He formulated the basic ideas of the theory of the structure of organic substances. The main provisions of the theory of the chemical structure of organic substances A.M. Butlerov. The main directions of development of this theory

Theory of A.M. Butlerov

1. Atoms in molecules are interconnected in a certain sequence by chemical bonds in accordance with their valency. The bonding order of atoms is called their chemical structure. Carbon in all organic compounds is tetravalent.

2. The properties of substances are determined not only by the qualitative and quantitative composition of molecules, but also by their structure.

3. Atoms or groups of atoms mutually influence each other, on which the reactivity of the molecule depends.

4. The structure of molecules can be established on the basis of the study of their chemical properties.

Organic compounds have a number of characteristic features that distinguish them from inorganic ones. Almost all of them (with rare exceptions) are combustible; most organic compounds do not dissociate into ions, which is due to the nature of the covalent bond in organic substances. The ionic type of bond is realized only in salts of organic acids, for example, CH3COONa.

homologous series- this is an infinite series of organic compounds that have a similar structure and, therefore, similar chemical properties and differ from each other by any number of CH2 - groups (homologous difference).

Even before the creation of the theory of structure, substances of the same elemental composition, but with different properties, were known. Such substances were called isomers, and this phenomenon itself was called isomerism.

At the heart of isomerism, as shown by A.M. Butlerov, lies the difference in the structure of molecules consisting of the same set of atoms.

isomerism- this is the phenomenon of the existence of compounds that have the same qualitative and quantitative composition, but a different structure and, consequently, different properties.

There are 2 types of isomerism: structural isomerism and spatial isomerism.

Structural isomerism

Structural isomers- compounds of the same qualitative and quantitative composition, differing in the order of binding atoms, i.e. chemical structure.

Spatial isomerism

Spatial isomers(stereoisomers) with the same composition and the same chemical structure differ in the spatial arrangement of atoms in the molecule.
Spatial isomers are optical and cis-trans isomers (geometric).

Cis-trans isomerism

lies in the possibility of substituents being located on one or on opposite sides of the plane of the double bond or non-aromatic ring. cis isomers substituents are on the same side of the plane of the ring or double bond, in trans isomers- in different ways.

In the butene-2 ​​CH3–CH=CH–CH3 molecule, CH3 groups can be located either on one side of the double bond, in the cis isomer, or on opposite sides, in the trans isomer.

Optical isomerism

Appears when carbon has four different substituents.
If any two of them are interchanged, another spatial isomer of the same composition is obtained. The physicochemical properties of such isomers differ significantly. Compounds of this type are distinguished by their ability to rotate the plane of polarized light passed through a solution of such compounds by a certain amount. In this case, one isomer rotates the plane of polarized light in one direction, and its isomer in the opposite direction. Due to such optical effects, this kind of isomerism is called optical isomerism.

Topic: The main provisions of the theory of the structure of organic compounds by A. M. Butlerova.

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 work 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 tetravalence by carbon atoms in organic substances. The theory also fulfilled its prognostic function: on its basis, scientists predicted the existence of still unknown compounds, described properties and discovered them. So, in 1862-1864. A. M. Butlerov considered 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 XX 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 the structure of the atom, the theory of chemical bonding, ideas about the mechanisms of chemical reactions. At present, this theory has a universal character, that is, it is valid not only for organic substances, but also for inorganic ones.

First position. Atoms in molecules are connected in a certain order in accordance with their valency. Carbon in all organic and most inorganic compounds is tetravalent.

It is obvious that the last part of the first provision of the theory can be easily explained by the fact that carbon atoms in compounds are in an excited state:

tetravalent carbon atoms can combine with each other, forming various 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):

Second position. The properties of substances depend not only on their qualitative and quantitative composition, but also on the structure of their molecules.

This position explains the phenomenon.

Substances that have the same composition, but different chemical or spatial structure, 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

positions of multiple bonds:

deputies

positions of functional groups

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 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, one can conclude that it contains one mobile hydrogen atom, that is, that it is monobasic.

The main directions in the development of the theory of the structure of chemical compounds and its significance.

At the time of A. M. Butlerov, organic chemistry widely used

empirical (molecular) and structural formulas. The latter reflect the order of connection of atoms in a molecule according to their valency, which is indicated by dashes.

