The author of the theory of the structure of organic substances in chemistry. The main provisions of the theory of the chemical structure of organic substances AM Butlerov. And also other works that may interest you

Created by A.M. Butlerov in the 60s of the XIX century, the theory of the chemical structure of organic compounds brought the necessary clarity to the reasons for the variety of organic compounds, revealed the relationship between the structure and properties of these substances, made it possible to explain the properties of already known and predict the properties of not yet discovered organic compounds.

Discoveries in the area organic chemistry (carbon tetravalence, the ability to form long chains) allowed Butlerov in 1861 to formulate the main generations of the theory:

1) The atoms in the molecules are connected according to their valence (carbon-IV, oxygen-II, hydrogen-I), the sequence of the connection of atoms is reflected by the structural formulas.

2) The properties of substances depend not only on chemical composition, but also on the order of connection of atoms in a molecule (chemical structure). Exists isomers, that is, substances that have the same quantitative and qualitative composition, but a different structure, and, therefore, different properties.

C 2 H 6 O: CH 3 CH 2 OH - ethyl alcohol and CH 3 OCH 3 - dimethyl ether

C 3 H 6 - propene and cyclopropane - CH 2 \u003d CH − CH 3

3) Atoms mutually influence each other, this is a consequence of the different electronegativity of the atoms that form the molecules (O\u003e N\u003e C\u003e H), and these elements have a different effect on the displacement of common electron pairs.

4) By the structure of the molecule of organic matter, you can predict its properties, and by the properties, you can determine the structure.

The TCOC received further development after the establishment of the structure of the atom, the adoption of the concept of the types of chemical bonds, the types of hybridization, the discovery of the phenomenon of spatial isomerism (stereochemistry).

Ticket number 7 (2)

Electrolysis as a redox process. Electrolysis of melts and solutions by the example of sodium chloride. Practical use electrolysis.

Electrolysisis a redox process that occurs on the electrodes during the passage of a constant electric current through a melt or electrolyte solution

The essence of electrolysis is the implementation of chemical energy due to electrical energy. Reactions - reduction at the cathode and oxidation at the anode.

The cathode (-) donates electrons to cations, and the anode (+) receives electrons from anions.

NaCl melt electrolysis

NaCl -―\u003e Na + + Cl -

K (-): Na + + 1e -―\u003e Na 0 | 2 percent recovery

A (+): 2Cl-2e -―\u003e Cl 2 0 | 1 percent oxidation

2Na + + 2Cl - -―\u003e 2Na + Cl 2

Electrolysis of an aqueous solution of NaCl

In the electrolysis of NaC solution | ions Na + and Cl -, as well as water molecules, participate in water. With the passage of current, Na + cations move to the cathode, and Cl - anions - to the anode. But at the cathode instead of Na ions, water molecules are reduced:

2H 2 O + 2e -―\u003e H 2 + 2OH -

and chloride ions are oxidized at the anode:

2Cl - -2e -―\u003e Cl 2

As a result, hydrogen is at the cathode, chlorine at the anode, and NaOH accumulates in the solution

In ionic form: 2H 2 O + 2e -―\u003e H 2 + 2OH-

2Cl - -2e -―\u003e Cl 2

electrolysis

2H 2 O + 2Cl - -―\u003e H 2 + Cl 2 + 2OH -

electrolysis

In molecular form: 2H 2 O + 2NaCl -―\u003e 2NaOH + H 2 + Cl 2

Electrolysis Application:

1) Protection of metals from corrosion

2) Obtaining active metals (sodium, potassium, alkaline earth, etc.)

3) Purification of some metals from impurities (electric refining)

Ticket number 8 (1)

Similar information:

A) Theory of knowledge is a science that studies the forms, methods and methods of the emergence and patterns of development of knowledge, its relationship to reality, the criteria for its truth.

The generally accepted basic provisions of Butlerov's theory are considered the foundation of modern chemistry. The scientist was the first to explain the features. He studied in detail the nature of the interconnections of atoms.

Background of the theory

Alexander Butlerov became the founder of a new theory just when science accumulated many questions to which scientists could not find answers. For example, explanations required the phenomena of valence and isomerism. In addition, chemists continued to argue about how to correctly write chemical formulas. Butlerov clarified this issue. He proved that the formulas should reflect the structure of the substance.

