Founder of the theory of the chemical structure of organic compounds. Theory of the structure of organic substances

How science took shape at the beginning of the 19th century, when the Swedish scientist J. Ya. Berzelius first introduced the concept of organic substances and organic chemistry. The first theory in organic chemistry is the theory of radicals. Chemists discovered that during chemical transformations, groups of several atoms pass unchanged from a molecule of one substance to a molecule of another substance, just as atoms of elements pass from molecule to molecule. Such “immutable” groups of atoms are called radicals.

However, not all scientists agreed with the radical theory. Many generally rejected the idea of ​​atomism - the idea of ​​​​the complex structure of a molecule and the existence of an atom as its component part. What has been indisputably proven today and does not raise the slightest doubt, in the 19th century. was the subject of fierce controversy.

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All substances that contain a carbon atom, other than carbonates, carbides, cyanides, thiocyanates and carbonic acid, are organic compounds. This means that they are capable of being created by living organisms from carbon atoms through enzymatic or other reactions. Today, many organic substances can be synthesized artificially, which allows the development of medicine and pharmacology, as well as the creation of high-strength polymer and composite materials.

Classification of organic compounds

Organic compounds are the most numerous class of substances. There are about 20 types of substances here. They differ in chemical properties and differ in physical qualities. Their melting point, mass, volatility and solubility, as well as their state of aggregation under normal conditions are also different. Among them:

• hydrocarbons (alkanes, alkynes, alkenes, alkadienes, cycloalkanes, aromatic hydrocarbons);
• aldehydes;
• ketones;
• alcohols (dihydric, monohydric, polyhydric);
• ethers;
• esters;
• carboxylic acids;
• amines;
• amino acids;
• carbohydrates;
• fats;
• proteins;
• biopolymers and synthetic polymers.

This classification reflects the characteristics of the chemical structure and the presence of specific atomic groups that determine the difference in the properties of a particular substance. In general, the classification, which is based on the configuration of the carbon skeleton and does not take into account the characteristics of chemical interactions, looks different. According to its provisions, organic compounds are divided into:

• aliphatic compounds;
• aromatics;
• heterocyclic substances.

These classes of organic compounds can have isomers in different groups of substances. The properties of isomers are different, although their atomic composition may be the same. This follows from the provisions laid down by A.M. Butlerov. Also, the theory of the structure of organic compounds is the guiding basis for all research in organic chemistry. It is placed on the same level as Mendeleev's Periodic Law.

The very concept of chemical structure was introduced by A.M. Butlerov. It appeared in the history of chemistry on September 19, 1861. Previously, there were different opinions in science, and some scientists completely denied the existence of molecules and atoms. Therefore, there was no order in organic and inorganic chemistry. Moreover, there were no patterns by which one could judge the properties of specific substances. At the same time, there were compounds that, with the same composition, exhibited different properties.

The statements of A.M. Butlerov largely directed the development of chemistry in the right direction and created a very solid foundation for it. Through it, it was possible to systematize the accumulated facts, namely, the chemical or physical properties of certain substances, the patterns of their entry into reactions, etc. Even the prediction of ways to obtain compounds and the presence of some general properties became possible thanks to this theory. And most importantly, A.M. Butlerov showed that the structure of the molecule of a substance can be explained from the point of view of electrical interactions.

Logic of the theory of the structure of organic substances

Since before 1861 many in chemistry rejected the existence of an atom or molecule, the theory of organic compounds became a revolutionary proposal for the scientific world. And since A. M. Butlerov himself proceeds only from materialistic conclusions, he managed to refute philosophical ideas about organic matter.

He was able to show that the molecular structure can be recognized experimentally through chemical reactions. For example, the composition of any carbohydrate can be determined by burning a certain amount of it and counting the resulting water and carbon dioxide. The amount of nitrogen in an amine molecule is also calculated during combustion by measuring the volume of gases and isolating the chemical amount of molecular nitrogen.

If we consider Butlerov's judgments about structure-dependent chemical structure in the opposite direction, a new conclusion arises. Namely: knowing the chemical structure and composition of a substance, one can empirically assume its properties. But most importantly, Butlerov explained that in organic matter there is a huge number of substances that exhibit different properties, but have the same composition.

