Number of known substances in organic chemistry. History of the development of organic chemistry

Few people thought about the role of organic chemistry in the life of modern man. But it is huge, it is difficult to overestimate it. From the very morning, when a person wakes up and goes to wash, and until the very evening, when he goes to bed, he is constantly accompanied by products of organic chemistry. A toothbrush, clothes, paper, cosmetics, furniture and interior items and much more - she gives us all this. But once everything was completely different, and very little was known about organic chemistry.

Let us consider how the history of the development of organic chemistry developed in stages.

1. The period of development until the XIV century, called spontaneous.

2. XV - XVII centuries - the beginning of development or, iatrochemistry, alchemy.

3. Century XVIII - XIX - the dominance of the theory of vitalism.

4. XIX - XX centuries - intensive development, scientific stage.

The Beginning, or the Spontaneous Stage in the Formation of the Chemistry of Organic Compounds

This period implies the very origin of the concept of chemistry, the origins. And the origins go back to Ancient Rome and Egypt, in which very capable inhabitants learned to extract objects and clothes from natural raw materials - leaves and stems of plants - for coloring. These were indigo, which gives a rich blue color, and alizorin, which colors literally everything in juicy and attractive shades of orange and red. Unusually agile inhabitants of different nationalities of the same time also learned how to get vinegar, make alcoholic beverages from sugar and starch-containing substances of plant origin.

It is known that very common products in use during this historical period were animal fats, resins and vegetable oils, which were used by healers and cooks. And also various poisons were densely used, as the main weapon of internecine relations. All these substances are products of organic chemistry.

But, unfortunately, as such, the concept of "chemistry" did not exist, and the study of specific substances in order to clarify the properties and composition did not occur. Therefore, this period is called spontaneous. All discoveries were random, non-purposeful nature of everyday significance. This continued until the next century.

The iatrochemical period is a promising beginning of development

Indeed, it was in the 16th-17th centuries that direct ideas about chemistry as a science began to emerge. Thanks to the work of scientists of that time, some organic substances were obtained, the simplest devices for distillation and sublimation of substances were invented, special chemical utensils were used for grinding substances, separating natural products into ingredients.

The main direction of work of that time was medicine. The desire to obtain the necessary medicines led to the fact that essential oils and other raw materials were extracted from plants. So, Karl Scheele obtained some organic acids from plant materials:

• apple;
• lemon;
• gallic;
• dairy;
• oxalic.

It took the scientist 16 years to study plants and isolate these acids (from 1769 to 1785). This was the beginning of development, the foundations of organic chemistry were laid, which was directly defined and named as a branch of chemistry later (beginning of the 18th century).

In the same period of the Middle Ages, G. F. Ruel isolated uric acid crystals from urea. Other chemists obtained succinic acid from amber, tartaric acid. The method of dry distillation of vegetable and animal raw materials, thanks to which acetic acid, diethyl ether, and wood alcohol is obtained, is in use.

This was the beginning of the intensive development of the organic chemical industry in the future.

Vis vitalis, or "Life Force"

XVIII - XIX centuries for organic chemistry are very twofold: on the one hand, there are a number of discoveries that are of grandiose significance. On the other hand, for a long time the growth and accumulation of the necessary knowledge and correct ideas is hampered by the dominant theory of vitalism.

This theory was introduced into use and designated as the main one by Jens Jacobs Berzelius, who at the same time himself gave the definition of organic chemistry (the exact year is unknown, either 1807 or 1808). According to the provisions of this theory, organic substances can be formed only in living organisms (plants and animals, including humans), since only living beings have a special "life force" that allows these substances to be produced. While it is absolutely impossible to obtain organic substances from inorganic substances, since they are products of inanimate nature, non-combustible, without vis vitalis.

The same scientist proposed the first classification of all compounds known at that time into inorganic (non-living, all substances like water and salt) and organic (living, those like olive oil and sugar). Berzelius was also the first to specify specifically what organic chemistry is. The definition sounded like this: it is the study of substances isolated from living organisms.

During this period, scientists easily carried out the transformation of organic substances into inorganic ones, for example, during combustion. However, nothing is known about the possibility of reverse transformations.

