Student's Handbook of Organic Chemistry. Basic concepts and laws of organic chemistry All formulas in organic chemistry

24.11.202227.05.2017

If you entered the university, but by this time you have not figured out this difficult science, we are ready to reveal a few secrets to you and help you learn organic chemistry from scratch (for "dummies"). You just have to read and listen.

Fundamentals of organic chemistry

Organic chemistry is singled out as a separate subspecies due to the fact that the object of its study is everything that contains carbon.

Organic chemistry is a branch of chemistry that deals with the study of carbon compounds, the structure of such compounds, their properties and methods of connection.

As it turned out, carbon most often forms compounds with the following elements - H, N, O, S, P. By the way, these elements are called organogens.

Organic compounds, the number of which today reaches 20 million, are very important for the full existence of all living organisms. However, no one doubted, otherwise a person would simply have thrown the study of this unknown into the back burner.

The goals, methods and theoretical concepts of organic chemistry are presented as follows:

Separation of fossil, animal or vegetable raw materials into separate substances;
Purification and synthesis of various compounds;
Revealing the structure of substances;
Determination of the mechanics of the course of chemical reactions;
Finding the relationship between the structure and properties of organic substances.

A bit from the history of organic chemistry

You may not believe it, but even in ancient times, the inhabitants of Rome and Egypt understood something in chemistry.

As we know, they used natural dyes. And often they had to use not a ready-made natural dye, but extract it by isolating it from a whole plant (for example, alizarin and indigo contained in plants).

We can also remember the culture of drinking alcohol. The secrets of the production of alcoholic beverages are known in every nation. Moreover, many ancient peoples knew the recipes for preparing "hot water" from starch- and sugar-containing products.

This went on for many, many years, and only in the 16th and 17th centuries did some changes, small discoveries, begin.

In the 18th century, a certain Scheele learned to isolate malic, tartaric, oxalic, lactic, gallic and citric acids.

Then it became clear to everyone that the products that could be isolated from plant or animal raw materials had many common features. At the same time, they differed greatly from inorganic compounds. Therefore, the servants of science urgently needed to separate them into a separate class, and the term “organic chemistry” appeared.

Despite the fact that organic chemistry itself as a science appeared only in 1828 (it was then that Mr. Wöhler managed to isolate urea by evaporating ammonium cyanate), in 1807 Berzelius introduced the first term in the nomenclature in organic chemistry for teapots:

Branch of chemistry that studies substances derived from organisms.

The next important step in the development of organic chemistry is the theory of valence, proposed in 1857 by Kekule and Cooper, and the theory of the chemical structure of Mr. Butlerov from 1861. Even then, scientists began to discover that carbon is tetravalent and is able to form chains.

In general, since then, science has regularly experienced upheavals and unrest due to new theories, discoveries of chains and compounds, which allowed organic chemistry to also actively develop.

Science itself appeared due to the fact that scientific and technological progress was not able to stand still. He kept on walking, demanding new solutions. And when coal tar was no longer enough in the industry, people simply had to create a new organic synthesis, which eventually grew into the discovery of an incredibly important substance, which is still more expensive than gold - oil. By the way, it was thanks to organic chemistry that her "daughter" was born - a subscience, which was called "petrochemistry".

But this is a completely different story that you can study for yourself. Next, we suggest you watch a popular science video about organic chemistry for dummies:

Well, if you have no time and urgently need help professionals, you always know where to find them.

Organic chemistry is the science that studies carbon compounds calledorganic substances. In this regard, organic chemistry is also called chemistry of carbon compounds.

The most important reasons for the separation of organic chemistry into a separate science are as follows.

1. Numerous organic compounds in comparison with inorganic ones.

The number of known organic compounds (about 6 million) significantly exceeds the number of compounds of all other elements of the periodic system of Mendeleev. At present, about 700,000 inorganic compounds are known, and approximately 150,000 new organic compounds are now obtained in one year. This is explained not only by the fact that chemists are especially intensively engaged in the synthesis and study of organic compounds, but also by the special ability of the element carbon to give compounds containing an almost unlimited number of carbon atoms linked in chains and cycles.