In addition, there were several concepts that were opposite to the views expressed by Butlerov. This was the theory of the radicals. Jens Berzelius became its founder. He argued that molecules have special elements - radicals that pass from one substance to another. There was also a theory of types. Its supporters believed that all complex substances are derivatives of simple organic matter - water, hydrogen, ammonia, etc. All these concepts contradicted each other. Science needed a theory that would put everything in its place.

New ideas of Butlerov

Alexander Mikhailovich Butlerov (1828-1886) was one of the outstanding chemists of his time. He dealt with theoretical issues of his science a lot. In 1858, the scientist spoke at a meeting of the Paris Chemical Society. At the same time, for the first time, the main provisions of Butlerov's theory sounded from his lips.

The researcher used new terms in his report, which later became entrenched in international science. For example, it was he who became the author of the concept of the structure of connections. The scientist believed that the structure of different substances allows them to be attributed to the same groups (in particular, this is methane, chloroform, methyl alcohol etc.).

Study of the synthesis of substances

In 1861, in the published report "On the chemical structure of matter", the main provisions of the theory of chemical structure of AM Butlerov were formulated. The scientist described in detail the methods of synthesis and use of different reactions. One of the most important theses of the chemist was his assertion that each chemical has one formula. Its importance lies in the fact that it characterizes all properties and shows the connection of atoms within molecules.

Butlerov's theory also envisioned that new substances could be produced using controlled reactions. In the years that followed, the famous chemist and his students carried out many experiments to prove this assumption. They managed to synthesize new substances such as isobutylene and some alcohols. For their era, these discoveries were of colossal significance, which can be compared only with the importance of determining other elements by Mendeleev (for example, ekabor).

Systematization of chemistry

In the 19th century, the main provisions of Butlerov's theory completely changed the idea of \u200b\u200bscientists about the elements. In particular, the researcher was the first to suggest that molecules are not a chaotic accumulation of atoms. On the contrary, they have an ordered structure. Atoms are connected to each other in a certain sequence, which also determines the nature of the whole substance.

Butlerov, developing his theory, relied on mathematical principles and laws. With the help of this science, he was able to explain most of the processes and relationships in chemicals. It was a real revolution for contemporaries. The fact was that even if scientists knew some facts about the nature of certain substances, they could not build their knowledge into a clear systematized picture. The main provisions of the theory of the structure of Butlerov solved this problem. Now chemistry was not a scattered piggy bank of facts, but a harmonious system, where everything was subject to strict mathematical logic.

Variety of substances

The famous theory of Butlerov pays much attention to isomerism - a phenomenon consisting in the existence of isomers - substances equal in molecular mass and atomic composition, which at the same time differ from each other in the arrangement of atoms and structure. This feature explains the variety of properties of substances in nature.

Butlerov proved his theory on the example of butane. According to the scientist's idea, there should have been two types of this substance in nature. However, science knew only one butane at the time. Butlerov conducted many experiments and nevertheless received a new substance, similar in composition, but different in properties. It was named isobutane.

Influence of atoms on each other

Butlerov discovered another important pattern. With the formation of chemical bonds, the process of transition of electrons from one atom to another begins. At the same time, their density changes. Electron pairs arise, which affect the property of the newly formed substance. The scientist studied this phenomenon using the example of hydrogen chloride, where chlorine changes the electron density of hydrogen bonds.

Butlerov and the main provisions of the theory of structure were able to explain the nature of the transformation of substances. Later, the discovered principle was studied in detail by his followers and students. Understanding the mechanism of change in substances allowed scientists to understand how to synthesize new elements. A special surge of these discoveries began at the end of the 19th century. Then European and American scientists in new laboratories, using the methods proposed by Butlerov, were able to produce new substances.

Chemical bonds

Butlerov believed that the structure of substances can be studied by chemical methods. This position was confirmed thanks to the many successful experiments of the scientist. Also, the researcher was a supporter of the idea that formulas can be correct only if they reflect the order of chemical bonds of different atoms. Butlerov has been analyzing this assumption for many years.

