be slightly greater than that of alcohols and carboxylic acids with the same molecular weight.
Synthesis methods. Oxidation of secondary alcohols.
From tertiary peroxoethers by Krige rearrangement.
Cycloketones can be prepared by Ružička's cyclization.
Aromatic ketones can be prepared by the Friedel-Crafts reaction
Chemical properties. There are three main types of ketone reactions.
The first is associated with a nucleophilic attack on the carbon atom of the carbonyl group. For example, the interaction of ketones with cyanide anion or organometallic compounds. The same type (nucleophilic addition) includes the interaction of a carbonyl group with alcohols, leading to acetals and hemiacetals.
Interaction with alcohols:
CH3COCH3 + 2C2H5OH → C2H5—O—C(CH3)2—O—C2H5
with Grignard reagents:
C2H5—C(O)—C2H5 + C2H5MgI → (C2H5)3OMgI → (C2H5)3OH, tertiary alcohol. Reactions with aldehydes, and especially with methanal, are noticeably more active, with secondary alcohols being formed with aldehydes, and primary alcohols with methanal.
Ketones also react with nitrogenous bases, for example, with ammonia and primary amines to form imines:
CH3—C(O)—CH3 + CH3NH2 → CH3—C(N—CH3)—CH3 + H2O
The second type of reaction is the deprotonation of the beta carbon atom relative to the carbonyl group. The resulting carbanion is stabilized due to conjugation with the carbonyl group, the ease of proton removal increases, therefore carbonyl compounds are relatively strong CH acids.
The third is the coordination of electrophiles at the lone pair of the oxygen atom, for example, Lewis acids such as AlCl3
A separate type of reaction includes the reduction of ketones - Leuckart reduction with yields close to quantitative.
17.compare questions 15 and 16.
18. Monobasic saturated carboxylic acids(monobasic saturated carboxylic acids) - carboxylic acids in which a saturated hydrocarbon radical is connected to one carboxyl group -COOH. They all have the general formula СnH2n+1COOH, where n = 0, 1, 2, ...
Nomenclature. The systematic names of monobasic saturated carboxylic acids are given by the name of the corresponding alkane with the addition of the suffix -ova and the word acid.
Skeletal isomerism in the hydrocarbon radical manifests itself, starting with butanoic acid, which has two isomers:
CH3-CH2-CH2-COOH n-butanoic acid; CH3-CH(CH3)-COOH 2-methylpropanoic acid.
Interclass isomerism appears starting with acetic acid:
CH3-COOH acetic acid; H-COO-CH3 methyl formate (methyl ester of formic acid); HO-CH2-COH hydroxyethanal (hydroxyacetic aldehyde); HO-CHO-CH2 hydroxyethylene oxide.
19. Esters- organic compounds, derivatives of carboxylic or mineral acids, in which the hydroxyl group -OH of the acidic function is replaced by an alcohol residue. They differ from ethers, in which two hydrocarbon radicals are connected by an oxygen atom (R1-O-R2).
Fats, or triglycerides- natural organic compounds, complete esters of glycerol and monobasic fatty acids; belong to the class of lipids. Along with carbohydrates and proteins, fats are one of the main components of the cells of animals, plants and microorganisms. Liquid fats of vegetable origin are usually called oils, just like butter.
Carbonic acids- Class organic compounds, whose molecules contain one or more functional carboxyl groups -COOH. The acidic properties are due to the fact that this group can abstract a proton relatively easily. With rare exceptions, carboxylic acids are weak. For example, acetic acid CH3COOH has an acidity constant of 1.75·10−5. Di- and tricarboxylic acids are stronger than monocarboxylic acids.
Fat is a good heat insulator, so in many warm-blooded animals it is deposited in the subcutaneous adipose tissue, reducing heat loss. A particularly thick subcutaneous fat layer is characteristic of aquatic mammals (whales, walruses, etc.). At the same time, in animals living in hot climates (camels, jerboas), fat reserves are deposited for
Structural function
Phospholipids form the basis of the bilayer cell membranes, cholesterol - regulators of membrane fluidity. In archaea, the membranes contain derivatives of isoprenoid hydrocarbons. Waxes form a cuticle on the surface of above-ground organs (leaves and young shoots) of plants. They are also produced by many insects (for example, bees build honeycombs from them, and scale insects and scale insects form protective covers).
Regulatory
Vitamins - lipids (A, D, E)
Hormonal (steroids, eicosanoids, prostaglandins, etc.)
Cofactors (dolichol)
Signaling molecules (diglycerides, jasmonic acid; MP3 cascade)
Protective (shock-absorbing)
A thick layer of fat protects internal organs many animals from damage due to impacts (for example, sea lions weighing up to a ton can jump onto a rocky shore from cliffs 4-5 m high).
20-21-22. Monobasic unsaturated acids- derivatives of unsaturated hydrocarbons in which one hydrogen atom is replaced by a carboxyl group.
Nomenclature, isomerism. In the group of unsaturated acids, the empirical names most often used are: CH2=CH-COOH - acrylic (propenoic) acid, CH2=C(CH3)-COOH - methacrylic (2-methylpropenoic) acid. Isomerism in the group of unsaturated monobasic acids is associated with:
a) isomerism of the carbon skeleton; b) the position of the double bond; c) cis-trans isomerism.
Methods of obtaining.1. Dehydrohalogenation of halogenated acids:
CH3-CH2-CHCl-COOH ---KOH(conc)---> CH3-CH=CH-COOH
2. Dehydration of hydroxy acids: HO-CH2-CH2-COOH -> CH2=CH-COOH
Physical properties. Lower unsaturated acids are water-soluble liquids with a strong pungent odor; higher - solid, water-insoluble, odorless substances.
Chemical properties unsaturated carboxylic acids are due to both the properties of the carboxyl group and the properties of the double bond. Acids with a double bond located close to the carboxyl group - alpha, beta-unsaturated acids - have specific properties. In these acids, the addition of hydrogen halides and hydration go against Markovnikov’s rule: CH2 = CH-COOH + HBr -> CH2Br-CH2-COOH
With careful oxidation, dihydroxy acids are formed: CH2 = CH-COOH + [O] + H20 -> HO-CH2-CH(OH)-COOH
During vigorous oxidation, the double bond is broken and a mixture is formed different products, from which the position of the double bond can be determined. Oleic acid C17H33COOH is one of the most important higher unsaturated acids. It is a colorless liquid that hardens when cold. Its structural formula: CH3-(CH2)7-CH=CH-(CH2)7-COOH.
23. Dibasic saturated carboxylic acids(dibasic saturated carboxylic acids) - carboxylic acids in which a saturated hydrocarbon radical is connected to two carboxyl groups -COOH. They all have the general formula HOOC(CH2)nCOOH, where n = 0, 1, 2, ...
Nomenclature. The systematic names of dibasic saturated carboxylic acids are given by the name of the corresponding alkane with the addition of the suffix -dioic and the word acid.
Skeletal isomerism in the hydrocarbon radical appears starting with butanedioic acid, which has two isomers:
HOOC-CH2-CH2-COOH n-butanedioic acid (ethane-1,2-dicarboxylic acid);
CH3-CH(COOH)-COOH ethane-1,1-dicarboxylic acid.
24-25. OXY ACIDS (hydroxycarboxylic acids), have in the molecule, along with the carboxyl group - COOH, a hydroxyl group - OH, for example. HOCH2COOH (glycolic acid). Contained in plant and animal organisms (lactic, citric, tartaric and other acids).
Distribution in nature
Hydroxy acids are very widespread; Thus, tartaric, citric, malic, lactic and other acids are classified as hydroxy acids, and their name reflects the primary natural source in which the substance was found.
Synthesis methods
The Reformatsky reaction is a method for the synthesis of β-hydroxycarboxylic acid esters.
"Fruit acids." Many hydroxy acids are used in cosmetics as keratolytics. However, marketers changed the name a little - to make them more attractive in cosmetology, they are often called “fruit acids”.
26-27. OXY ACIDS (alcohol acids), dual-function compounds, both alcohols and acids, containing both an aqueous residue and a carboxyl group. Depending on the position of OH in relation to COOH (next to each other, in one, two, three places), a-, /?-, y-, b-hydroxy acids are distinguished. To obtain oxygen, there are many methods, the most important of which are the careful oxidation of glycols: CH3.CH(OH).CH2.OH + 02 = CH3. .CH(OH).COOH; saponification of oxynitriles CH3.CH(OH).CN -* CH3.CH(OH).COOH; exchange of halogen in halide acids for OH: CH2C1.COOH + KOH = CH2(OH).COOH + + KS1, effect of HN02 on amino acids: CH2(NH2). COOH + HN02 = CH2(OH) + N2 + + H20. In the animal body, hydroxy acids are formed during deamination (see) of amino acids, during the oxidation of fatty acids (see Acetone bodies, Metabolism—protein), during glycolysis (see), fermentation (see), and other chemicals. processes. Hydroxy acids are thick liquids or crystalline. substances. In chem. in relation to O. they react both like alcohols and like drugs: they give, for example. both ethers and esters; under the influence of halogen compounds of phosphorus, both OH are replaced by a halogen; Hydrohalic acids react only with alcohol OH.—Special reactions characterize a-, i)-, y- and b-hydroxy acids: a-hydroxy acids, losing water from two molecules, give cyclic esters, lactides: 2CH2(OH). COOH = 2H20 + CH2.O.CO (glycolide); с.о.сн2 /З-О., releasing water, they form unsaturated compounds: CH2(OH).CH2.COOH-H20 = CH2:CH. .COOH; y- and d-hydroxy acids form anhydrides - lactones: CH3.CH(OH).CH2.CH2.COOH= =H2O+CH3.CH.CH2.CH2.CO. O. are widely distributed in animal and plant organisms. Representatives of aliphatic a-O. are glycolic acid, CH2OH.COOH(hydroxyacetic acid), lactic acid; from /?-hydroxy acids - hydracrylic, CH2OH.CH2COOH, /9-hydroxy-butyric acid; U-O. are unknown in free form, since they lose water and become lactones. Among dibasic O., malic acid (hydroxyamber) is important; COOH.CHON.CH2.COOH, widely distributed in plants; has left rotation in weak solutions, right rotation in strong ones; synthetic ones are inactive. Dibasic tetraatomic acids include tartaric acids (dioxysuccinic acids). Of the other O.—lemon, HO.CO.CH2. .(SON)(COOH).CH2.COOH, very common in the plant world (in grapes, lemons) and found in animals (in milk); in the form of iron citrate it is used in medicine. Of the aromatic O. (phenolic acids) are important in medicine salicylic acid, gallic acid and their derivatives; phenyl ester of salicylic acid (salol), sulfosalicylic acid, C6H3.OH.S03H.COOH (protein reagent), acetylsalicylic acid (aspirin). In plants there are many different O. of the aromatic series, derivatives of which include, among other things, tannins, which are of important technical importance. About biol. the significance of individual O. and the methods of their quantitative determination—see. Acetone bodies, Bro-Glycolysis, Deamination, Blood, Lactic acid, Urine, Muscle, Beta(^)-hydroxybutyric acid.