For ease of recording, abbreviated structural formulas are often used, in which only the bonds between carbon or carbon and oxygen atoms are indicated by dashes.

And fibers, products from which are used in technology, everyday life, medicine, and agriculture. The value of the theory of chemical structure of A. M. Butlerov for organic chemistry can be compared with the value of the Periodic law and the Periodic system of chemical elements of 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.

The first appeared at the beginning of the 19th century. radical theory(J. Gay-Lussac, F. Wehler, J. Liebig). Radicals were called groups of atoms that pass unchanged during chemical reactions from one compound to another. This concept of radicals has been preserved, but most of the other provisions of the theory of radicals turned out to be incorrect.

According to type theory(C. Gerard) all organic substances can be divided into types corresponding to certain inorganic substances. For example, R-OH alcohols and R-O-R ethers were considered as representatives of the H-OH type of water, in which hydrogen atoms are replaced by radicals. The theory of types created a classification of organic substances, some of the principles of which are currently applied.

The modern theory of the structure of organic compounds was created by the outstanding Russian scientist A.M. Butlerov.

The main provisions 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 valency. 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 part of the molecule, but also on the order in which they are interconnected.

3. The atoms or groups of atoms that make up the molecule mutually influence each other, on which the chemical activity and reactivity of the molecules depend.

4. The study of the properties of substances allows you 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 single bonds or through a chain of conjugated (alternating) single 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- Nepre- Aroma-

ny efficient tic

Aliphatic Carbocyclic

Limit Unsaturated Limit Unsaturated Aromatic

(Alkanes) (Cycloalkanes) (Arenas)

With P H 2 P+2 C P H 2 P With P H 2 P -6

alkenes polyenes and alkynes

With P H 2 P polyynes C P H 2 P -2

Rice. 1. Classification of organic compounds according to the structure of the carbon skeleton

Classes of derivatives of hydrocarbons by the presence of functional groups:

Halogen derivatives R–Gal: CH 3 CH 2 Cl (chloroethane), C 6 H 5 Br (bromobenzene);

Alcohols and phenols R–OH: CH 3 CH 2 OH (ethanol), C 6 H 5 OH (phenol);

Thiols R–SH: CH 3 CH 2 SH (ethanethiol), C 6 H 5 SH (thiophenol);

Ethers R–O–R: CH 3 CH 2 –O–CH 2 CH 3 (diethyl ether),

complex R–CO–O–R: CH 3 CH 2 COOSH 2 CH 3 (acetic acid ethyl ester);

Carbonyl compounds: aldehydes R–CHO:

ketones R–CO–R: CH 3 COCH 3 (propanone), C 6 H 5 COCH 3 (methylphenyl ketone);

Carboxylic acids R-COOH: (acetic acid), (benzoic acid)

Sulfonic acids R–SO 3 H: CH 3 SO 3 H (methanesulfonic acid), C 6 H 5 SO 3 H (benzenesulfonic acid)

Amines R–NH 2: CH 3 CH 2 NH 2 (ethylamine), CH 3 NHCH 3 (dimethylamine), C 6 H 5 NH 2 (aniline);

Nitro compounds R–NO 2 CH 3 CH 2 NO 2 (nitroethane), C 6 H 5 NO 2 (nitrobenzene);

Organometallic (organoelement) compounds: CH 3 CH 2 Na (ethyl sodium).

A series of structurally similar compounds with similar chemical properties, in which the individual members of the series differ from each other only in the number of -CH 2 - groups, is called homologous line, and the -CH 2 group is a homological difference . For members of the homologous series, the vast majority of reactions proceed in the same way (the only exceptions are the first members of the series). Therefore, knowing the chemical reactions of only one member of the series, it can be argued with a high degree of probability that the same type of transformation occurs with the rest of the members of the homologous series.

For any homologous series, a general formula can be derived that reflects the ratio between the carbon and hydrogen atoms of the members of this series; such the formula is called the general formula of the homologous series. Yes, C P H 2 P+2 is the formula of alkanes, С P H 2 P+1 OH - aliphatic monohydric alcohols.