He distinguished three types of bonds - simple, double and triple. The scientist was right, but further development science has shown that there are other chemical bonds. In particular, now specialists can also characterize them with the help of physical parameters.

Development of the Butlerov theory

AM Butlerov's new theory of the structure of chemical compounds was materialistic in nature. The scientist was the first to boldly declared that researchers are able to study the properties of atoms, from which all elements are built. At the same time, Butlerov himself regarded his theory as temporary. He believed that his successors should develop it, since it did not fully explain some of the facts of chemical science.

The scientist was right. Later, Butlerov's theory developed in two directions. The first was that science was able to determine not only the order of connection, but also the spatial arrangement of atoms in a molecule. This is how stereochemistry arose. This discipline began to investigate in detail Butlerov himself spoke about this new direction, although during his lifetime he did not have time to study this theoretical question.

The second direction in the development of the scientist's theory was the emergence of a doctrine devoted to the electronic structure of atoms. It is not only a chemical but also a physical discipline. The essence of the mutual influence of atoms was investigated in more detail and the reasons for the manifestation of different properties were explained. It was the basic provisions of Butlerov's theory that allowed scientists to achieve such success.

Just as in inorganic chemistry, the fundamental theoretical basis is the Periodic Law and Periodic system chemical elements of D.I. Mendeleev, so in organic chemistry the leading scientific basis is the theory of the structure of organic compounds Butlerov-Kekule-Cooper.

Like any other scientific theory, the theory of the structure of organic compounds was the result of a generalization of the richest factual material accumulated by organic chemistry, which took shape as a science at the beginning of the 19th century. More and more new carbon compounds were discovered, the number of which increased like an avalanche (Table 1).

Table 1
The number of organic compounds known in different years

To explain this variety of organic compounds, scientists of the early 19th century. could not. The phenomenon of isomerism raised even more questions.

For example, ethyl alcohol and dimethyl ether are isomers: these substances have the same composition C 2 H 6 O, but a different structure, that is, a different order of connection of atoms in molecules, and therefore different properties.

F. Wöhler, already familiar to you, in one of his letters to J. Ya. Berzelius described organic chemistry as follows: “Organic chemistry can now drive anyone crazy. It seems to me like a dense forest, full of amazing things, an endless thicket, from which you cannot get out, where you dare not enter ... "

The development of chemistry was greatly influenced by the work of the English scientist E. Frankland, who, relying on the ideas of atomistics, introduced the concept of valence (1853).

In the hydrogen molecule H 2, one covalent chemical is formed communication N-Nthat is, hydrogen is monovalent. The valence of a chemical element can be expressed by the number of hydrogen atoms that one atom of a chemical element attaches to itself or replaces. For example, sulfur in hydrogen sulfide and oxygen in water are divalent: H 2 S, or H-S-H, H 2 O, or H-O-H, and nitrogen in ammonia is trivalent:

In organic chemistry, the concept of "valence" is analogous to the concept of "oxidation state", with which you are used to working in the course of inorganic chemistry in basic school. However, they are not the same thing. For example, in a nitrogen molecule N 2, the oxidation state of nitrogen is zero, and the valence is three:

In hydrogen peroxide H 2 O 2, the oxidation state of oxygen is -1, and the valence is two:

In the ammonium ion NH + 4, the oxidation state of nitrogen is -3, and the valence is four:

Usually in relation to ionic compounds (sodium chloride NaCl and many other inorganic substances with an ionic bond), the term "valence" of atoms is not used, but their oxidation state is considered. Therefore, in inorganic chemistry, where most substances have a non-molecular structure, it is preferable to use the concept of "oxidation state", and in organic chemistry, where most compounds have a molecular structure, as a rule, the concept of "valence" is used.

The theory of chemical structure is the result of generalizing the ideas of prominent organic scientists from three European countries: the German F. Kekule, the Englishman A. Cooper and the Russian A. Butlerov.

In 1857, F. Kekulé classified carbon as a tetravalent element, and in 1858, simultaneously with A. Cooper, he noted that carbon atoms are able to combine with each other in various chains: linear, branched and closed (cyclic).