28-29. in an ammonia molecule, successively replace hydrogen atoms with hydrocarbon radicals, you get compounds that belong to the class of amines. Accordingly, amines are primary (RNH2), secondary (R2NH), tertiary (R3N). The -NH2 group is called the amino group.
There are aliphatic, aromatic, alicyclic and heterocyclic amines depending on which radicals are associated with the nitrogen atom.
The names of amines are constructed by adding the prefix amino- to the name of the corresponding hydrocarbon (primary amines) or the ending -amine to the listed names of radicals associated with the nitrogen atom (for any amines).
Methods of obtaining:1. Hoffmann's reaction. One of the first methods for producing primary amines was the alkylation of ammonia with alkyl halides . 2. Zinin’s reaction- a convenient way to obtain aromatic amines by reducing aromatic nitro compounds. The following are used as reducing agents: H2 (on a catalyst). Sometimes hydrogen is generated directly at the time of the reaction, for which metals (zinc, iron) are treated with dilute acid.
Physical properties of amines. The presence of a lone electron pair on the nitrogen atom causes more high temperatures boiling point than the corresponding alkanes. Amines have an unpleasant, pungent odor. At room temperature and atmospheric pressure, the first representatives of a number of primary amines are gases that dissolve well in water. As the carbon radical increases, the boiling point increases and solubility in water decreases.
Chemical properties of amines. Basic properties of amines
Amines are bases because the nitrogen atom can provide an electron pair to form bonds with electron-starved species through a donor-acceptor mechanism (meeting the Lewis definition of basicity). Therefore, amines, like ammonia, are able to interact with acids and water, adding a proton to form the corresponding ammonium salts.
Ammonium salts are highly soluble in water, but poorly soluble in organic solvents. Aqueous solutions of amines have an alkaline reaction.
The basic properties of amines depend on the nature of the substituents. In particular, aromatic amines are weaker bases than aliphatic ones, because the free electron pair of nitrogen enters into conjugation with the -system of the aromatic nucleus, which reduces the electron density on the nitrogen atom (-M effect). On the contrary, the alkyl group is a good donor of electron density (+I-effect).
Oxidation of amines. The combustion of amines is accompanied by the formation of carbon dioxide, nitrogen and water: 4CH3NH2+9O2=4СO2+2N2+10Н2О
Aromatic amines spontaneously oxidize in air. Thus, aniline quickly turns brown in air due to oxidation.
Addition of alkyl halides Amines add haloalkanes to form a salt
Reaction of amines with nitrous acid Great value has a diazotization reaction of primary aromatic amines under the action of nitrous acid, obtained in situ by the reaction of sodium nitrite with hydrochloric acid.
Primary aliphatic amines react with nitrous acid to form alcohols, and secondary aliphatic and aromatic amines give N-nitroso derivatives: R-NH2 + NaNO2+HCl=R-OH+N2+NaCl+H2O; NH+NaNO2+HCl=R2N-N=O+NaCl+H2O
In aromatic amines, the amino group facilitates substitution at the ortho and para positions of the benzene ring. Therefore, aniline halogenation occurs quickly and in the absence of catalysts, and three hydrogen atoms of the benzene ring are replaced at once, and a white precipitate of 2,4,6-tribromoaniline precipitates:
This reaction with bromine water is used as a qualitative reaction for aniline.
Application
Amines are used in the pharmaceutical industry and organic synthesis (CH3NH2, (CH3)2NH, (C2H5)2NH, etc.); in the production of nylon (NH2-(CH2)6-NH2 - hexamethylenediamine); as a raw material for the production of dyes and plastics (aniline).
30. Amino acids (aminocarboxylic acids)- organic compounds, the molecule of which simultaneously contains carboxyl and amine groups. Amino acids can be considered as derivatives of carboxylic acids in which one or more hydrogen atoms are replaced by amine groups.
General chemical properties. 1. Amino acids can exhibit both acidic properties due to the presence of the carboxyl group -COOH in their molecules, and basic properties due to the amino group -NH2. Due to this, solutions of amino acids in water have the properties of buffer solutions.
A zwitterion is an amino acid molecule in which the amino group is represented as -NH3+ and the carboxy group is represented as -COO-. Such a molecule has a significant dipole moment with zero net charge. It is from such molecules that the crystals of most amino acids are built.
Some amino acids have multiple amino groups and carboxyl groups. For these amino acids it is difficult to talk about any specific zwitterion.
2. An important feature of amino acids is their ability to polycondensate, leading to the formation of polyamides, including peptides, proteins and nylon-66.
3. The isoelectric point of an amino acid is the pH value at which the maximum proportion of amino acid molecules has zero charge. At this pH, the amino acid is least mobile in the electric field, and this property can be used to separate amino acids, as well as proteins and peptides.
4. Amino acids can usually undergo all the reactions characteristic of carboxylic acids and amines.
Optical isomerism. All α-amino acids found in living organisms, except glycine, contain an asymmetric carbon atom (threonine and isoleucine contain two asymmetric atoms) and have optical activity. Almost all naturally occurring α-amino acids are L-form, and only L-amino acids are included in proteins synthesized on ribosomes.
This feature of “living” amino acids is very difficult to explain, since in reactions between optically inactive substances or racemates (which, apparently, were represented by organic molecules on the ancient Earth), L and D forms are formed in equal quantities. Maybe. the choice of one of the forms (L or D) is simply the result of a random coincidence: the first molecules with which template synthesis could begin had a certain shape, and it was to them that the corresponding enzymes “adapted.”
31. Amino acids are organic amphoteric compounds. They contain two functional groups of opposite nature in the molecule: an amino group with basic properties and a carboxyl group with acidic properties. Amino acids react with both acids and bases:
H2N-CH2-COOH + HCl→ Cl[H3N-CH2-COOH],
H2N-CH2-COOH + NaOH → H2N-CH2-COONa + H2O.
When amino acids are dissolved in water, the carboxyl group removes a hydrogen ion, which can attach to the amino group. In this case, an internal salt is formed, the molecule of which is a bipolar ion:
H2N-CH2—COOH +H3N-CH2—COO-.
Aqueous solutions of amino acids have a neutral, alkaline or acidic environment depending on the number of functional groups. Thus, glutamic acid forms an acidic solution (two -COOH groups, one -NH2), lysine forms an alkaline solution (one -COOH, two -NH2 groups).
Like primary amines, amino acids react with nitrous acid, with the amino group converted to a hydroxo group and the amino acid to a hydroxy acid: H2N-CH(R)-COOH + HNO2 → HO-CH(R)-COOH + N2+ H2O
Measuring the volume of nitrogen released allows you to determine the amount of amino acid (Van-Slyke method).
Amino acids can react with alcohols in the presence of hydrogen chloride gas, turning into an ester (more precisely, a hydrochloride salt of an ester): H2N-CH(R)-COOH + R"OH H2N-CH(R)-COOR" + H2O.
Amino acid esters do not have a bipolar structure and are volatile compounds. The most important property of amino acids is their ability to condense to form peptides.
32. Carboxyl group combines two functional groups - carbonyl =CO and hydroxyl -OH, mutually influencing each other.
The acidic properties of carboxylic acids are due to a shift in electron density to carbonyl oxygen and the resulting additional (compared to alcohols) polarization of the O-H bond.
In an aqueous solution, carboxylic acids dissociate into ions: R-COOH = R-COO- + H+
Solubility in water and high boiling points of acids are due to the formation of intermolecular hydrogen bonds.
Amino group - monovalent group -NH2, ammonia residue (NH3). The amino group is found in many organic compounds - amines, amino acids, amino alcohols, etc. Compounds containing the -NH2 group are, as a rule, basic in nature, due to the presence of a lone electron pair on the nitrogen atom.
In electrophilic substitution reactions in aromatic compounds, the amino group is an orienting agent of the first kind, i.e. activates the ortho- and para-positions in the benzene ring.
33. Polycondensation- the process of synthesizing polymers from polyfunctional (most often bifunctional) compounds, usually accompanied by the release of low molecular weight by-products (water, alcohols, etc.) during the interaction of functional groups.
The molecular weight of the polymer formed during the polycondensation process depends on the ratio of the starting components and reaction conditions.
Polycondensation reactions can involve either one monomer with two different functional groups: for example, the synthesis of poly-ε-caproamide (nylon-6, capron) from ε-aminocaproic acid, or two monomers carrying different functional groups, for example, the synthesis of nylon-6 66 by polycondensation of adipic acid and hexamethylenediamine; in this case, polymers of a linear structure are formed (linear polycondensation, see Fig. 1). If the monomer (or monomers) carry more than two functional groups, cross-linked polymers with a three-dimensional network structure are formed (three-dimensional polycondensation). In order to obtain such polymers, “cross-linking” polyfunctional components are often added to the mixture of monomers.
Of particular note are the reactions of the synthesis of polymers from cyclic monomers using the ring opening mechanism - addition, for example, the synthesis of nylon-6 from caprolactam (cyclic amide of ε-aminocaproic acid); Despite the fact that the release of a low-molecular fragment does not occur, such reactions are more often referred to as polycondensation.
Peptide bond- a type of amide bond that occurs during the formation of proteins and peptides as a result of the interaction of the α-amino group (-NH2) of one amino acid with the α-carboxyl group (-COOH) of another amino acid.
The C-N bond in the peptide bond is partially double in nature, which is manifested, in particular, in a decrease in its length to 1.32 angstroms. This results in the following properties:
4 bond atoms (C, N, O and H) and 2 α-carbons are in the same plane. The R-groups of amino acids and the hydrogens at α-carbons are outside this plane.
The H and O in the peptide bond, as well as the α-carbons of two amino acids, are trans oriented (the trans isomer is more stable). In the case of L-amino acids, which is the case in all natural proteins and peptides, the R-groups are also trans-oriented.
Rotation around a C-N bond is not possible, but rotation around a C-C bond is possible.
peptides (Greek πεπτος - nutritious) - a family of substances whose molecules are built from α-amino acid residues linked into a chain by peptide (amide) bonds -C(O)NH-.
