Creation of the theory of the structure of organic compounds. Theory of the structure of organic compounds

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

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

Currently, a little less than 30 million various organic substances are known, and this list is constantly updated. 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 sequential (linear) connection of carbon atoms to each other is possible, but also branched and even cyclic;

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

In addition, a wide variety of organic compounds is also facilitated by the fact that carbon atoms are able to form bonds with the atoms of many other chemical elements, for example, hydrogen, oxygen, nitrogen, phosphorus, sulfur, halogens. Hydrogen, oxygen and nitrogen are the 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 in an “artificial” way, i.e. outside of living matter. However, the theory of vitalism did not last very long, in view of the fact that one by one substances were discovered, the synthesis of which 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. So, for example, dimethyl ether and ethyl alcohol have exactly the same elemental composition, however, 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 interacts with it, releasing hydrogen gas.

Researchers of the 19th century put forward many assumptions about how organic substances are nevertheless arranged. Significantly important assumptions were put forward by the German scientist F.A. Kekule, who was the first to put forward the idea that atoms of different chemical elements have specific valence values, and carbon atoms in organic compounds are tetravalent and can combine with each other, forming chains. Later, starting from the assumptions of Kekule, the Russian scientist Alexander Mikhailovich Butlerov developed a theory of the structure of organic compounds, which has not lost its relevance in our time. Consider the main provisions of this theory:

1) all atoms in the 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 various 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 examining 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 substance, you can predict its properties.

Just as the periodic law of D.I. Mendelev became the scientific foundation of inorganic chemistry, the theory of the structure of organic substances A.M. Butlerova actually became the starting point in the development of organic chemistry as a science. It should be noted that after the creation of Butler'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 molecules, but also on the order in which the atoms in these molecules are connected to each other.

In this regard, such a phenomenon as isomerism is widespread among organic substances.

Isomerism is a phenomenon when different substances have exactly the same molecular composition, i.e. the 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) Position isomerism:

multiple bond

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. There are no assignments for optical isomerism at the Unified State Examination, so we will consider only the geometric one.

If there is a double C=C bond or a cycle in the molecule of any compound, 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 lies in the fact that the double bond between carbon atoms actually has a planar structure, and substituents at these carbon atoms can be fixedly located either above or below this plane:

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

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

Note that geometric isomerism is impossible if at least one carbon atom in the double bond has two identical substituents. For example, cis-trans- isomerism is impossible for propene:

propene has no cis-trans-isomers, since at one of the carbon atoms in the double bond there are two identical "substituents" (hydrogen atoms)

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

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

The concept of a chemical structure as a sequence of atoms connected to each other was significantly expanded with the advent of the 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 of influence of some parts of the molecule on others:

1) Inductive effect

2) Mesomeric effect

Inductive effect

To demonstrate this phenomenon, let us take, for example, a molecule of 1-chloropropane (CH 3 CH 2 CH 2 Cl). The bond between carbon and chlorine is polar because chlorine has a much higher electronegativity than carbon. As a result of the displacement of the 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 of electron density from one atom to another is often indicated by an arrow pointing towards the more electronegative atom:

However, it is interesting 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 somewhat lesser extent, from the second carbon atom to the first, and also from the third to the second:

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

In the case when an atom or group of atoms has a 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 carbon atoms. In this case, the substituent is said to have a positive inductive effect (+ I) (is electron-donating).

So, substituents with + I-effect are saturated hydrocarbon radicals. At the same time, the expression I-effect increases with elongation 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 in different valence states also have different electronegativity. Sp carbon atoms have a higher electronegativity than sp 2 carbon atoms, which in turn are more electronegative than sp 3 carbon atoms.

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

Negative mesomeric effect (– M) have substituents that pull the electron density away 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 the electron density due to the 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 starts at the center of the electron density and ends where the electron density shifts. So, for example, in the vinyl chloride molecule, the mesomeric effect occurs when the lone electron pair of the chlorine atom is conjugated with the electrons of the π-bond between 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, shifts towards the extreme carbon atom, on which a partial negative charge arises as a result:

If a molecule contains 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.

Chemistry is a science that gives us all the variety of materials and household items that we, without hesitation, use every day. But in order to come to the discovery of such a variety of compounds that is known today, many chemists had to go through a difficult scientific path.