The works of F. Kekule and A. Cooper served as the basis for the development of a scientific theory explaining the phenomenon of isomerism, the relationship between the composition, structure and properties of molecules of organic compounds. This theory was created by the Russian scientist A.M.Butlerov. It was his inquisitive mind that "dared to penetrate" into the "dense forest" of organic chemistry and begin transforming this "boundless thicket" into a regular park filled with sunlight with a system of paths and alleys. The main ideas of this theory were first expressed by A.M. Butlerov in 1861 at the congress of German naturalists and doctors in the city of Speyer.

Briefly formulate the main provisions and consequences of the theory of the structure of organic compounds Butlerov-Kekule-Cooper as follows.

1. The atoms in the molecules of substances are connected in a certain sequence according to their valence. Carbon in organic compounds is always tetravalent, and its atoms are able to combine with each other, forming various chains (linear, branched, and cyclic).

Organic compounds can be arranged in rows of substances similar in composition, structure and properties - homologous rows.

Butlerov Alexander Mikhailovich (1828-1886)

For example, CH 4 methane is the ancestor of the homologous series of saturated hydrocarbons (alkanes). Its closest homologue is ethane C 2 H 6, or CH 3 -CH 3. The next two members of the homologous series of methane are propane C 3 H 8, or CH 3 -CH 2 -CH 3, and butane C 4 H 10, or CH 3 -CH 2 -CH 2 -CH 3, etc.

It is easy to see that for homologous series one can derive a general formula for the series. So, for alkanes this general formula is C n H 2n + 2.

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

This position of the theory of the structure of organic compounds explains the phenomenon of isomerism. Obviously, for C 4 H 10 butane, in addition to the molecule of linear structure CH 3 -CH 2 -CH 2 -CH 3, a branched structure is also possible:

This is a completely new substance with its own individual properties that differ from the properties of linear butane.

Butane, in a molecule of which the atoms are arranged in a linear chain, is called normal butane (n-butane), and butane, whose carbon chain is branched, is called isobutane.

There are two main types of isomerism - structural and spatial.

In accordance with the accepted classification, three types of structural isomerism are distinguished.

Isomerism of the carbon skeleton. The compounds differ in the order of arrangement of carbon-carbon bonds, for example, the considered n-butane and isobutane. It is this type of isomerism that is characteristic of alkanes.

Isomerism of the position of a multiple bond (C \u003d C, C \u003d C) or a functional group (i.e., a group of atoms that determine the belonging of a compound to one or another class of organic compounds), for example:

Interclass isomerism... Isomers of this type of isomerism belong to different classes of organic compounds, for example, the abovementioned ethyl alcohol (class of saturated monohydric alcohols) and dimethyl ether (class of ethers).

There are two types of spatial isomerism: geometric and optical.

Geometric isomerism is characteristic, first of all, for compounds with a double carbon-carbon bond, since at the site of such a bond the molecule has a planar structure (Fig. 6).

Figure: 6.
Ethylene Molecule Model

For example, for butene-2, if the same groups of atoms at carbon atoms with a double bond are on one side of the plane of the C \u003d C bond, then the molecule is a cis isomer, if on opposite sides it is a trans isomer.

Optical isomerism is possessed, for example, by substances whose molecules have an asymmetric, or chiral, carbon atom bonded to four various deputies. Optical isomers are mirror images of each other, like two palms, and are not compatible. (Now, obviously, the second name of this type of isomerism has become clear to you: Greek chiros - hand - a sample of an asymmetrical figure.) For example, in the form of two optical isomers, there is 2-hydroxypropanoic (lactic) acid containing one asymmetric carbon atom.

Isomeric pairs arise in chiral molecules, in which the isomer molecules are related in their spatial organization to one another in the same way as an object and its mirror image are related to each other. A pair of such isomers always has the same chemical and physical properties, with the exception of optical activity: if one isomer rotates the plane of polarized light clockwise, then the other is necessarily counterclockwise. The first isomer is called dextrorotatory, and the second is called levorotatory.

The importance of optical isomerism in the organization of life on our planet is very great, since optical isomers can differ significantly both in their biological activity and in compatibility with other natural compounds.

3. The atoms in the molecules of substances influence each other. You will consider the mutual influence of atoms in molecules of organic compounds in the further study of the course.

