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The scientist who created the theory of the chemical structure of organic substances. Butlerov Alexander Mikhailovich

The contribution to chemistry of the Russian chemist, academician of the St. Petersburg Academy of Sciences and professor of St. Petersburg University, the creator of the theory of chemical structure is described in this article.

Butlerov Alexander Mikhailovich contribution to chemistry:

Alexander Mikhailovich in 1858 opened new way synthesis of methylene iodide. In doing so, he performed many tasks and works on its derivatives.

The chemist was able to synthesize methylene diacetate and, in the process of saponification, obtained a polymer of formaldehyde. On its basis, in 1861, Butlerov was the first to obtain urotropine and methyleneitan, while carrying out the first synthesis of a sugar element.

Butlerov's contribution to the study of chemistry was fully revealed in his revealing report of 1861. In it he:

He proved the imperfection of the theories of chemistry that existed at that time.
Emphasized the importance of the theory of atomicity.
Defined the concept of chemical structure.
Formulated 8 rules for the formation of chemical compounds.
Butlerov was the first to show the difference between the reactivity of different compounds.

Alexander Mikhailovich put forward the idea that atoms in molecules mutually influence each other. He explained in 1864 the process of isomerism of most compounds of organic origin. In the process of experiments, in favor of his idea, the scientist investigated the structure of butyl tertiary alcohol and isobutylene. He also carried out the polymerization of ethylene hydrocarbons.

Butlerov's main role in chemistry is that he is the founder of the theory of tautomerism, laying its foundations.

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 system of D.I. Mendeleev in terms of 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 as sugar, vegetable and animal fats, coloring, fragrant and medicinal substances. Gradually, people learned to process 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 proteins, nucleic acids, vitamins, etc. Organic chemistry is of great importance for the development of medicine, since the vast majority medicines are organic compounds not only of natural origin, but also obtained mainly by synthesis. Exceptional value wandered macromolecular organic compounds (synthetic resins, plastics, fibers, synthetic rubbers, dyes, herbicides, insecticides, fungicides, defoliants…). The importance of organic chemistry for the production of food and industrial goods is enormous.

Modern organic chemistry has penetrated deeply into the chemical processes that occur during the storage and processing of food products: the processes of drying, rancidity and saponification of oils, fermentation, baking, fermentation, obtaining drinks, in the production of dairy products, etc. The discovery and study of enzymes, perfumes and cosmetics also played an important role.

One of the reasons for the great variety of organic compounds is the peculiarity of their structure, which is manifested in the formation of covalent bonds and chains by carbon atoms, different in type and length. 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 chain can include oxygen, nitrogen, sulfur, phosphorus, arsenic, silicon, tin, lead, titanium, iron, etc.

The manifestation of these properties by carbon is associated with several reasons. It has been confirmed that the energies of the C–C and C–O bonds are comparable. Carbon has the ability to form three types of hybridization of orbitals: 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 ─). At the same time, these types of bonds form carbon atoms 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 properties.

It also fully confirms the fundamentals 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 certain order according to their valency, which determines the structure of 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 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, open carbon chain - straight or branched:

N N N N N N

│ │ │ │ │ │ │

N─ S─S─S─S─ N N─S─S─S─N

│ │ │ │ │ │ │

N N N N N │ N

Normal butane isobutane (methyl propane)

2. a) Alicyclic compounds- compounds that have closed (cyclic) carbon chains in molecules:

cyclobutane cyclohexane

b) Aromatic compounds, in the molecules of which there is a benzene skeleton - a six-membered cycle 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 divided 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 distinguish:

1. Limit saturated There are only single bonds in the carbon skeleton.

─С─С─С─

2. Unsaturated unsaturated– there are multiple (=, ≡) bonds in the carbon skeleton.

─С=С─ ─С≡С─

3. aromatic– unlimiting cycles with ring conjugation of (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

slide 1>

Lecture objectives:

Educational:
- to form concepts about the essence of the theory of the chemical structure of organic substances, based on the knowledge of students about the electronic structure of atoms of elements, their position in the Periodic system of D.I. Mendeleev, on the degree of oxidation, the nature of the chemical bond, and other major theoretical provisions:
  - the sequence of carbon atoms in the chain,
  - mutual influence of atoms in a molecule,
  - dependence of the properties of organic substances on the structure of molecules;
- form an idea of the development of theories in organic chemistry;
- learn the concepts: isomers and isomerism;
- explain the meaning of the structural formulas of organic substances and their advantages over molecular ones;
- show the necessity and prerequisites for the creation of a theory of chemical structure;
- Continue developing your writing skills.
Educational:
- develop mental techniques of analysis, comparison, generalization;
- develop abstract thinking;
- to train the attention of students in the perception of a large amount of material;
- develop the ability to analyze information and highlight the most important material.
Educational:
- for the purpose of patriotic and international education, provide students with historical information about the life and work of scientists.