34. Proteins (proteins, polypeptides) - high-molecular organic substances consisting of amino acids connected in a chain by peptide bonds. In living organisms, the amino acid composition of proteins is determined by the genetic code; in most cases, 20 standard amino acids are used during synthesis. Many of their combinations give a wide variety of properties of protein molecules. In addition, amino acids in a protein are often subject to post-translational modifications, which can occur both before the protein begins to perform its function and during its “work” in the cell. Often in living organisms, several protein molecules form complex complexes, for example, the photosynthetic complex.
In order to understand the intricate layout (architectonics) of a protein macromolecule, we should consider several levels of organization. The primary, simplest structure is a polypeptide chain, i.e., a string of amino acids linked together by peptide bonds. In the primary structure, all bonds between amino acids are covalent and therefore strong. The next, higher level of organization is the secondary structure, when the protein thread is twisted in the form of a spiral. Hydrogen bonds are formed between the -COOH groups located on one turn of the helix and the -NH2 groups on the other turn. They arise from hydrogen, most often found between two negative atoms. Hydrogen bonds are weaker than covalent bonds, but with a large number of them they ensure the formation of a fairly strong structure. A string of amino acids (polypeptide) then coagulates, forming a ball, or fibril or globule, specific for each protein. This creates a complex configuration called the tertiary structure. It is usually determined using the method of X-ray diffraction analysis, which makes it possible to establish the position in space of atoms and groups of atoms in crystals and complex compounds.
The bonds that support the tertiary structure of the protein are also weak. They arise, in particular, due to hydrophobic interactions. These are the forces of attraction between non-polar molecules or between non-polar regions of molecules in an aqueous environment. The hydrophobic residues of some amino acids in an aqueous solution come closer together, “stick together,” and thus stabilize the protein structure. In addition to hydrophobic forces, electrostatic bonds between electronegative and electropositive radicals of amino acid residues play a significant role in maintaining the tertiary structure of a protein. The tertiary structure is also maintained by a small number of covalent disulfide -S-S bonds that occur between the sulfur atoms of sulfur-containing amino acids. I must say that it is also tertiary; protein structure is not finite. Macromolecules of the same protein or molecules of other proteins are often attached to a protein macromolecule. For example, the complex molecule of hemoglobin, a protein found in red blood cells, consists of four globin macromolecules: two alpha chains and two beta chains, each of which is connected to iron-containing heme. As a result of their combination, a functioning hemoglobin molecule is formed. Only in such a package does hemoglobin work fully, i.e. is it able to carry oxygen. Due to the connection of several protein molecules with each other, a quaternary structure is formed. If the peptide chains are arranged in the form of a ball, then such proteins are called globular. If polypeptide chains are arranged in bundles of threads, they are called fibrillar proteins. Starting from the secondary structure, the spatial structure (conformation) of protein macromolecules, as we have found out, is maintained mainly by weak chemical bonds. Influenced external factors(changes in temperature, salt composition of the environment, pH, under the influence of radiation and other factors) weak bonds that stabilize the macromolecule are broken, and the structure of the protein, and therefore its properties, change. This process is called denaturation. Breaking of some weak bonds, changes in the conformation and properties of the protein also occur under the influence of physiological factors (for example, under the influence of hormones). In this way, the properties of proteins are regulated: enzymes, receptors, transporters. These changes in protein structure are usually easily reversible. Breaking a large number of weak bonds leads to denaturation of the protein, which can be irreversible (for example, the coagulation of egg whites when boiling eggs). Sometimes protein denaturation has a biological meaning. For example, a spider secretes a drop of secretion and sticks it to some support. Then, continuing to secrete the secretion, he slightly pulls the thread, and this weak tension is enough for the protein to denature, pass from a soluble form to an insoluble one, and the thread acquires strength.
35-36. Monosaccharides(from Greek monos: single, sacchar: sugar), - organic compounds, one of the main groups of carbohydrates; the most simple form Sahara; are usually colorless, water soluble, transparent solids. Some monosaccharides have a sweet taste. Monosaccharides, the building blocks from which disaccharides (such as sucrose) and polysaccharides (such as cellulose and starch) are synthesized, contain hydroxyl groups and an aldehyde group (aldoses) or a keto group (ketoses). Each carbon atom to which a hydroxyl group is attached (except the first and last) is chiral, giving rise to many isomeric forms. For example, galactose and glucose are aldohexoses, but have different chemical and physical properties. Monosaccharides, like all carbohydrates, contain only 3 elements (C, O, H).
Monosaccharides are divided into trioses, tetroses, pentoses, hexoses, etc. (3, 4, 5, 6, etc. carbon atoms in the chain); no natural monosaccharides with a carbon chain containing more than 9 carbon atoms have been found. Monosaccharides containing a 5-membered ring are called furanoses, and those containing a 6-membered ring are called pyranoses.
Isomerism. For monosaccharides containing n asymmetric carbon atoms, the existence of 2n stereoisomers is possible (see Isomerism).
38. Chemical properties. Monosaccharides enter into chemical reactions characteristic of carbonyl and hydroxyl groups. Feature monosaccharides - the ability to exist in open (acyclic) and cyclic forms and give derivatives of each form. Most monosacs cyclize in aqueous solution to form hemiacetals or hemiketals (depending on whether they are aldoses or ketoses) between the alcohol and the carbonyl group of the same sugar. Glucose, for example, readily forms hemiacetals by joining its C1 and O5 to form a 6-membered ring called a pyranoside. The same reaction can take place between C1 and O4 to form a 5-membered furanoside.
Monosaccharides in nature. Monosaccharides are part of complex carbohydrates (glycosides, oligosaccharides, polysaccharides) and mixed carbohydrate-containing biopolymers (glycoproteins, glycolipids, etc.). In this case, monosaccharides are connected to each other and to the non-carbohydrate part of the molecule by glycosidic bonds. When hydrolyzed by acids or enzymes, these bonds can be broken to release monosaccharides. In nature, free monosaccharides, with the exception of D-glucose and D-fructose, are rare. Biosynthesis of monosaccharides from carbon dioxide and water occurs in plants (see Photosynthesis); With the participation of activated derivatives of monosaccharides - nucleoside diphosphate sugars - the biosynthesis of complex carbohydrates, as a rule, occurs. The breakdown of monosaccharides in the body (for example, alcoholic fermentation, glycolysis) is accompanied by the release of energy.
Application. Some free monosaccharides and their derivatives (for example, glucose, fructose and its diphosphate, etc.) are used in Food Industry and medicine.
37. Glucose (C6H12O6)(“grape sugar”, dextrose) is found in the juice of many fruits and berries, including grapes, which is where the name of this type of sugar comes from. It is a six-hydroxy sugar (hexose).
Physical properties. A white crystalline substance with a sweet taste, highly soluble in water, insoluble in ether, poorly soluble in alcohol.
Molecule structure
CH2(OH)-CH(OH)-CH(OH)-CH(OH)-CH(OH)-C=O
Glucose can exist in the form of cycles (α and β glucose).
α and β glucose
Transition of glucose from the Fischer projection to the Haworth projection. Glucose is the final product of hydrolysis of most disaccharides and polysaccharides.
Biological role. Glucose is the main product of photosynthesis and is formed in the Calvin cycle.
In the human and animal body, glucose is the main and most universal source of energy for metabolic processes. All cells of the animal body have the ability to metabolize glucose. At the same time, not all cells of the body, but only some of their types, have the ability to use other energy sources - for example, free fatty acids and glycerol, fructose or lactic acid.
Transport of glucose from the external environment to the inside animal cell carried out by active transmembrane transfer with the help of a special protein molecule - a hexose carrier (transporter).
Glucose in cells can undergo glycolysis to produce energy in the form of ATP. The first enzyme in the glycolysis chain is hexokinase. Cell hexokinase activity is under the regulating influence of hormones - thus, insulin sharply increases hexokinase activity and, consequently, the utilization of glucose by cells, and glucocorticoids reduce hexokinase activity.
Many energy sources other than glucose can be directly converted into glucose in the liver - for example, lactic acid, many free fatty acids and glycerol, or free amino acids, especially the simplest ones such as alanine. The process of producing glucose in the liver from other compounds is called gluconeogenesis.
Those energy sources for which there is no direct biochemical conversion into glucose can be used by liver cells to produce ATP and subsequent energy supply for the processes of gluconeogenesis, resynthesis of glucose from lactic acid, or energy supply for the process of synthesis of glycogen polysaccharide reserves from glucose monomers. Glucose is again easily produced from glycogen by simple breakdown.
Due to the critical importance of maintaining stable blood glucose levels, humans and many other animals have a complex system hormonal regulation parameters of carbohydrate metabolism. When 1 gram of glucose is oxidized to carbon dioxide and water, 17.6 kJ of energy is released. The stored maximum “potential energy” in a glucose molecule in the form of oxidation state −4 carbon atoms (C−4) can be reduced during metabolic processes to C+4 (in a CO2 molecule). Its restoration to the previous level can be carried out by autotrophs.
Fructose, or fruit sugar C6H12O6- a monosaccharide, which is present in free form in almost all sweet berries and fruits. Many people prefer to replace sugar not with synthetic drugs, but with natural fructose.
Unlike glucose, which serves as a universal source of energy, fructose is not absorbed by insulin-dependent tissues. It is almost completely absorbed and metabolized by liver cells. Virtually no other cells in the human body (except sperm) can use fructose. In liver cells, fructose is phosphorylated and then broken down into trioses, which are either used for fatty acid synthesis, which can lead to obesity, as well as increased triglyceride levels (which in turn increases the risk of atherosclerosis), or used for glycogen synthesis ( is also partially converted to glucose during gluconeogenesis). However, the conversion of fructose to glucose is a complex, multi-step process, and the liver's ability to process fructose is limited. The question of whether fructose should be included in the diet of diabetics, since its absorption does not require insulin, has been intensively studied in recent years.
Although fructose does not increase (or only slightly) blood glucose levels in a healthy person, fructose often leads to an increase in blood glucose levels in people with diabetes. On the other hand, due to a lack of glucose in the cells, the bodies of diabetics can burn fat, leading to depletion of fat reserves. In this case, fructose, which is easily converted into fat and does not require insulin, can be used to restore them. The advantage of fructose is that a sweet taste can be imparted to a dish with relatively small amounts of fructose, since with the same calorie content as sugar (380 kcal/100 g), it is 1.2-1.8 times sweeter. However, studies show that fructose consumers do not reduce their calorie intake; instead, they eat sweeter foods.