Fate was pleased to dispose so that it was the student of Jens Berzelius, Friedrich Wehler, who contributed to the beginning of the collapse of the theory of his teacher.

A German scientist worked on cyanide compounds and in one of his experiments he managed to obtain crystals similar to uric acid. As a result of more careful research, he was convinced that he really managed to get organic matter from inorganic without any vis vitalis. No matter how skeptical Berzelius was, he was forced to admit this indisputable fact. Thus was dealt the first blow to the vitalistic views. The history of the development of organic chemistry began to gain momentum.

A series of discoveries that crushed vitalism

The success of Wöhler inspired the chemists of the 18th century, so widespread tests and experiments began in order to obtain organic substances in artificial conditions. Several such syntheses, which are of decisive and greatest importance, have been made.

1. 1845 - Adolf Kolbe, who was a student of Wöhler, managed to obtain acetic acid, which is an organic substance, from simple inorganic substances C, H 2, O 2 by a multi-stage complete synthesis.
2. 1812 Konstantin Kirchhoff synthesized glucose from starch and acid.
3. 1820 Henri Braconnot denatured the protein with acid and then treated the mixture with nitric acid and obtained the first of the 20 amino acids synthesized later - glycine.
4. 1809 Michel Chevrel studied the composition of fats, trying to break them down into their constituent components. As a result, he received fatty acids and glycerin. 1854 Jean Berthelot continued the work of Chevrel and heated glycerin with the result - a fat that exactly repeats the structure of natural compounds. In the future, he managed to obtain other fats and oils, which were somewhat different in molecular structure from their natural counterparts. That is, he proved the possibility of obtaining new organic compounds of great importance in the laboratory.
5. J. Berthelot synthesized methane from hydrogen sulfide (H 2 S) and carbon disulfide (CS 2).
6. 1842 Zinin managed to synthesize aniline, a dye from nitrobenzene. In the future, he managed to obtain a number of aniline dyes.
7. A. Bayer creates his own laboratory, in which he is actively and successfully synthesizing organic dyes similar to natural ones: alizarin, indigo, anthroquinone, xanthene.
8. 1846 synthesis of nitroglycerin by the scientist Sobrero. He also developed a theory of types, which says that substances are similar to some of the inorganic ones and can be obtained by replacing hydrogen atoms in the structure.
9. 1861 A. M. Butlerov synthesized a sugary substance from formalin. He also formulated the provisions of the theory of the chemical structure of organic compounds, which are relevant to this day.

All these discoveries determined the subject of organic chemistry - carbon and its compounds. Further discoveries were aimed at studying the mechanisms of chemical reactions in organic matter, at establishing the electronic nature of interactions, and at examining the structure of compounds.

The second half of the XIX and XX centuries - the time of global chemical discoveries

The history of the development of organic chemistry has undergone ever greater changes over time. The work of many scientists on the mechanisms of internal processes in molecules, in reactions and systems has yielded fruitful results. So, in 1857, Friedrich Kekule developed the theory of valency. He also belongs to the greatest merit - the discovery of the structure of the benzene molecule. At the same time, A. M. Butlerov formulated the provisions of the theory of the structure of compounds, in which he indicated the tetravalence of carbon and the phenomenon of the existence of isomerism and isomers.

V. V. Markovnikov and A. M. Zaitsev delve into the study of the mechanisms of reactions in organic matter and formulate a number of rules that explain and confirm these mechanisms. In 1873 - 1875. I. Wislicenus, van't Hoff and Le Bel study the spatial arrangement of atoms in molecules, discover the existence of stereoisomers and become the founders of a whole science - stereochemistry. Many different people were involved in creating the field of organics that we have today. Therefore, scientists of organic chemistry deserve attention.

The end of the 19th and 20th centuries were the times of global discoveries in pharmaceuticals, the paint and varnish industry, and quantum chemistry. Let us consider the discoveries that ensured the maximum importance of organic chemistry.