Huge work, numerous successful and unsuccessful experiments, a colossal theoretical knowledge base - all this led to the formation of various areas of industrial chemistry, made it possible to synthesize and use modern materials: rubbers, plastics, plastics, resins, alloys, various glasses, silicones, and so on.

One of the most famous, honored chemists who made an invaluable contribution to the development of organic chemistry was the Russian man A. M. Butlerov. We will briefly consider his works, merits and results of work in this article.

short biography

The date of birth of the scientist is September 1828, the number varies in different sources. He was the son of Lieutenant Colonel Mikhail Butlerov, he lost his mother quite early. He lived all his childhood in his grandfather's family estate, in the village of Podlesnaya Shentala (now a district of the Republic of Tatarstan).

He studied in different places: first in a closed private school, then in a gymnasium. Later he entered Kazan University in the Department of Physics and Mathematics. However, despite this, he was most interested in chemistry. The future author of the theory of the structure of organic compounds remained on the spot after graduation as a teacher.

1851 - the time of defending the first dissertation work of a scientist on the topic "Oxidation of organic compounds". After a brilliant performance, he was given the opportunity to manage all chemistry at his university.

The scientist died in 1886 where he spent his childhood, in the family estate of his grandfather. He was buried in the local family chapel.

The scientist's contribution to the development of chemical knowledge

Butlerov's theory of the structure of organic compounds is, of course, his main work. However, not the only one. It was this scientist who first created the Russian school of chemists.

Moreover, scientists who later had great weight in the development of all science came out of its walls. These are the following people:

Markovnikov;
Zaitsev;
Kondakov;
Favorsky;
Konovalov;
Lvov and others.

Works in organic chemistry

There are many such works. After all, Butlerov spent almost all his free time in the laboratory of his university, carrying out various experiments, drawing conclusions and conclusions. This is how the theory of organic compounds was born.

There are several particularly capacious works of the scientist:

he created a report for a conference on the topic "On the chemical structure of matter";
dissertation work "About essential oils";
first scientific work "Oxidation of organic compounds".

Before its formulation and creation, the author of the theory of the structure of organic compounds studied the works of other scientists from different countries for a long time, studied their works, including experimental ones. Only later, having generalized and systematized the knowledge gained, did he reflect all the conclusions in the provisions of his nominal theory.

Theory of the structure of organic compounds A. M. Butlerova

The 19th century is marked by the rapid development of almost all sciences, including chemistry. In particular, vast discoveries on carbon and its compounds continue to be accumulated, striking everyone with their diversity. However, no one dares to systematize and streamline all this factual material, bring to a common denominator and reveal common patterns on which everything is built.

Butlerov A.M. was the first to do this. It was he who owns the ingenious theory of the chemical structure of organic compounds, the provisions of which he spoke en masse at the German conference of chemists. This was the beginning of a new era in the development of science, organic chemistry rose to

The scientist himself went to this gradually. He conducted many experiments and predicted the existence of substances with given properties, discovered some types of reactions and saw the future behind them. He studied the works of his colleagues and their discoveries a lot. Only against this background, through careful and painstaking work, did he manage to create his masterpiece. And now the theory of the structure of organic compounds in this is practically the same as the periodic system in the inorganic.

Discoveries of a scientist before creating a theory

What discoveries were made and theoretical justifications given to scientists before the theory of the structure of organic compounds by A. M. Butlerov appeared?

The domestic genius was the first to synthesize such organic substances as urotropine, formaldehyde, methylene iodide and others.
He synthesized a sugar-like substance (tertiary alcohol) from inorganics, thereby dealing another blow to the theory of vitalism.
He predicted the future for polymerization reactions, calling them the best and most promising.
Isomerism was explained for the first time only by him.

Of course, these are only the main milestones of his work. In fact, many years of painstaking work of a scientist can be described for a long time. However, the theory of the structure of organic compounds has become the most significant today, the provisions of which will be discussed further.

The first position of the theory

In 1861, the great Russian scientist, at a congress of chemists in the city of Speyer, shared with colleagues his views on the causes of the structure and diversity of organic compounds, expressing all this in the form of theoretical provisions.

The very first point is as follows: all atoms within a single molecule are connected in a strict sequence, which is determined by their valency. In this case, the carbon atom exhibits a valency index of four. Oxygen has a value of this indicator equal to two, hydrogen - to one.