General provisions of the theory

Considering and studying organic compounds, A.M. Butlerov derived some of the most important principles. He combined them into a theory explaining the structure of chemical substances of organic origin. The theory is as follows:

• in molecules of organic substances, atoms are connected to each other in a strictly defined sequence, which depends on valence;
• chemical structure is the immediate order according to which atoms in organic molecules are connected;
• the chemical structure determines the presence of the properties of an organic compound;
• depending on the structure of molecules with the same quantitative composition, different properties of the substance may appear;
• all atomic groups involved in the formation of a chemical compound have a mutual influence on each other.

All classes of organic compounds are built according to the principles of this theory. Having laid the foundations, A. M. Butlerov was able to expand chemistry as a field of science. He explained that due to the fact that in organic substances carbon exhibits a valence of four, the diversity of these compounds is determined. The presence of many active atomic groups determines whether a substance belongs to a certain class. And it is precisely due to the presence of specific atomic groups (radicals) that physical and chemical properties appear.

Hydrocarbons and their derivatives

These organic compounds of carbon and hydrogen are the simplest in composition among all the substances in the group. They are represented by a subclass of alkanes and cycloalkanes (saturated hydrocarbons), alkenes, alkadienes and alkatrienes, alkynes (unsaturated hydrocarbons), as well as a subclass of aromatic substances. In alkanes, all carbon atoms are connected only by a single C-C bond, which is why not a single H atom can be incorporated into the hydrocarbon composition.

In unsaturated hydrocarbons, hydrogen can be incorporated at the site of the double C=C bond. Also, the C-C bond can be triple (alkynes). This allows these substances to enter into many reactions involving the reduction or addition of radicals. For the convenience of studying their ability to react, all other substances are considered to be derivatives of one of the classes of hydrocarbons.

Alcohols

Alcohols are organic chemical compounds that are more complex than hydrocarbons. They are synthesized as a result of enzymatic reactions in living cells. The most typical example is the synthesis of ethanol from glucose as a result of fermentation.

In industry, alcohols are obtained from halogen derivatives of hydrocarbons. As a result of the replacement of the halogen atom with a hydroxyl group, alcohols are formed. Monohydric alcohols contain only one hydroxyl group, polyhydric alcohols contain two or more. An example of a dihydric alcohol is ethylene glycol. Polyhydric alcohol is glycerin. The general formula of alcohols is R-OH (R is the carbon chain).

Aldehydes and ketones

After alcohols enter into reactions of organic compounds associated with the abstraction of hydrogen from the alcohol (hydroxyl) group, the double bond between oxygen and carbon closes. If this reaction proceeds through the alcohol group located at the terminal carbon atom, it results in the formation of an aldehyde. If the carbon atom with the alcohol is not located at the end of the carbon chain, then the result of the dehydration reaction is the production of a ketone. The general formula of ketones is R-CO-R, aldehydes R-COH (R is the hydrocarbon radical of the chain).

Esters (simple and complex)

The chemical structure of organic compounds of this class is complicated. Ethers are considered to be reaction products between two alcohol molecules. When water is removed from them, a compound of the R-O-R pattern is formed. Reaction mechanism: abstraction of a hydrogen proton from one alcohol and a hydroxyl group from another alcohol.

Esters are reaction products between an alcohol and an organic carboxylic acid. Reaction mechanism: elimination of water from the alcohol and carbon group of both molecules. Hydrogen is separated from the acid (at the hydroxyl group), and the OH group itself is separated from the alcohol. The resulting compound is depicted as R-CO-O-R, where the beech R denotes the radicals - the remaining parts of the carbon chain.

Carboxylic acids and amines

Carboxylic acids are special substances that play important role in the functioning of the cell. The chemical structure of organic compounds is as follows: a hydrocarbon radical (R) with a carboxyl group (-COOH) attached to it. The carboxyl group can only be located at the outermost carbon atom, because the valency of C in the (-COOH) group is 4.

Amines are simpler compounds that are derivatives of hydrocarbons. Here, at any carbon atom there is an amine radical (-NH2). There are primary amines in which a group (-NH2) is attached to one carbon (general formula R-NH2). In secondary amines, nitrogen combines with two carbon atoms (formula R-NH-R). In tertiary amines, nitrogen is connected to three carbon atoms (R3N), where p is a radical, a carbon chain.

Amino acids

Amino acids are complex compounds that exhibit the properties of both amines and acids of organic origin. There are several types of them, depending on the location of the amine group in relation to the carboxyl group. The most important are alpha amino acids. Here the amine group is located at the carbon atom to which the carboxyl group is attached. This allows the creation of a peptide bond and the synthesis of proteins.