39. Oligosaccharides- these are oligomers consisting of several (no more than 20) monomers - monosaccharides, in contrast to polysaccharides, consisting of tens, hundreds or thousands of monosaccharides; - compounds built from several monosaccharide residues (from 2 to 10) linked by a glycosidic bond.
A very important and widespread special case of oligosaccharides are disaccharides - dimers consisting of two molecules of monosaccharides.
You can also talk about tri-, tetra-, etc. saccharides
40. Disaccharides- the general name of a subclass of oligosaccharides in which the molecule consists of two monomers - monosaccharides. Disaccharides are formed by a condensation reaction between two monosaccharides, usually hexoses. The condensation reaction involves the removal of water. The bond between monosaccharides resulting from the condensation reaction is called a glycosidic bond. Typically, this bond is formed between the 1st and 4th carbon atoms of adjacent monosaccharide units (1,4-glycosidic bond).
The condensation process can be repeated countless times, resulting in the formation of huge polysaccharide molecules. Once monosaccharide units are combined, they are called residues. The most common disaccharides are lactose and sucrose.
Mutarotation(from Latin muto-change and rotatio - rotation), change in optical value. rotation of solutions of optically active compounds due to their epimerization. Characteristic of monosaccharides, reducing oligosaccharides, lactones, etc. Mutarotation can be catalyzed by acids and bases. In the case of glucose, mutarotation is explained by the establishment of equilibrium: At equilibrium, 38% of the alpha form and 62% of the beta form are present. Intermediate the aldehyde form is contained in negligibly small concentrations. Advantages, the formation of the b-form is explained by the fact that it is more thermodynamically stable.
The “silver mirror” and “copper mirror” reactions are characteristic of aldehydes
1) “Silver mirror” reaction, formation of an Ag precipitate on the walls of the test tube
2) “Copper mirror” reaction, precipitation of a red Cu2O precipitate
40. In turn, disaccharides, which arise in some cases during hydrolysis of polysaccharides(maltose during the hydrolysis of starch, cellobiose during the hydrolysis of cellulose) or existing in the body in free form (lactose, sucrose, trehalose, etc.), are hydrolyzed under the catalytic action of o- and p-glycosidases to individual monosaccharides. All glycosidases, with the exception of trehalase (ot, omrehalose-glucohydroxygases), are distinguished by a wide range of specificity, accelerating the hydrolysis of almost any glycosides that are derivatives of one or another a- or (3-monosaccharide. Thus, a-glucosidase accelerates the hydrolysis reaction of a- glucosides, including maltose; p-glucosidase - p-glucosides, including cellobiose; B-galactosidase - B-galactosides and among them lactose, etc. Examples of the action of a and P-glucosidases were given earlier
41. According to the failure chemical structure of disaccharides trehalose type (glycoside-glycosides) and maltose type (glycoside-glucose) have significantly different chemical properties: the former do not give any reactions characteristic of the aldehyde or ketone group, i.e. they do not oxidize, are not reduced, do not form osazones, enter into a polycodensation reaction (do not resin), do not mutarotate, etc. For disaccharides such as maltose, all the mentioned reactions, on the contrary, are very characteristic. The reason for this difference is quite clear from what was said above about the two types of disaccharide structure and the properties of the monosaccharide residues included in their composition. It lies in the fact that only in disaccharides such as maltose is ringed tautomerism possible, as a result of which a free aldehyde or ketone group is formed, which exhibits its characteristic properties.
For alcohol hydroxyls, both types of disaccharides give the same reactions: they form ethers and esters, and interact with metal oxide hydrates.
exists in nature big number disaccharides; The most important among them are the above-mentioned trehalose and maltose, as well as sucrose, cellobiose and lactose.
42. Maltose(from the English malt - malt) - malt sugar, a natural disaccharide consisting of two glucose residues; found in large quantities in sprouted grains (malt) of barley, rye and other grains; also found in tomatoes, pollen and nectar of a number of plants. M. is easily soluble in water and has a sweet taste; is a reducing sugar because it has an unsubstituted hemiacetal hydroxyl group. The biosynthesis of M. from b-D-glucopyranosylphosphate and D-glucose is known only in some species of bacteria. In animal and plant organisms, magnesium is formed by the enzymatic breakdown of starch and glycogen (see Amylase). The breakdown of M. into two glucose residues occurs as a result of the action of the enzyme a-glucosidase, or maltase, which is found in the digestive juices of animals and humans, in sprouted grains, in molds and yeast. The genetically determined absence of this enzyme in the human intestinal mucosa leads to congenital intolerance to M., a serious disease that requires the exclusion of M., starch, and glycogen from the diet or the addition of the enzyme maltase to food.
When maltose is boiled with dilute acid and under the action of an enzyme, maltase is hydrolyzed (two glucose molecules C6H12O6 are formed). Maltose is easily absorbed by the human body. Molecular weight - 342.32 T melting point - 108 (anhydrous)
43. Lactose(from Latin lactis - milk) C12H22O11 - a carbohydrate of the disaccharide group, found in milk and dairy products. The lactose molecule consists of residues of glucose and galactose molecules. Lactose is sometimes called milk sugar.
Chemical properties. When boiled with dilute acid, lactose is hydrolyzed.
Lactose is obtained from milk whey.
Application. Used to prepare culture media, for example in the production of penicillin. Used as an excipient (excipient) in the pharmaceutical industry.
From lactose, lactulose is obtained - a valuable drug for the treatment of intestinal disorders, such as constipation.
44. Sucrose C12H22O11, or beet sugar, cane sugar, in everyday life just sugar - a disaccharide consisting of two monosaccharides - α-glucose and β-fructose.
Sucrose is a very common disaccharide in nature; it is found in many fruits, fruits and berries. The sucrose content is especially high in sugar beets and sugar cane, which are used for the industrial production of table sugar.
Sucrose has high solubility. Chemically, fructose is quite inert, i.e. when moving from one place to another, it is almost not involved in metabolism. Sometimes sucrose is stored as a reserve nutrient.
Sucrose, entering the intestine, is quickly hydrolyzed by alpha-glucosidase in the small intestine into glucose and fructose, which are then absorbed into the blood. Alpha-glucosidase inhibitors, such as acarbose, inhibit the breakdown and absorption of sucrose, as well as other carbohydrates hydrolyzed by alpha-glucosidase, in particular starch. It is used in the treatment of type 2 diabetes. Synonyms: alpha-D-glucopyranosyl-beta-D-fructofuranoside, beet sugar, cane sugar.
Chemical and physical properties. Molecular weight 342.3 amu. Gross formula (Hill system): C12H22O11. The taste is sweetish. Solubility (grams per 100 grams): in water 179 (0°C) and 487 (100°C), in ethanol 0.9 (20°C). Slightly soluble in methanol. Insoluble in diethyl ether. Density 1.5879 g/cm3 (15°C). Specific rotation for sodium D-line: 66.53 (water; 35 g/100 g; 20°C). When cooled with liquid air and illuminated with bright light, sucrose crystals phosphoresce. Does not exhibit reducing properties - does not react with Tollens' reagent and Fehling's reagent. The presence of hydroxyl groups in the sucrose molecule is easily confirmed by reaction with metal hydroxides. If a solution of sucrose is added to copper(II) hydroxide, a bright blue solution of copper sucrose is formed. There is no aldehyde group in sucrose: when heated with an ammonia solution of silver (I) oxide, it does not give a “silver mirror”; when heated with copper (II) hydroxide, it does not form red copper (I) oxide. Among the isomers of sucrose with the molecular formula C12H22O11, maltose and lactose can be distinguished.
Reaction of sucrose with water. If you boil a solution of sucrose with a few drops of hydrochloric or sulfuric acid and neutralize the acid with alkali, and then heat the solution, molecules with aldehyde groups appear, which reduce copper (II) hydroxide to copper (I) oxide. This reaction shows that sucrose undergoes hydrolysis under the catalytic action of acid, resulting in the formation of glucose and fructose: C12H22O11 + H2O → C6H12O6 + C6H12O6
Natural and anthropogenic sources. Contained in sugar cane, sugar beets (up to 28% dry matter), plant juices and fruits (for example, birch, maple, melon and carrots). The source of sucrose - from beets or cane - is determined by the ratio of the content of stable carbon isotopes 12C and 13C. Sugar beets have a C3 mechanism for assimilating carbon dioxide (via phosphoglyceric acid) and preferentially absorb the 12C isotope; Sugarcane has a C4 mechanism for absorbing carbon dioxide (via oxaloacetic acid) and preferentially absorbs the 13C isotope.
45. Cellobiose- a carbohydrate from the group of disaccharides, consisting of two glucose residues connected by a β-glucosidic bond; the main structural unit of cellulose.
White crystalline substance, highly soluble in water. Cellobiose is characterized by reactions involving an aldehyde (hemiacetal) group and hydroxyl groups. During acid hydrolysis or under the action of the enzyme β-glucosidase, cellobiose is broken down to form 2 glucose molecules.
Cellobiose is obtained by partial hydrolysis of cellulose. Cellobiose is found in free form in the sap of some trees.
46. Polysaccharides- the general name for a class of complex high-molecular carbohydrates, the molecules of which consist of tens, hundreds or thousands of monomers - monosaccharides.
Polysaccharides are necessary for the life of animal and plant organisms. They are one of the main sources of energy generated as a result of the body's metabolism. They take part in immune processes, provide cell adhesion in tissues, and constitute the bulk of organic matter in the biosphere.
The diverse biological activity of polysaccharides of plant origin has been established: antibiotic, antiviral, antitumor, antidote [source not specified 236 days]. Polysaccharides of plant origin play an important role in reducing lipemia and vascular atheromatosis due to their ability to form complexes with proteins and lipoproteins in blood plasma.
Polysaccharides include, in particular:
dextrin is a polysaccharide, a product of starch hydrolysis;
starch is the main polysaccharide deposited as an energy reserve in plant organisms;
glycogen is a polysaccharide deposited as an energy reserve in the cells of animal organisms, but is found in small quantities in plant tissues;
cellulose is the main structural polysaccharide of plant cell walls;
galactomannans - storage polysaccharides of some plants of the legume family, such as guarana and locust bean gum;
glucomannan is a polysaccharide obtained from konjac tubers, consisting of alternating units of glucose and mannose, soluble dietary fiber, reduces appetite;
amyloid - used in the production of parchment paper.
Cellulose ( from lat. cellula - cell, the same as fiber) - [C6H7O2(OH)3]n, polysaccharide; main component cell membranes all higher plants.