DURING THE CLASSES

1. Organizational part

- Greetings
- Preparing students for the lesson
- Obtaining information about absentees.

2. Learning new things

Lecture plan:<Appendix 1 . Slide 2>

I. Prestructural theories:
- vitalism;
– the theory of radicals;
- type theory.
II. Brief information about the state of chemical science by the 60s of the XIX century. Conditions for creating a theory of the chemical structure of substances:
- the need to create a theory;
- prerequisites for the theory of chemical structure.
III. The essence of the theory of the chemical structure of organic substances A.M. Butlerov. The concept of isomerism and isomers.
IV. The value of the theory of the chemical structure of organic substances A.M. Butlerov and its development.

3. Homework: synopsis, p. 2.

4. Lecture

I. Knowledge about organic substances has been accumulating gradually since ancient times, but as an independent science, organic chemistry arose only at the beginning of the 19th century. Registration of independence of org.chemistry is associated with the name of the Swedish scientist J. Berzelius<Appendix 1 . Slide 3>. In 1808-1812. he published his large manual on chemistry, in which he originally intended to consider, along with mineral substances, also substances of animal and vegetable origin. But the part of the textbook devoted to organic substances appeared only in 1827.
J. Berzelius saw the most significant difference between inorganic and organic substances in the fact that the former can be obtained synthetically in laboratories, while the latter are allegedly formed only in living organisms under the influence of a certain "life force" - a chemical synonym for "soul", "spirit", "divine origin" of living organisms and their constituent organic substances.
The theory that explained the formation of organic compounds by the intervention of "life force" was called vitalism. She has been popular for some time. In the laboratory, it was possible to synthesize only the simplest carbon-containing substances, such as carbon dioxide - CO 2, calcium carbide - CaC 2, potassium cyanide - KCN.
Only in 1828 did the German scientist Wöhler<Appendix 1 . Slide 4> managed to obtain the organic substance urea from an inorganic salt - ammonium cyanate - NH 4 CNO.
NH 4 CNO -– t –> CO (NH 2) 2
In 1854 the French scientist Berthelot<Appendix 1 . Slide 5>Received triglyceride. This led to the need to change the definition of organic chemistry.
Scientists tried to unravel the nature of the molecules of organic substances based on the composition and properties, sought to create a system that would make it possible to link together the disparate facts that had accumulated by the beginning of the 19th century.
The first attempt to create a theory that sought to generalize the data available on organic substances is associated with the name of the French chemist J. Dumas<Appendix 1 . Slide 6>. It was an attempt to consider from a unified point of view a fairly large group of org. compounds, which today we would call ethylene derivatives. Organic compounds turned out to be derivatives of some radical C 2 H 4 - etherine:
C 2 H 4 * HCl - ethyl chloride (etherine hydrochloride)
The idea embedded in this theory - an approach to organic matter as consisting of 2 parts - later formed the basis of a broader theory of radicals (J. Berzelius, J. Liebig, F. Wöhler). This theory is based on the notion of a "dualistic structure" of substances. J. Berzelius wrote: “each organic substance consists of 2 constituent parts carrying the opposite electrical charge. One of these components, namely the electronegative part, J. Berzelius considered oxygen, while the rest, actually organic, should have been the electropositive radical.

The main provisions of the theory of radicals:<Appendix 1 . Slide 7>

- the composition of organic substances includes radicals that carry a positive charge;
- radicals are always constant, do not undergo changes, they pass without changes from one molecule to another;
- radicals can exist in free form.

