Just as in inorganic chemistry the fundamental theoretical basis is the Periodic Law and the Periodic Table of Chemical Elements by D.I. Mendeleev, so in organic chemistry the leading scientific basis is the Butlerov-Kekule-Cooper theory of the structure of organic compounds.
Like any other scientific theory, the theory of the structure of organic compounds was the result of a generalization of the richest factual material that organic chemistry, which took shape as a science at the beginning of the 19th century, had accumulated. More and more new carbon compounds were discovered, the number of which increased like an avalanche (Table 1).
Table 1
Number of organic compounds known in different years
Scientists of the early 19th century explained this diversity of organic compounds. they couldn't. 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 known to you, described organic chemistry in one of his letters to J. J. Berzelius: “Organic chemistry can now drive anyone crazy. It seems to me like a dense forest, full of amazing things, a boundless thicket from which you cannot get out, into which you do not dare to penetrate...”
The development of chemistry was greatly influenced by the work of the English scientist E. Frankland, who, based on the ideas of atomism, introduced the concept of valence (1853).
In the hydrogen molecule H2, one covalent chemical bond H-H is formed, i.e. hydrogen is monovalent. The valence of a chemical element can be expressed by the number of hydrogen atoms that one atom of the chemical element adds 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 “valency” is an analogue of the concept of “oxidation state”, which you are used to working with in the course of inorganic chemistry in basic school. However, this is not the same thing. For example, in the nitrogen molecule N2, the oxidation state of nitrogen is zero, and the valence is three:
In hydrogen peroxide H2O2, 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 ionic bonds), the term “valency” 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 “valency” is used.
The theory of chemical structure is the result of a generalization of the ideas of outstanding organic scientists from three European countries: the German F. Kekule, the Englishman A. Cooper and the Russian A. Butlerov.
In 1857, F. Kekule classified carbon as a tetravalent element, and in 1858, together with A. Cooper, he noted that carbon atoms are capable of connecting with each other into 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 that explains 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 flooded with sunlight with a system of paths and alleys. The basic ideas of this theory were first expressed by A. M. Butlerov in 1861 at the congress of German naturalists and doctors in Speyer.
The main provisions and consequences of the Butlerov-Kekule-Cooper theory of the structure of organic compounds can be briefly formulated as follows.
1. Atoms in 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), Russian chemist, professor at Kazan University (1857-1868), from 1869 to 1885 - professor at St. Petersburg University. Academician of the St. Petersburg Academy of Sciences (since 1874). Creator of the theory of the chemical structure of organic compounds (1861). Predicted and studied the isomerism of many organic compounds. Synthesized many substances.
For example, methane CH 4 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 homological 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. It is obvious that for butane C 4 H 10, in addition to a molecule with a 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, different from the properties of butane with a linear structure.
Butane, in the molecule of which the atoms are arranged in a linear chain, is called normal butane (n-butane), and butane, the chain of carbon atoms of which 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. Compounds differ in the order of carbon-carbon bonds, for example, n-butane and isobutane discussed. It is this type of isomerism that is characteristic of alkanes.
Isomerism of the position of a multiple bond (C=C, C=C) or a functional group (i.e., a group of atoms that determines whether a compound belongs to a particular class of organic compounds), for example:
Interclass isomerism. Isomers of this type of isomerism belong to different classes of organic compounds, for example, ethyl alcohol (class of saturated monohydric alcohols) and dimethyl ether (class of ethers) discussed above.
There are two types of spatial isomerism: geometric and optical.
Geometric isomerism is characteristic, first of all, of compounds with a double carbon-carbon bond, since at the site of such a bond the molecule has a planar structure (Fig. 6).
Rice. 6.
Ethylene molecule model
For example, for butene-2, if identical groups of atoms at the carbon atoms at the double bond are on one side of the plane of the C=C bond, then the molecule is a cis isomer, if on opposite sides it is a trans isomer.
Optical isomerism is observed, for example, in 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 for this type of isomerism has become clear to you: Greek chiros - hand - an example of an asymmetrical figure.) For example, 2-hydroxypropanoic (lactic) acid, containing one asymmetric carbon atom, exists in the form of two optical isomers.
In chiral molecules, isomeric pairs arise in which the isomer molecules are related to each other in their spatial organization 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 necessarily rotates 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. Atoms in molecules of substances influence each other. You will consider the mutual influence of atoms in the molecules of organic compounds during 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 discussed in detail at the profile level of 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 of propane is: C 3 H 8.