Cellulose consists of residues of glucose molecules, which are formed during the acid hydrolysis of cellulose:
(C6H10O5)n + nH2O -> nC6H12O6
Cellulose is a long thread containing 300-2500 glucose residues, without side branches. These threads are interconnected by many hydrogen bonds, which gives cellulose greater mechanical strength. Mammals (like most other animals) do not have enzymes that can break down cellulose. However, many herbivores (for example, ruminants) have symbiont bacteria in the digestive tract that break down and help the hosts absorb this polysaccharide.
By industrial method, cellulose is produced by cooking at pulp mills that are part of industrial complexes (mills). Based on the type of reagents used, the following methods of pulp cooking are distinguished:
Sulfite. The cooking solution contains sulfurous acid and a salt thereof, for example sodium hydrogen sulfite. This method is used to obtain cellulose from low-resin wood species: spruce, fir.
Alkaline:
Natronny. A sodium hydroxide solution is used. The soda method can be used to obtain cellulose from deciduous wood and annual plants.
Sulfate. The most common method today. The reagent used is a solution containing sodium hydroxide and sodium sulfide, called white liquor. The method gets its name from sodium sulfate, from which sulfide for white liquor is obtained at pulp mills. The method is suitable for producing cellulose from any type of plant material. Its disadvantage is the release of a large amount of foul-smelling sulfur compounds: methyl mercaptan, dimethyl sulfide, etc. as a result of adverse reactions.
The technical cellulose obtained after cooking contains various impurities: lignin, hemicelluloses. If cellulose is intended for chemical processing (for example, to produce artificial fibers), then it is subjected to refining - treatment with a cold or hot alkali solution to remove hemicelluloses.
To remove residual lignin and make the pulp white, it is bleached. Traditional chlorine bleaching includes two steps:
chlorine treatment - to destroy lignin macromolecules;
alkali treatment - to extract the resulting products of lignin destruction.
47. Starch- polysaccharides of amylose and amylopectin, the monomer of which is alpha-glucose. Starch, synthesized by different plants under the influence of light (photosynthesis), has several various compositions and grain structure.
Biological properties. Starch, being one of the products of photosynthesis, is widespread in nature. For plants it is a reserve nutrients and is found mainly in fruits, seeds and tubers. The grains of cereal plants are the richest in starch: rice (up to 86%), wheat (up to 75%), corn (up to 72%), and potato tubers (up to 24%).
For the human body, starch, along with sucrose, serves as the main supplier of carbohydrates - one of the most important components of food. Under the action of enzymes, starch is hydrolyzed to glucose, which is oxidized in cells to carbon dioxide and water, releasing the energy necessary for the functioning of a living organism.
Biosynthesis. Some of the glucose produced in green plants during photosynthesis is converted into starch:
6CO2 + 6H2O → C6H12O6 + 6O2
nC6H12O6(glucose) → (C6H10O5)n + nH2O
IN general view this can be written as 6nCO2 + 5nH2O → (C6H10O5)n 6nO2.
Starch accumulates in tubers, fruits, and plant seeds as a reserve nutrition. Thus, potato tubers contain up to 24% starch, wheat grains - up to 64%, rice - 75%, corn - 70%.
Glycogen is a polysaccharide, formed by glucose residues; the main storage carbohydrate in humans and animals. Glycogen (also sometimes called animal starch, although the term is imprecise) is the primary storage form of glucose in animal cells. Deposited in the form of granules in the cytoplasm in many types of cells (mainly liver and muscles). Glycogen forms an energy reserve that can be quickly mobilized if necessary to compensate for a sudden lack of glucose. Glycogen storage, however, is not as dense in calories per gram as triglyceride (fat) storage. Only glycogen stored in liver cells (hepatocytes) can be converted into glucose to fuel the entire body, and hepatocytes are able to store up to 8 percent of their weight in the form of glycogen, which is the highest concentration of any cell type. The total mass of glycogen in the liver can reach 100-120 grams in adults. In muscles, glycogen is converted into glucose exclusively for local consumption and accumulates in much lower concentrations (no more than 1% of the total muscle mass), while at the same time its total muscle reserve can exceed the reserve accumulated in hepatocytes. Not a large number of glycogen was found in the kidneys, and even less in certain types brain cells (glial) and white blood cells.
48. Chitin(C8H13O5N) (French chitine, from Greek chiton: chiton - clothing, skin, shell) - a natural compound from the group of nitrogen-containing polysaccharides. Chemical name: poly-N-acetyl-D-glucose-2-amine, a polymer of N-acetylglucosamine residues linked by b-(1,4)-glycosidic bonds. The main component of the exoskeleton (cuticle) of arthropods and a number of other invertebrates, it is part of the cell wall of fungi and bacteria.
Distribution in nature. Chitin is one of the most common polysaccharides in nature; every year on Earth, about 10 gigatons of chitin are formed and decomposed in living organisms.
Performs protective and support functions, ensuring cell rigidity - found in the cell walls of fungi.
The main component of the exoskeleton of arthropods.
Chitin is also formed in the bodies of many other animals - various worms, coelenterates, etc.
In all organisms that produce and use chitin, it is not found in pure form, and in combination with other polysaccharides, and is very often associated with proteins. Despite the fact that chitin is a substance very similar in structure, physical and chemical properties And biological role to cellulose, chitin could not be found in organisms that form cellulose (plants, some bacteria).
Chemistry of chitin. IN natural form Chitins of different organisms differ somewhat from each other in composition and properties. The molecular weight of chitin reaches 260,000.
Chitin is insoluble in water and resistant to dilute acids, alkalis, alcohol and other organic solvents. Soluble in concentrated solutions of some salts (zinc chloride, lithium thiocyanate, calcium salts).
When heated with concentrated solutions of mineral acids, it is destroyed (hydrolyzed), eliminating acetyl groups.
Practical use. One of the derivatives of chitin, obtained from it industrially, is chitosan. The raw materials for its production are crustacean shells (krill, king crab), as well as products of microbiological synthesis.
49. Aromatic hydrocarbons, organic compounds consisting of carbon and hydrogen and containing benzene nuclei. The simplest and most important representatives of A. u. - benzene (I) and its homologues: methylbenzene, or toluene (II), dimethylbenzene, or xylene, etc. also include benzene derivatives with unsaturated side chains, for example styrene (III). There are many known A.u. with several benzene nuclei in the molecule, for example diphenylmethane (IV), diphenyl C6H5-C6H5, in which both benzene nuclei are directly linked to each other; in naphthalene (V) both rings share 2 carbon atoms; such hydrocarbons are called A.u. with condensed nuclei.
Benzene C6H6, PhH) is an organic chemical compound, a colorless liquid with a pleasant sweetish odor. Aromatic hydrocarbon. Benzene is a component of gasoline, is widely used in industry, and is a raw material for the production of medicines, various plastics, synthetic rubber, and dyes. Although benzene is a constituent of crude oil, it is synthesized on an industrial scale from other components. Toxic, carcinogen.
Homologues- Compounds belonging to the same class, but differing from each other in composition by an integer number of CH2 groups. The totality of all homologues forms a homological series.
Physical properties. Colorless liquid with a peculiar pungent odor. Melting point = 5.5 °C, boiling point = 80.1 °C, density = 0.879 g/cm³, molecular weight = 78.11 g/mol. Like all hydrocarbons, benzene burns and produces a lot of soot. Forms explosive mixtures with air, mixes well with ethers, gasoline and other organic solvents; with water it forms an azeotropic mixture with a boiling point of 69.25 °C. Solubility in water 1.79 g/l (at 25 °C).
Structure. Benzene in composition belongs to unsaturated hydrocarbons (homologous series CnH2n-6), but unlike hydrocarbons of the ethylene series, C2H4 exhibits the properties inherent in saturated hydrocarbons under harsh conditions, but benzene is more prone to substitution reactions. This “behavior” of benzene is explained by its special structure: the presence of a conjugated 6π-electron cloud in the structure. Modern performance about the electronic nature of bonds in benzene is based on the hypothesis of Linus Pauling, who proposed to depict the benzene molecule as a hexagon with an inscribed circle, thereby emphasizing the absence of fixed double bonds and the presence of a single electron cloud covering all six carbon atoms of the cycle.
50. Aromatic compounds (arenes)- cyclic organic compounds that contain an aromatic bond system. They may have saturated or unsaturated side chains.
The most important aromatic hydrocarbons include benzene C6H6 and its homologues: toluene C6H5CH3, xylene C6H4(CH3)2, etc.; naphthalene C10H8, anthracene C14H10 and their derivatives. Distinctive chemical properties- increased stability of the aromatic nucleus and tendency to substitution reactions. The main sources of aromatic hydrocarbons are coal tar, oil and petroleum products. Synthetic methods of production are of great importance. Aromatic hydrocarbons are the starting products for the production of ketones, aldehydes and aromatic acids, as well as many other substances. There are also heterocyclic arenes, among which the most often found in pure form and in the form of compounds are pyridine, pyrrole, furan and thiophene, indole, purine, quinoline.
Borazole (“inorganic benzene”) is also aromatic, but its properties differ markedly from those of organic arenes.
Electrophilic substitution reactions"(eng. substitution electrophilic reaction) - substitution reactions in which the attack is carried out by an electrophile - a particle that is positively charged or has a deficiency of electrons. When a new bond is formed, the outgoing particle, the electrophage, is split off without its electron pair. The most popular leaving group is the H+ proton.
51-52. Aromatic electrophilic substitution reactions
For aromatic systems, there is actually one mechanism of electrophilic substitution - SEAr. The SE1 mechanism (similar to the SN1 mechanism) is extremely rare, and SE2 (similar to the SN2 mechanism) is not found at all.
SEAr reaction mechanism or aromatic electrophilic substitution reaction (eng. substitution electrophilic aromatic) is the most common and most important among the substitution reactions of aromatic compounds and consists of two stages. At the first stage, the electrophile is added, and at the second stage, the electrofuge is separated.
During the reaction, a positively charged intermediate is formed (in Figure 2b). It is called the Ueland intermediate, aronium ion or σ-complex. This complex is generally very reactive and is easily stabilized, quickly eliminating the cation. The rate-limiting step in the vast majority of SEAr reactions is the first step.
Reaction rate = k**
The attacking species is usually relatively weak electrophiles, so in most cases the SEAr reaction proceeds under the action of a catalyst - Lewis acid. The most commonly used are AlCl3, FeCl3, FeBr3, ZnCl2.