1. 1881 M. Conrad and M. Gudzeit synthesized anesthetics, veronal and salicylic acid.
2. 1883 L. Knorr received antipyrine.
3. 1884 F. Stoll received a pyramidon.
4. 1869 The Hyatt brothers received the first artificial fiber.
5. 1884 D. Eastman synthesized celluloid photographic film.
6. 1890 L. Depassy copper-ammonia fiber was obtained.
7. 1891 Ch. Cross and his colleagues received viscose.
8. 1897 F. Miescher and Buchner founded the theory (cell-free fermentation and enzymes as biocatalysts were discovered).
9. 1897 F. Miescher discovered nucleic acids.
10. Beginning of the 20th century - new chemistry of organoelement compounds.
11. 1917 Lewis discovered the electronic nature of the chemical bond in molecules.
12. 1931 Hückel is the founder of quantum mechanisms in chemistry.
13. 1931-1933 Laimus Pauling substantiates the theory of resonance, and later his employees reveal the essence of directions in chemical reactions.
14. 1936 Nylon synthesized.
15. 1930-1940 A. E. Arbuzov gives rise to the development of organophosphorus compounds, which are the basis for the production of plastics, medicines and insecticides.
16. 1960 Academician Nesmeyanov and his students create the first synthetic food in the laboratory.
17. 1963 Du Vigne receives insulin, a huge advance in medicine.
18. 1968 Indian H. G. Korana managed to get a simple gene, which helped in deciphering the genetic code.

Thus, the importance of organic chemistry in people's lives is simply colossal. Plastics, polymers, fibers, paints and varnishes, rubbers, rubbers, PVC materials, polypropylenes and polyethylenes and many other modern substances, without which life is simply not possible today, have gone a difficult way to their discovery. Hundreds of scientists have contributed many years of painstaking work to form a common history of the development of organic chemistry.

Modern system of organic compounds

Having traveled a long and difficult path in development, organic chemistry does not stand still today. More than 10 million compounds are known, and this number is growing every year. Therefore, there is a certain systematized structure of the arrangement of substances that organic chemistry gives us. The classification of organic compounds is presented in the table.

The study of the whole variety of substances and the reactions they enter into is the subject of organic chemistry today.

Types of chemical bonds in organic substances

For any compounds, electron-static interactions within molecules are characteristic, which in organics are expressed in the presence of covalent polar and covalent non-polar bonds. In organometallic compounds, the formation of a weak ionic interaction is possible.

Occur between C-C interactions in all organic molecules. Covalent polar interaction is characteristic of different non-metal atoms in a molecule. For example, C-Hal, C-H, C-O, C-N, C-P, C-S. These are all bonds in organic chemistry that exist to form compounds.

Varieties of formulas of substances in organic matter

The most common formulas expressing the quantitative composition of a compound are called empirical formulas. Such formulas exist for every inorganic substance. But when it came to compiling formulas in organics, scientists faced many problems. Firstly, the mass of many of them is in the hundreds, and even thousands. It is difficult to determine an empirical formula for such a huge substance. Therefore, over time, such a branch of organic chemistry as organic analysis appeared. The scientists Liebig, Wehler, Gay-Lussac and Berzelius are considered its founders. It was they, together with the works of A. M. Butlerov, who determined the existence of isomers - substances that have the same qualitative and quantitative composition, but differ in molecular structure and properties. That is why the structure of organic compounds is expressed today not by an empirical, but by a structural complete or structural abbreviated formula.

These structures are a characteristic and distinctive feature that organic chemistry has. Formulas are written using dashes denoting chemical bonds. for example, the abbreviated structural formula of butane would be CH 3 - CH 2 - CH 2 - CH 3 . The complete structural formula shows all the chemical bonds present in the molecule.

There is also a way to write down the molecular formulas of organic compounds. It looks the same as empirical in inorganic. For butane, for example, it will be: C 4 H 10. That is, the molecular formula gives an idea only of the qualitative and quantitative composition of the compound. Structural bonds characterize the bonds in a molecule, therefore, they can be used to predict the future properties and chemical behavior of a substance. These are the features that organic chemistry has. Formulas are written in any form, each of them is considered correct.

Types of reactions in organic chemistry

There is a certain classification of organic chemistry according to the type of reactions that occur. Moreover, there are several such classifications, according to various criteria. Let's consider the main ones.