Gradually science accumulated facts that contradicted the theory of radicals. So J. Dumas carried out the replacement of hydrogen with chlorine in hydrocarbon radicals. Scientists, adherents of the theory of radicals, it seemed incredible that chlorine, charged negatively, played the role of hydrogen, positively charged in compounds. In 1834, J. Dumas was given the task of investigating an unpleasant incident during a ball in the palace of the French king: candles emitted suffocating smoke when burned. J. Dumas found that the wax from which the candles were made was treated with chlorine for bleaching. At the same time, chlorine entered the wax molecule, replacing part of the hydrogen contained in it. The suffocating fumes that frightened the royal guests turned out to be hydrogen chloride (HCl). Later, J. Dumas received trichloroacetic acid from acetic acid.
Thus, the electropositive hydrogen was replaced by the extremely electronegative element chlorine, while the properties of the compound remained almost unchanged. Then J. Dumas concluded that the dualistic approach should be replaced by an approach to the organizational connection as a whole.

The radical theory was gradually abandoned, but it left a deep mark on organic chemistry:<Appendix 1 . Slide 8>
- the concept of "radical" is firmly established in chemistry;
- the statement about the possibility of the existence of free radicals, about the transition in a huge number of reactions of certain groups of atoms from one compound to another, turned out to be true.

In the 40s. 19th century The doctrine of homology was initiated, which made it possible to clarify some relationships between the composition and properties of compounds. Homological series, homological difference were revealed, which made it possible to classify organic substances. The classification of organic substances on the basis of homology led to the emergence of type theory (40-50s of the XIX century, C. Gerard, A. Kekule and others)<Appendix 1 . slide 9>

The Essence of Type Theory<Appendix 1 . Slide 10>

- The theory is based on an analogy in the reactions between organic and some inorganic substances, taken as types (types: hydrogen, water, ammonia, hydrogen chloride, etc.). Replacing hydrogen atoms in the type of substance with other groups of atoms, scientists predicted various derivatives. For example, the replacement of a hydrogen atom in a water molecule by a methyl radical leads to the formation of an alcohol molecule. Substitution of two hydrogen atoms - to the appearance of an ether molecule<Appendix 1 . slide 11>

C. Gerard directly said in this regard that the formula of a substance is only an abbreviated record of its reactions.

All org. substances were considered derivatives of the simplest inorganic substances - hydrogen, hydrogen chloride, water, ammonia<Appendix 1 . slide 12>

<Appendix 1 . slide 13>

- molecules of organic substances are a system consisting of atoms, the order of connection of which is unknown; the properties of compounds are affected by the totality of all atoms of the molecule;
- it is impossible to know the structure of a substance, since the molecules change during the reaction. The formula of a substance does not reflect the structure, but the reactions in which the given substance. For each substance, one can write as many rational formulas as there are different types of transformations that the substance can experience. The theory of types allowed for a plurality of "rational formulas" for substances, depending on what reactions they want to express with these formulas.

The theory of types played a big role in the development of organic chemistry <Appendix 1 . slide 14>

- allowed to predict and discover a number of substances;
- had a positive impact on the development of the doctrine of valency;
- drew attention to the study of chemical transformations of organic compounds, which allowed a deeper study of the properties of substances, as well as the properties of predicted compounds;
- created a systematization of organic compounds that was perfect for that time.

It should not be forgotten that in reality theories arose and succeeded each other not sequentially, but existed simultaneously. Chemists often misunderstood each other. F. Wöhler in 1835 said that “organic chemistry can now drive anyone crazy. It seems to me a dense forest full of wonderful things, a huge thicket without an exit, without an end, where you dare not penetrate ... ".

None of these theories has become a theory of organic chemistry in the full sense of the word. The main reason for the failure of these ideas is their idealistic essence: the internal structure of molecules was considered fundamentally unknowable, and any reasoning about it was quackery.

A new theory was needed, which would stand on materialistic positions. Such a theory was theory of chemical structure A.M. Butlerov <Appendix 1 . Slides 15, 16>, which was created in 1861. Everything rational and valuable that was in the theories of radicals and types was subsequently assimilated by the theory of chemical structure.

The need for the appearance of the theory was dictated by:<Appendix 1 . Slide 17>

– increased industrial requirements for organic chemistry. It was necessary to provide the textile industry with dyes. In order to develop the food industry, it was necessary to improve the methods of processing agricultural products.
In connection with these problems, new methods for the synthesis of organic substances began to be developed. However, scientists had serious difficulties in the scientific substantiation of these syntheses. So, for example, it was impossible to explain the valency of carbon in compounds using the old theory.
Carbon is known to us as a 4-valent element (This has been proven experimentally). But here it seems to retain this valency only in methane CH 4. In ethane C 2 H 6, according to our ideas, carbon should be. 3-valent, and in propane C 3 H 8 - fractional valency. (And we know that valence should be expressed only in whole numbers).
What is the valency of carbon in organic compounds?