2. Organic substances are of exceptional importance both because of their extremely diverse practical application and because they play a crucial role in the life processes of organisms.

3. There are significant differences in the properties and reactivity of organic compounds from inorganic, as a result, the need arose for the development of many specific methods for the study of organic compounds.

The subject of organic chemistry is the study of methods for the preparation, composition, structure, and applications of the most important classes of organic compounds.

2. Brief historical review of the development of organic chemistry

Organic chemistry as a science took shape at the beginning of the 19th century, but man's acquaintance with organic substances and their application for practical purposes began in ancient times. The first known acid was vinegar, or an aqueous solution of acetic acid. The ancient peoples knew the fermentation of grape juice, they knew the primitive method of distillation and used it to obtain turpentine; Gauls and Germans knew how to make soap; in Egypt, Gaul and Germany they knew how to brew beer.

In India, Phoenicia and Egypt, the art of dyeing with the help of organic substances was highly developed. In addition, ancient peoples used such organic substances as oils, fats, sugar, starch, gum, resins, indigo, etc.

The period of development of chemical knowledge in the Middle Ages (approximately until the 16th century) was called the period of alchemy. However, the study of inorganic substances was much more successful than the study of organic substances. Information about the latter has remained almost as limited as in more ancient ages. Some progress has been made through the improvement of distillation methods. In this way, in particular, several essential oils were isolated and strong wine alcohol was obtained, which was considered one of the substances with which you can prepare the philosopher's stone.

End of the 18th century was marked by notable successes in the study of organic substances, and organic substances began to be studied from a purely scientific point of view. During this period, a number of the most important organic acids (oxalic, citric, malic, gallic) were isolated from plants and described, and it was found that oils and fats contain, as a common component, the “sweet beginning of oils” (glycerin), etc.

Gradually began to develop studies of organic substances - the products of vital activity of animal organisms. For example, urea and uric acid were isolated from human urine, and hippuric acid was isolated from cow and horse urine.

The accumulation of significant factual material was a strong impetus to a deeper study of organic matter.

The concepts of organic substances and organic chemistry were first introduced by the Swedish scientist Berzelius (1827). In a chemistry textbook that has gone through many editions, Berzelius is convinced that “in living nature, the elements obey different laws than in lifeless nature” and that organic substances cannot be formed under the influence of ordinary physical and chemical forces, but require a special “life force” for their formation. ". He defined organic chemistry as "the chemistry of plant and animal substances, or substances formed under the influence of the vital force." The subsequent development of organic chemistry proved the fallacy of these views.

In 1828, Wöhler showed that an inorganic substance - ammonium cyanate - when heated, turns into a waste product of an animal organism - urea.

In 1845, Kolbe synthesized a typical organic substance - acetic acid, using charcoal, sulfur, chlorine and water as starting materials. In a relatively short period, a number of other organic acids were synthesized, which had previously been isolated only from plants.

In 1854, Berthelot succeeded in synthesizing substances belonging to the class of fats.

In 1861, A. M. Butlerov, by the action of lime water on paraformaldehyde, for the first time carried out the synthesis of methylenenitane, a substance belonging to the class of sugars, which, as is known, play an important role in the vital processes of organisms.

All these scientific discoveries led to the collapse of vitalism - the idealistic doctrine of "life force".

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Of all the variety of chemical compounds, most (over four million) contain carbon. Almost all of them are organic. Organic compounds are found in nature, such as carbohydrates, proteins, vitamins, they play an important role in the life of animals and plants. Many organic substances and their mixtures (plastics, rubber, oil, natural gas, and others) are of great importance for the development of the country's national economy.