Mechanisms of chemical reactions according to the methods of breaking and forming bonds:

• homolytic or radical;
• heterolytic or ionic.

Reactions by types of transformations:

• chain radical;
• nucleophilic aliphatic substitution;
• nucleophilic aromatic substitution;
• elimination reactions;
• electrophilic addition;
• condensation;
• cyclization;
• electrophilic substitution;
• rearrangement reactions.

According to the method of starting the reaction (initiation) and according to the kinetic order, reactions are also sometimes classified. These are the main features of the reactions that organic chemistry has. The theory describing the details of the course of each chemical reaction was discovered in the middle of the 20th century and is still being confirmed and supplemented with each new discovery and synthesis.

It should be noted that, in general, reactions in organic matter proceed under more severe conditions than in inorganic chemistry. This is due to the greater stabilization of the molecules of organic compounds due to the formation of intra and intermolecular strong bonds. Therefore, almost no reaction is complete without an increase in temperature, pressure, or the use of a catalyst.

Modern definition of organic chemistry

In general, the development of organic chemistry followed an intensive path over several centuries. A huge amount of information has been accumulated about substances, their structures and reactions in which they can enter. Millions of useful and simply necessary raw materials used in various fields of science, technology and industry have been synthesized. The concept of organic chemistry today is perceived as something grandiose and large, numerous and complex, diverse and significant.

At one time, the first definition of this great branch of chemistry was that given by Berzelius: it is a chemistry that studies substances isolated from organisms. A lot of time has passed since that moment, many discoveries have been made and a large number of mechanisms of intrachemical processes have been realized and revealed. As a result, today there is a different concept of what organic chemistry is. The definition is given to it as follows: it is the chemistry of carbon and all its compounds, as well as methods for their synthesis.

ORGANIC CHEMISTRY

Basic concepts of organic chemistry

Organic chemistry – is the branch of chemistry that studies the compounds of carbon. Carbon stands out among all the elements in that its atoms can bind to each other in long chains or cycles. It is this property that allows carbon to form the millions of compounds studied by organic chemistry.

Theory of the chemical structure of A. M. Butlerov.

The modern theory of the structure of molecules explains both the huge number of organic compounds and the dependence of the properties of these compounds on their chemical structure. It also fully confirms the basic principles of the theory of chemical structure, developed by the outstanding Russian scientist A. M. Butlerov.

The main provisions of this theory (sometimes called structural):

1) atoms in molecules are interconnected in a certain order by chemical bonds according to their valency;

2) the properties of a substance are determined not only by the qualitative composition, but also by the structure and the mutual influence of atoms.

3) by the properties of a substance, you can determine its structure, and by the structure - properties.

An important consequence of the theory of structure was the conclusion that each organic compound must have one chemical formula that reflects its structure. This conclusion theoretically substantiated the well-known even then phenomenon isomerism, - the existence of substances with the same molecular composition, but with different properties.

Isomers– substances that have the same composition but different structure

Structural formulas. The existence of isomers required the use of not only simple molecular formulas, but also structural formulas that reflect the order of bonding of atoms in the molecule of each isomer. In structural formulas, a covalent bond is indicated by a dash. Each dash means a common electron pair that links the atoms in the molecule.

Structural formula - conditional image of the structure of a substance, taking into account chemical bonds.

Classification of organic compounds.

To classify organic compounds by types and build their names in the molecule of an organic compound, it is customary to distinguish the carbon skeleton and functional groups.

carbon skeleton represents a sequence of chemically bonded carbon atoms.

Types of carbon skeletons. Carbon skeletons are divided into acyclic(not containing cycles) , cyclic and heterocyclic.

In a heterocyclic skeleton, one or more atoms other than carbon are included in the carbon cycle. In the carbon skeletons themselves, individual carbon atoms must be classified according to the number of chemically bonded carbon atoms. If a given carbon atom is bonded to one carbon atom, then it is called primary, with two - secondary, three - tertiary and four - Quaternary.

Since carbon atoms can form between themselves not only single, but also multiple (double and triple) bonds, then compounds containing only single C-C bonds are called rich, compounds with multiple bonds are called unsaturated.

hydrocarbons– compounds in which carbon atoms are bonded only to hydrogen atoms.