The modern theory of the structure of organic compounds is based not only on the chemical, but also on the electronic and spatial structure of substances, which is considered in detail at profile level studying chemistry.

In organic chemistry, several types of chemical formulas are widely used.

The molecular formula reflects the qualitative composition of the compound, that is, it shows the number of atoms of each of the chemical elements that form the molecule of the substance. For example, the molecular formula for propane is C 3 H 8.

The structural formula reflects the order in which atoms are joined in a molecule according to their valence. The structural formula of propane is as follows:

Often there is no need to depict in detail the chemical bonds between carbon and hydrogen atoms, therefore, in most cases, abbreviated structural formulas are used. For propane, this formula is written as follows: CH 3 -CH 2 -CH 3.

The structure of molecules of organic compounds is reflected using different models... The best known are volumetric (scale) and ball-and-stick models (Fig. 7).

Figure: 7.
Ethane Molecule Models:
1 - ball-and-stick; 2 - large-scale

New words and concepts

Isomerism, isomers.
Valence.
Chemical structure.
The theory of the structure of organic compounds.
Homologous series and homologous difference.
Molecular and structural formulas.
Molecular models: volumetric (scale) and ball-and-stick.

Questions and tasks

What is valency? How does it differ from the oxidation state? Give examples of substances in which the values \u200b\u200bof the oxidation state and valence of atoms are numerically the same and different,
Determine the valence and oxidation state of atoms in substances, the formulas of which are Cl 2, CO 2, C 2 H 6, C 2 H 4.
What is isomerism; isomers?
What is homology; homologues?
How, using knowledge of isomerism and homology, to explain the diversity of carbon compounds?
What is meant by the chemical structure of molecules of organic compounds? Formulate the position of the theory of structure, which explains the difference in the properties of isomers, Formulate the position of the theory of structure, which explains the variety of organic compounds.
What contribution did each of the scientists - the founders of the theory of chemical structure - make to this theory? Why did the contribution of the Russian chemist play a leading role in the formation of this theory?
The existence of three isomers of the composition C 5 H 12 is possible, Write down their full and abbreviated structural formulas,
Using the model of a substance molecule presented at the end of the paragraph (see, Fig. 7), make up its molecular and abbreviated structural formulas.
Calculate the mass fraction of carbon in the molecules of the first four members of the homologous series of alkanes.

In the most general and systematic form, the theory of chemical structure (abbreviated as TCS) was first formulated by the Russian chemist A.M.Butlerov in 1861 and subsequently developed and supplemented by him and his students and followers (primarily V.V. Markovnikov, A. M. Zaitsev and others), as well as many foreign chemists (Ya.G. Van't Hoff, J. A. Le Belém, and others).

Let us consider the main provisions of classical TCS and comment on them from the standpoint of modern structural chemistry.

1. Each atom in a molecule is capable of forming a certain number of chemical bonds with other atoms.

Already in the first half of the 19th century. in chemistry, ideas were formed about the ability of atoms to combine with each other in certain respects. As Butlerov put it, each atom “has a certain amount of force that produces chemical phenomena (affinities). During the chemical combination ... part of this force or all of it is consumed. " Thus, two features of the interatomic chemical interaction were emphasized: a) discreteness - all the affinity inherent in the atom was assumed to be composed of separate portions or, according to Butlerov, “separate units of chemical force”, which was clearly expressed by the symbolism of valence strokes (for example, H-O- H, H-C≡N, etc.), where each stroke characterized one chemical bond; b) saturation - the number of chemical bonds formed by an atom is limited, due to which there exist, for example, such neutral molecular systems of various stability as CH, CH2, CH3, CH4, but there are no CH5, CH6 molecules, etc.

A quantitative measure of the ability of an atom to form chemical bonds is its valence. Formation in the 1850s. the concepts of valence and chemical bond served as the most important prerequisite for the creation of TCS. However, before the beginning of the XX century. the physical meaning of the valence stroke, and, consequently, the nature of the chemical bond and valence remained unclear, which sometimes led to paradoxes. So, studying the properties of unsaturated hydrocarbons, Butlerov adopted in 1870 the idea of \u200b\u200bthe German chemist E. Erlenmeyer on the existence of multiple bonds in them. Meanwhile, it remained unclear why the multiple bond turned out to be less strong (prone to addition reactions) than a single bond (which did not enter into these reactions). There was other evidence of the inequality of some or all of the chemical bonds in the molecule.

