Butlerov's theory of the structure of organic compounds briefly. Butlerov Alexander Mikhailovich

The chemical nature of organic compounds, the properties that distinguish them from inorganic compounds, as well as their diversity are explained in the theory of chemical structure formulated by Butlerov in 1861 (see § 38).

According to this theory, the properties of compounds are determined by their qualitative and quantitative composition, chemical structure, i.e., the sequential order of connection between the atoms that form the molecule, and their mutual influence. The theory of the structure of organic compounds, developed and supplemented by the latest views in the field of chemistry and physics of atoms and molecules, especially ideas about the spatial structure of molecules, the nature of chemical bonds and the nature of the mutual influence of atoms, forms the theoretical basis of organic chemistry.

In the modern theory of the structure of organic compounds, the following provisions are basic.

1. All features of organic compounds are determined, first of all, by the properties of the element carbon.

In accordance with the place that carbon occupies in the periodic table, there are four electrons in the outer electron layer of its atom (-shell). It does not show a pronounced tendency to donate or gain electrons, in this regard it occupies an intermediate position between metals and non-metals and is characterized by a pronounced ability to form covalent bonds. The structure of the outer electron layer of the carbon atom can be represented by the following diagrams:

An excited carbon atom can participate in the formation of four covalent bonds. Therefore, in the vast majority of its compounds, carbon exhibits a covalency of four.

Thus, the simplest organic compound, the hydrocarbon methane, has the composition . Its structure can be depicted by structure (a) or electronic-structural (or electronic) (b) formulas:

The electronic formula shows that the carbon atom in the methane molecule has a stable eight-electron outer shell (electron octet), and the hydrogen atoms have a stable two-electron shell (electron doublet).

All four covalent carbon bonds in methane (and in other similar compounds) are equal and symmetrically directed in space. The carbon atom is located, as it were, in the center of a tetrahedron (regular tetrahedral pyramid), and the four atoms connected to it (in the case of methane, four atoms at the vertices of the tetrahedron (Fig. 120). The angles between the directions of any pair of bonds (carbon bond angles) are the same and amount to 109 ° 28".

This is explained by the fact that in a carbon atom, when it forms covalent bonds with four other atoms, from one s- and three p-orbitals, as a result of -hybridization, four hybrid -orbitals are formed symmetrically located in space, elongated towards the vertices of the tetrahedron.

Rice. 120. Tetrahedral model of the methane molecule.

Rice. 121. Scheme of formation of -bonds in a methane molecule.

As a result of the overlap of -hybrid electron clouds of carbon with electron clouds of other atoms (in methane with spherical clouds of -electrons of hydrogen atoms), four tetrahedrally oriented covalent -bonds are formed (Fig. 121; see also p. 131).

The tetrahedral structure of the methane molecule is clearly expressed by its spatial models - spherical (Fig. 122) or segmental (Fig. 123). White balls (segments) represent hydrogen atoms, black ones represent carbon atoms. The ball model characterizes only the relative spatial arrangement of atoms, the segment model also gives an idea of ​​the relative interatomic distances (distances between nuclei. As shown in Fig. 122, the structural formula of methane can be considered as a projection of its spatial model onto the drawing plane.

2. An exceptional property of carbon, which determines the variety of organic compounds, is the ability of its atoms to connect with strong covalent bonds to each other, forming carbon chains of almost unlimited length

The valences of carbon atoms that did not undergo mutual connection are used to attach other atoms or groups (in hydrocarbons - for the addition of hydrogen).

Thus, the hydrocarbons ethane and propane contain chains of two and three carbon atoms, respectively.

Rice. 122. Ball model of the methane molecule.

Rice. 123. Segment model of the methane molecule.

Their structure is expressed by the following structural and electronic formulas:

Compounds are known that contain hundreds or more carbon atoms in their chains.

Increasing the carbon chain by one carbon atom leads to an increase in composition by group. Such a quantitative change in composition leads to a new compound having slightly different properties, i.e., already qualitatively different from the original compound; however, the general nature of the connections remains. So, in addition to the hydrocarbons methane, ethane, propane, there are butane, pentane, etc. Thus, in a huge variety of organic substances, series of similar compounds can be identified, in which each subsequent member differs from the previous one by a group. Such series are called homological series, their members are homologues in relation to each other, and the existence of such series is called the phenomenon of homology.