Carbohydrates and fats

Carbohydrates are aldehyde alcohols or keto alcohols. These are compounds with a linear or cyclic structure, as well as polymers (starch, cellulose and others). Their most important role in the cell is structural and energetic. Fats, or rather lipids, perform the same functions, only they participate in other biochemical processes. From the point of view of chemical structure, fat is an ester of organic acids and glycerol.

Slide 1>

Lecture objectives:

• Educational:
  • to form concepts about the essence of the theory of the chemical structure of organic substances, relying on students’ knowledge of the electronic structure of atoms of elements, their position in the Periodic Table of D.I. Mendeleev, about the degree of oxidation, the nature of the chemical bond and other major theoretical principles:
    • the sequence of arrangement 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 progress of the development of theories in organic chemistry;
  • master the concepts: isomers and isomerism;
  • explain the meaning of the structural formulas of organic substances and their advantages over molecular ones;
  • show the need and prerequisites for creating a theory of chemical structure;
  • Continue to develop note-taking skills.
• Developmental:
  • develop mental techniques of analysis, comparison, generalization;
  • develop abstract thinking;
  • train students' attention when perceiving large amounts 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.

PROGRESS OF THE LESSON

1. Organizational part

- Greetings
– Preparing students for the lesson
– Receiving information about absentees.

2. Learning new things

Lecture outline:<Appendix 1 . Slide 2>

I. Pre-structural theories:
– vitalism;
– theory of radicals;
– theory of types.
II. Brief information about the state of chemical science in the 60s of the 19th 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 significance of the theory of the chemical structure of organic substances A.M. Butlerov and its development.

3. Homework: abstract, paragraph 2.

4. Lecture

I. Knowledge about organic substances has accumulated gradually since ancient times, but organic chemistry emerged as an independent science only at the beginning of the 19th century. The establishment of independence of organizational 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 initially intended to consider, along with minerals, also substances of animal and plant 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 in laboratories synthetically, while the latter are supposedly formed only in living organisms under the influence of a certain “vital 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 “vital force” was called vitalism. She was 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 necessitated a change in the definition of organic chemistry.
Scientists tried, based on the composition and properties, to unravel the nature of the molecules of organic substances, and sought to create a system that would make it possible to connect 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>. This was an attempt to consider from a unified point of view a fairly large group of organic 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 contained in this theory - the approach to an organic substance as consisting of 2 parts - subsequently formed the basis of a broader theory of radicals (J. Berzelius, J. Liebig, F. Wöhler). This theory is based on the idea of ​​the “dualistic structure” of substances. J. Berzelius wrote: “every organic substance consists of 2 components that carry an opposite electric charge.” J. Berzelius considered oxygen to be one of these components, namely the electronegative part, while the rest, actually organic, should have been an electropositive radical.

Basic 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 from one molecule to another without changes;
– radicals can exist in free form.

Gradually, science accumulated facts that contradicted the theory of the radicals. This is how J. Dumas replaced hydrogen with chlorine in hydrocarbon radicals. It seemed incredible to scientists who were adherents of the radical theory that chlorine, charged negatively, could play the role of hydrogen, charged positively, in compounds. In 1834, J. Dumas received the task of investigating an unpleasant incident during a ball in the palace of the French king: candles emitted choking smoke when burning. J. Dumas established that the wax from which the candles were made was treated with chlorine by the manufacturer for bleaching. In this case, 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). Subsequently, J. Dumas obtained trichloroacetic acid from acetic acid.
Thus, the electropositive hydrogen was replaced by the extremely electronegative element chlorine, and 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 single whole.

The radical theory was gradually rejected, but it left a deep mark on organic chemistry:<Appendix 1 . Slide 8>
– the concept of “radical” has become firmly established in chemistry;
– the statement about the possibility of the existence of radicals in a free form, 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 XIX century The study of homology was initiated, which made it possible to clarify some of the relationships between the composition and properties of compounds. Homologous series and homologous differences were identified, which made it possible to classify organic substances. Classification of organic substances based on homology led to the emergence of the theory of types (40-50s of the 19th century, C. Gerard, A. Kekule, etc.)<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, accepted as types (types: hydrogen, water, ammonia, hydrogen chloride, etc.). By replacing hydrogen atoms in the type of substance with other groups of atoms, scientists predicted various derivatives. For example, replacing a hydrogen atom in a water molecule with a methyl radical results in the formation of an alcohol molecule. Substitution of two hydrogen atoms results in 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 recording 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 influenced 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 substance undergoes. For each substance, you can write as many rational formulas as there are different types of transformations the substance can undergo. The theory of types allowed for a multiplicity of “rational formulas” for substances, depending on what reactions they wanted to express with these formulas.