In this case, the reaction mechanism is as follows (using the example of benzene chlorination, FeCl3 catalyst):
1. At the first stage, the catalyst interacts with the attacking particle to form an active electrophilic agent
At the second stage, in fact, the SEAr mechanism is implemented
53. Heterocyclic compounds(heterocycles) - organic compounds containing cycles, which, along with carbon, also include atoms of other elements. They can be considered as carbocyclic compounds with heterosubstituents (heteroatoms) in the ring. The most diverse and well studied are aromatic nitrogen-containing heterocyclic compounds. Limiting cases of heterocyclic compounds are compounds that do not contain carbon atoms in the ring, for example, pentazole.
Pyrrole- an aromatic five-membered nitrogen heterocycle, has weak basic properties. Contained in bone oil (which is obtained by dry distillation of bones), as well as in coal tar. Pyrrole rings are part of porphyrins - plant chlorophyll, heme of hemoglobins and cytochromes and a number of other biologically important compounds.
Structure and properties. Pyrrole is a colorless liquid with an odor similar to chloroform, which slowly darkens when exposed to air. It is slightly hygroscopic, slightly soluble in water and highly soluble in most organic solvents. The structure of pyrrole was proposed in 1870 by Bayer, based on its oxidation with chromic acid to maleimide and its formation during the distillation of succinimide with zinc dust.
Acidity and metalation. Pyrrole is a weak NH acid (pKa 17.5 in water) and reacts with alkali metals and their amides in liquid ammonia or inert solvents, deprotonating at position 1 and forming the corresponding salts. The reaction with Grignard reagents proceeds similarly, in which N-magnesium salts are formed. N-substituted pyrroles react with butyl and phenyllithium, metalating at the α-position.
54. INDOL (benzo[b]pyrrole), mol. m. 117.18; colorless crystals with a faint naphthalene odor; m.p. 52.5 °C, bp. 254 °C; d456 1.0718; sublimes when heated. up to 150°C; m 7.03.10-30 Kl.m (benzene, 25 °C); distills with water vapor, diethyl ether and NH3; well sol. in org. r-retailers, hot water, liquid NH3. The molecule has a flat configuration.
Indole is a weak base (pKa -2.4). When protonated, it forms a 3H-indolium cation (form I), which upon interaction. with a neutral molecule, indole gives dimer (II). As a weak compound (pKa 17), indole with Na in liquid NH3 forms N-sodium indole, with KOH at 130°C - N-potassium indole. It is aromatic. Holy you. Electroph. replacement goes Ch. arr. to position 3. Nitration is usually carried out with benzoyl nitrate, sulfonation with pyridine sulfotrioxide, bromination with dioxane dibromide, chlorination with SO2Cl2, alkylation with active alkyl halides. Acetylation in acetic acid also occurs in position 3, in the presence. CH3COONa - to position 1; 1,3-diacetylindole is formed in acetic anhydride. Indole easily attaches to the double bond of a,b-unsaturated ketones and nitriles.
Aminomethylation (Mannich solution) occurs in position 1 under mild conditions, and in position 3 in hard conditions. Substitution into the benzene ring (predominantly in positions 4 and 6) occurs only in acidic environments when position 3 is blocked. H2O2, peracids or in the light, indole is oxidized into indoxyl, which is then converted. in trimer or indigo. More severe oxidation under the influence of O3, MnO2 leads to the rupture of the pyrrole ring with the formation of 2-formamidobenzaldehyde. When indole is hydrogenated with hydrogen under mild conditions, the pyrrole ring is reduced, and under harsher conditions, the benzene ring is also reduced.
Indole is found in essential oils jasmine and citrus fruits, is part of Kam.-Ug. resin. The indole ring is a fragment of important natural molecules. compounds (eg tryptophan, serotonin, melatonin, bufotenin). Typically, indole is isolated from the naphthalene fraction of Kam.-Ug. resin or obtained by dehydrogenation of o-ethylaniline with the last. cyclization of the resulting product. Indole and its derivatives are also synthesized by cyclization of arylhydrazones of carbonyl compounds. (Fischer district), interaction. arylamines with a-halo- or a-hydroxycarbonyl compounds. (Bishler district), etc. The indole core is part of indole alkaloids. Indole itself is an odor fixer in perfumery; its derivatives are used in the production of biologically active compounds. (hormones, hallucinogens) and medications. Wed (eg, indopan, indomethacin).
55. Imidazole- an organic compound of the heterocycle class, a five-membered ring with two nitrogen atoms and three carbon atoms in the ring, isomeric to pyrazole.
Properties. In unsubstituted imidazole, positions 4 and 5 (carbon atoms) are equivalent due to tautomerism. Aromatic, reacts with diazonium salts (combination). It is nitrated and sulfonated only in an acidic environment at position 4, halogens enter at position 2 in an alkaline environment, and at position 4 in an acidic environment. It is easily alkylated and acylated at the imine N, opens the cycle when interacting with solutions of strong acids and peroxides. Catalyzes the hydrolysis of difficultly saponified esters and amides of carboxylic acids.
A large number of different ionic liquids are produced based on imidazole.
Receipt methods. From ortho-phenylenediamine via benzimidazole and 4,5-imidazole dicarboxylic acid.
The interaction of glyoxal (oxalaldehyde) with ammonia and formaldehyde.
Biological role. The imidazole cycle is part of the essential amino acid histidine. Structural fragment of histamine, purine bases, dibazole.
56. Pyridine- a six-membered aromatic heterocycle with one nitrogen atom, a colorless liquid with a strong unpleasant odor; miscible with water and organic solvents. Pyridine is a weak base, gives salts with strong mineral acids, and easily forms double salts and complex compounds.
Receipt. The main source for pyridine is coal tar.
Chemical properties. Pyridine exhibits properties characteristic of tertiary amines: it forms N-oxides, N-alkylpyridinium salts, and can act as a sigma-donor ligand.
At the same time, pyridine has obvious aromatic properties. However, the presence of a nitrogen atom in the conjugation ring leads to a serious redistribution of electron density, which leads to a strong decrease in the activity of pyridine in electrophilic aromatic substitution reactions. In such reactions, the meta positions of the ring react predominantly.
Pyridine is characterized by aromatic nucleophilic substitution reactions that occur predominantly at the ortho-para positions of the ring. This reactivity indicates the electron-deficient nature of the pyridine ring, which can be summarized in the following rule of thumb: the reactivity of pyridine as an aromatic compound roughly corresponds to the reactivity of nitrobenzene.
Application. Used in the synthesis of dyes, medicinal substances, insecticides, in analytical chemistry, as a solvent for many organic and some non-organic organic matter, for denaturing alcohol.
Safety. Pyridine is toxic and affects the nervous system and skin.
57. Biological role. Nicotinic acid is a pyridine derivative. It is absorbed in the stomach and duodenum, and then undergoes amination, resulting in nicotinoamide, which in the body, in combination with proteins, forms more than 80 enzymes. This is the main physiological role of vitamin B5. Thus, nicotinic acid is part of such important redox enzymes as dehydrogenesis, which catalyze the removal of hydrogen from organic substances that are oxidized. The hydrogen thus removed is passed on by these enzymes to redox enzymes, which include riboflavin. In addition, in the mammalian body, pyridine nucleotides are formed from nicotinamide (niacin) and nicotinic acid, which serve as the coenzymes NAD and NADP. A deficiency of these precursors in animals causes pellagra, a disease manifested by symptoms of the skin, gastrointestinal tract and nervous system (dermatitis, diarrhea, dementia). As coenzymes, NAD and NADP, niacin precursors, are involved in many redox reactions catalyzed by dehydrogenases. The biological effect of nicotinic acid manifests itself in the form of stimulation of the secretory function of the stomach and digestive glands (in its presence in the stomach the concentration of free of hydrochloric acid). Under the influence of vitamin B5, glycogen biosynthesis increases and hyperglycemia decreases, the detoxifying function of the liver increases, blood vessels dilate, and blood microcirculation improves.
Between nicotinic acid and sulfur-containing amino acids there is a connection. Increased urinary excretion of methylnicotinamide in case of protein deficiency is normalized by the inclusion of sulfur-containing amino acids in the diet. At the same time, the content of phosphopyrinucleotides in the liver is also normalized.
58. Pyrimidine (C4N2H4, Pyrimidine, 1,3- or m-diazine, miazin) is a heterocyclic compound with a flat molecule, the simplest representative of 1,3-diazines.
Physical properties. Pyrimidine is colorless crystals with a characteristic odor.
Chemical properties. The molecular weight of pyrimidine is 80.09 g/mol. Pyrimidine exhibits the properties of a weak diacid base, since nitrogen atoms can add protons through donor-acceptor bonds, thereby acquiring a positive charge. The reactivity in electrophilic substitution reactions of pyrimidine is reduced due to a decrease in electron density at positions 2,4,6 caused by the presence of two nitrogen atoms in the ring. Substitution becomes possible only in the presence of electron-donating substituents and is directed to the least deactivated position 5. However, in contrast, pyrimidine is active towards nucleophilic reagents that attack carbons 2, 4 and 6 in the ring.
Receipt. Pyrimidine is obtained by reduction of halogenated pyrimidine derivatives. Or from 2,4,6-trichloropyrimidine, obtained by treating barbituric acid with phosphorus chloroxide.
Pyrimidine derivatives widely distributed in living nature, where they participate in many important biological processes. In particular, derivatives such as cytosine, thymine, uracil are part of nucleotides, which are the structural units of nucleic acids; the pyrimidine core is part of some B vitamins, in particular B1, coenzymes and antibiotics.
59. Purine (C5N4H4, Purine)- a heterocyclic compound, the simplest representative of imidazopyrimidines.
Purine derivatives play an important role in the chemistry of natural compounds (purine bases DNA and RNA; coenzyme NAD; alkaloids, caffeine, theophylline and theobromine; toxins, saxitoxin and related compounds; uric acid) and, thanks to this, in pharmaceuticals.
Adenine- nitrogenous base, amino derivative of purine (6-aminopurine). Forms two hydrogen bonds with uracil and thymine (complementarity).
Physical properties. Adenine is colorless crystals that melt at a temperature of 360-365 C. It has a characteristic absorption maximum (λmax) at 266 mmk (pH 7) with a molar extinction coefficient (εmax) of 13500.
Chemical formula C5H5N5, molecular weight 135.14 g/mol. Adenine exhibits basic properties (pKa1=4.15; pKa2=9.8). When interacting with nitric acid, adenine loses its amino group, turning into hypoxanthine (6-hydroxypurine). IN aqueous solutions crystallizes into a crystalline hydrate with three water molecules.
Solubility. It is highly soluble in water, especially hot water; as the temperature of the water decreases, the solubility of adenine in it decreases. Poorly soluble in alcohol, chloroform, ether, as well as in acids and alkalis - insoluble.