The chemistry of carbon compounds is called organic chemistry. This is how the great Russian organic chemist A.M. Butlerov. However, not all carbon compounds are usually classified as organic. Such simple substances as carbon monoxide (II) CO, carbon dioxide CO2, carbonic acid H2CO3 and its salts, for example, CaCO3, K2CO3, are classified as inorganic compounds. The composition of organic substances in addition to carbon may include other elements. The most common are hydrogen, halogens, oxygen, nitrogen, sulfur and phosphorus. There are also organic substances containing other elements, including metals.

2. The structure of the carbon atom (C), the structure of its electron shell

2.1 The value of the carbon atom (C) in the chemical structure of organic compounds

CARBON (lat. Carboneum), C, a chemical element of subgroup IVa of the periodic system; atomic number 6, atomic mass 12.0107, refers to non-metals. Natural carbon consists of two stable nuclides - 12C (98.892% by mass) and 13C (1.108%) and one unstable - C with a half-life of 5730 years.

distribution in nature. Carbon accounts for 0.48% of the mass of the earth's crust, in which it occupies 17th place among other elements in terms of content. The main carbon-bearing rocks are natural carbonates (limestones and dolomites); the amount of carbon in them is about 9.610 tons.

In the free state, carbon occurs in nature in the form of fossil fuels, as well as in the form of minerals - diamond and graphite. About 1013 tons of carbon is concentrated in fossil fuels such as hard and brown coal, peat, shale, bitumen, which form powerful accumulations in the bowels of the Earth, as well as in natural combustible gases. Diamonds are extremely rare. Even diamond-bearing rocks (kimberlites) contain no more than 9-10% of diamonds weighing, as a rule, no more than 0.4 g. Large diamonds found are usually given a special name. The largest Cullinan diamond weighing 621.2 g (3106 carats) was found in South Africa (Transvaal) in 1905, and the largest Russian Orlov diamond weighing 37.92 g (190 carats) was found in Siberia in the middle 17th century

Black-gray opaque, greasy to the touch with a metallic sheen, graphite is an accumulation of flat polymeric molecules of carbon atoms, loosely layered on top of each other. In this case, the atoms within the layer are more strongly interconnected than the atoms between the layers.

Diamond is another matter. In its colorless, transparent and highly refractive crystal, each carbon atom is chemically bonded to four of the same atoms located at the vertices of the tetrahedron. All bonds are the same length and are very strong. They form a continuous three-dimensional frame in space. The entire diamond crystal is, as it were, one giant polymer molecule that has no "weak" places, because the strength of all bonds is the same.

The density of diamond at 20°C is 3.51 g/cm 3 , graphite - 2.26 g/cm 3 . The physical properties of diamond (hardness, electrical conductivity, coefficient of thermal expansion) are practically the same in all directions; it is the hardest of all substances found in nature. In graphite, these properties in different directions - perpendicular or parallel to the layers of carbon atoms - differ greatly: with small lateral forces, the parallel layers of graphite shift relative to each other and it delaminates into separate flakes that leave a mark on the paper. According to its electrical properties, diamond is a dielectric, while graphite conducts electricity.

Diamond, when heated without air access above 1000 ° C, turns into graphite. Graphite under constant heating under the same conditions does not change up to 3000 ° C, when it sublimates without melting. The direct transition of graphite to diamond occurs only at temperatures above 3000°C and enormous pressure - about 12 GPa.

The third allotropic modification of carbon - carbine - was obtained artificially. It is a finely crystalline black powder; in its structure, long chains of carbon atoms are parallel to each other. Each chain has the structure of (-C=C) L or (=C=C=) L. The average density of carbine between graphite and diamond is 2.68-3.30 g/cm 3 . One of the most important features of carbine is its compatibility with the tissues of the human body, which allows it to be used, for example, in the manufacture of artificial blood vessels that are not rejected by the body (Fig. 1).