Hydrocarbons are recognized in organic chemistry as ancestral. A variety of compounds are considered as derivatives of hydrocarbons obtained by introducing functional groups into them.

Functional groups. Most organic compounds, in addition to carbon and hydrogen atoms, contain atoms of other elements (not included in the skeleton). These atoms or their groups, which largely determine the chemical and physical properties of organic compounds, are called functional groups.

The functional group turns out to be the final feature according to which the compounds belong to one or another class.

The most important functional groups

homologous series. The concept of a homologous series is useful for describing organic compounds. homologous series form compounds that differ from each other by the -CH 2 - group and have similar chemical properties. CH 2 groups are called homological difference .

An example of a homologous series is the series of saturated hydrocarbons (alkanes). Its simplest representative is methane CH 4 . The homologues of methane are: ethane C 2 H 6, propane C 3 H 8, butane C 4 H 10, pentane C 5 H 12, hexane C 6 H 14, heptane C 7 H 16, etc. The formula of any subsequent homologue can be obtained by adding to the formula of the previous hydrocarbon homological difference.

The composition of the molecules of all members of the homologous series can be expressed by one general formula. For the considered homologous series of saturated hydrocarbons, such a formula will be C n H 2n+2, where n is the number of carbon atoms.

Nomenclature of organic compounds. At present, the systematic nomenclature of IUPAC (IUPAC - International Union of Pure and Applied Chemistry) is recognized.

According to IUPAC rules, the name of an organic compound is built from the name of the main chain that forms the root of the word, and the names of functions used as prefixes or suffixes.

For the correct construction of the name, it is necessary to select the main chain and number the carbon atoms in it.

The numbering of carbon atoms in the main chain starts from the end of the chain, closer to which the older group is located. If there are several such possibilities, then the numbering is carried out in such a way that either a multiple bond or another substituent present in the molecule receives the smallest number.

In carbocyclic compounds, the numbering starts from the carbon atom at which the highest characteristic group is located. If in this case it is impossible to choose a unique numbering, then the cycle is numbered so that the substituents have the smallest numbers.

In the group of cyclic hydrocarbons, aromatic hydrocarbons are especially distinguished, which are characterized by the presence of a benzene ring in the molecule. Some well-known representatives of aromatic hydrocarbons and their derivatives have trivial names, the use of which is permitted by IUPAC rules: benzene, toluene, phenol, benzoic acid.

The C 6 H 5 - radical formed from benzene is called phenyl, not benzyl. Benzyl is the C 6 H 5 CH 2 - radical formed from toluene.

Composing the name of an organic compound. The basis of the name of the compound is the root of the word, denoting a saturated hydrocarbon with the same number of atoms as the main chain ( meth-, et-, prop-, but-, pent: hex- etc.). Then follows a suffix characterizing the degree of saturation, -en if there are no multiple bonds in the molecule, -en in the presence of double bonds and -in for triple bonds, (eg pentane, pentene, pentene). If there are several multiple bonds in the molecule, then the number of such bonds is indicated in the suffix: - di en, - three en, and after the suffix, the position of the multiple bond must be indicated in Arabic numerals (for example, butene-1, butene-2, butadiene-1.3):

Further, the name of the oldest characteristic group in the molecule is placed in the suffix, indicating its position with a number. Other substituents are designated by prefixes. However, they are not listed in order of seniority, but alphabetically. The position of the substituent is indicated by a number before the prefix, for example: 3 -methyl; 2 -chlorine, etc. If there are several identical substituents in the molecule, then their number is indicated in front of the name of the corresponding group (for example, di methyl-, trichloro-, etc.). All numbers in the names of molecules are separated from words by a hyphen, and from each other by commas. Hydrocarbon radicals have their own names.

Limit hydrocarbon radicals:

Unsaturated hydrocarbon radicals:

Aromatic hydrocarbon radicals:

Let's take the following connection as an example:

1) The choice of the chain is unambiguous, therefore, the root of the word is pent; followed by suffix − en, indicating the presence of a multiple bond;

2) the order of numbering provides the highest group (-OH) with the lowest number;

3) the full name of the compound ends with a suffix denoting the senior group (in this case, the suffix - ol indicates the presence of a hydroxyl group); the position of the double bond and the hydroxyl group is indicated by numbers.