Consequently, the hydrocarbons methane, stage, propane, butane, etc. are homologues of the same series, which is called the series of saturated, or saturated, hydrocarbons (alkanes) or, according to the first representative, the methane series.

Due to the tetrahedral orientation of carbon bonds, its atoms included in the chain are located not in a straight line, but in a zigzag pattern, and, due to the possibility of rotation of the atoms around the bond axis, the chain in space can take on different shapes (conformations):

This structure of the chains makes it possible for terminal (b) or other non-adjacent carbon atoms (c) to come closer together; As a result of the formation of bonds between these atoms, carbon chains can close into rings (cycles), for example:

Thus, the diversity of organic compounds is also determined by the fact that with the same number of carbon atoms in a molecule, compounds with an open, open chain of carbon atoms are possible, as well as substances whose molecules contain cycles (cyclic compounds).

3. Covalent bonds between carbon atoms formed by one pair of generalized electrons are called simple (or ordinary) bonds.

The bond between carbon atoms can be carried out not by one, but by two or three common pairs of electrons. Then we get chains with multiple - double or triple bonds; These connections can be depicted as follows:

The simplest compounds containing multiple bonds are the hydrocarbons ethylene (with a double bond) and acetylene (with a triple bond):

Hydrocarbons with multiple bonds are called unsaturated or unsaturated. Ethylene and acetylene are the first representatives of two homologous series - ethylene and acetylene hydrocarbons.

Rice. 124. Scheme of formation of -bonds in an ethane molecule.

A simple covalent bond (or C:C), formed by the overlap of two -hybrid electron clouds along a line connecting the centers of atoms (along the bond axis), as, for example, in ethane (Fig. 124), is an -bond (see § 42 ). Bonds are also -bonds - they are formed by the overlap along the bond axis of the -hybrid cloud of the C atom and the spherical cloud of the -electron of the H atom.

The nature of multiple carbon-carbon bonds is somewhat different. Thus, in the ethylene molecule, when a double covalent bond (or) is formed in each of the carbon atoms, one -orbital and only two p-orbitals (-hybridization) participate in hybridization; one of the p orbitals of each C atom does not hybridize. As a result, three -hybrid electron clouds are formed, which participate in the formation of three -bonds. There are a total of five bonds in the ethylene molecule (four and one); all of them are located in the same plane at angles of about 120° to each other (Fig. 125).

Thus, one of the electron pairs in the bond carries out an -bond, and the second is formed by p-electrons that do not participate in hybridization; their clouds retain the shape of a volumetric figure eight, are oriented perpendicular to the plane in which the -bonds are located, and overlap above and below this plane (Fig. 126), forming an -bond (see § 42).

Rice. 125. Scheme of formation of -bonds in an ethylene molecule.

Rice. 126. Scheme of formation of an -bond in an ethylene molecule.

Therefore, the double bond C=C is a combination of one and one -bonds.

A triple bond (or ) is a combination of one -bond and two -bonds. For example, when an acetylene molecule is formed in each of the carbon atoms, one -orbital and only one p-orbital (-hybridization) participates in hybridization; As a result, two -hybrid electron clouds are formed, participating in the formation of two -bonds. Clouds of two p-electrons of each C atom do not hybridize, retain their configuration and participate in the formation of two -bonds. Thus, in acetylene there are only three -bonds (one and two) directed along one straight line, and two -bonds oriented in two mutually perpendicular planes (Fig. 127).

Multiple (i.e., double and triple) bonds are easily converted into simple bonds during reactions; the triple first turns into a double, and the last one into a simple one. This is due to their high reactivity and occurs when any atoms are added to a pair of carbon atoms connected by a multiple bond.

The transition of multiple bonds into simple ones is explained by the fact that usually - bonds have less strength and therefore greater lability compared to - bonds. When β-bonds are formed, p-electron clouds with parallel axes overlap to a much lesser extent than electron clouds that overlap along the bond axis (i.e., hybrid, β-electron or bond-axis-oriented p-electron clouds).

Rice. 127. Scheme of formation of -bonds in an acetylene molecule.

Rice. 128. Models of the ethylene molecule: a - spherical; b - segmental.

Multiple bonds are stronger than simple ones. Thus, the energy of breaking a bond is , bonds, and bonds only .

From the above it follows that in the formulas, two dashes out of three in a connection and one dash out of two in a connection express connections that are less strong than a simple connection.