With the creation of quantum chemistry, it became clear that each valence stroke corresponds, as a rule, to a two-center two-electron bond and that chemical bonds can differ in energy, length, polarity, polarizability, directionality in space, multiplicity, etc. (see Chemical bond) ...

The concept of a chemical bond entails the separation of atoms of a molecule into chemically bound and chemically unbound ones (see Fig.), From which the second position of TCS follows.

H / O \\ H Chemically bonded atoms

Chemically unbound atoms

2. Atoms in a molecule are linked to each other in a certain order, according to their valence. It is the “order of chemical interaction”, or, in other words, the “method of mutual chemical bond” of atoms in a molecule, that Butlerov called the chemical structure. As a result, the chemical structure, clearly expressed by the structural formula (sometimes also referred to as graphic, but in last years - topological), shows which pairs of atoms are chemically related to each other, and which are not, i.e., the chemical structure characterizes the topology of the molecule (see Molecule). At the same time, Butlerov specifically emphasized that only one chemical structure corresponds to each compound and, therefore, only one structural (graphic) formula.

The considered position of TCS is generally valid today. However, firstly, the molecular structure can not always be conveyed by one classical structural formula (see Benzene), and secondly, in non-rigid molecules, the bond order of atoms can spontaneously change and rather quickly (see Molecule), and, thirdly , modern chemistry has discovered a wide range of molecules with "unusual" structures (say, in some carboranes, a carbon atom is bonded to five neighboring atoms).

3. The physical and chemical properties of a compound are determined both by its qualitative and quantitative composition and by its chemical structure, as well as by the nature of the bonds between atoms.

This position is central in the TCS. It was his approval in chemistry that made Butlerov's main scientific merit. A number of important consequences follow from this position: the explanation of isomerism by the difference in the chemical structure of isomers, the idea of \u200b\u200bthe mutual influence of atoms in a molecule, and also reveals the meaning and significance of the structural formulas of molecules.

In 1874 TCS was enriched with stereochemical concepts (see Stereochemistry), within the framework of which it was possible to explain the phenomena of optical, geometric, and conformational isomerism (see Isomerism).

In modern chemistry, the term "structure of a molecule" is understood "in three ways: a) as a chemical structure (that is, the topology of a molecule); b) as a spatial structure that characterizes the arrangement and movement of nuclei in space; c) as an electronic structure (see Molecule, Chemical bond).

Thus, the main position of TCS, from the modern point of view, can be represented as follows: the physical and chemical properties of compounds are determined by their quantitative and qualitative elemental composition, as well as the chemical (topological), spatial (nuclear) and electronic structure of their molecules.

4. The chemical structure can be studied by chemical methods, ie, by analysis and synthesis.

Developing this position, Butlerov formulated a number of rules for "recognizing the chemical structure" and widely applied them in his experimental works.

Currently, the structure of molecules is studied by both chemical and physical methods (see Spectral analysis).

5. The atoms included in the molecule, both chemically bound and unbound, exert a certain influence on each other, which is manifested in the reactivity of individual atoms and bonds of the molecule, as well as in its other properties.

TCS, like any scientific theory, is based on some model concepts that have a certain area of \u200b\u200bapplicability and reflect only certain aspects of reality. So, speaking of TCS, one should not forget that in reality a molecule is a single integral system of nuclei and electrons and the separation of individual atoms, functional groups, chemical bonds, lone electron pairs, etc., is an approximation. But as soon as this approximation proved to be effective in solving various chemical problems, it became widespread. At the same time, the theoretical, mental dismemberment, structuring of an object (molecule) that is integral in nature makes it necessary to introduce additional concepts into the theory, taking into account the fact that the selected molecular fragments (atoms, bonds, etc.) are in fact connected and interact with each other. ... For this purpose, the concept of mutual influence of atoms (BBA) was created.