The structural formula reflects the order of connection of atoms in a molecule according to valency. The structural formula of propane is:
There is often no need to depict in detail the chemical bonds between carbon and hydrogen atoms, so 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 various models. The most well-known are volumetric (scale) and ball-and-stick models (Fig. 7).
Rice. 7.
Ethane molecule models:
1 - ball-and-rod; 2 - scale
New words and concepts
- Isomerism, isomers.
- Valence.
- Chemical structure.
- Theory of the structure of organic compounds.
- Homologous series and homologous difference.
- Molecular and structural formulas.
- Models of molecules: volumetric (scale) and ball-and-stick.
Questions and tasks
- What is valence? How does it differ from oxidation state? Give examples of substances in which the values of the oxidation state and valency of the atoms are numerically the same and different,
- Determine the valency and oxidation state of atoms in substances whose formulas 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, explain the diversity of carbon compounds?
- What is meant by the chemical structure of molecules of organic compounds? Formulate the provisions of the theory of structure, which explains the difference in the properties of isomers. Formulate the provisions of the theory of structure, which explain the diversity 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 development of this theory?
- There may be three isomers of the composition C 5 H 12. Write down their full and abbreviated structural formulas,
- Based on the model of the substance molecule presented at the end of the paragraph (see, Fig. 7), compose 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.
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 valency 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 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 different orders of atoms). Spatial isomers have identical 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 has been discovered for obtaining optical isomers of organic molecules. 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.
Lesson content: Theories of the structure of organic compounds: prerequisites for their creation, basic principles. Chemical structure as the order of connection and mutual influence of atoms in molecules. Homology, isomerism. Dependence of the properties of substances on the chemical structure. Main directions of development of the theory of chemical structure. The dependence of the appearance of toxicity in organic compounds on the composition and structure of their molecules (the length of the carbon chain and the degree of its branching, the presence of multiple bonds, the formation of cycles and peroxide bridges, the presence of halogen atoms), as well as on the solubility and volatility of the compound.
Lesson objectives:
- Organize student activities to familiarize and initially consolidate the basic principles of the theory of chemical structure.
- Show students the universal nature of the theory of chemical structure using the example of inorganic isomers and the mutual influence of atoms in inorganic substances.
Lesson progress:
1. Organizational moment.
2. Updating students' knowledge.
1) What does organic chemistry study?
2) What substances are called isomers?
3) What substances are called homologues?
4) Name the theories known to you that arose in organic chemistry at the beginning of the 19th century.
5) What shortcomings did the theory of radicals have?
6) What shortcomings did type theory have?
3. Setting goals and objectives for the lesson.
The concept of valency formed an important part of A.M.’s theory of chemical structure. Butlerov in 1861
The periodic law formulated by D.I. Mendeleev in 1869, revealed the dependence of the valency of an element on its position in the periodic table.
The wide variety of organic substances that have the same qualitative and quantitative composition, but different properties, remained unclear. For example, about 80 different substances were known that corresponded to the composition C 6 H 12 O 2. Jens Jakob Berzelius proposed calling these substances isomers.
Scientists from many countries, with their work, have paved the way for the creation of a theory explaining the structure and properties of organic substances.
At a congress of German naturalists and doctors in the city of Speyer, a report was read entitled “Something in the chemical structure of bodies.” The author of the report was Kazan University professor Alexander Mikhailovich Butlerov. It was this very “something” that constituted the theory of chemical structure, which formed the basis of our modern ideas about chemical compounds.
Organic chemistry received a solid scientific basis, which ensured its rapid development in the next century until the present day. This theory made it possible to predict the existence of new compounds and their properties. The concept of chemical structure made it possible to explain such a mysterious phenomenon as isomerism.
The main principles of the theory of chemical structure are as follows:
1. Atoms in molecules of organic substances are combined in a certain sequence according to their valence.
2. The properties of substances are determined by the qualitative, quantitative composition, order of connection and mutual influence of atoms and groups of atoms in the molecule.
3. The structure of molecules can be established based on the study of their properties.
Let's consider these provisions in more detail. Molecules of organic substances contain atoms of carbon (valence IV), hydrogen (valence I), oxygen (valency II), nitrogen (valency III). Each carbon atom in molecules of organic substances forms four chemical bonds with other atoms, and carbon atoms can be connected in chains and rings. Based on the first principle of the theory of chemical structure, we will draw up structural formulas of organic substances. For example, it has been established that methane has the composition CH4. Taking into account the valences of carbon and hydrogen atoms, only one structural formula of methane can be proposed:
The chemical structure of other organic substances can be described by the following formulas:
ethanol
The second position of the theory of chemical structure describes the relationship known to us: composition - structure - properties. Let's see the manifestation of this pattern using the example of organic substances.