Nomenclature of organic compounds: trivial, rational and systematic nomenclature. Trivial nomenclature is a collection of historically established names. So, by the name it is immediately clear where malic, succinic or citric acid came from, how pyruvic acid was obtained (pyrolysis of tartaric acid), experts in the Greek language can easily guess that acetic acid is something sour, and glycerin is sweet. With the synthesis of new organic compounds and the development of the theory of their structure, other nomenclatures were created, reflecting the structure of the compound (its belonging to a certain class).

Rational nomenclature builds the name of a compound based on the structure of a simpler compound (the first member of the homologous series). CH 3 IS HE- carbinol, CH 3 CH 2 IS HE- methylcarbinol, CH 3 CH(OH) CH 3 - dimethylcarbinol, etc.

IUPAC nomenclature (systematic nomenclature). According to the IUPAC (International Union for Pure and Applied Chemistry) nomenclature, the names of hydrocarbons and their functional derivatives are based on the name of the corresponding hydrocarbon with the addition of prefixes and suffixes inherent in this homologous series.

In order to correctly (and unambiguously) name an organic compound according to the systematic nomenclature, one must:

1) choose the longest sequence of carbon atoms (the parent structure) as the main carbon skeleton and give its name, paying attention to the degree of unsaturation of the compound;

2) reveal all the functional groups present in the compound;

3) determine which group is the eldest (see table), the name of this group is reflected in the name of the compound as a suffix and is placed at the end of the name of the compound; all other groups are given in the name in the form of prefixes;

4) number the carbon atoms of the main chain, giving the highest group the smallest of the numbers;

5) list the prefixes in alphabetical order (in this case, multiplying prefixes di-, tri-, tetra-, etc. are not taken into account);

6) compose the full name of the compound.

Connection class	Functional group formula		Suffix or ending
carboxylic acids		Carboxy-	Oic acid
Sulphonic acids			Sulfonic acid
Aldehydes
		Hydroxy-
		Mercapto-
	С≡≡С
Halogen derivatives	-Br, -I, -F, -Cl	Bromine-, iodine-, fluorine-, chlorine-	-bromide, -iodide, -fluoride, -chloride
Nitro compounds

In doing so, you must remember:

In the names of alcohols, aldehydes, ketones, carboxylic acids, amides, nitriles, acid halides, the suffix defining the class follows the suffix of the degree of unsaturation: for example, 2-butenal;

Compounds containing other functional groups are referred to as hydrocarbon derivatives. The names of these functional groups are prefixed to the name of the parent hydrocarbon: for example, 1-chloropropane.

The names of acid functional groups, such as the sulfonic acid or phosphinic acid group, are placed after the name of the hydrocarbon skeleton: for example, benzenesulfonic acid.

Derivatives of aldehydes and ketones are often named after the parent carbonyl compound.

Esters of carboxylic acids are called as derivatives of parent acids. The ending -oic acid is replaced by -oate: for example, methyl propionate is the methyl ester of propanoic acid.

To indicate that a substituent is bonded to the nitrogen atom of the parent structure, a capital N is used before the name of the substituent: N-methylaniline.

Those. you need to start with the name of the parent structure, for which it is absolutely necessary to know by heart the names of the first 10 members of the homologous series of alkanes (methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane). You also need to know the names of the radicals formed from them - while the ending -an changes to -yl.

Consider the compound that is part of the drugs used to treat eye diseases:

CH 3 - C (CH 3) \u003d CH - CH 2 - CH 2 - C (CH 3) \u003d CH - CHO

The basic parent structure is an 8 carbon chain containing an aldehyde group and both double bonds. Eight carbon atoms - octane. But there are 2 double bonds - between the second and third atoms and between the sixth and seventh. One double bond - the ending -an must be replaced by -ene, double bonds 2, which means -diene, i.e. octadiene, and at the beginning we indicate their position, naming atoms with lower numbers - 2,6-octadiene. We have dealt with the ancestral structure and infinity.

But there is an aldehyde group in the compound, it is not a hydrocarbon, but an aldehyde, so we add the suffix -al, without a number, it is always the first - 2,6-octadienal.

Another 2 substituents are methyl radicals at the 3rd and 7th atoms. So, in the end we get: 3,7-dimethyl - 2,6-octadienal.