The properties and state of each atom or functional group of a molecule are determined not only by their nature, but also by their environment. For example, the introduction of an OH group into a molecule can lead to different results:

Therefore, when studying the nature and intensity of the effect of various substituents on the properties of a molecule, proceed as follows: consider reaction series, i.e., a number of compounds of the same type that differ from each other either by the presence of a substituent, or by the arrangement of multiple bonds, for example: CH2 \u003d CH-CH \u003d CH- CH3, H2C \u003d CH-CH2-CH \u003d CH2, etc., or for some other details of the structure. At the same time, the ability of substances of this series to participate in the same type of reactions is being investigated, for example, the bromination of phenol and benzene is studied. The observed differences are associated with the effect of various substituents on the rest of the molecule.

As for organic compounds, one of them characteristic features is the ability of a substituent to transfer its influence to the chains of covalently bonded atoms (see Chemical bond). Of course, the substituents are also influenced by the rest of the molecule. The transfer of the influence of the substituent on the a- and n-bonds leads to a change in these bonds. If the influence of substituents is transmitted with the participation of a-bonds, then the substituent is said to exhibit an inductive, or I-effect. If there are π-bonds in the chain, they also polarize (π-effect). In addition, if the chain contains a system of conjugated multiple bonds (-C \u003d C-C \u003d C-) or a substituent with a lone electron pair with a multiple bond (CH3-O-CH \u003d CH2) or with an aromatic nucleus, then the transfer of influence occurs along system of π-bonds (conjugation effect, or C-effect), while the electron cloud is partially shifted to the region of the neighboring σ-bond. For example, substituents such as -Br, -Cl, -OH, -NH2, which have lone electron pairs, are donors of π-electrons. Therefore, they are said to have a + C-effect. At the same time, they shift towards themselves the electron density along the σ-bonds, i.e., they have the -I-effect. For -Br, -Cl, the I-effect predominates, for -OH and -NH2-, on the contrary, + C-effect. Therefore, say, in phenol, the π-electron density on the benzene nucleus is higher than in benzene, which facilitates the occurrence of electrophilic substitution reactions in phenol (in comparison with benzene).

The theory of chemical structure is also widely used in inorganic chemistry, especially after the creation of the coordination theory by A. Werner in 1893 (see Coordination compounds).

Chemical structure theory

a theory that describes the structure of organic compounds, that is, the sequence (order) of arrangement of atoms and bonds in a molecule, the mutual influence of atoms, as well as the relationship of the structure with physical and chemical properties substances.

For the first time, the main provisions of H. s. t. were expressed by A. M. Butlerov in the report "On the chemical structure of substances" (Congress of German naturalists, Speyer, 1861); he wrote: “Proceeding from the idea that each chemical atom that is part of the body takes part in the formation of this latter and acts here with a certain amount of its chemical force (affinity), I call the chemical structure the distribution of the action of this force, as a result of which chemical atoms , indirectly or directly influencing each other, are combined into a chemical particle ”(Selected Works on Organic Chemistry, 1951, pp. 71-72). Subsequently, these provisions were developed by him in a number of articles and the book "Introduction to the complete study of organic chemistry" (Kazan, 1864-66; German edition: Leipzig, 1867-1868) - the first manual on organic chemistry, in which all the material is systematized from the standpoint of X . from. t. Creation of H. s. This was preceded by the establishment of such important concepts as the atom and the molecule (1st International Congress of Chemists, Karlsruhe, 1860), as well as the postulation by F.A.Kekule and A.S. Cooper of the tetravalence of carbon (1857-58). Graphical formulas of organic compounds, close to the formulas following from H. c. so, were proposed in 1858 by Cooper (see Organic Chemistry).

The main provisions of H. s. t. are as follows: a) in organic molecules, atoms are connected to each other in a certain order according to their valence, which determines the chemical structure of molecules; b) the chemical and physical properties of organic compounds depend both on the nature and number of atoms included in their composition, and on the chemical structure of molecules; c) for each empirical formula, a certain number of theoretically possible structures (isomers) can be derived; d) each organic compound has one formula of the chemical structure, which gives an idea of \u200b\u200bthe properties of this compound; e) in molecules there is a mutual influence of atoms, both connected and not directly connected with each other. The latter thesis of the theory was developed by Butlerov's student V.V. Markovnikov (see Markovnikov's rule) and later by many other scientists.