It was not clear why there are substances with the same composition, but different properties: C 6 H 12 O 6 is the molecular formula of glucose, but the same formula is also fructose (a sugary substance - an integral part of honey).

Pre-structural theories could not explain the diversity of organic substances. (Why can carbon and hydrogen, two elements, form such a large number of different compounds?).

It was necessary to systematize the existing knowledge from a unified point of view and develop a unified chemical symbolism.

A scientifically substantiated answer to these questions was given by the theory of the chemical structure of organic compounds, created by the Russian scientist A.M. Butlerov.

Basic prerequisites who paved the way for the emergence of the theory of chemical structure were<Appendix 1 . Slide 18>

- the doctrine of valency. In 1853, E. Frankland introduced the concept of valency, established the valence for a number of metals, investigating organometallic compounds. Gradually, the concept of valence was extended to many elements.

An important discovery for organic chemistry was the hypothesis of the ability of carbon atoms to form chains (A. Kekule, A. Cooper).

One of the prerequisites was the development of a correct understanding of atoms and molecules. Until the 2nd half of the 50s. 19th century There were no generally accepted criteria for defining the concepts: "atom", "molecule", "atomic mass", "molecular mass". Only at the International Congress of Chemists in Karlsruhe (1860) were these concepts clearly defined, which predetermined the development of the theory of valence, the emergence of the theory of chemical structure.

The main provisions of the theory of chemical structure of A.M. Butlerov(1861)

A.M. Butlerov formulated the most important ideas of the theory of the structure of organic compounds in the form of basic provisions, which can be divided into 4 groups.<Appendix 1 . Slide 19>

1. All atoms that form the molecules of organic substances are connected in a certain sequence according to their valence (i.e., the molecule has a structure).

<Appendix 1 . Slides 19, 20>

In accordance with these ideas, the valency of elements is conventionally depicted by dashes, for example, in methane CH 4.<Appendix 1 . Slide 20> >

Such a schematic representation of the structure of molecules is called structure formulas and structural formulas. Based on the provisions on the 4-valency of carbon and the ability of its atoms to form chains and cycles, the structural formulas of organic substances can be depicted as follows:<Appendix 1 . Slide 20>

In these compounds, carbon is tetravalent. (The dash symbolizes a covalent bond, a pair of electrons).

2. The properties of a substance depend not only on which atoms and how many of them are part of the molecules, but also on the order of connection of atoms in molecules. (i.e. properties depend on the structure) <Appendix 1 . Slide 19>

This position of the theory of the structure of organic substances explained, in particular, the phenomenon of isomerism. There are compounds that contain the same number of atoms of the same elements but are bound in a different order. Such compounds have different properties and are called isomers.
The phenomenon of the existence of substances with the same composition, but different structure and properties is called isomerism.<Appendix 1 . Slide 21>

The existence of isomers of organic substances explains their diversity. The phenomenon of isomerism was predicted and proved (experimentally) by A.M. Butlerov on the example of butane

So, for example, the composition of C 4 H 10 corresponds to two structural formulas:<Appendix 1 . Slide 22>

Miscellaneous mutual arrangement carbon atoms in the y / w molecules appears only with butane. The number of isomers increases with the number of carbon atoms of the corresponding hydrocarbon, for example, pentane has three isomers, and decane has seventy-five.

3. By the properties of a given substance, one can determine the structure of its molecule, and by the structure of the molecule, one can predict properties. <Appendix 1 . Slide 19>

From the course of inorganic chemistry, it is known that the properties of inorganic substances depend on the structure of crystal lattices. Distinctive properties of atoms from ions are explained by their structure. In the future, we will see that organic substances with the same molecular formulas, but different structures, differ not only in physical, but also in chemical properties.