In Fig. 128 and 129 show spherical and segmented spatial models of compounds with double (ethylene) and triple (acetylene) bonds.

4. The theory of structure explained numerous cases of isomerism in organic compounds.

Chains of carbon atoms can be straight or branched:

Thus, the composition has three saturated hydrocarbons (pentane) with different chain structures - one with a straight chain (normal structure) and two with a branched chain (iso structure):

The composition has three unsaturated hydrocarbons, two of normal structure, but isomeric in the position of the double bond, and one of isostructure:

Rice. 129. Models of the acetylene molecule: a spherical; b - segmental.

These unsaturated compounds are isomers of two cyclic hydrocarbons, which also have a composition and are isomeric to each other in terms of cycle size:

With the same composition, compounds may differ in structure due to different positions in the carbon chain and other non-carbon atoms, for example:

Isomerism can be caused not only by a different order of connection of atoms. Several types of spatial isomerism (stereoisometry) are known, which consists in the fact that the corresponding isomers (stereoisomers) with the same composition and order of connection of atoms differ in different arrangements of atoms (or groups of atoms) in space.

Thus, if a compound contains a carbon atom bonded to four different atoms or groups of atoms (an asymmetric atom), then two spatially isomeric forms of such a compound are possible. In Fig. 130 shows two tetrahedral models of lactic acid, in which the asymmetric carbon atom (marked with an asterisk in the formula) is located in the center of the tetrahedron. It is easy to notice that these models cannot be combined in space: they are built mirror-like and reflect the spatial configuration of the molecules of two different substances (in this example, lactic acids), differing in some physical, and mainly biological properties. Such isomerism is called mirror stereoisomerism, and the corresponding isomers are called mirror isomers.

Rice. 130. Tetrahedral models of molecules of mirror isomers of lactic acid.

The difference in the spatial structure of mirror isomers can also be represented using structural formulas, which show the different arrangement of atomic groups at an asymmetric atom; for example, for those shown in Fig. 130 mirror image isomers of lactic acid:

As already indicated, carbon atoms; connected by a double bond, lie in the same plane with four bonds connecting them to other atoms; the angles between the directions of these connections are approximately the same (Fig. 126). When different atoms or groups are connected to each of the carbon atoms in a double bond, so-called geometric stereoisomerism, or cis-trans isomerism, is possible. An example is the spatial geometric isomers of dichlorethylene

In the molecules of one isomer, the chlorine atoms are located on one side of the double bond, and in the molecules of the other - on opposite sides. The first configuration is called cis, the second - trans configuration. Geometric isomers differ from each other in physical and chemical properties.

Their existence is due to the fact that the double bond excludes the possibility of free rotation of the connected atoms around the bond axis (such rotation requires breaking the -bond; see Fig. 126).

5. Mutual influence in molecules of organic substances is manifested primarily by atoms directly connected to each other. In this case, it is determined by the nature of the chemical bond between them, the degree of difference in their relative electronegativity and, consequently, the degree of polarity of the bond.

For example, judging by the summary formulas, then in a methane molecule and in a methyl alcohol molecule all four hydrogen atoms should have the same properties. But, as will be shown later, in methyl alcohol one of the hydrogen atoms is capable of being replaced by an alkali metal, while in methane the hydrogen atoms do not show this ability. This is explained by the fact that in alcohol the hydrogen atom is directly bonded not to carbon, but to oxygen

In the given structural formulas, the arrows on the bond lines conventionally indicate the displacement of pairs of electrons forming a covalent bond due to different electronegativity of the atoms. In methane, such a shift in the bond is small, since the electronegativity of carbon (2.5) only slightly exceeds the electronegativity of hydrogen in Table. 6, p. 118). In this case, the methane molecule is symmetrical. In the alcohol molecule, the bond is significantly polarized, since oxygen (electronegativity 3.5) attracts an electron pair much more; therefore, a hydrogen atom connected to an oxygen atom acquires greater mobility, i.e., it is easier to break off in the form of a proton.

In organic molecules, the mutual influence of atoms not directly connected to each other is also important. Thus, in methyl alcohol, under the influence of oxygen, the reactivity of not only the hydrogen atom associated with oxygen increases, but also the hydrogen atoms not directly associated with oxygen, but connected with carbon. Due to this, methyl alcohol is quite easily oxidized, while methane is relatively resistant to oxidizing agents. This is explained by the fact that the oxygen of the hydroxyl group significantly attracts a pair of electrons to itself in the bond connecting it to carbon, which has a lower electronegativity.