Ethane and ethyl alcohol have different qualitative compositions. The alcohol molecule, unlike ethane, contains an oxygen atom. How will this affect the properties?
The introduction of an oxygen atom into a molecule dramatically changes the physical properties of the substance. This confirms the dependence of properties on the qualitative composition.
Let's compare the composition and structure of the hydrocarbons methane, ethane, propane and butane.
Methane, ethane, propane and butane have the same qualitative composition, but different quantitative ones (the number of atoms of each element). According to the second position of the theory of chemical structure, they should have different properties.
| Substance | Boiling point°C | Melting point,°C |
| CH 4 | – 182,5 | – 161,5 |
| C 2 H 6 | – 182,8 | – 88,6 |
| C 3 H 8 | – 187,6 | – 42,1 |
| C 4 H 10 | – 138,3 | – 0,5 |
As can be seen from the table, with an increase in the number of carbon atoms in a molecule, the boiling and melting temperatures increase, which confirms the dependence of the properties on the quantitative composition of the molecules.
The molecular formula C4H10 corresponds not only to butane, but also to its isomer isobutane:
Isomers have the same qualitative (carbon and hydrogen atoms) and quantitative (4 carbon atoms and ten hydrogen atoms) composition, but differ from each other in the order of connection of atoms (chemical structure). Let's see how the difference in the structure of isomers will affect their properties.
A branched hydrocarbon (isobutane) has higher boiling and melting points than a normal hydrocarbon (butane). This can be explained by the closer proximity of molecules to each other in butane, which increases the forces of intermolecular attraction and, therefore, requires more energy to separate them.
The third position of the theory of chemical structure shows the feedback between the composition, structure and properties of substances: composition - structure - properties. Let's consider this using the example of compounds with the composition C 2 H 6 O.
Let's imagine that we have samples of two substances with the same molecular formula C 2 H 6 O, which was determined through qualitative and quantitative analysis. But how can we find out the chemical structure of these substances? Studying their physical and chemical properties will help answer this question. When the first substance interacts with metallic sodium, the reaction does not occur, but the second actively interacts with it, releasing hydrogen. Let us determine the quantitative ratio of substances in the reaction. To do this, add a certain mass of sodium to the known mass of the second substance. Let's measure the volume of hydrogen. Let's calculate the amounts of substances. In this case, it turns out that out of two moles of the substance under study, one mole of hydrogen is released. Therefore, each molecule of this substance is the source of one hydrogen atom. What conclusion can be drawn? Only one hydrogen atom differs in properties and, therefore, in structure (which atoms it is associated with) from all the others. Taking into account the valence of carbon, hydrogen and oxygen atoms, only one formula can be proposed for a given substance:
For the first substance, a formula can be proposed in which all hydrogen atoms have the same structure and properties:
A similar result can be obtained by studying the physical properties of these substances.
Thus, based on studying the properties of substances, we can draw a conclusion about its chemical structure.
The importance of the theory of chemical structure can hardly be overestimated. She armed chemists with a scientific basis for studying the structure and properties of organic substances. The Periodic Law formulated by D.I. has a similar meaning. Mendeleev. The theory of structure summarized all the scientific views prevailing in chemistry at that time. Scientists were able to explain the behavior of organic substances during chemical reactions. Based on the theory of A.M. Butlerov predicted the existence of isomers of some substances, which were later obtained. Just like the Periodic Law, the theory of chemical structure received its further development after the formation of the theory of atomic structure, chemical bonding and stereochemistry.
Lecture 15
Theory of the structure of organic substances. Main classes of organic compounds.
Organic chemistry – the science that studies organic matter. Otherwise it can be defined as chemistry of carbon compounds. The latter occupies a special place in the periodic table of D.I. Mendeleev for the variety of compounds, of which about 15 million are known, while the number of inorganic compounds is five hundred thousand. Organic substances have been known to mankind for a long time, such as sugar, vegetable and animal fats, dyes, fragrant and medicinal substances. Gradually, people learned by processing these substances to obtain a variety of valuable organic products: wine, vinegar, soap, etc. Advances in organic chemistry are based on achievements in the field of chemistry of protein substances, nucleic acids, vitamins, etc. Organic chemistry is of great importance for the development of medicine, since the vast majority of medicines are organic compounds not only of natural origin, but also obtained mainly through synthesis. The exceptional significance of the high molecular weight organic compounds (synthetic resins, plastics, fibers, synthetic rubbers, dyes, herbicides, insecticides, fungicides, defoliants...). Organic chemistry is of great importance for the production of food and industrial goods.