4. Atoms and groups of atoms in the molecules of substances mutually influence each other.

<Appendix 1 . Slide 19>

As we already know, the properties of inorganic compounds containing hydroxo groups depend on whether they are bonded to atoms of metals or nonmetals. For example, both bases and acids contain a hydroxo group:<Appendix 1 . Slide 23>

However, the properties of these substances are completely different. The reason for the different chemical nature of the group - OH (in aqueous solution) is due to the influence of atoms and groups of atoms associated with it. With an increase in the non-metallic properties of the central atom, dissociation according to the type of base is weakened and dissociation according to the type of acid increases.

Organic compounds can also have different properties, which depend on which atoms or groups of atoms the hydroxyl groups are attached to.

The question of the mutual infusion of atoms A.M. Butlerov analyzed in detail on April 17, 1879 at a meeting of the Russian Physical and Chemical Society. He said that if two different elements are associated with carbon, for example, Cl and H, then “they do not depend here on one another to the same extent as on carbon: there is no dependence between them, that connection that exists in a particle of hydrochloric acid … But does it follow from this that there is no relationship between hydrogen and chlorine in the CH 2 Cl 2 compound? I answer this with a resounding denial.”

As a specific example, he further cites the increase in the mobility of chlorine during the transformation of the CH 2 Cl group into COCl and says in this regard: “It is obvious that the character of the chlorine in the particle has changed under the influence of oxygen, although this latter has not combined with chlorine directly.”<Appendix 1 . Slide 23>

The question of the mutual influence of directly unbound atoms was the main theoretical core of V.V. Morkovnikov.

In the history of mankind, relatively few scientists are known whose discoveries are of worldwide significance. In the field of organic chemistry, such merits belong to A.M. Butlerov. In terms of significance, the theory of A.M. Butlerov is compared with the Periodic Law.

The theory of the chemical structure of A.M. Butlerov:<Appendix 1 . Slide 24>

- made it possible to systematize organic substances;
– answered all the questions that had arisen by that time in organic chemistry (see above);
- made it possible to theoretically foresee the existence of unknown substances, to find ways of their synthesis.

Almost 140 years have passed since the TCS of organic compounds was created by A.M. Butlerov, but even now chemists of all countries use it in their work. The latest achievements of science supplement this theory, clarify and find new confirmations of the correctness of its basic ideas.

The theory of chemical structure remains the foundation of organic chemistry today.

TCS of organic compounds A.M. Butlerova made a significant contribution to the creation of a general scientific picture of the world, contributed to the dialectical - materialistic understanding of nature:<Appendix 1 . Slide 25>

– the law of transition of quantitative changes into qualitative ones can be traced on the example of alkanes:<Appendix 1 . Slide 25>.

Only the number of carbon atoms changes.

– law of unity and struggle of opposites traced to the phenomenon of isomerism<Appendix 1 . Slide 26>

Unity - in composition (same), location in space.
The opposite is in the structure and properties (different sequence of arrangement of atoms).
These two substances coexist together.

– law of negation of negation - on isomerism.<Appendix 1 . Slide 27>

Isomers coexisting negate each other by their existence.

Having developed the theory, A.M. Butlerov did not consider it absolute and unchangeable. He argued that it should develop. TCS of organic compounds did not remain unchanged. Its further development proceeded mainly in 2 interrelated directions:<Appendix 1 . Slide 28>

Stereochemistry is the study of the spatial structure of molecules.

The doctrine of the electronic structure of atoms (allowed to understand the nature of the chemical bond of atoms, the essence of the mutual influence of atoms, to explain the reason for the manifestation of certain chemical properties by a substance).

Just as in inorganic chemistry the fundamental theoretical basis is the Periodic law and the Periodic system of chemical elements of D. I. Mendeleev, so in organic chemistry the leading scientific basis is the theory of the structure of organic compounds of 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
Number of organic compounds known in different years

Explain this variety of organic compounds scientists early XIX in. could not. Even more questions were raised by the phenomenon of isomerism.

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

F. Wöhler, already known to you, in one of his letters to J. J. Berzelius, described organic chemistry as follows: “Organic chemistry can now drive anyone crazy. It seems to me a dense forest, full of amazing things, a boundless thicket from which you can’t get out, where you don’t dare to penetrate ... "

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

In the hydrogen molecule H 2, one covalent chemical is formed H-H connection, i.e., 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", which you are used to working with in the course of inorganic chemistry in elementary school. However, they are not the same. For example, in a nitrogen molecule N 2, the oxidation state of nitrogen is zero, and the valency is three:

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

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

Usually, in relation to ionic compounds (sodium chloride NaCl and many other inorganic substances with an ionic bond), 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, use the concept of "valence".