Therefore, the given compound is called penten-4-ol-2.

Trivial nomenclature is a collection of non-systematic historical names of organic compounds (example: acetone, acetic acid, formaldehyde, etc.).

Isomerism.

It was shown above that the ability of carbon atoms to form four covalent bonds, including those with other carbon atoms, opens up the possibility of the existence of several compounds of the same elemental composition - isomers. All isomers are divided into two large classes - structural isomers and spatial isomers.

Structural called isomers with different order of connection of atoms.

Spatial isomers have the same substituents on each carbon atom and differ only in their mutual arrangement in space.

Structural isomers. In accordance with the above classification of organic compounds by types, three groups are distinguished among structural isomers:

1) compounds that differ in carbon skeletons:

2) compounds that differ in the position of the substituent or multiple bond in the molecule:

3) compounds containing various functional groups and belonging to different classes of organic compounds:

Spatial isomers(stereoisomers). Stereoisomers can be divided into two types: geometric isomers and optical isomers.

geometric isomerism characteristic of compounds containing a double bond or cycle. In such molecules, it is often possible to draw a conditional plane in such a way that substituents on different carbon atoms can be on the same side (cis-) or on opposite sides (trans-) of this plane. If a change in the orientation of these substituents relative to the plane is possible only due to the breaking of one of the chemical bonds, then one speaks of the presence of geometric isomers. Geometric isomers differ in their physical and chemical properties.

Mutual influence of atoms in a molecule.

All the atoms that make up a molecule are interconnected and experience mutual influence. This influence is transmitted mainly through a system of covalent bonds with the help of so-called electronic effects.

Electronic effects are the shift of electron density in a molecule under the influence of substituents.

Atoms bound by a polar bond carry partial charges, denoted by the Greek letter delta (δ). An atom that “pulls” the electron density of the δ bond in its direction acquires a negative charge δ − . When considering a pair of atoms linked by a covalent bond, the more electronegative atom is called an electron acceptor. Its δ-bond partner will accordingly have an equal electron density deficit, i.e., a partial positive charge δ +, and will be called an electron donor.

The displacement of the electron density along the chain of σ-bonds is called the inductive effect and is denoted by I.

The inductive effect is transmitted through the circuit with damping. The direction of displacement of the electron density of all σ-bonds is indicated by straight arrows.

Depending on whether the electron density moves away from the considered carbon atom or approaches it, the inductive effect is called negative (-I) or positive (+I). The sign and magnitude of the inductive effect are determined by differences in electronegativity between the carbon atom in question and the group that causes it.

Electron-withdrawing substituents, i.e. an atom or a group of atoms that displaces the electron density of a σ bond from a carbon atom exhibits a negative inductive effect (−I effect).

Electron-donor substituents, i.e., an atom or a group of atoms that shift the electron density to the carbon atom, exhibit a positive inductive effect (+ I-effect).

The I-effect is exhibited by aliphatic hydrocarbon radicals, i.e., alkyl radicals (methyl, ethyl, etc.).

Most functional groups show -I-effect: halogens, amino group, hydroxyl, carbonyl, carboxyl groups.

The inductive effect also manifests itself in the case when the bonded carbon atoms differ in the state of hybridization. So, in the propene molecule, the methyl group exhibits + I-effect, since the carbon atom in it is in the sp3-hybrid state, and the sp2-hybridized atom (with a double bond) acts as an electron acceptor, since it has a higher electronegativity:

When the inductive effect of the methyl group is transferred to the double bond, the mobile π-bond is affected first of all.

The effect of a substituent on the distribution of electron density transmitted through π bonds is called the mesomeric effect (M). The mesomeric effect can also be negative and positive. In structural formulas, it is represented by a curved arrow starting at the center of the electron density and ending at the place where the electron density shifts.

The presence of electronic effects leads to a redistribution of the electron density in the molecule and the appearance of partial charges on individual atoms. This determines the reactivity of the molecule.