H. s. T. made it possible to explain the known cases of isomerism (position and skeleton), which remained incomprehensible to chemists of that time. Butlerov's (1863) prediction about the possibility of determining the spatial arrangement of atoms in a molecule came true. In 1874, J. Van't Hoff and, independently of him, the French chemist J. Le Bel, expressed the idea that the four valences of carbon have a clear spatial orientation and are directed to the vertices of a tetrahedron, in the center of which is a carbon atom. This proposition about a certain spatial orientation of chemical bonds formed the basis of a new branch of organic chemistry - stereochemistry (see Stereochemistry). It made it possible to explain a number of already known by that time cases of geometric and mainly optical isomerism, as well as the phenomenon that later received the name of tautomerism (see Tautomerism) (Butlerov, 1862; German chemist K. Laar, 1885).

Butlerov confirmed the correctness of his theory by synthesizing a number of organic compounds. H. c. T. had a tremendous predictive ability in the direction of the synthesis of organic compounds and the establishment of the structure of already known substances. Therefore, Butlerov's theory contributed to the rapid development of chemical science, including synthetic organic chemistry, and the chemical industry.

Further development of H. c. so enriched organic chemistry with new concepts, for example, about the cyclic structure of benzene (Kekule, 1865) and the oscillation (displacement) of double bonds in its molecule (1872) (this idea played a very large role in the chemistry of aromatic and heterocyclic compounds), special properties compounds with conjugated bonds (the theory of partial valences, F.K.I. Thiele, 1899) and others. The development of stereochemistry led to the creation of a theory of stress (A. Bayer, 1885), explaining the different stability of cycles depending on their size, and later - to conformational analysis (See. Conformational analysis) (German chemists G. Sachse, 1890, and E. More, 1918). The main provisions of H. s. so received confirmation in the study of organic compounds by chemical, physical and calculation methods.

Fundamental value in H. s. that is, they have an idea of \u200b\u200bthe mutual influence of atoms in the molecules of organic compounds. However, H. c. T. could not explain the nature of this influence, its internal mechanism. This became possible thanks to the advances in physics, which made it possible to reveal the essence of the concepts of "valence" and "chemical bond". Since the beginning of the 20th century. electronic representations arise in organic chemistry (see Electronic theories in organic chemistry), which are based on electronic interpretations of the nature of ions (J.J. Thomson), ionic bonds (W. Kossel), and covalent bonds (German physicist I. Stark, G . N. Lewis). Electronic representations made it possible to explain the reason for the mutual influence of atoms (static and dynamic displacement of the electron density in the molecule) and to predict the direction of reactions depending on the chemical structure of the reactants. Since the end of the 20s. 20th century the chemical bond began to be interpreted from the standpoint of quantum chemistry (see Quantum chemistry).

Butlerov's theory underlies the nomenclature and systematics of organic compounds (see Chemical nomenclature), and the use of his structural formulas helps both to determine the ways of synthesizing new substances and to establish the structure of complex (including natural) compounds.

Lit .: Butlerov A.M., Soch., T. 1-3, M., 1953-1958; Markovnikov V.V., Fav. works, M., 1955; A century of the theory of chemical structure. Sat. articles, M., 1961; Bykov GV, History of the classical theory of chemical structure, M., 1960; his, History of electronic theories of organic chemistry, M., 1963; Zhdanov Yu. A., Theory of the structure of organic compounds, M., 1971; Reutov OA, Theoretical foundations of organic chemistry, M., 1964; Tatevsky V.M., Classical theory of molecular structure and quantum mechanics, I., 1973.

Big soviet encyclopedia... - M .: Soviet encyclopedia. 1969-1978 .

See what the "Chemical structure theory" is in other dictionaries:

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Books

Quantum theory of molecular systems. Unified Approach, D. Cook, The book presents the first in the world literature a detailed modern analysis of conceptual issues of the theory of chemical structure from the point of view of a physicist. The presentation is presented within ... Category: Physical chemistry. Chemical physics Publisher: Intellect,