As a result, the effective charge of the carbon atom becomes more positive, which causes an additional displacement of electron pairs also in the bonds in methyl alcohol, compared to the same bonds in the methane molecule. Under the action of oxidizing agents, H atoms bonded to the same carbon atom with which the OH group is bonded are much easier to break off than in hydrocarbons and combine with oxygen, forming water. In this case, the carbon atom associated with the OH group undergoes further oxidation (see § 171).

The mutual influence of atoms not directly connected to each other can be transmitted over a considerable distance along a chain of carbon atoms and is explained by a shift in the density of electron clouds in the entire molecule under the influence of atoms or groups of different electronegativity present in it. Mutual influence can also be transmitted through the space surrounding the molecule - as a result of overlapping electron clouds of approaching atoms.

Man has long learned to use various substances to prepare food, dyes, clothing, and medicines. 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 studying organic substances, new difficulties have arisen: based on theories about inorganic substances, it is impossible to reveal the laws 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 designated the valency of elements with dashes, we will depict the ethane molecule in the order of connection of atoms, that is, we will write the 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

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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 by 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 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 Ultimate 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 polyines C P H 2 P -2

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

Classes of hydrocarbon derivatives based on 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 COOCH 2 CH 3 (ethyl acetic acid);

Carbonyl compounds: aldehydes R–CHO:

ketones R–СО–R: CH 3 COCH 3 (propanone), C 6 H 5 COCH 3 (methyl phenylketone);

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 compounds similar in structure, possessing similar chemical properties, in which individual members of the series differ from each other only in the number of -CH 2 - groups, is called homologous series and the -CH 2 group is a homological difference . For members of a homologous series, the vast majority of reactions proceed in the same way (with the exception of only the first members of the series). Consequently, knowing the chemical reactions of only one member of the series, it can be stated with a high degree of probability that the same type of transformation occurs with the remaining members of the homologous series.

For any homologous series, a general formula can be derived that reflects the relationship between the carbon and hydrogen atoms of the members of this series; like this the formula is called general formula of the homologous series. Yes, S P H 2 P+2 – formula of alkanes, C 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, from the name it is immediately clear where malic, succinic or citric acid was isolated, how pyruvic acid was obtained (pyrolysis of grape acid), connoisseurs of the Greek language will easily guess that acetic acid is something sour, and glycerin is sweet. As new organic compounds were synthesized and the theory of their structure developed, other nomenclatures were created that reflected the structure of the compound (its belonging to a certain class).

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

IUPAC nomenclature (systematic nomenclature). According to IUPAC (International Union of 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.

To correctly (and unambiguously) name an organic compound using systematic nomenclature, you must:

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

2) identify All functional groups present in the compound;

3) establish which group is senior (see table), the name of this group is reflected in the name of the compound in the form of a suffix and it 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 lowest number;

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

6) write down the full name of the compound.

It is necessary to 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 called hydrocarbon derivatives. The names of these functional groups are placed as prefixes before the name of the parent hydrocarbon: for example, 1-chloropropane.

The names of acidic functional groups, such as sulfonic acid or phosphinic acid, 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 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 the substituent is bonded to the nitrogen atom of the parent structure, use a capital letter N 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 - in this case, the ending -an changes to -il.

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

CH 3 – C(CH 3) = CH – CH 2 – CH 2 – C(CH 3) = CH – CHO

The basic parent structure is a chain of 8 carbon atoms, including an aldehyde group and both double bonds. Eight carbon atoms are 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 with -ene, there are 2 double bonds, which means -diene, i.e. octadiene, and at the beginning we indicate their position, naming the atoms with lower numbers - 2,6-octadiene. We have dealt with the original structure and indefiniteness.

But the compound contains an aldehyde group, 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.