Type theory played a major role in the development of organic chemistry <Appendix 1 . Slide 14>

– made it possible to predict and discover a number of substances;
– had a positive impact on the development of the doctrine of valence;
– paid 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 the predicted compounds;
- created a systematization of organic compounds that was perfect for that time.

We should not forget that in reality theories arose and replaced each other not sequentially, but existed simultaneously. Chemists often did not understand each other well. F. Wöhler said in 1835 that “organic chemistry today can drive anyone crazy. It seems to me like a dense forest full of wonderful things, a huge thicket with no exit, no end, where you don’t dare to penetrate...”

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

A new theory was needed that would take a materialist position. This 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 later assimilated by the theory of chemical structure.

The need for a 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 methods of processing agricultural products.
In connection with these problems, new methods for the synthesis of organic substances began to be developed. However, scientists have had serious difficulties in scientifically substantiating these syntheses. For example, it was impossible to explain the valence 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 valence only in CH4 methane. In ethane C 2 H 6, if we follow our ideas, carbon should be. 3-valent, and in propane C 3 H 8 - fractional valence. (And we know that valence must be expressed only in whole numbers).
What is the valence 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 - the molecular formula of glucose, but the same formula for fructose (a sugary substance - a component of honey).

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

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

A scientifically based 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 prepared the ground for the emergence of the theory of chemical structure were<Appendix 1 . Slide 18>

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

An important discovery for organic chemistry was the hypothesis about 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. XIX 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 valency and the emergence of the theory of chemical structure.

Basic principles 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 principles that can be divided into 4 groups.<Appendix 1 . Slide 19>

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

<Appendix 1 . Slides 19, 20>

In accordance with these ideas, the valence 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 structural formulas and 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 what atoms and how many of them are included in the molecules, but also on the order of connection of atoms in the 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 bonded 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 proven (experimentally) by A.M. Butlerov using the example of butane

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

Different relative positions of carbon atoms in carbon dioxide molecules appear 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 the crystal lattices. The 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 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 which atoms they are connected to - metal or non-metal atoms. 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 character of the OH group (in aqueous solution) is due to the influence of the atoms and groups of atoms associated with it. With increasing nonmetallic properties of the central atom, dissociation according to the base type weakens and dissociation according to the acid type increases.

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

The question of mutual infusion of atoms A.M. Butlerov discussed it in detail on April 17, 1879 at a meeting of the Russian Physicochemical Society. He said that if two different elements are associated with carbon, for example, Cl and H, then “they do not depend on each other to the same extent as on carbon: there is no dependence between them, the connection that exists in a particle of hydrochloric acid ... But does it follow from this that in the compound CH 2 Cl 2 there is no relationship between hydrogen and chlorine? I answer this with a decisive 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 on this occasion: “It is obvious that the character of the chlorine present in the particle was changed under the influence of oxygen, although the latter did not combine with the chlorine directly.”<Appendix 1 . Slide 23>

The question of the mutual influence of directly non-bonded atoms was the main theoretical core of the works of V.V. Morkovnikova.

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

Theory of chemical structure A.M. Butlerova:<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 predict the existence of unknown substances and 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 from all countries use it in their work. The latest achievements of science supplement this theory, clarify it and find new confirmation 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>

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

Only the number of carbon atoms changes.

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

Unity – in composition (identical), location in space.
The opposite is in 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 deny each other by their existence.

Having developed the theory, A.M. Butlerov did not consider it absolute and unchangeable. He argued that it must develop. The TCS of organic compounds has not remained unchanged. Its further development proceeded mainly in two 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 us to understand the nature of the chemical bond of atoms, the essence of the mutual influence of atoms, and explain the reason for the manifestation of certain chemical properties by a substance).

The basis for the creation of the theory of the chemical structure of organic compounds is A.M. Butlerov was inspired by the atomic-molecular theory (works of A. Avagadro and S. Cannizzaro). It would be wrong to assume that before its creation, nothing was known in the world 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 identification of organic chemistry as an independent science occurred back in 1807 (J. Berzelius).

