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

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

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

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

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

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

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

H / O \ H Chemically bonded atoms

Chemically unbonded atoms

2. Atoms in a molecule are connected to each other in a certain order, according to their valency. It was the “order of chemical interaction”, or, in other words, the “method of mutual chemical bonding” of atoms in a molecule, that Butlerov called the chemical structure. As a result, the chemical structure, clearly expressed by the structural formula (sometimes also called graphic, and in recent years - topological), shows which pairs of atoms are chemically bonded and which are not, i.e., the chemical structure characterizes the topology of the molecule (see Molecule ). At the same time, Butlerov specifically emphasized that each compound corresponds to only one chemical structure and, consequently, only one structural (graphic) formula.

The considered provision of TCS is generally valid today. However, firstly, it is far from always possible to convey the molecular structure by one classical structural formula (see Benzene), secondly, in non-rigid molecules, the bond order of atoms can spontaneously change and quite quickly (see Molecule), and, thirdly , modern chemistry has discovered a wide range of molecules with "unusual" structures (for example, in some carboranes, the carbon atom is bonded to five neighboring atoms).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 action 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 components that carry the opposite electric charge." One of these components, namely the electronegative part, J. Berzelius considered oxygen, while the rest, actually organic, should have been an 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 undergo. 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 valence;
- 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 valence. (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>

A different mutual arrangement of carbon atoms in the molecules of UV 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 the 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 in the CH 2 Cl 2 compound there is no relationship between hydrogen and chlorine? I answer this with a resounding denial.”

As a specific example, he further cites an increase in the mobility of chlorine during the transformation of the CH 2 Cl group into COCl and says on this occasion: “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 directly with chlorine.”<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).

Chemical structure of a molecule represents its most characteristic and unique side, since it determines its general properties (mechanical, physical, chemical and biochemical). Any change in the chemical structure of a molecule entails a change in its properties. In the case of minor structural changes made to one molecule, small changes in its properties follow (usually affecting physical properties), but if the molecule has experienced deep structural changes, then its properties (especially chemical ones) will be profoundly changed.

For example, Alpha-aminopropionic acid (Alpha-alanine) has the following structure:

Alpha alanine

What we see:

1. The presence of certain atoms (C, H, O, N),
2. a certain number of atoms belonging to each class, which are connected in a certain order;

All these design features determine a number of properties of Alpha-alanine, such as: solid state of aggregation, boiling point 295 ° C, solubility in water, optical activity, chemical properties of amino acids, etc.

In the presence of a bond between the amino group and another carbon atom (i.e., there has been a slight structural change), which corresponds to beta-alanine:

beta alanine

The general chemical properties are still characteristic of amino acids, but the boiling point is already 200°C and there is no optical activity.

If, for example, two atoms in this molecule are connected by an N atom in the following order (deep structural change):

then the formed substance - 1-nitropropane in its physical and chemical properties is completely different from amino acids: 1-nitro-propane is a yellow liquid, with a boiling point of 131 ° C, insoluble in water.

Thus, structure-property relationship allows you to describe the general properties of a substance with a known structure and, conversely, allows you to find the chemical structure of a substance, knowing its general properties.

General principles of the theory of the structure of organic compounds

In the essence of determining the structure of an organic compound, the following principles lie, which follow from the relationship between their structure and properties:

a) organic substances, in an analytically pure state, have the same composition, regardless of the method of their preparation;

b) organic substances, in an analytically pure state, have constant physical and chemical properties;

c) organic substances with a constant composition and properties, has only one unique structure.

In 1861 the great Russian scientist A. M. Butlerov in his article “On the chemical structure of matter”, he revealed the main idea of ​​the theory of chemical structure, which consists in the influence of the method of bonding atoms in organic matter on its properties. He summarized all the knowledge and ideas about the structure of chemical compounds available by that time in the theory of the structure of organic compounds.

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

can be summarized as follows:

1. In the molecule of an organic compound, the atoms are connected in a certain sequence, which determines its structure.
2. The carbon atom in organic compounds has a valence of four.
3. With the same composition of a molecule, several options for connecting the atoms of this molecule to each other are possible. Such compounds having the same composition but different structures were called isomers, and a similar phenomenon was called isomerism.
4. Knowing the structure of an organic compound, one can predict its properties; Knowing the properties of an organic compound, one can predict its structure.
5. The atoms that form a molecule are subject to mutual influence, which determines their reactivity. Directly bonded atoms have a greater influence on each other, the influence of not directly bonded atoms is much weaker.

Pupil A.M. Butlerov - V. V. Markovnikov continued to study the issue of the mutual influence of atoms, which was reflected in 1869 in his dissertation work "Materials on the mutual influence of atoms in chemical compounds."

The merit of A.M. Butlerov and the importance of the theory of chemical structure is exceptionally great for chemical synthesis. The opportunity arose to predict the basic properties of organic compounds, to foresee the ways of their synthesis. Thanks to the theory of chemical structure, chemists first appreciated the molecule as an ordered system with a strict bond order between atoms. And at present, the main provisions of Butlerov's theory, despite changes and clarifications, underlie modern theoretical concepts of organic chemistry.