Prevalence and significance in nature. Adenine is part of many compounds vital for living organisms, such as: adenine, adenosine phosphotases, adenosine phosphoric acids, nucleic acids, adenine nucleotides, etc. In the form of these compounds, adenine is widely distributed in living nature.
Guanine- a nitrogenous base, an amino derivative of purine (6-hydroxy-2-aminopurine), is an integral part of nucleic acids. In DNA, during replication and transcription, it forms three hydrogen bonds with cytosine (complementarity). First isolated from guano.
Physical properties. Colorless, amorphous crystalline powder. Melting point 365 °C. A solution of guanine in HCl fluoresces. In alkaline and acidic environments it has two absorption maxima (λmax) in the ultraviolet spectrum: at 275 and 248 mmk (pH 2) and 246 and 273 mmk (pH 11).
Chemical properties. Chemical formula - C5H5N5O, molecular weight - 151.15 g/mol. Exhibits basic properties, pKa1= 3.3; pKa2= 9.2; pKa3=12.3. Reacts with acids and alkalis to form salts.
Solubility. Well soluble in acids and alkalis, poorly soluble in ether, alcohol, ammonia and neutral solutions, insoluble in water .
Qualitative reactions. To determine guanine, it is precipitated with metaphosphoric and picric acids; with diazosulfonic acid in a solution of Na2CO3 it gives a red color.
Distribution in nature and significance. Part of nucleic acids.
60. Nucleosides are glycosylamines containing a nitrogenous base bound to a sugar (ribose or deoxyribose).
Nucleosides can be phosphorylated by cell kinases at the primary alcohol group of the sugar, resulting in the formation of the corresponding nucleotides.
Nucleotides- phosphorus esters of nucleosides, nucleoside phosphates. Free nucleotides, in particular ATP, cAMP, ADP, play an important role in energy and information intracellular processes, and are also components of nucleic acids and many coenzymes.
Nucleotides are esters of nucleosides and phosphoric acids. Nucleosides, in turn, are N-glycosides containing a heterocyclic fragment linked through a nitrogen atom to the C-1 atom of a sugar residue.
The structure of nucleotides. In nature, the most common nucleotides are β-N-glycosides of purines or pyrimidines and pentoses - D-ribose or D-2-ribose. Depending on the structure of pentose, a distinction is made between ribonucleotides and deoxyribonucleotides, which are monomers of molecules of complex biological polymers (polynucleotides) - RNA or DNA, respectively.
The phosphate residue in nucleotides usually forms an ester bond with the 2", 3" or 5" hydroxyl groups of ribonucleosides; in the case of 2" deoxynucleosides, the 3" or 5" hydroxyl groups are esterified.
Compounds consisting of two nucleotide molecules are called dinucleotides, three - trinucleotides, a small number - oligonucleotides, and many - polynucleotides, or nucleic acids.
The names of nucleotides are abbreviations in the form of standard three- or four-letter codes.
If the abbreviation begins with a lowercase letter “d” (English d), it means deoxyribonucleotide; the absence of the letter "d" means ribonucleotide. If the abbreviation begins with the lowercase letter “c” (English c), then we are talking about the cyclic form of the nucleotide (for example, cAMP).
The first capital letter of the abbreviation indicates a specific nitrogenous base or group of possible nucleic bases, the second letter indicates the number of phosphoric acid residues in the structure (M - mono-, D - di-, T - tri-), and the third capital letter is always the letter F (“-phosphate”; English P).
Latin and Russian codes for nucleic bases:
A - A: Adenine; G - G: Guanine; C - C: Cytosine; T - T: Thymine (5-methyluracil), not found in RNA, takes the place of uracil in DNA; U - U: Uracil, not found in DNA, takes the place of thymine in RNA.
The first appeared at the beginning of the 19th century. radical theory(J. Gay-Lussac, F. Wehler, J. Liebig). Radicals are groups of atoms that pass without change during chemical reactions from one compound to another. This concept of radicals has been preserved, but most other provisions of the theory of radicals turned out to be incorrect.
According to type theories(C. Gerard) all organic substances can be divided into types corresponding to certain inorganic substances. For example, alcohols R-OH and ethers R-O-R were considered to be representatives of the water type H-OH, in which the hydrogen atoms are replaced by radicals. The theory of types created a classification of organic substances, some of the principles of which are used today.
The modern theory of the structure of organic compounds was created by the outstanding Russian scientist A.M. Butlerov.
Basic principles of the theory of the structure of organic compounds A.M. Butlerov
1. Atoms in a molecule are arranged in a certain sequence according to their valence. The valency of the carbon atom in organic compounds is four.
2. The properties of substances depend not only on which atoms and in what quantities are included in the molecule, but also on the order in which they are connected to each other.
3. Atoms or groups of atoms that make up a molecule mutually influence each other, which determines the chemical activity and reactivity of the molecules.
4. Studying the properties of substances allows us to determine their chemical structure.
The mutual influence of neighboring atoms in molecules is the most important property of organic compounds. This influence is transmitted either through a chain of simple bonds or through a chain of conjugated (alternating) simple and double bonds.
Classification of organic compounds is based on the analysis of two aspects of the structure of molecules - the structure of the carbon skeleton and the presence of functional groups.
Organic compounds
Hydrocarbons Heterocyclic compounds
Limit- Unprecedent- Aroma-
efficient practical
Aliphatic Carbocyclic
Ultimate Unsaturated Alicyclic Aromatic
(Alkanes) (Cycloalkanes) (Arenas)
WITH P H 2 P+2 C P H 2 P WITH P H 2 P-6
End of work -
This topic belongs to the section:
Introduction. Fundamentals of modern theory of structure
Organic compounds.. introduction.. bioorganic chemistry studies the structure and properties of substances involved in life processes in..
If you need additional material on this topic, or you did not find what you were looking for, we recommend using the search in our database of works:
What will we do with the received material:
If this material was useful to you, you can save it to your page on social networks:
| Tweet |
All topics in this section:
Alkenes Alkadienes Alkynes
SpN2p SpN2p-2 SpN2p-2 Fig. 1. Classification of organic compounds by structure
Electronic structure of the carbon atom. Hybridization.
For the valence electron layer of the C atom, located in the main subgroup of the fourth group of the second period of D. I. Mendeleev’s Periodic Table, the main quantum number n = 2, secondary (orbital
Conjugate systems
There are two types of conjugate systems (and couplings). 1. p, p-conjugation - electrons are delocalized
TOPIC 3. Chemical structure and isomerism of organic compounds
Isomerism of organic compounds. If two or more individual substances have the same quantitative composition (molecular formula), but differ from each other in
Conformations of organic molecules
Rotation around the C–C s-bond is relatively easy, and the hydrocarbon chain can take different shapes. Conformational forms easily transform into each other and therefore are not different compounds
Conformations of cyclic compounds.
Cyclopentane. The five-membered ring in flat form has bond angles of 108°, which is close to normal value for sp3-hybrid atom. Therefore, in flat cyclopentane, in contrast to the cycle
Configuration isomers
These are stereoisomers with different arrangements around certain atoms of other atoms, radicals or functional groups in space relative to each other. There are concepts of diastere
General characteristics of reactions of organic compounds.
Acidity and basicity of organic compounds. To assess the acidity and basicity of organic compounds highest value have two theories - the Brønsted theory and theo
Bronsted bases are neutral molecules or ions that can accept a proton (proton acceptors).
Acidity and basicity are not absolute, but relative properties of compounds: acidic properties are found only in the presence of a base; basic properties - only in the presence of ki
General characteristics of reactions of organic compounds
Most organic reactions involve several sequential (elementary) steps. A detailed description of the totality of these stages is called a mechanism. Reaction mechanism -
Selectivity of reactions
In many cases, an organic compound contains several unequal reaction centers. Depending on the structure of the reaction products, they speak of regioselectivity, chemoselectivity, and
Radical reactions.
Chlorine reacts with saturated hydrocarbons only under the influence of light, heat or in the presence of catalysts, and all hydrogen atoms are successively replaced by chlorine: CH4
Electrophilic addition reactions
Unsaturated hydrocarbons - alkenes, cycloalkenes, alkadienes and alkynes - exhibit the ability to undergo addition reactions, since they contain double or triple bonds. More important in vivo is twofold
And elimination from a saturated carbon atom
Nucleophilic substitution reactions at an sp3-hybridized carbon atom: heterolytic reactions caused by the polarization of the s-bond carbon - heteroatom (halogenopro
Nucleophilic substitution reactions involving the sp2-hybridized carbon atom.
Let us consider the mechanism of reactions of this type using the example of the interaction of carboxylic acids with alcohols (esterification reaction). In the carboxyl group of an acid, p,p-conjugation occurs, since the pair is
Nucleophilic substitution reactions in the series of carboxylic acids.
Only from a purely formal standpoint can the carboxyl group be considered a combination of carbonyl and hydroxyl functions. In fact, their mutual influence on each other is such that completely and
Organic compounds.
Oxidation-reduction reactions (ORR) occupy a large place in organic chemistry. OVR is of utmost importance for life processes. With their help, the body will satisfy
Participating in life processes
The vast majority of organic substances involved in metabolic processes are compounds with two or more functional groups. Such compounds are usually classified
Diatomic phenols
Diatomic phenols - pyrocatechol, resorcinol, hydroquinone - are part of many natural compounds. All of them give a characteristic staining with ferric chloride. Pyrocatechol (o-dihydroxybenzene, catecho
Dicarboxylic and unsaturated carboxylic acids.
Carboxylic acids containing one carboxyl group are called monobasic, two are called dibasic, etc. Dicarboxylic acids are white crystalline substances, having
Amino alcohols
2-Aminoethanol (ethanolamine, colamine) – structural component complex lipids, is formed by opening the strained three-membered rings of ethylene oxide and ethyleneimine with ammonia or water, respectively
Hydroxy and amino acids.
Hydroxy acids contain both hydroxyl and carboxyl groups in the molecule, amino acids contain carboxyl and amino groups. Depending on the location of the hydroxy or amino group
Oxoacids
Oxoacids are compounds containing both carboxyl and aldehyde (or ketone) groups. In accordance with this, aldehyde acids and keto acids are distinguished. The simplest aldehyde acid
Heterofunctional benzene derivatives as medicines.
Recent decades have been characterized by the emergence of many new drugs and preparations. At the same time, some groups of previously known medicinal drugs continue to be of great importance.