Modern organic chemistry has deeply penetrated into the chemical processes occurring during the storage and processing of food products: the processes of drying, rancidity and saponification of oils, fermentation, baking, fermentation, production of drinks, in the production of dairy products, etc. The discovery and study of enzymes and perfumes and cosmetics also played a major role.
One of the reasons for the wide variety of organic compounds is the uniqueness of their structure, which is manifested in the formation of covalent bonds and chains by carbon atoms, varying in type and length. Moreover, the number of bonded carbon atoms in them can reach tens of thousands, and the configuration of carbon chains can be linear or cyclic. In addition to carbon atoms, the chains may contain oxygen, nitrogen, sulfur, phosphorus, arsenic, silicon, tin, lead, titanium, iron, etc.
The manifestation of these properties by carbon is due to several reasons. It was confirmed that the energies of the C–C and C–O bonds are comparable. Carbon has the ability to form three types of orbital hybridization: four sp 3 - hybrid orbitals, their orientation in space is tetrahedral and corresponds to simple covalent bonds; three hybrid sp 2 orbitals located in the same plane, in combination with a non-hybrid orbital, form double multiples connections (─С = С─); also with the help of sp - hybrid orbitals of linear orientation and non-hybrid orbitals between carbon atoms arise triple multiples bonds (─ C ≡ C ─). Moreover, carbon atoms form these types of bonds not only with each other, but also with other elements. Thus, the modern theory of the structure of matter explains not only a significant number of organic compounds, but also the influence of their chemical structure on their properties.
It also fully confirms the basics theories of chemical structure, developed by the great Russian scientist A.M. Butlerov. ITS main provisions:
1) in organic molecules, atoms are connected to each other in a certain order according to their valence, which determines the structure of the molecules;
2) the properties of organic compounds depend on the nature and number of their constituent atoms, as well as on the chemical structure of the molecules;
3) each chemical formula corresponds to a certain number of possible isomer structures;
4) each organic compound has one formula and has certain properties;
5) in molecules there is a mutual influence of atoms on each other.
Classes of organic compounds
According to the theory, organic compounds are divided into two series - acyclic and cyclic compounds.
1. Acyclic compounds.(alkanes, alkenes) contain an open, unclosed carbon chain - straight or branched:
N N N N N N N
│ │ │ │ │ │ │
N─ S─S─S─S─ N H─S─S─S─N
│ │ │ │ │ │ │
N N N N N │ N
Normal butane isobutane (methylpropane)
2. a) Alicyclic compounds– compounds that have closed (cyclic) carbon chains in their molecules:
cyclobutane cyclohexane
b) Aromatic compounds, the molecules of which contain a benzene skeleton - a six-membered ring with alternating single and double bonds (arenes):
c) Heterocyclic compounds– cyclic compounds containing, in addition to carbon atoms, nitrogen, sulfur, oxygen, phosphorus and some trace elements, which are called heteroatoms.
furan pyrrole pyridine
In each row, organic substances are distributed into classes - hydrocarbons, alcohols, aldehydes, ketones, acids, esters in accordance with the nature of the functional groups of their molecules.
There is also a classification according to the degree of saturation and functional groups. According to the degree of saturation they are distinguished:
1. Extremely saturated– the carbon skeleton contains only single bonds.
─С─С─С─
2. Unsaturated unsaturated– in the carbon skeleton there are multiple (=, ≡) bonds.
─С=С─ ─С≡С─
3. Aromatic– unsaturated cycles with ring conjugation (4n + 2) π-electrons.
By functional groups
1. Alcohols R-CH 2 OH
2. Phenols 
3. Aldehydes R─COH Ketones R─C─R
4. Carboxylic acids R─COOH O
5. Esters R─COOR 1
Alexander Mikhailovich Butlerov was born on September 3 (15), 1828 in the city of Chistopol, Kazan province, into the family of a landowner, a retired officer. He received his first education at a private boarding school, then studied at the gymnasium and the Kazan Imperial University. He taught from 1849, and in 1857 became an ordinary professor of chemistry at the same university. He was its rector twice. In 1851 he defended his master's thesis “On the oxidation of organic compounds”, and in 1854 at Moscow University - his doctoral thesis “On essential oils”. Since 1868 he was an ordinary professor of chemistry at St. Petersburg University, and since 1874 - an ordinary academician of the St. Petersburg Academy of Sciences. In addition to chemistry, Butlerov paid attention to practical issues of agriculture, gardening, and beekeeping; under his leadership, tea cultivation began in the Caucasus. He died in the village of Butlerovka, Kazan province, on August 5 (17), 1886.