Prerequisites for the theory of the structure of organic compounds

A broad 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. Of great importance was the introduction of the terms “radical” and “isomerism”, as well as the formation of the theory of radicals (L. Guiton de Morveau, A. Lavoisier, J. Liebig, J. Dumas, J. Berzelius), successes 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 doctors in Speyer.

Basic principles of the theory of the structure of organic compounds A.M. Butlerov

1. The atoms that form a molecule of an organic substance are connected to each other 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 connections of atoms “chemical structure.” Graphically, connections 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 of connection of atoms in the molecule. Having studied the properties, you can depict the substance.

Let's consider an example: a substance has a gross formula of 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

C2H6O + HCl = C2H5Cl + H2O

This substance can have 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 structures. 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 differently in space (Fig. 3)).

Rice. 2. 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 (hydroxy group), -SH (thio group), -CO (carbonyl group), -COOH (carboxyl group). Moreover, the chemical properties of an organic substance depend less on the hydrocarbon skeleton than on the functional group. It is the functional groups that provide the diversity of organic compounds, due to which they are classified (alcohols, aldehydes, carboxylic acids, etc. Carbon-carbon bonds (multiple double and triple) are sometimes included among the functional groups. 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. Example of stereoisomerism: a – cyclohexane, “chair” form, b – cyclohexane, “bathtub” form

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

Topic: Basic principles of the theory of the structure of organic compounds by A. M. Butlerov.

The theory of the chemical structure of organic compounds, put forward by A. M. Butlerov in the second half of the last century (1861), was confirmed by the works of many scientists, including Butlerov’s students and himself. It turned out to be possible on its basis to explain many phenomena that had not yet been interpreted: homology, the manifestation of tetravalency by carbon atoms in organic substances. The theory also fulfilled its predictive function: on its basis, scientists predicted the existence of still unknown compounds, described their properties and discovered them. So, in 1862–1864. A. M. Butlerov examined propyl, butyl and amyl alcohols, determined the number of possible isomers and derived the formulas of these substances. Their existence was later experimentally proven, and some of the isomers were synthesized by Butlerov himself.

During the 20th century. the provisions of the theory of the chemical structure of chemical compounds were developed on the basis of new views that spread in science: the theory of atomic structure, the theory of chemical bonds, ideas about the mechanisms of chemical reactions. Currently, this theory is universal, that is, it is valid not only for organic substances, but also for inorganic ones.

First position. Atoms in molecules are combined in a specific order according to their valency. Carbon in all organic and most inorganic compounds is tetravalent.

Obviously, the last part of the first position of the theory can be easily explained by the fact that in compounds the carbon atoms are in an excited state:

Tetravalent carbon atoms can combine with each other to form different chains:

The order of connection of carbon atoms in molecules can be different and depends on the type of covalent chemical bond between carbon atoms - single or multiple (double and triple):

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

This position explains the phenomenon.

Substances that have the same composition, but different chemical or spatial structures, and therefore different properties, are called isomers.

Main types:

Structural isomerism, in which substances differ in the order of bonding of atoms in molecules: carbon skeleton

positions of multiple bonds:

deputies

positions of functional groups

Third position. The properties of substances depend on the mutual influence of atoms in molecules.

For example, in acetic acid only one of the four hydrogen atoms reacts with an alkali. Based on this, it can be assumed that only one hydrogen atom is bonded to oxygen:

On the other hand, from the structural formula of acetic acid we can conclude that it contains one mobile hydrogen atom, that is, that it is monobasic.

The main directions of development of the theory of the structure of chemical compounds and its significance.

During the time of A.M. Butlerov, organic chemistry was widely used

empirical (molecular) and structural formulas. The latter reflect the order of connection of atoms in a molecule according to their valency, which is indicated by dashes.

For ease of recording, abbreviated structural formulas are often used, in which dashes indicate only the bonds between carbon atoms or carbon and oxygen.

And fibers, products from which are used in technology, everyday life, medicine, and agriculture. The significance of the theory of chemical structure of A.M. Butlerov for organic chemistry can be compared with the significance of the Periodic Law and the Periodic Table of Chemical Elements of D.I. Mendeleev for inorganic chemistry. It is not for nothing that both theories have so much in common in the ways of their formation, directions of development and general scientific significance.