Classification of organic reactions

− Classification according to the type of breaking of chemical bonds in reacting particles. Of these, two large groups of reactions can be distinguished - radical and ionic.

Radical reactions - these are processes that go with a homolytic rupture of a covalent bond. In a homolytic rupture, a pair of electrons forming a bond is divided in such a way that each of the formed particles receives one electron. As a result of homolytic rupture, free radicals are formed:

A neutral atom or particle with an unpaired electron is calledfree radical.

Ionic reactions- these are processes that occur with heterolytic breaking of covalent bonds, when both bond electrons remain with one of the previously bound particles:

As a result of heterolytic bond cleavage, charged particles are obtained: nucleophilic and electrophilic.

A nucleophilic particle (nucleophile) is a particle that has a pair of electrons in the outer electronic level. Due to the pair of electrons, the nucleophile is able to form a new covalent bond.

An electrophilic particle (electrophile) is a particle that has an unfilled outer electronic level. The electrophile represents unfilled, vacant orbitals for the formation of a covalent bond due to the electrons of the particle with which it interacts.

−Classification according to the composition and structure of the initial substances and reaction products. In organic chemistry, all structural changes are considered relative to the carbon atom (or atoms) involved in the reaction. The most common types of transformations are:

accession

substitution

cleavage (elimination)

polymerization

In accordance with the above, the chlorination of methane by the action of light is classified as a radical substitution, the addition of halogens to alkenes as an electrophilic addition, and the hydrolysis of alkyl halides as a nucleophilic substitution.

Structural formulas

The theory of valency has played a major role in the development of the theory of chemistry in general and organic chemistry in particular. Based on the theory of valence, Kekule suggested that the carbon atom is tetravalent, and in 1858 he tried, based on this assumption, to present the structure of the simplest organic molecules and radicals. In the same 1858, the Scottish chemist Archibald Scott Cooper (1831-1892) suggested depicting the forces connecting atoms (or connections, as they are usually called), in the form of dashes. After the first organic molecule was "built", it became quite clear why organic molecules, as a rule, are much larger and more complex than inorganic ones.

According to Kekule's ideas, carbon atoms can connect to each other using one or more of their four valence bonds, forming long chains - straight or branched. Apparently, no other atoms have this remarkable ability to the extent that carbon has it.

So, imagining that each carbon atom has four valence bonds, and each hydrogen atom has one such bond, we can draw three simple hydrocarbon(compounds whose molecules are formed only by carbon and hydrogen atoms), methane CH 4, ethane C 2 H 6 and propane C 3 H 8, as follows:

By increasing the number of carbon atoms, this sequence can be continued, and almost indefinitely. By adding oxygen (two valence bonds) or nitrogen (three valence bonds) to the hydrocarbon chain, one can present the structural formulas of the molecules of ethyl alcohol (C 2 H 6 O) and methylamine (CH 5 N):

Assuming the possibility of two bonds between neighboring atoms ( double bond) or three bonds ( triple bond), you can depict the structural formulas of compounds such as ethylene (C 2 H 4), acetylene (C 2 H 2), methyl cyanide (C 2 H 3 N), acetone (C 3 H 6 O) and acetic acid (C 2 H 4O2):

The usefulness of structural formulas was so obvious that many organic chemists adopted them at once. They recognized as completely outdated all attempts to depict organic molecules as structures built from radicals. As a result, it was considered necessary, when writing the formula of a compound, to show its atomic structure.

The Russian chemist Alexander Mikhailovich Butlerov (1823-1886) used this new system of structural formulas in his theory of the structure of organic compounds. In the 60s of the last century, he showed how, with the help of structural formulas, the reasons for the existence of isomers can be clearly explained (see Chapter 5). So, for example, ethyl alcohol and dimethyl ether have the same empirical formula C 2 H 6 O, but the structural formulas of these compounds differ significantly:

therefore, it is not surprising that a change in the arrangement of atoms leads to two sets of very different properties. In ethyl alcohol, one of the six hydrogen atoms is attached to an oxygen atom, while in dimethyl ether, all six hydrogen atoms are attached to carbon atoms. The oxygen atom holds the hydrogen atom weaker than the carbon atom, so that metallic sodium added to ethanol replaces hydrogen (one-sixth of the total). Sodium added to dimethyl ether does not displace hydrogen at all. Thus, when compiling structural formulas, one can be guided by chemical reactions, and structural formulas, in turn, can help to understand the essence of reactions.