The largest event in the development of organic chemistry was the creation in 1961 by the great Russian scientist A.M. Butlerov theory of the chemical structure of organic compounds.

Before A.M. Butlerov, it was considered impossible to know the structure of the molecule, that is, the order of the chemical bond between atoms. Many scientists even denied the reality of atoms and molecules.

A.M. Butlerov refuted this opinion. He started from the right materialistic and philosophical ideas about the reality of the existence of atoms and molecules, about the possibility of knowing the chemical bond of atoms in a molecule. He showed that the structure of a molecule can be established empirically by studying the chemical transformations of a substance. Conversely, knowing the structure of the molecule, one can derive the chemical properties of the compound.

The theory of chemical structure explains the diversity of organic compounds. It is due to the ability of tetravalent carbon to form carbon chains and rings, combine with atoms of other elements and the presence of isomerism in the chemical structure of organic compounds. This theory laid the scientific foundations of organic chemistry and explained its most important regularities. The basic principles of his theory A.M. Butlerov stated in the report "On the theory of chemical structure".

The main provisions of the theory of structure are as follows:

1) in molecules, atoms are connected to each other in a certain sequence in accordance with their valency. The bonding order of atoms is called chemical structure;

2) the properties of a substance depend not only on which atoms and in what quantity are part of its molecule, but also on the order in which they are interconnected, that is, on the chemical structure of the molecule;

3) atoms or groups of atoms that formed a molecule mutually influence each other.

In the theory of chemical structure, much attention is paid to the mutual influence of atoms and groups of atoms in a molecule.

Chemical formulas that show the order in which atoms are combined in molecules are called structural formulas or building formulas.

The value of the theory of chemical structure of A.M. Butlerov:

1) is an essential part of the theoretical foundation of organic chemistry;

2) in importance it can be compared with the Periodic system of elements of D.I. Mendeleev;

3) it made it possible to systematize a huge amount of practical material;

4) made it possible to predict in advance the existence of new substances, as well as indicate ways to obtain them.

The theory of chemical structure serves as the guiding basis in all research in organic chemistry.

12 Phenols, hydroxy derivatives aromatic compounds, containing one or more hydroxyl groups (–OH) attached to the carbon atoms of the aromatic nucleus. By the number of OH groups, monoatomic phosphorus is distinguished, for example, oxybenzene C 6 H 5 OH, usually called simply phenol, oxytoluenes CH 3 C 6 H 4 OH - the so-called cresols, oxynaphthalenes - naphthols, diatomic, for example dioxybenzenes C 6 H 4 (OH) 2 ( hydroquinone, pyrocatechin, resorcinol), polyatomic, for example pyrogallol, phloroglucinol. F. - colorless crystals with a characteristic odor, less often liquids; well soluble in organic solvents (alcohol, ether, oenzol). Possessing acidic properties, F. form salt-like products - phenolates: ArOH + NaOH (ArONa + H 2 O (Ar is an aromatic radical). Alkylation and acylation of phenolates leads to F. esters - simple ArOR and complex ArOCOR (R - organic radical). Esters can be obtained by direct interaction of phosphorus with carboxylic acids, their anhydrides, and acid chlorides.When phenols are heated with CO 2, phenolic acids are formed, for example salicylic acid. Unlike alcohols, the hydroxyl group F. with great difficulty is replaced by a halogen. Electrophilic substitution in the nucleus of F. (halogenation, nitration, sulfonation, alkylation, etc.) is carried out much more easily than in unsubstituted aromatic hydrocarbons; replacement groups are sent to ortho- and pair-positions to the OH group (see. Rule orientations). Catalytic hydrogenation of F. leads to alicyclic alcohols, for example, C 6 H 5 OH is reduced to cyclohexanol. F. is also characterized by condensation reactions, for example, with aldehydes and ketones, which is used in industry to obtain phenol- and resorcinol-formaldehyde resins, diphenylolpropane, and other important products.

F. is obtained, for example, by hydrolysis of the corresponding halogen derivatives, alkaline melting of arylsulfonic acids ArSO 2 OH, isolated from coal tar, brown coal tar, etc. F. is an important raw material in the production of various polymers, adhesives, paints and varnishes, dyes, and drugs ( phenolphthalein, salicylic acid, salol), surfactants and fragrances. Some F. are used as antiseptics and antioxidants (for example, polymers, lubricating oils). For qualitative identification of F., solutions of ferric chloride are used, which form colored products with F.. F. toxic (see. Wastewater.).