He proposed to call such a feature chemical. Later, the designations of expressing it on paper using graphic full structural, abbreviated and molecular formulas were adopted.

This also includes the phenomenon of the connection of carbon particles with each other in endless chains of various structures (linear, cyclic, branched).

In general, Butlerov's theory of the structure of organic compounds, with its first position, determined the significance of valence and a single formula for each compound, reflecting the properties and behavior of a substance during reactions.

The second position of the theory

In this paragraph, an explanation was given to the diversity of organic compounds in the world. Based on the carbon compounds in the chain, the scientist suggested that there are unequal compounds in the world that have different properties, but are completely identical in molecular composition. In other words, there is a phenomenon of isomerism.

With this position, the theory of the structure of organic compounds of A. M. Butlerov not only explained the essence of isomers and isomerism, but the scientist himself confirmed everything by practical experience.

So, for example, he synthesized an isomer of butane - isobutane. Then he predicted for pentane the existence of not one, but three isomers, based on the structure of the compound. And he synthesized them all, proving his case.

Disclosure of the third provision

The next point of the theory says that all atoms and molecules within the same compound are able to influence the properties of each other. The nature of the behavior of a substance in reactions of various types, the chemical and other properties exhibited, will depend on this.

Thus, on the basis of this provision, several differing in the type and structure of the functional defining group are distinguished.

The theory of the structure of organic compounds by A. M. Butlerov is summarized in almost all textbooks on organic chemistry. After all, it is she who is the basis of this section, the explanation of all the patterns on which molecules are built.

The Importance of Theory for Modernity

Certainly it is great. This theory allowed:

combine and systematize all the factual material accumulated by the time of its creation;
explain the patterns of structure, properties of various compounds;
give a full explanation of the reasons for such a large variety of compounds in chemistry;
gave rise to numerous syntheses of new substances based on the provisions of the theory;
allowed the advancement of views, the development of atomic and molecular science.

Therefore, to say that the author of the theory of the structure of organic compounds, whose photo can be seen below, did a lot, is to say nothing. Butlerov can rightfully be considered the father of organic chemistry, the ancestor of its theoretical foundations.

His scientific vision of the world, the genius of thinking, the ability to foresee the result played a role in the final analysis. This man possessed colossal capacity for work, patience and tirelessly experimented, synthesized, and trained. I was wrong, but I always learned a lesson and made the right perspective conclusions.

Only such a set of qualities and business acumen, perseverance made it possible to achieve the desired effect.

Studying organic chemistry at school

In the course of secondary education, not much time is devoted to studying the basics of organics. Only one quarter of the 9th grade and the whole year of the 10th stage (according to the program of Gabrielyan O.S.). However, this time is enough for the guys to be able to study all the main classes of compounds, the features of their structure and nomenclature, and their practical significance.

The basis for starting the development of the course is the theory of the structure of organic compounds by A. M. Butlerov. Grade 10 is devoted to a full consideration of its provisions, and in the future - to their theoretical and practical confirmation in the study of each class of substances.

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 Alicyclic Aromatic

(Alkanes) (Cycloalkanes) (Arenas)

WITH P H 2 P+2 C P H 2 P WITH P H 2 P-6

End of work -

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The chemical structure of a substance as the order of connection of atoms in molecules. Mutual influence of atoms and atomic groups in a molecule. In this case, the tetravalence of carbon atoms and the monovalence of hydrogen atoms are strictly observed. The properties of substances depend not only on the qualitative and quantitative composition, but also on the order of connection of atoms in a molecule, the phenomenon of isomerism.