TOPIC 10. Biologically important heterocyclic compounds
Heterocyclic compounds (heterocycles) are compounds that include one or more atoms other than carbon (heteroatoms) in the cycle. Heterocyclic systems underlie
TOPIC 11. Amino acids, peptides, proteins
Structure and properties of amino acids and peptides. Amino acids are compounds in whose molecules amino and carboxyl groups are simultaneously present. Natural a-amine
Spatial structure of polypeptides and proteins
High molecular weight polypeptides and proteins, along with the primary structure, are characterized by higher levels of organization, which are usually called secondary, tertiary and quaternary structures.
TOPIC 12. Carbohydrates: mono, di- and polysaccharides
Carbohydrates are divided into simple (monosaccharides) and complex (polysaccharides). Monosaccharides (monoses). These are heteropolyfunctional compounds containing carbonyl and several g
TOPIC 13. Nucleotides and nucleic acids
Nucleic acids (polynucleotides) are biopolymers whose monomer units are nucleotides. The nucleotide is a three-component structure consisting
Nucleosides.
Heterocyclic bases form N-glycosides with D-ribose or 2-deoxy-D-ribose. In nucleic acid chemistry, such N-glycosides are called nucleosides. D-ribose and 2-deoxy-D-ribose in p
Nucleotides.
Nucleotides are called phosphates of nucleosides. Phosphoric acid usually esterifies the alcohol hydroxyl at C-5" or C-3" in a ribose or deoxyribose residue (the atoms of the nitrogenous base ring are numbered
Steroids
Steroids are widely distributed in nature and perform a variety of functions in the body. To date, about 20,000 steroids are known; more than 100 of them are used in medicine. Steroids have
Steroid hormones
Hormones - biologically active substances, formed as a result of the activity of the endocrine glands and taking part in the regulation of metabolism and physiological functions in organism.
Sterols
As a rule, the cells are very rich in sterols. Depending on the source of isolation, zoosterols (from animals), phytosterols (from plants), mycosterols (from fungi) and sterols of microorganisms are distinguished. IN
Bile acids
In the liver, sterols, particularly cholesterol, are converted into bile acids. The aliphatic side chain at C17 in bile acids, derivatives of the cholane hydrocarbon, consists of 5 carbon atoms
Terpenes and terpenoids
This name combines a number of hydrocarbons and their oxygen-containing derivatives - alcohols, aldehydes and ketones, the carbon skeleton of which is built from two, three or more isoprene units. Sami
Vitamins
Vitamins are usually called organic substances, the presence of which in small quantities in the food of humans and animals is necessary for their normal functioning. This is a classic op.
Fat-soluble vitamins
Vitamin A is a sesquiterpene and is found in butter, milk, egg yolk, and fish oil; lard and margarine do not contain it. This is a growth vitamin; lack of it in food causes
Water-soluble vitamins
At the end of the last century, thousands of sailors on Japanese ships suffered, and many of them died painful deaths from the mysterious beriberi disease. One of the mysteries of beriberi was that the sailors on the
Topic: Basic principles of the theory of the structure of organic compounds by A. M. Butlerov.
The theory of the chemical structure of organic compounds, put forward by A. M. Butlerov in the second half of the last century (1861), was confirmed by the works of many scientists, including Butlerov’s students and himself. It turned out to be possible on its basis to explain many phenomena that until then had no interpretation: homology, the manifestation of tetravalency by carbon atoms in organic substances. The theory also fulfilled its predictive function: on its basis, scientists predicted the existence of still unknown compounds, described their properties and discovered them. So, in 1862–1864. A. M. Butlerov examined propyl, butyl and amyl alcohols, determined the number of possible isomers and derived the formulas of these substances. Their existence was later experimentally proven, and some of the isomers were synthesized by Butlerov himself.
During the 20th century. the provisions of the theory of the chemical structure of chemical compounds were developed on the basis of new views that have spread in science: the theory of atomic structure, the theory of chemical bonds, ideas about mechanisms chemical reactions. Currently, this theory is universal, that is, it is valid not only for organic substances, but also for inorganic ones.
First position. Atoms in molecules are combined in a specific order according to their valency. Carbon in all organic and most inorganic compounds is tetravalent.
Obviously, the last part of the first position of the theory can be easily explained by the fact that in compounds the carbon atoms are in an excited state:
Tetravalent carbon atoms can combine with each other to form different chains:
The order of connection of carbon atoms in molecules can be different and depends on the type of covalent chemical bond between carbon atoms - single or multiple (double and triple):
This position explains the phenomenon.
Substances that have the same composition, but different chemical or spatial structures, and therefore different properties, are called isomers.
Main types:
Structural isomerism, in which substances differ in the order of bonding of atoms in molecules: carbon skeleton
Third position. The properties of substances depend on the mutual influence of atoms in molecules.
For example, in acetic acid only one of the four hydrogen atoms reacts with an alkali. Based on this, it can be assumed that only one hydrogen atom is bonded to oxygen:
On the other hand, from the structural formula of acetic acid we can conclude that it contains one mobile hydrogen atom, that is, that it is monobasic.The main directions of development of the theory of the structure of chemical compounds and its significance.
During the time of A.M. Butlerov, organic chemistry was widely used
empirical (molecular) and structural formulas. The latter reflect the order of connection of atoms in a molecule according to their valence, which is indicated by dashes.
For ease of recording, abbreviated structural formulas are often used, in which dashes indicate only the bonds between carbon atoms or carbon and oxygen.
And fibers, products from which are used in technology, everyday life, medicine, and agriculture. The significance of A. M. Butlerov’s theory of chemical structure for organic chemistry can be compared with the significance of the Periodic Law and the Periodic Table chemical elements D. I. Mendeleev for inorganic chemistry. It is not for nothing that both theories have so much in common in the ways of their formation, directions of development and general scientific significance.
How science took shape at the beginning of the 19th century, when the Swedish scientist J. Ya. Berzelius first introduced the concept of organic substances and organic chemistry. The first theory in organic chemistry is the theory of radicals. Chemists discovered that during chemical transformations, groups of several atoms pass unchanged from a molecule of one substance to a molecule of another substance, just as atoms of elements pass from molecule to molecule. Such “immutable” groups of atoms are called radicals.
However, not all scientists agreed with the radical theory. Many generally rejected the idea of atomism - the idea of the complex structure of a molecule and the existence of an atom as its component part. What has been indisputably proven today and does not raise the slightest doubt, in the 19th century. was the subject of fierce controversy.
Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year guidelines discussion programs Integrated LessonsFor cooking, dyes, clothing, and medicines, people have long learned to use various substances. Over time, a sufficient amount of information has accumulated about the properties of certain substances, which has made it possible to improve methods for their production, processing, etc. And it turned out that many mineral (inorganic substances) can be obtained directly.
But some substances used by man were not synthesized by him, because they were obtained from living organisms or plants. These substances were called organic. Organic substances could not be synthesized in the laboratory. At the beginning of the 19th century, such a doctrine as vitalism (vita - life) was actively developing, according to which organic substances arise only thanks to the “vital force” and it is impossible to create them “artificially”.
But as time passed and science developed, new facts appeared about organic substances that ran counter to the existing vitalist theory.
In 1824, the German scientist F. Wöhler synthesized oxalic acid for the first time in the history of chemical science – organic matter from inorganic substances (cyanogen and water):
(CN) 2 + 4H 2 O → COOH - COOH + 2NH 3
In 1828, Wöller heated sodium cyanate with ammonium sulfur and synthesized urea - waste product of animal organisms:
NaOCN + (NH 4) 2 SO 4 → NH 4 OCN → NH 2 OCNH 2
These discoveries played an important role in the development of science in general, and chemistry in particular. Chemical scientists began to gradually move away from vitalistic teaching, and the principle of dividing substances into organic and inorganic revealed its inconsistency.
Currently substances still divided into organic and inorganic, but the separation criterion is slightly different.
Substances are called organic containing carbon, they are also called carbon compounds. There are about 3 million such compounds, the remaining compounds are about 300 thousand.
Substances that do not contain carbon are called inorganic And. But there are exceptions to the general classification: there are a number of compounds that contain carbon, but they belong to inorganic substances (carbon monoxide and dioxide, carbon disulfide, carbonic acid and its salts). All of them are similar in composition and properties to inorganic compounds.
In the course of the study of organic substances, new difficulties emerged: based on theories about inorganic substances It is impossible to reveal the regularities of the structure of organic compounds and explain the valence of carbon. Carbon in different compounds had different valences.
In 1861, the Russian scientist A.M. Butlerov was the first to synthesize a sugary substance.
When studying hydrocarbons, A.M. Butlerov realized that they represent a completely special class of chemicals. Analyzing their structure and properties, the scientist identified several patterns. They formed the basis of the theories of chemical structure.
1. The molecule of any organic substance is not random; the atoms in the molecules are connected to each other in a certain sequence according to their valencies. Carbon in organic compounds is always tetravalent.
2. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structural formula).
3. The chemical structure can be determined using chemical methods. (Modern physical methods are also currently used).
4. The properties of substances depend not only on the composition of the molecules of the substance, but on their chemical structure (the sequence of combination of atoms of elements).
5. By the properties of a given substance one can determine the structure of its molecule, and by the structure of the molecule – anticipate properties.
6. Atoms and groups of atoms in a molecule exert mutual influence on each other.
This theory became the scientific foundation of organic chemistry and accelerated its development. Based on the provisions of the theory, A.M. Butlerov described and explained the phenomenon isomerism, predicted the existence of various isomers and obtained some of them for the first time.
Consider the chemical structure of ethane – C2H6. Having denoted the valence of elements with dashes, we will depict the ethane molecule in the order of connection of atoms, that is, we will write structural formula. According to the theory of A.M. Butlerov, it will have the following form:
Hydrogen and carbon atoms are bound into one particle, the valence of hydrogen is equal to one, and that of carbon – four. Two carbon atoms connected by a carbon bond – carbon (C – WITH). Ability of carbon to form C – The C-bond is understandable based on the chemical properties of carbon. The carbon atom has four electrons on its outer electron layer; the ability to give up electrons is the same as the ability to gain missing ones. Therefore, carbon most often forms compounds with a covalent bond, that is, due to the formation of electron pairs with other atoms, including carbon atoms with each other.
This is one of the reasons for the diversity of organic compounds.
Compounds that have the same composition but different structures are called isomers. The phenomenon of isomerism – one of the reasons for the diversity of organic compounds
Still have questions? Do you want to know more about the theory of the structure of organic compounds?
To get help from a tutor -.
The first lesson is free!
blog.site, when copying material in full or in part, a link to the original source is required.