Categories ,

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

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

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

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

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

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

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

4) According to the structure of the molecule of organic matter, its properties can be predicted, and the structure can be determined from the properties.

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

Ticket number 7 (2)

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

Electrolysis- this is a redox process that occurs on the electrodes when a direct electric current passes through the melt or electrolyte solution

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

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

NaCl melt electrolysis

NaCl-―> Na + +Cl -

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

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

2Na + +2Cl - -―>2Na+Cl 2

Electrolysis of an aqueous solution of NaCl

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

2H 2 O + 2e-―> H 2 + 2OH -

and chloride ions are oxidized at the anode:

2Cl - -2e-―>Cl 2

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

In ionic form: 2H 2 O+2e-―>H 2 +2OH-

2Cl - -2e-―>Cl 2

electrolysis

2H 2 O+2Cl - -―>H 2 +Cl 2 +2OH -

electrolysis

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

Application of electrolysis:

1) Protection of metals from corrosion

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

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

Ticket number 8 (1)

Related information:

1. A) Theory of knowledge - a science that studies the forms, methods and techniques of the emergence and development of knowledge, its relation to reality, the criteria for its truth.

The basis for the creation of the theory of the chemical structure of organic compounds A.M. Butlerov was the atomic and molecular theory (works by A. Avagadro and S. Cannizzaro). It would be wrong to assume that before its creation the world knew nothing about organic substances and no attempts were made to substantiate the structure of organic compounds. By 1861 (the year A.M. Butlerov created the theory of the chemical structure of organic compounds), the number of known organic compounds reached hundreds of thousands, and the separation of organic chemistry as an independent science occurred as early as 1807 (J. Berzelius).

Background of the theory of the structure of organic compounds

A wide study of organic compounds began in the 18th century with the work of A. Lavoisier, who showed that substances obtained from living organisms consist of several elements - carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus. The introduction of the terms “radical” and “isomerism” was of great importance, as well as the formation of the theory of radicals (L. Giton de Morvo, A. Lavoisier, J. Liebig, J. Dumas, J. Berzelius), success in the synthesis of organic compounds (urea, aniline, acetic acid, fats, sugar-like substances, etc.).

The term "chemical structure", as well as the foundations of the classical theory of chemical structure, were first published by A.M. Butlerov on September 19, 1861 in his report at the Congress of German Naturalists and Physicians in Speyer.

The main provisions of the theory of the structure of organic compounds A.M. Butlerov

1. The atoms that form the molecule of an organic substance are interconnected in a certain order, and one or more valences from each atom are spent on bonding with each other. There are no free valences.

Butlerov called the sequence of connection of atoms "chemical structure". Graphically, the bonds between atoms are indicated by a line or a dot (Fig. 1).

Rice. 1. Chemical structure of the methane molecule: A - structural formula, B - electronic formula

2. The properties of organic compounds depend on the chemical structure of the molecules, i.e. the properties of organic compounds depend on the order in which the atoms are connected in the molecule. By studying the properties, you can depict the substance.

Consider an example: a substance has the gross formula C 2 H 6 O. It is known that when this substance interacts with sodium, hydrogen is released, and when an acid acts on it, water is formed.

C 2 H 6 O + Na = C 2 H 5 ONa + H 2

C 2 H 6 O + HCl \u003d C 2 H 5 Cl + H 2 O

This substance can correspond to two structural formulas:

CH 3 -O-CH 3 - acetone (dimethyl ketone) and CH 3 -CH 2 -OH - ethyl alcohol (ethanol),

based on the chemical properties characteristic of this substance, we conclude that it is ethanol.

Isomers are substances that have the same qualitative and quantitative composition, but different chemical structure. There are several types of isomerism: structural (linear, branched, carbon skeleton), geometric (cis- and trans-isomerism, characteristic of compounds with a multiple double bond (Fig. 2)), optical (mirror), stereo (spatial, characteristic of substances , capable of being located in space in different ways (Fig. 3)).

Rice. 2. An example of geometric isomerism

3. The chemical properties of organic compounds are also influenced by other atoms present in the molecule. Such groups of atoms are called functional groups, due to the fact that their presence in the molecule of a substance gives it special chemical properties. For example: -OH (hydroxo group), -SH (thio group), -CO (carbonyl group), -COOH (carboxyl group). Moreover, the chemical properties of organic matter depend to a lesser extent on the hydrocarbon skeleton than on the functional group. It is the functional groups that provide the variety of organic compounds, due to which they are classified (alcohols, aldehydes, carboxylic acids, etc. The functional groups sometimes include carbon-carbon bonds (multiple double and triple). If there are several identical functional groups, then it is called homopolyfunctional (CH 2 (OH) -CH (OH) -CH 2 (OH) - glycerol), if several, but different - heteropolyfunctional (NH 2 -CH (R) -COOH - amino acids).

Fig.3. An example of stereoisomerism: a - cyclohexane, "chair" form, b - cyclohexane, "bath" form

4. The valency of carbon in organic compounds is always four.