Fullerenes got their name not in honor of the chemist, but in honor of the American architect R. Fuller, who proposed building hangars and other structures in the form of domes, the surface of which is formed by pentagons and hexagons (such a dome was built, for example, in Moscow's Sokolniki Park).

Carbon is also characterized by a state with a disordered structure - this is the so-called. amorphous carbon (soot, coke, charcoal) fig. 2. Obtaining carbon (C):

Most of the substances around us are organic compounds. These are the tissues of animals and plants, our food, medicines, clothing (cotton, wool and synthetic fibers), fuels (oil and natural gas), rubber and plastics, detergents. Currently, more than 10 million such substances are known, and their number increases significantly every year due to the fact that scientists isolate unknown substances from natural objects and create new compounds that do not exist in nature.

Such a variety of organic compounds is associated with the unique feature of carbon atoms to form strong covalent bonds, both among themselves and with other atoms. Carbon atoms, connecting to each other with both single and multiple bonds, can form chains of almost any length and cycles. A wide variety of organic compounds is also associated with the existence of the phenomenon of isomerism.

Almost all organic compounds also contain hydrogen, often they include atoms of oxygen, nitrogen, less often - sulfur, phosphorus, halogens. Compounds containing atoms of any elements (with the exception of O, N, S and halogens) directly bonded to carbon are grouped under the name organoelement compounds; the main group of such compounds is organometallic compounds (Fig. 3).

A huge number of organic compounds require their clear classification. The basis of an organic compound is the skeleton of a molecule. The skeleton can have an open (non-closed) structure, then the compound is called acyclic (aliphatic; aliphatic compounds are also called fatty compounds, since they were first isolated from fats), and a closed structure, then it is called cyclic. The skeleton can be carbon (consist only of carbon atoms) or contain other atoms other than carbon - the so-called. heteroatoms, most often oxygen, nitrogen and sulfur. Cyclic compounds are divided into carbocyclic (carbon), which can be aromatic and alicyclic (containing one or more rings), and heterocyclic.

Hydrogen and halogen atoms are not included in the skeleton, and heteroatoms are included in the skeleton only if they have at least two carbon bonds. So, in ethyl alcohol CH3CH2OH, the oxygen atom is not included in the skeleton of the molecule, but in dimethyl ether CH3OCH3 is included in it.

In addition, the acyclic skeleton can be unbranched (all atoms are arranged in one row) and branched. Sometimes an unbranched skeleton is called linear, but it should be remembered that the structural formulas that we most often use convey only the bond order, and not the actual arrangement of atoms. Thus, a "linear" carbon chain has a zigzag shape and can twist in space in various ways.

There are four types of carbon atoms in the skeleton of a molecule. A carbon atom is called primary if it forms only one bond with another carbon atom. The secondary atom is bonded to two other carbon atoms, the tertiary atom to three, and the quaternary uses all four of its bonds to form bonds with carbon atoms.

The next classification feature is the presence of multiple bonds. Organic compounds containing only simple bonds are called saturated (limiting). Compounds containing double or triple bonds are called unsaturated (unsaturated). In their molecules, there are fewer hydrogen atoms per carbon atom than in the limiting ones. Cyclic unsaturated hydrocarbons of the benzene series are isolated into a separate class of aromatic compounds.

The third classification feature is the presence of functional groups, groups of atoms, characteristic of this class of compounds and determining its chemical properties. According to the number of functional groups, organic compounds are divided into monofunctional - contain one functional group, polyfunctional - contain several functional groups, such as glycerol, and heterofunctional - several different groups in one molecule, such as amino acids.

Depending on which carbon atom has a functional group, the compounds are divided into primary, for example, ethyl chloride CH 3 CH 2 C1, secondary - isopropyl chloride (CH3) 2CHC1 and tertiary - butyl chloride (CH 8) 8 CCl.

Organic chemistry - branch of chemistry that studies carbon compounds, their structure, properties , methods of synthesis, as well as the laws of their transformations. Organic compounds are called carbon compounds with other elements (mainly with H, N, O, S, P, Si, Ge, etc.).