By the first half of the 19th century, an enormous amount of factual material had been accumulated in organic chemistry, the further study of which was hampered by the lack of any systematizing basis. Starting from the 20s of the 19th century, successive theories began to appear, claiming to be a generalized description of the structure of organic compounds. One of them was the theory of types, developed in the 1960s by the French scientist C. Gerard. According to this theory, all organic compounds were considered as derivatives of the simplest inorganic substances, taken as types.Sh. Gerard

Shortly before the appearance of the theory of the structure of A.M. Butlerov, the German chemist F.A. Kekule (1857) developed the theory of valence in relation to organic compounds, which established such facts as the tetravalency of the carbon atom and its ability to form carbon chains due to combination with carbon atoms.A. M. Butlerova F.A. Kekule

Theoretical developments of the pre-Butler period made a certain contribution to the knowledge of the structure of organic compounds. But none of the early theories was universal. And only A.M. Butlerov managed to create such a logically complete theory of structure, which to this day serves as the scientific basis of organic chemistry. Theory of the structure of A.M. Butlerov is based on a materialistic approach to a real molecule and proceeds from the possibility of knowing its structure experimentally. A.M. Butlerov attached fundamental importance to chemical reactions when establishing the structure of substances. Theory of the structure of A.M. Butlerova not only explained already known facts, her scientific significance lay in predicting the existence of new organic compounds. A.M. Butlerov A.M. Butlerova A.M. Butlerov A.M. Butlerov

Isomers are substances that have the same molecular formula, but different chemical structures, and therefore have different properties. Isomerism received a genuine explanation only in the second half of the 19th century on the basis of the theory of chemical structure by A.M. Butlerov (structural isomerism) and the stereochemical teachings of Ya. G. Van't Hoff (spatial isomerism). Ya. G. van't Hoff

FormulaName Number of isomers CH 4 methane1 C4H6C4H6 ethane1 C3H8C3H8 propane1 C 4 H 10 butane2 C 5 H 12 pentane3 C 6 H 14 hexane5 C 7 H 16 heptane9 C 8 H 18 octane18 C 9 H 20 nonane35 C 10 H 22 decane75 C 11 H 24 undecane159 C 12 H 26 dodecane355 C 13 H 28 tridecane802 C 14 H 30 tetradecane1 858 C 15 H 32 pentadecane4 347 C 20 H 42 eicosane C 25 H 52 pentacosane C 30 H 62 triacontane C 40 H 82 tetracontane

Structural isomers are those that correspond to different structural formulas of organic compounds (with different orders of atoms). Spatial isomers have the same substituents on each carbon atom and differ only in their relative location in space.

Spatial isomers (stereoisomers). Stereoisomers can be divided into two types: geometric isomers and optical isomers. Geometric isomerism is characteristic of compounds containing a double bond or ring. In such molecules it is often possible to draw a conventional plane in such a way that the substituents on different carbon atoms can be on the same side (cis-) or on opposite sides (trans-) of this plane. If a change in the orientation of these substituents relative to the plane is possible only due to the breaking of one of the chemical bonds, then they speak of the presence of geometric isomers. Geometric isomers differ in their physical and chemical properties.

A new method for obtaining optical isomers of organic molecules has been discovered. When Alice found herself in her own, but “mirror” room, she was surprised: the room seemed similar, but still completely different. Mirror isomers of chemical molecules differ in the same way: they look similar, but behave differently. A critical area of ​​organic chemistry is the separation and synthesis of these mirror variants. (Illustration by John Tenniel for Lewis Carroll's book "Alice Through the Looking Glass")

American scientists have learned to obtain optical isomers of aldehyde-based compounds, finally carrying out an important reaction that chemists have been working on for many years. In the experiment, they combined two catalysts operating on different principles. As a result of the combined action of these catalysts, two active organic molecules are formed, which combine to form the desired substance. Using this reaction as an example, the possibility of synthesizing a whole class of biologically important organic compounds is demonstrated.

At least 130 organic synthesis reactions are now known in which more or less pure chiral isomers are obtained. If the catalyst itself has chiral properties, then an optically active product will be obtained from an optically inactive substrate. This rule was derived at the beginning of the 20th century and remains basic today. The principle of selective action of a catalyst in relation to optical isomers is similar to a handshake: it is “convenient” for the catalyst to bind to only one of the chiral isomers, and therefore only one of the reactions is preferentially catalyzed. By the way, the term “chiral” comes from the Greek chéir hand.

Organic chemistry- a branch of chemistry in which carbon compounds, their structure, properties, and interconversions are studied.

The very name of the discipline - “organic chemistry” - arose quite a long time ago. The reason for this lies in the fact that most of the carbon compounds encountered by researchers at the initial stage of the development of chemical science were of plant or animal origin. However, as an exception, individual carbon compounds are classified as inorganic. For example, carbon oxides, carbonic acid, carbonates, bicarbonates, hydrogen cyanide and some others are considered to be inorganic substances.