13 Alkanes

general characteristics

Hydrocarbons are the simplest organic compounds, consisting of two elements: carbon and hydrogen. Limit hydrocarbons, or alkanes (international name), are compounds whose composition is expressed by the general formula C n H 2n + 2, where n is the number of carbon atoms. In molecules of saturated hydrocarbons, carbon atoms are interconnected by a simple (single) bond, and all other valences are saturated with hydrogen atoms. Alkanes are also called saturated hydrocarbons or paraffins (The term "paraffins" means "having a low affinity").

The first member of the homologous series of alkanes is methane CH 4 . The ending -an is typical for the names of saturated hydrocarbons. This is followed by ethane C 2 H 6, propane C 3 H 8, butane C 4 H 10. Starting from the fifth hydrocarbon, the name is formed from the Greek numeral, indicating the number of carbon atoms in the molecule, and the ending -an. These are C 5 H 12 pentane, C 6 H 14 hexane, C 7 H 16 heptane, C 8 H 18 octane, C 9 H 20 nonane, C 10 H 22 decane, etc.

In the homologous series, a gradual change in the physical properties of hydrocarbons is observed: the boiling and melting points increase, and the density increases. Under normal conditions (temperature ~ 22 ° C), the first four members of the series (methane, ethane, propane, butane) are gases, C 5 H 12 to C 16 H 34 are liquids, and C 17 H 36 are solids.

Alkanes, starting from the fourth member of the series (butane), have isomers.

All alkanes are saturated with hydrogen to the limit (maximum). Their carbon atoms are in a state of sp 3 hybridization, which means they have simple (single) bonds.

Nomenclature

The names of the first ten members of the series of saturated hydrocarbons have already been given. To emphasize that an alkane has an unbranched carbon chain, the word normal (n-) is often added to the name, for example:

CH 3 -CH 2 -CH 2 -CH 3 CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3

n-butane n-heptane

(normal butane) (normal heptane)

When a hydrogen atom is detached from an alkane molecule, one-valve particles are formed, called hydrocarbon radicals (abbreviated as R). The names of monovalent radicals are derived from the names of the corresponding hydrocarbons with the ending –an replaced by -yl. Here are the relevant examples:

Radicals are formed not only by organic but also by inorganic compounds. So, if we take away the OH hydroxyl group from nitric acid, we get a monovalent radical - NO 2, called a nitro group, etc.

When two hydrogen atoms are removed from a hydrocarbon molecule, divalent radicals are obtained. Their names are also derived from the names of the corresponding saturated hydrocarbons with the ending -an replaced by -ylidene (if the hydrogen atoms are detached from one carbon atom) or -ylene (if the hydrogen atoms are detached from two adjacent carbon atoms). The CH 2 = radical is called methylene.

The names of radicals are used in the nomenclature of many derivatives of hydrocarbons. For example: CH 3 I - methyl iodide, C 4 H 9 Cl - butyl chloride, CH 2 Cl 2 - methylene chloride, C 2 H 4 Br 2 - ethylene bromide (if bromine atoms are bonded to different carbon atoms) or ethylidene bromide (if bromine atoms are bonded to one carbon atom).

Two nomenclatures are widely used for the name of isomers: the old - rational and modern - substitution, which is also called systematic or international (proposed by the International Union of Pure and Applied Chemistry IUPAC).

According to the rational nomenclature, hydrocarbons are considered as derivatives of methane, in which one or more hydrogen atoms are replaced by radicals. If the same radicals are repeated several times in the formula, then they are indicated by Greek numerals: di - two, three - three, tetra - four, penta - five, hexa - six, etc. For example:

Rational nomenclature is convenient for not very complex connections.