The unique ability of carbon atoms to bind to each other, forming chains of various lengths, cyclic structures of various sizes, framework compounds, compounds with many elements, different in composition and structure, determines the diversity of organic compounds. To date, the number of known organic compounds is much more than 10 million and increases every year by 250-300 thousand. The world around us is built mainly from organic compounds, these include: food, clothing, fuel, dyes, medicines, detergents, materials for various branches of technology and the national economy. Organic compounds play a key role in the existence of living organisms.

At the junction of organic chemistry with inorganic chemistry, biochemistry and medicine, the chemistry of organometallic and elemental compounds, bioorganic and medical chemistry, and the chemistry of macromolecular compounds arose.

The main method of organic chemistry is synthesis. Organic chemistry studies not only compounds derived from plant and animal sources (natural substances), but mainly compounds created artificially through laboratory and industrial synthesis.

History of the development of organic chemistry

Methods for obtaining various organic substances have been known since antiquity. So, the Egyptians and Romans used dyes of plant origin - indigo and alizarin. Many nations owned the secrets of the production of alcoholic beverages and vinegar from sugar and starch-containing raw materials.

During the Middle Ages, practically nothing was added to this knowledge, some progress began only in the 16-17 centuries (the period of iatrochemistry), when new organic compounds were isolated by distillation of plant products. In 1769-1785 K.V. Scheele isolated several organic acids: malic, tartaric, citric, gallic, lactic and oxalic. In 1773 G.F. Ruel isolated urea from human urine. Substances isolated from animal and vegetable raw materials had much in common, but differed from inorganic compounds. This is how the term "Organic Chemistry" arose - a branch of chemistry that studies substances isolated from organisms (definition Y.Ya. Berzelius, 1807). At the same time, it was believed that these substances can only be obtained in living organisms due to the "life force".

It is generally accepted that organic chemistry as a science appeared in 1828, when F. Wöhler first received an organic substance - urea - as a result of evaporation of an aqueous solution of an inorganic substance - ammonium cyanate (NH 4 OCN). Further experimental work demonstrated indisputable arguments of the inconsistency of the "life force" theory. For example, A. Kolbe synthesized acetic acid, M. Berthelot received methane from H 2 S and CS 2, and A.M. Butlerov synthesized saccharides from formalin.

In the middle of the 19th century the rapid development of synthetic organic chemistry continues, the first industrial production of organic substances is created ( A. Hoffman, W. Perkin Sr.- synthetic dyes, fuchsin, cyanine and aza dyes). Open N.N. Zinin(1842) of the method for the synthesis of aniline served as the basis for the creation of the aniline-dye industry. In the laboratory A. Bayer natural dyes were synthesized - indigo, alizarin, indigo, xanthene and anthraquinone.

An important stage in the development of theoretical organic chemistry was the development F. Kekule theory of valency in 1857, as well as the classical theory of chemical structure A.M. Butlerov in 1861, according to which atoms in molecules are combined in accordance with their valence, the chemical and physical properties of compounds are determined by the nature and number of atoms in them, as well as the type of bonds and the mutual influence of directly unbound atoms. In 1865 F. Kekule proposed the structural formula of benzene, which became one of the most important discoveries in organic chemistry. V.V. Markovnikov And A.M. Zaitsev formulated a number of rules that for the first time connected the direction of organic reactions with the structure of the substances entering into them. In 1875 Van't Hoff And Le Bel proposed a tetrahedral model of the carbon atom, according to which the valences of carbon are directed to the vertices of the tetrahedron, in the center of which the carbon atom is located. Based on this model, combined with experimental studies I. Wislicenus(! 873), which showed the identity of the structural formulas of (+)-lactic acid (from sour milk) and (±)-lactic acid, stereochemistry arose - the science of the three-dimensional orientation of atoms in molecules, which predicted in the case of the presence of 4 different substituents at carbon atom (chiral structures) the possibility of the existence of space-mirror isomers (antipodes or enantiomers).