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, simultaneously with A. Cooper, he noted that carbon atoms can 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. Such a theory was created by the Russian scientist A. M. Butlerov. It was his inquisitive mind that "dared to penetrate" the "dense forest" of organic chemistry and begin the transformation of 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 Speyer.

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

1. The atoms in the molecules of substances are connected in a certain sequence according to their valency. 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 series of substances similar in composition, structure and properties - homologous series.

Butlerov Alexander Mikhailovich (1828-1886)

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 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 butane C 4 H 10, in addition to the linear structure molecule 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 those of linear butane.

Butane, in the molecule of which the atoms are arranged in the form of 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 considered. 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 determine 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 (the class of saturated monohydric alcohols) and dimethyl ether (the class of ethers) discussed above.

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 the molecule has a planar structure at the site of such a bond (Fig. 6).

Rice. 6.
Model of the ethylene molecule

For example, for butene-2, if the same groups of atoms at carbon atoms in a double bond are on one side of the C=C bond plane, then the molecule is a cisisomer, if on opposite sides it is a transisomer.

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 asymmetric 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 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 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 the 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 the profile level of the study of chemistry.

Several types of chemical formulas are widely used in organic chemistry.

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:

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, such a formula is written as follows: CH 3 -CH 2 -CH 3.

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

Rice. 7.
Models of the ethane molecule:
1 - ball-and-stick; 2 - scale

New words and concepts

Isomerism, isomers.
Valence.
Chemical structure.
Theory of the structure of organic compounds.
Homological series and homological difference.
Formulas molecular and structural.
Models of molecules: volumetric (scale) and spherical.

Questions and tasks

What is valence? How is it different from oxidation state? Give examples of substances in which the values of the oxidation state and valence of 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, 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 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 formation of this theory?
It is possible that there are three isomers of the composition C 5 H 12. Write down their full and abbreviated structural formulas,
According to the model of the 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.

Lecture Grade 11 elevated level Theory of organic structure. Alkanes, cycloalkanes

The main provisions of the theory of chemical structure of A.M. Butlerov

1) Atoms in molecules are connected to each other in a certain sequence according to their valencies.

The sequence of interatomic bonds in a molecule is called its chemical structure and is reflected in one structural formula(structure formula).

2) The chemical structure can be established by chemical methods. Currently, modern physical methods are also used.

3) The properties of substances depend on their chemical structure.

4) By the properties of a given substance, you can determine the structure of its molecule, and by the structure of the molecule, you can predict the properties.

5) Atoms and groups of atoms in a molecule have mutual influence Each other.

1) The structure of the carbon atom.

The electronic structure of the carbon atom is depicted as follows: 1s 2 2s 2 2p 2 or schematically

Carbon in organic compounds is tetravalent.

This is due to the fact that during the formation of a covalent bond, the carbon atom passes into an excited state, in which the electron pair in the 2s orbital is separated and one electron occupies the vacant p orbital. Schematically:

As a result, there are no longer two, but four unpaired electrons.

2) Sigma and pi-bonds.

Overlapping atomic orbitals along the line connecting the nuclei of atoms, leads to the formation σ-bonds.

Between two atoms in a chemical particle is possible only one σ-bond. All σ-bonds have axial symmetry about the internuclear axis.

At additional overlapping atomic orbitals perpendicular to the communication line and parallel to each other, 1s2 2s2 3s2

π bonds.

As a result, between the atoms there are multiple bonds:

Single (σ)	Double (σ+π)	Triple (σ + π + π)
S-S, S-N, S-O		С≡С and С≡N

3) Hybridization.

Since the four electrons of the carbon atom are different (2s- and 2p-electrons), the bonds should also be different, but it is known that the bonds in the methane molecule are equivalent. Therefore, to explain the spatial structure of organic molecules, the method is used hybridization.

1. When socialization of four orbitals of an excited carbon atom (one 2s- and three 2p-orbitals) formed four new equivalent sp 3 hybrid orbitals shaped like an elongated dumbbell. Due to mutual repulsion sp 3- hybrid orbitals are directed in space to the vertices tetrahedron and the angles between them are equal 109 0 28" (best location). This state of the carbon atom is called the first valence state.