According to substitutional nomenclature, the name is based on one carbon chain, and all other fragments of the molecule are considered as substituents. In this case, the longest chain of carbon atoms is chosen, and the chain atoms are numbered from the end closest to the hydrocarbon radical. Then they name: 1) the number of the carbon atom to which the radical is associated (starting with the simplest radical); 2) hydrocarbon, which corresponds to a long chain. If the formula contains several identical radicals, then before their name indicate the number in words (di-, tri-, tetra-, etc.), and the numbers of the radicals are separated by commas. Here is how hexane isomers should be named according to this nomenclature:

Here's a more complex example:

Both substitutional and rational nomenclature are used not only for hydrocarbons, but also for other classes of organic compounds. For some organic compounds, historically established (empirical) or so-called trivial names are used (formic acid, sulfuric ether, urea, etc.).

When writing the formulas of isomers, it is easy to notice that the carbon atoms occupy an unequal position in them. A carbon atom that is connected to only one carbon atom in the chain is called primary, with two - secondary, with three - tertiary, with four - Quaternary. So, for example, in the last example, carbon atoms 1 and 7 are primary, 4 and 6 are secondary, 2 and 3 are tertiary, 5 is quaternary. The properties of hydrogen atoms, other atoms, and functional groups depend on which carbon atom they are associated with: primary, secondary, or tertiary. This must always be taken into account.

Receipt. Properties.

physical properties. Under normal conditions, the first four members of the homologous series of alkanes (C 1 - C 4) are gases. Normal alkanes from pentane to heptadecane (C 5 - C 17) are liquids, starting from C 18 and above are solids. As the number of carbon atoms in the chain increases, i.e. with an increase in the relative molecular weight, the boiling and melting points of alkanes increase. With the same number of carbon atoms in a molecule, branched alkanes have lower boiling points than normal alkanes.

Alkanes are practically insoluble in water, since their molecules are low-polar and do not interact with water molecules, they dissolve well in non-polar organic solvents such as benzene, carbon tetrachloride, etc. Liquid alkanes mix easily with each other.

The main natural sources of alkanes are oil and natural gas. Various oil fractions contain alkanes from C 5 H 12 to C 30 H 62 . Natural gas consists of methane (95%) with an admixture of ethane and propane.

Of the synthetic methods for obtaining alkanes, the following can be distinguished:

1. Obtaining from unsaturated hydrocarbons. The interaction of alkenes or alkynes with hydrogen ("hydrogenation") occurs in the presence of metal catalysts (Ni, Pd) at
heating:

CH s -C≡CH + 2H 2 → CH 3 -CH 2 -CH 3.

2. Obtaining from halogenated. When monohalogenated alkanes are heated with sodium metal, alkanes with twice the number of carbon atoms are obtained (Wurtz reaction):

C 2 H 5 Br + 2Na + Br-C 2 H 5 → C 2 H 5 -C 2 H 5 + 2NaBr.

A similar reaction is not carried out with two different halogen-substituted alkanes, since this produces a mixture of three different alkanes

3. Obtaining from salts of carboxylic acids. When anhydrous salts of carboxylic acids are fused with alkalis, alkanes are obtained containing one less carbon atom compared to the carbon chain of the original carboxylic acids:

4. Obtaining methane. In an electric arc burning in a hydrogen atmosphere, a significant amount of methane is formed:

C + 2H 2 → CH 4.

The same reaction occurs when carbon is heated in a hydrogen atmosphere to 400–500°C at elevated pressure in the presence of a catalyst.

In laboratory conditions, methane is often obtained from aluminum carbide:

Al 4 C 3 + 12H 2 O \u003d ZSN 4 + 4Al (OH) 3.

Chemical properties. Under normal conditions, alkanes are chemically inert. They are resistant to many reagents: they do not interact with concentrated sulfuric and nitric acids, with concentrated and molten alkalis, they are not oxidized by strong oxidizing agents - potassium permanganate KMnO 4, etc.

The chemical stability of alkanes is explained by the high strength of C-C and C-H s-bonds, as well as their non-polarity. Nonpolar C-C and C-H bonds in alkanes are not prone to ionic cleavage, but are capable of cleaving homolytically under the action of active free radicals. Therefore, alkanes are characterized by radical reactions, as a result of which compounds are obtained where hydrogen atoms are replaced by other atoms or groups of atoms. Therefore, alkanes enter into reactions proceeding according to the mechanism of radical substitution, denoted by the symbol S R (from English, substitution radicalic). According to this mechanism, hydrogen atoms are most easily replaced at tertiary, then at secondary and primary carbon atoms.