§1.3. The main provisions of the theory of the chemical structure of organic compounds A.M. Butlerova. The chemical structure of a substance as the order of connection of atoms in molecules. The dependence of the properties of substances on the chemical structure of molecules. Mutual influence of atoms and atomic groups in a molecule.
By the sixties of the last century, organic chemistry had accumulated a huge amount of factual material that required explanation. Against the background of the continuous accumulation of experimental facts, the insufficiency of theoretical concepts of organic chemistry was especially acute. Theory lagged behind practice and experiment. This lag was painfully reflected in the course of experimental research in laboratories; chemists conducted their research to a large extent at random, blindly, often without understanding the nature of the substances they synthesized and the essence of the reactions that led to their formation. Organic chemistry, in Wöhler's apt expression, resembled a dense forest full of wonderful things, a huge thicket with no exit, no end. "Organic chemistry is like a dense forest that is easy to enter but impossible to exit." So, apparently, it was destined that it was Kazan that gave the world a compass, with which it is not scary to enter the “Dense Forest of Organic Chemistry”. And this compass, which is still used today Butlerov's theory of chemical structure. From the 60s of the century before last to the present, any textbook on organic chemistry in the world begins with the postulates of the theory of the great Russian chemist Alexander Mikhailovich Butlerov.
The main provisions of the theory of chemical structure A.M. Butlerov
1st position
Atoms in molecules are connected to each other in a certain sequence according to their valences.. The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected by one structural formula (structure formula).

This provision applies to the structure of the molecules of all substances. In the molecules of saturated hydrocarbons, carbon atoms, connecting with each other, form chains. In this case, the tetravalence of carbon atoms and the monovalence of hydrogen atoms are strictly observed.

2nd position. The properties of substances depend not only on the qualitative and quantitative composition, but also on the order of connection of atoms in a molecule(the phenomenon of isomerism).
Studying the structure of hydrocarbon molecules, A. M. Butlerov came to the conclusion that these substances, starting with butane (C 4 N 10 ), a different order of connection of atoms is possible with the same composition of molecules. So, in butane, a twofold arrangement of carbon atoms is possible: in the form of a straight (unbranched) and a branched chain.

These substances have the same molecular formula, but different structural formulas and different properties (boiling point). Therefore, they are different substances. Such substances are called isomers.

And the phenomenon in which there can be several substances that have the same composition and the same molecular weight, but differ in the structure of molecules and properties, is called the phenomenon isomerism. Moreover, with an increase in the number of carbon atoms in hydrocarbon molecules, the number of isomers increases. For example, there are 75 isomers (various substances) that correspond to the formula C 10 N 22 , and 1858 isomers with formula C 14 H 30 .

For composition C 5 H 12 the following isomers may exist (there are three of them) -

3rd position. By the properties of a given substance, one can determine the structure of its molecule, and by the structure, one can predict the properties.Proof of this provision. This provision can be proved using the example of inorganic chemistry.
Example. If a given substance changes the color of purple litmus to pink, interacts with metals that are up to hydrogen, with basic oxides, bases, then we can assume that this substance belongs to the class of acids, i.e. It contains hydrogen atoms and an acidic residue. And, conversely, if a given substance belongs to the class of acids, then it exhibits the above properties. For example: N 2 S O 4 - sulfuric acid

4th position. Atoms and groups of atoms in the molecules of substances mutually influence each other.
Proof of this position

This position can be proved using the example of inorganic chemistry. For this, it is necessary to compare the properties of aqueous solutions N H 3, HC1, H 2 O (indicator action). In all three cases, substances contain hydrogen atoms, but they are connected to different atoms, which have a different effect on hydrogen atoms, so the properties of the substances are different.
Butlerov's theory was the scientific foundation of organic chemistry and contributed to its rapid development. Based on the provisions of the theory, A.M. Butlerov gave an explanation for the phenomenon of isomerism, predicted the existence of various isomers, and obtained some of them for the first time.
In the autumn of 1850, Butlerov passed the exams for a master's degree in chemistry and immediately began his doctoral dissertation "On Essential Oils", which he defended at the beginning of the next year.

On February 17, 1858, Butlerov made a report at the Paris Chemical Society, where he first outlined his theoretical ideas about the structure of matter. His report aroused general interest and lively debate: “The ability of atoms to combine with each other is different. Particularly interesting in this respect is carbon, which, according to August Kekule, is tetravalent, Butlerov said in his report If we imagine valence in the form of tentacles with which atoms bind together, one cannot fail to notice that the method of communication is reflected in the properties of the corresponding connections."

No one has yet expressed such thoughts. Perhaps the time has come, Butlerov continued, when our research should become the basis of a new theory of the chemical structure of substances. This theory will be distinguished by the accuracy of mathematical laws and will make it possible to foresee the properties of organic compounds.