2. When sp 2 hybridizations one s and two p orbitals mix to form three hybrid orbitals, whose axes are located in the same plane and directed relative to each other at an angle of 120°. This state of the carbon atom is called the second valence state.

3. When sp hybridization, one s and one p orbitals merge and two hybrid orbitals are formed, whose axes are located on the same straight line and directed in different directions from the nucleus of the considered carbon atom at an angle of 180°. This state of the carbon atom is called the third valence state.

TYPES OF HYBRIDIZATION in organic substances.

4) Isomerism.

Isomers are substances that have the same composition (the number of atoms of each type), but a different mutual arrangement of atoms - a different structure.

For example, there are two substances with the molecular formula C 4 H 10:

n-butane (with linear skeleton): CH 3 - CH 2 - CH 2 - CH 3 and iso-butane, or 2-methylpropane:CH 3 - CH - CH 3

‌ │

CH 3They are isomers.

Isomerism happens structural and spatial.

Structural isomerism.

1.isomerism carbon skeleton- due to a different order of communication between the carbon atoms that form the skeleton of the molecule (see butane and isobutane).

2.Isomerism of the position of a multiple bond or functional group- due to the different position of any reactive group with the same carbon skeleton of the molecules. So, propane corresponds to two isomeric alcohols:

CH 3 - CH 2 - CH 2 - OH - propanol-1 or n-propyl alcohol

and CH 3 - CH - CH 3

OH - propanol-2 or isopropyl alcohol.

isomerism multiple bond positions, e.g. in butene-1 and butene-2

CH 3 - CH 2 - CH \u003d CH 2 - butene-1

CH 3 - CH \u003d CH - CH 3 - butene-2.

3. Interclass isomerism- isomerism of substances related to different classes of organic compounds:

Alkenes and cycloalkanes (with C 3)

Alkynes and dienes (with C 3)

Alcohols and ethers (with C 2)

Aldehydes and ketones (with C 3)

Monobasic limiting carboxylic acids and esters (with C 2)

Spatial isomerism- divided into two types: geometric(or cis-trans-isomerism) and optical.

geometric isomerism characteristic of compounds containing double bonds or a cyclopropane ring; it is due to the impossibility of free rotation of atoms around a double bond or in a cycle. In these cases, the substituents may be located either on one side of the plane of the double bond or ring (cis - position), or on opposite sides (trance - position).

The terms "cis" and "trans" usually refer to a pair of identical substituents, and if all substituents are different, then conditionally to one of the pairs.
- two forms of ethylene-1,2-dicarboxylic acid - cis form, or maleic acid (I), and trans form, or fumaric acid (II) SHAPE \* MERGEFORMAT

Optical isomerism characteristic of molecules of organic substances that are not compatible with their mirror image (i.e., with a molecule corresponding to this mirror image). Most often, optical activity is due to the presence in the molecule asymmetricatom carbon, i.e., a carbon atom bonded to four different substituents. An example is lactic acid:

OH (asymmetric carbon atom is marked with an asterisk).

The lactic acid molecule, under no movement in space, can coincide with its mirror image. These two forms of acid are related to each other as right hand to the left, and are called optical antipodes (enantiomers).

Physical and Chemical properties optical isomers are often very similar, but they can differ greatly in biological activity, taste and smell.

Classification of organic substances.

Substance class	Characteristic	General formula	Suffix or prefix
C o bric	Alkanes	All connections are single	C n H 2n+2
Alkenes	1 double C=C connection	C n H 2n
dienes	2 doubles C=C connections	C n H 2n-2
Alkynes	1 triple bond С≡С	C n H 2n-2
Cycloalkanes	Closed ring carbon chain	C n H 2n
Arenes (aromatic hydrocarbons)		C n H 2n-6	…-benzene
Oxygen-containing connections	Alcohols		C n H 2n+2 O CH 3 OH
Phenols	benzene ring and in it	C n H 2n-6O C 6 H 5 OH
Aldehydes		C n H 2n O NSNO
Ketones		C n H 2n O C 3 H 6 O
carboxylic acids		C n H 2n O 2 UNSD	…-oic acid
Esters		C n H 2n O 2
	Nitro compounds		C n H 2n+1 NO 2
Amines		C n H 2n+3 N CH 3 NH 2
Amino acids	Contains -NH 2 and -COOH	C n H 2n+1 NO 2