Currently, just under 30 million different organic substances are known, and this list is constantly growing. Such a huge number of organic compounds is associated primarily with the following specific properties of carbon:

1) carbon atoms can be connected to each other in chains of arbitrary length;

2) not only a sequential (linear) connection of carbon atoms with each other is possible, but also a branched and even cyclic one;

3) different types of bonds between carbon atoms are possible, namely single, double and triple. Moreover, the valence of carbon in organic compounds is always four.

In addition, the wide variety of organic compounds is also facilitated by the fact that carbon atoms are able to form bonds with atoms of many other chemical elements, for example, hydrogen, oxygen, nitrogen, phosphorus, sulfur, and halogens. In this case, hydrogen, oxygen and nitrogen are most common.

It should be noted that for quite a long time organic chemistry represented a “dark forest” for scientists. For some time, the theory of vitalism was even popular in science, according to which organic substances cannot be obtained “artificially”, i.e. outside of living matter. However, the theory of vitalism did not last very long, due to the fact that one after another substances were discovered whose synthesis is possible outside living organisms.

Researchers were perplexed by the fact that many organic substances have the same qualitative and quantitative composition, but often have completely different physical and chemical properties. For example, dimethyl ether and ethyl alcohol have exactly the same elemental composition, but under normal conditions dimethyl ether is a gas, and ethyl alcohol is a liquid. In addition, dimethyl ether does not react with sodium, but ethyl alcohol reacts with it, releasing hydrogen gas.

Researchers of the 19th century put forward many assumptions regarding how organic substances actually work. Significantly important assumptions were put forward by the German scientist F.A. Kekule, who was the first to express the idea that atoms of different chemical elements have specific valence values, and carbon atoms in organic compounds are tetravalent and are capable of combining with each other to form chains. Later, starting from Kekule’s assumptions, the Russian scientist Alexander Mikhailovich Butlerov developed a theory of the structure of organic compounds, which has not lost its relevance in our time. Let's consider the main provisions of this theory:

1) all atoms in molecules of organic substances are connected to each other in a certain sequence in accordance with their valency. Carbon atoms have a constant valency of four and can form chains of different structures with each other;

2) the physical and chemical properties of any organic substance depend not only on the composition of its molecules, but also on the order in which the atoms in this molecule are connected to each other;

3) individual atoms, as well as groups of atoms in a molecule, influence each other. This mutual influence is reflected in the physical and chemical properties of the compounds;

4) by studying the physical and chemical properties of an organic compound, its structure can be established. The opposite is also true - knowing the structure of the molecule of a particular substance, you can predict its properties.

Just as D.I. Mendelev’s periodic law became the scientific foundation of inorganic chemistry, the theory of the structure of organic substances by A.M. Butlerov actually became the starting point in the development of organic chemistry as a science. It should be noted that after the creation of Butlerov’s theory of structure, organic chemistry began its development at a very rapid pace.

Isomerism and homology

According to the second position of Butlerov’s theory, the properties of organic substances depend not only on the qualitative and quantitative composition of the molecules, but also on the order in which the atoms in these molecules are connected to each other.

In this regard, the phenomenon of isomerism is widespread among organic substances.

Isomerism is a phenomenon when different substances have exactly the same molecular composition, i.e. same molecular formula.

Very often, isomers differ greatly in physical and chemical properties. For example:

Types of isomerism

Structural isomerism

a) Isomerism of the carbon skeleton

b) Positional isomerism:

multiple connection

deputies:

functional groups:

c) Interclass isomerism:

Interclass isomerism occurs when compounds that are isomers belong to different classes of organic compounds.

Spatial isomerism

Spatial isomerism is a phenomenon when different substances with the same order of attachment of atoms to each other differ from each other by a fixed-different position of atoms or groups of atoms in space.

There are two types of spatial isomerism - geometric and optical. Tasks on optical isomerism are not found on the Unified State Exam, so we will consider only geometric ones.

If the molecule of a compound contains a double C=C bond or a ring, sometimes in such cases the phenomenon of geometric or cis-trans-isomerism.

For example, this type of isomerism is possible for butene-2. Its meaning is that the double bond between carbon atoms actually has a planar structure, and the substituents on these carbon atoms can be fixedly located either above or below this plane:

When identical substituents are on the same side of the plane they say that it is cis-isomer, and when they are different - trance-isomer.