A few years later, during a second trip abroad, Butlerov presented the theory he had created for discussion. He made a statement at the 36th Congress of German Naturalists and Physicians in Speyer. The convention took place in September 1861. He made a presentation before the chemical section. The topic had a more than modest name - “Something about the chemical structure of bodies.” In the report, Butlerov expresses the main provisions of his theory of the structure of organic compounds.
Proceedings of A.M. Butlerov

Office of A.M. Butlerov

The theory of chemical structure made it possible to explain many of the facts accumulated in organic chemistry at the beginning of the second half of the 19th century, proved that using chemical methods (synthesis, decomposition and other reactions) it is possible to establish the order of joining atoms in molecules (this proved the possibility of knowing the structure substances);

She introduced something new into the atomic and molecular theory (the order of arrangement of atoms in molecules, the mutual influence of atoms, the dependence of properties on the structure of molecules of a substance). The theory considered the molecules of matter as an ordered system endowed with the dynamics of interacting atoms. In this regard, the atomic and molecular theory received its further development, which was of great importance for the science of chemistry;

It made it possible to foresee the properties of organic compounds based on the structure, to synthesize new substances, adhering to the plan;

Allowed to explain the variety of organic compounds;

It gave a powerful impetus to the synthesis of organic compounds, the development of the industry of organic synthesis (the synthesis of alcohols, ethers, dyes, medicinal substances, etc.).

Having developed the theory and confirmed its correctness by the synthesis of new compounds, A.M. Butlerov did not consider the theory to be absolute and immutable. He argued that it should develop, and foresaw that this development would proceed through the resolution of contradictions between theoretical knowledge and emerging new facts.

The theory of chemical structure, as A.M. Butlerov, did not remain unchanged. Its further development proceeded mainly in two interrelated directions.

The first of them was predicted by A.M. Butlerov himself

He believed that science in the future will be able to establish not only the order of connection of atoms in a molecule, but also their spatial arrangement. The doctrine of the spatial structure of molecules, called stereochemistry (Greek "stereos" - spatial), entered science in the 80s of the last century. It made it possible to explain and predict new facts that did not fit into the framework of previous theoretical concepts.
The second direction is connected with the application in organic chemistry of the doctrine of the electronic structure of atoms, developed in physics of the twentieth century. This doctrine made it possible to understand the nature of the chemical bond of atoms, to find out the essence of their mutual influence, to explain the reason for the manifestation of certain chemical properties by a substance.

Structural formulas expanded and short

Reasons for the diversity of organic compounds

Carbon atoms form single (simple), double and triple bonds:

There are homologous series:

Isomers:

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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 absence of any systematizing basis. Beginning in the 1920s, 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 1990s 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 valency in relation to organic compounds, establishing such facts as the tetravalence of the carbon atom and its ability to form carbon chains by combining with carbon atoms.A. M. Butlerova F.A. Kekule

The 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, in establishing the structure of substances, attached fundamental importance to chemical reactions. Theory of the structure of A.M. Butlerova not only explained already known facts, her scientific significance was 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 structure and therefore have different properties. The true explanation of isomerism was received only in the second half of the 19th century on the basis of the theory of the chemical structure of A.M. Butlerov (structural isomerism) and the stereochemical doctrine of Ya. G. van't Hoff (spatial isomerism). Ya. G. van't Hoff

Formula Name Number of isomers CH 4 methane1 C4H6C4H6 ethane1 C3H8C3H8 propane1 C 4 H 10 butane 2 C 5 H 12 pentane 3 C 6 H 14 hexane 5 C 7 H 16 heptane 9 C 8 H 18 octane 18 C 9 H 20 nonane 35 C 10 H 22 decane 75 C 11 H 2 4 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 a different order of connection of atoms). Spatial isomers have the same substituents on each carbon atom and differ only in their mutual arrangement 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 conditional plane in such a way that 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 one speaks 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-like” room, she was surprised: the room seems to be similar, but still completely different. The mirror isomers of chemical molecules also differ in the same way: they look similar, but behave differently. The most important area of organic chemistry is the separation and synthesis of these mirror variants. (Illustration by John Tenniel for Lewis Carroll's Alice Through the Looking-Glass)

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

At least 130 reactions of organic synthesis 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 to this day. The principle of the selective action of a catalyst with respect to optical isomers is similar to a handshake: it is "convenient" for a catalyst to bind to only one of the chiral isomers, and therefore only one of the reactions is catalyzed preferentially. By the way, the term "chiral" comes from the Greek chéir hand.