1. Halogenation. When alkanes react with halogens (chlorine and bromine) under the action of UV radiation or high temperature, a mixture of products from mono- to polyhalogen-substituted alkanes is formed. The general scheme of this reaction is shown using methane as an example:

b) Chain growth. The chlorine radical takes away a hydrogen atom from the alkane molecule:

Cl + CH 4 → HCl + CH 3

In this case, an alkyl radical is formed, which takes away the chlorine atom from the chlorine molecule:

CH 3 + Cl 2 → CH 3 Cl + Cl

These reactions are repeated until chain termination occurs in one of the following reactions:

Cl + Cl → Cl 2, CH 3 + CH 3 → C 2 H 6, CH 3 + Cl → CH 3 Cl

Overall reaction equation:

In radical reactions (halogenation, nitration), first of all, hydrogen atoms are mixed at the tertiary, then at the secondary and primary carbon atoms. This is explained by the fact that the bond of the tertiary carbon atom with hydrogen is most easily broken homolytically (bond energy 376 kJ / mol), then the secondary one (390 kJ / mol) and only then the primary one (415 kJ / mol).

3. Isomerization. Normal alkanes can be converted to branched-chain alkanes under certain conditions:

4. Cracking is a hemolytic rupture of C-C bonds, which occurs when heated and under the action of catalysts.
When higher alkanes are cracked, alkenes and lower alkanes are formed; when methane and ethane are cracked, acetylene is formed:

C 8 H 18 → C 4 H 10 + C 4 H 8,

2CH 4 → C 2 H 2 + ZH 2,

C 2 H 6 → C 2 H 2 + 2H 2.

These reactions are of great industrial importance. In this way, high-boiling oil fractions (fuel oil) are converted into gasoline, kerosene and other valuable products.

5. Oxidation. With the mild oxidation of methane with atmospheric oxygen in the presence of various catalysts, methyl alcohol, formaldehyde, and formic acid can be obtained:

Soft catalytic oxidation of butane with atmospheric oxygen is one of the industrial methods for producing acetic acid:

t°
2C 4 H 10 + 5O 2 → 4CH 3 COOH + 2H 2 O.
cat

In air, alkanes burn to CO 2 and H 2 O:

C n H 2n + 2 + (Zn + 1) / 2O 2 \u003d nCO 2 + (n + 1) H 2 O.

Alkenes

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. Carbon atoms in a double bond are in a state of sp² hybridization.

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 "-an" with "-ene"; the position of the double bond is indicated by an Arabic numeral.

homologous series

Alkenes with more than three carbon atoms have isomers. Alkenes are characterized by isomerism of the carbon skeleton, double bond positions, interclass and geometric.

ethene	C2H4
propene	C3H6
n-butene	C4H8
n-pentene	C5H10
n-hexene	C6H12
n-heptene	C7H14
n-octene	C8H16
n-nonene	C9H18
n-decene	C10H20

Physical properties

Melting and boiling points increase with molecular weight and length of the main carbon chain.
Under normal conditions, alkenes from C2H4 to C4H8 are gases; from C5H10 to C17H34 - liquids, after C18H36 - solids. Alkenes are insoluble in water, but readily soluble in organic solvents.

Chemical properties

Alkenes are chemically active. Their chemical properties are determined by the presence of a double bond.
Ozonolysis: the alkene is oxidized to aldehydes (in the case of monosubstituted vicinal carbons), ketones (in the case of disubstituted vicinal carbons), or a mixture of aldehyde and ketone (in the case of a tri-substituted alkene on the double bond):

R1–CH=CH–R2 + O3 → R1–C(H)=O + R2C(H)=O + H2O
R1–C(R2)=C(R3)–R4+ O3 → R1–C(R2)=O + R3–C(R4)=O + H2O
R1–C(R2)=CH–R3+ O3 → R1–C(R2)=O + R3–C(H)=O + H2O

Ozonolysis under severe conditions - the alkene is oxidized to an acid:

R"–CH=CH–R" + O3 → R"–COOH + R"–COOH + H2O

Double bond attachment:
CH2=CH2 +Br2 → CH2Br-CH2Br

Oxidation with peracids:
CH2=CH2 + CH3COOOOH →
or
CH2=CH2 + HCOOH → HOCH2CH2OH

The largest event in the development of organic chemistry was the creation in 1961 by the great Russian scientist A.M. Butlerov's theory of the chemical structure of organic compounds.