Before Butlerov, a considerable number of attempts were made to create a doctrine of the chemical structure of organic compounds. This issue was repeatedly addressed by the most eminent chemists of that time, whose work was partially used by the Russian scientist for his theory of structure. For example, the German chemist August Kekule concluded that carbon can form four bonds with other atoms. Moreover, he believed that several formulas could exist for the same compound, but he always added that depending on the chemical transformation, this formula could be different. Kekule believed that the formulas do not reflect the order in which the atoms in the molecule are connected. Another prominent German scientist, Adolf Kolbe, generally considered it fundamentally impossible to elucidate the chemical structure of molecules.
Butlerov first expressed his basic ideas about the structure of organic compounds in 1861 in a report “On the chemical structure of matter,” which he presented to the participants of the Congress of German Naturalists and Doctors in Speyer. In his theory, he incorporated ideas from Kekule about valency (the number of bonds for a particular atom) and Scottish chemist Archibald Cooper that carbon atoms could form chains. The fundamental difference between Butlerov's theory and others was the provision about the chemical (and not mechanical) structure of molecules - the way in which atoms bonded with each other to form a molecule. In this case, each atom established a bond in accordance with the “chemical force” belonging specifically to it. In his theory, the scientist made a clear distinction between a free atom and an atom that has entered into a connection with another (it transforms into a new form, and as a result of mutual influence, the connected atoms, depending on the structural environment, have different chemical functions). The Russian chemist was convinced that formulas do not just schematically depict molecules, but also reflect their real structure. Moreover, each molecule has a specific structure, which changes only during chemical transformations. From the provisions of the theory it followed (later confirmed experimentally) that the chemical properties of an organic compound are determined by its structure. This statement is especially important, as it made it possible to explain and predict chemical transformations of substances. There is also an inverse relationship: the structural formula can be used to judge the chemical and physical properties of a substance. In addition, the scientist drew attention to the fact that the reactivity of compounds is explained by the energy with which the atoms bond.
With the help of the created theory, Butlerov was able to explain isomerism. Isomers are compounds in which the quantity and “quality” of atoms are the same, but at the same time they have different chemical properties, and therefore a different structure. The theory made it possible to clearly explain known cases of isomerism. Butlerov believed that it was possible to determine the spatial arrangement of atoms in a molecule. His predictions were later confirmed, which gave impetus to the development of a new branch of organic chemistry - stereochemistry. It should be noted that the scientist was the first to discover and explain the phenomenon of dynamic isomerism. Its meaning is that two or more isomers under certain conditions can easily transform into each other. Generally speaking, it was isomerism that became a serious test for the theory of chemical structure and was brilliantly explained by it.
The irrefutable provisions formulated by Butlerov very soon brought the theory universal recognition. The correctness of the ideas put forward was confirmed by experiments of the scientist and his followers. In their process, they proved the hypothesis of isomerism: Butlerov synthesized one of the four butyl alcohols predicted by the theory and deciphered its structure. In accordance with the rules of isomerism, which directly followed from the theory, the possibility of the existence of four valeric acids was also suggested. They were later received.
These are just isolated facts in a chain of discoveries: the chemical theory of the structure of organic compounds had amazing predictive ability.
In a relatively short period, a large number of new organic substances and their isomers were discovered, synthesized and studied. As a result, Butlerov’s theory gave impetus to the rapid development of chemical science, including synthetic organic chemistry. Thus, Butlerov’s numerous syntheses are the main products of entire industries.
The theory of chemical structure continued to develop, which brought many revolutionary ideas to organic chemistry at that time. For example, Kekule suggested the cyclic structure of benzene and the movement of its double bonds in the molecule, the special properties of compounds with conjugated bonds, and much more. Moreover, the mentioned theory made organic chemistry more visual - it became possible to draw molecular formulas.
And this, in turn, marked the beginning of the classification of organic compounds. It was the use of structural formulas that helped to determine ways of synthesizing new substances and to establish the structure of complex compounds, that is, it determined the active development of chemical science and its branches. For example, Butlerov began to conduct serious research into the polymerization process. In Russia, this initiative was continued by his students, which ultimately made it possible to discover an industrial method for producing synthetic rubber.