On in the form of structural formulas cis- And trance-isomers (using butene-2 ​​as an example) are depicted as follows:

Note that geometric isomerism is impossible if at least one carbon atom at the double bond has two identical substituents. For example, cis-trans- isomerism is not possible for propene:

As you can see from the illustration above, if we swap places between the methyl radical and the hydrogen atom located at the second carbon atom, on opposite sides of the plane, we get the same molecule that we just looked at from the other side.

The influence of atoms and groups of atoms on each other in molecules of organic compounds

The concept of chemical structure as a sequence of atoms connected to each other was significantly expanded with the advent of electronic theory. From the standpoint of this theory, it is possible to explain how atoms and groups of atoms in a molecule influence each other.

There are two possible ways in which one part of a molecule influences another:

1) Inductive effect

2) Mesomeric effect

Inductive effect

To demonstrate this phenomenon, let us take as an example the 1-chloropropane molecule (CH 3 CH 2 CH 2 Cl). The bond between carbon and chlorine atoms is polar because chlorine has a much higher electronegativity compared to carbon. As a result of the shift of electron density from the carbon atom to the chlorine atom, a partial positive charge (δ+) is formed on the carbon atom, and a partial negative charge (δ-) is formed on the chlorine atom:

The shift in electron density from one atom to another is often indicated by an arrow pointing towards the more electronegative atom:

However, an interesting point is that, in addition to the shift in electron density from the first carbon atom to the chlorine atom, there is also a shift, but to a slightly lesser extent, from the second carbon atom to the first, as well as from the third to the second:

This shift in electron density along a chain of σ bonds is called the inductive effect ( I). This effect fades away with distance from the influencing group and practically does not appear after 3 σ bonds.

In the case where an atom or group of atoms has greater electronegativity compared to carbon atoms, such substituents are said to have a negative inductive effect (- I). Thus, in the example discussed above, the chlorine atom has a negative inductive effect. In addition to chlorine, the following substituents have a negative inductive effect:

–F, –Cl, –Br, –I, –OH, –NH 2 , –CN, –NO 2 , –COH, –COOH

If the electronegativity of an atom or group of atoms is less than the electronegativity of a carbon atom, there is actually a transfer of electron density from such substituents to the carbon atoms. In this case, they say that the substituent has a positive inductive effect (+ I) (is electron donor).

So, substituents with + I-the effect is saturated hydrocarbon radicals. At the same time, the expression + I-effect increases with lengthening of the hydrocarbon radical:

–CH 3 , –C 2 H 5 , –C 3 H 7 , –C 4 H 9

It should be noted that carbon atoms located in different valence states also have different electronegativity. Carbon atoms in the sp 2 -hybridized state have greater electronegativity compared to carbon atoms in the sp 2 -hybridized state, which, in turn, are more electronegative than carbon atoms in the sp 3 -hybridized state.

Mesomeric effect (M), or conjugation effect, is the influence of a substituent transmitted through a system of conjugated π bonds.

The sign of the mesomeric effect is determined according to the same principle as the sign of the inductive effect. If a substituent increases the electron density in a conjugated system, it has a positive mesomeric effect (+ M) and is electron-donating. Double carbon-carbon bonds and substituents containing a lone electron pair: -NH 2 , -OH, halogens have a positive mesomeric effect.

Negative mesomeric effect (– M) have substituents that withdraw electron density from the conjugated system, while the electron density in the system decreases.

The following groups have a negative mesomeric effect:

–NO 2 , –COOH, –SO 3 H, -COH, >C=O

Due to the redistribution of electron density due to mesomeric and inductive effects in the molecule, partial positive or negative charges appear on some atoms, which is reflected in the chemical properties of the substance.

Graphically, the mesomeric effect is shown by a curved arrow that begins at the center of the electron density and ends where the electron density shifts. For example, in a vinyl chloride molecule, the mesomeric effect occurs when the lone electron pair of the chlorine atom couples with the electrons of the π bond between the carbon atoms. Thus, as a result of this, a partial positive charge appears on the chlorine atom, and the mobile π-electron cloud, under the influence of an electron pair, is shifted towards the outermost carbon atom, on which a partial negative charge arises as a result:

If a molecule has alternating single and double bonds, then the molecule is said to contain a conjugated π-electron system. An interesting property of such a system is that the mesomeric effect does not decay in it.