Before A.M. Butlerov, it was considered impossible to know the structure of the molecule, that is, the order of the chemical bond between atoms. Many scientists even denied the reality of atoms and molecules.

A.M. Butlerov refuted this opinion. He proceeded from correct materialistic and philosophical ideas about the reality of the existence of atoms and molecules, about the possibility of knowing the chemical bond of atoms in a molecule. He showed that the structure of a molecule can be established empirically by studying the chemical transformations of a substance. Conversely, knowing the structure of the molecule, one can derive the chemical properties of the compound.

The theory of chemical structure explains the diversity of organic compounds. It is due to the ability of tetravalent carbon to form carbon chains and rings, combine with atoms of other elements and the presence of isomerism in the chemical structure of organic compounds. This theory laid the scientific foundations of organic chemistry and explained its most important regularities. The basic principles of his theory A.M. Butlerov stated in the report "On the theory of chemical structure".

The main provisions of the theory of structure are as follows:

1) in molecules, atoms are connected to each other in a certain sequence in accordance with their valency. The bonding order of atoms is called chemical structure;

2) the properties of a substance depend not only on which atoms and in what quantity are part of its molecule, but also on the order in which they are interconnected, that is, on the chemical structure of the molecule;

3) atoms or groups of atoms that formed a molecule mutually influence each other.

In the theory of chemical structure, much attention is paid to the mutual influence of atoms and groups of atoms in a molecule.

Chemical formulas, which depict the order of connection of atoms in molecules, are called structural formulas or structure formulas.

The value of the theory of chemical structure of A.M. Butlerov:

1) is an essential part of the theoretical foundation of organic chemistry;

2) in importance it can be compared with the Periodic system of elements of D.I. Mendeleev;

3) it made it possible to systematize a huge amount of practical material;

4) made it possible to predict in advance the existence of new substances, as well as indicate ways to obtain them.

The theory of chemical structure serves as the guiding basis in all research in organic chemistry.

5. Isomerism. The electronic structure of atoms of elements of small periods. Chemical bond

The properties of organic substances depend not only on their composition, but also on the order of connection of atoms in a molecule.

Isomers are substances that have the same composition and the same molar mass, but different molecular structure, and therefore have different properties.

Scientific significance of the theory of chemical structure:

1) deepens ideas about the substance;

2) indicates the way to the knowledge of the internal structure of molecules;

3) makes it possible to understand the facts accumulated in chemistry; predict the existence of new substances and find ways to synthesize them.

All this theory greatly contributed to the further development of organic chemistry and the chemical industry.

The German scientist A. Kekule expressed the idea of ​​connecting carbon atoms to each other in a chain.

The doctrine of the electronic structure of atoms.

Features of the doctrine of the electronic structure of atoms: 1) made it possible to understand the nature of the chemical bond of atoms; 2) find out the essence of the mutual influence of atoms.

The state of electrons in atoms and the structure of electron shells.

Electron clouds are areas of the greatest probability of an electron being present, which differ in their shape, size, and orientation in space.

In the atom hydrogen a single electron during its movement forms a negatively charged cloud of a spherical (spherical) shape.

S-electrons are electrons that form a spherical cloud.

The hydrogen atom has one s-electron.

In the atom helium are two s-electrons.

Features of the helium atom: 1) clouds of the same spherical shape; 2) the highest density is equally removed from the core; 3) electron clouds are combined; 4) form a common two-electron cloud.

Features of the lithium atom: 1) has two electronic layers; 2) has a cloud of spherical shape, but is much larger than the inner two-electron cloud; 3) the electron of the second layer is weaker attracted to the nucleus than the first two; 4) is easily captured by other atoms in redox reactions; 5) has an s-electron.

Features of the beryllium atom: 1) the fourth electron is an s-electron; 2) the spherical cloud coincides with the cloud of the third electron; 3) there are two paired s-electrons in the inner layer and two paired s-electrons in the outer.

The more electron clouds overlap when atoms connect, the more energy is released and the stronger chemical bond.