Butlerov paid particular attention to one of the types of isomerism called tautomerism(dynamic isomerism), in which some substances always act as mixtures of two compounds. If one of these compounds is isolated in its pure form, it will immediately partially pass into another compound. Butlerov showed that tautomerism is due to the spontaneous transition of a hydrogen atom from an oxygen atom to a neighboring carbon atom (and vice versa).

To fully prove the validity of the system of structural formulas, it was necessary to determine the structural formula benzene- a hydrocarbon containing six carbon atoms and six hydrogen atoms. This was not done right away. It seemed that there was no such structural formula that, while meeting the requirements of valency, would at the same time explain the greater stability of the compound. The first versions of the structural formulas of benzene were very similar to the formulas of some hydrocarbons - compounds that are very unstable and not similar in chemical properties to benzene.

Kekule was able to solve this problem again. One day in 1865 (as he himself relates) Kekule was half asleep in an omnibus, and he dreamed that he saw atoms whirling in a dance. Suddenly, the end of one chain connected with its beginning, and a rotating ring was formed. And Kekule decided that this should be the structural formula of benzene. Until then, structural formulas were built only in the form of linear chains carbon atoms, but now Kekule introduced the concept of a "ring" (or "core") of carbon atoms and proposed the following structural formula for benzene:

This explanation was accepted and the understanding of structural formulas expanded.

He studies the composition, structure, properties and application of organic compounds.

All organic compounds have one thing in common: they necessarily contain carbon atoms. In addition to carbon, the molecules of organic compounds include hydrogen, oxygen, nitrogen, less often sulfur, phosphorus, and halogens.

Currently, more than twenty million organic compounds are known. This diversity is possible due to the unique properties of carbon, whose atoms are able to form strong chemical bonds both with each other and with other atoms.

There is no sharp boundary between inorganic and organic compounds. Some carbon compounds, such as carbon oxides, salts of carbonic acid, are classified as inorganic by the nature of their properties.

The simplest organic compounds are hydrocarbons containing only carbon and hydrogen atoms. Other organic compounds can be considered as derivatives of hydrocarbons.

This is the science that studies hydrocarbons and their derivatives.

There are organic compounds of natural origin (starch, cellulose, natural gas, oil, etc.) and synthetic (resulting from synthesis in laboratories and factories).

Organic compounds of natural origin also include substances formed in living organisms. These are, for example, nucleic acids, proteins, fats, carbohydrates, enzymes, vitamins, hormones. The structure and properties of these substances, their biological functions are studied by biochemistry, molecular biology and bioorganic chemistry.

The vast majority of drugs are organic compounds. The chemistry of medicinal substances is engaged in the creation of drugs and the study of their effect on the body.

A large number of synthetic organic compounds are obtained from the processing of oil (figure below), natural gas, coal and wood.

1 - raw materials for the chemical industry; 2 - asphalt; 3 - oils; 4 - fuel for aircraft; 5 - lubricants; 6 - diesel fuel; 7 - gasoline

Achievements of organic chemistry are used in the production of building materials, in mechanical engineering and agriculture, medicine, electrical and semiconductor industries. Without synthetic fuels, synthetic detergents, polymers and plastics, dyes, etc., it is impossible to imagine modern life.

The impact of organic substances obtained by man on living organisms and other objects of nature is different. The use of certain organic compounds in some cases leads to serious environmental problems. For example, the chlorine-containing insecticide DDT, previously used to control harmful insects, is currently prohibited for use due to accumulation in living organisms and slow decomposition in natural conditions.

It is assumed that fluorochlorohydrocarbons (freons) (for example, difluoro-dichloromethane CF 2 Cl 2) contribute to the destruction of the ozone layer of the atmosphere, which protects our planet from the harsh ultraviolet radiation of the Sun. For this reason, freons are replaced by less dangerous saturated hydrocarbons.