In 1917 Lewis proposed to consider the chemical bond using electron pairs.

In 1931 Hückel applied quantum theory to explain the properties of non-benzenoid aromatic systems, which founded a new direction in organic chemistry - quantum chemistry. This served as an impetus for the further intensive development of quantum chemical methods, in particular the method of molecular orbitals. The stage of penetration of orbital representations into organic chemistry was opened by the theory of resonance L. Pauling(1931-1933) and further work K. Fukui, R. Woodward And R. Hoffmann on the role of frontier orbitals in determining the direction of chemical reactions.

Mid 20th century characterized by a particularly rapid development of organic synthesis. This was determined by the discovery of fundamental processes, such as the production of olefins using ylides ( G. Wittig, 1954), diene synthesis ( O. Diels And C. Alder, 1928), hydroboration of unsaturated compounds ( G. Brown, 1959), nucleotide synthesis and gene synthesis ( A. Todd, H. Qur'an). Advances in the chemistry of organometallic compounds are largely due to the work A.N. Nesmeyanov And G.A. Razuvaeva. In 1951, the synthesis of ferrocene was carried out, the establishment of the "sandwich" structure of which R. Woodward And J. Wilkinson marked the beginning of the chemistry of metallocene compounds and, in general, the organic chemistry of transition metals.

In 20-30 years. A.E. Arbuzov creates the foundations of the chemistry of organophosphorus compounds, which subsequently led to the discovery of new types of physiologically active compounds, complexons, etc.

In the 60-80s. Ch. Pedersen, D. Cram And J.M. Linen develop the chemistry of crown ethers, cryptands, and other related structures capable of forming strong molecular complexes, and thereby approach the most important problem of "molecular recognition".

Modern organic chemistry continues its rapid development. New reagents, fundamentally new synthetic methods and techniques, new catalysts are introduced into the practice of organic synthesis, previously unknown organic structures are synthesized. The search for organic new biologically active compounds is constantly being conducted. Many more problems of organic chemistry are waiting to be solved, for example, a detailed establishment of the structure-property relationship (including biological activity), the establishment of the structure and stereodirected synthesis of complex natural compounds, the development of new regio- and stereoselective synthetic methods, the search for new universal reagents and catalysts .

The interest of the world community in the development of organic chemistry was vividly demonstrated by the awarding of the Nobel Prize in Chemistry in 2010. R. Heku, A. Suzuki and E. Negishi for his work on the use of palladium catalysts in organic synthesis for the formation of carbon-carbon bonds.

Classification of organic compounds

The classification is based on the structure of organic compounds. The basis of the description of the structure is the structural formula.

Main classes of organic compounds

Hydrocarbons - compounds consisting only of carbon and hydrogen. They, in turn, are divided into:

Saturated- contain only single (σ-bonds) and do not contain multiple bonds;

Unsaturated- contain at least one double (π-bond) and/or triple bond;

open chain(alicyclic);

closed circuit(cyclic) - contain a cycle

These include alkanes, alkenes, alkynes, dienes, cycloalkanes, arenes

Compounds with heteroatoms in functional groups- compounds in which the carbon radical R is associated with a functional group. Such compounds are classified according to the nature of the functional group:

Alcohol, phenols(contain hydroxyl group OH)

Ethers(contain the grouping R-O-R or R-O-R

Carbonyl compounds(contain the group RR "C = O), these include aldehydes, ketones, quinones.

Compounds containing a carboxyl group(COOH or COOR), these include carboxylic acids, esters

Element- and organometallic compounds

Heterocyclic compounds - contain heteroatoms in the ring. They differ in the nature of the cycle (saturated, aromatic), in the number of atoms in the cycle (three-, four-, five-, six-membered cycles, etc.), in the nature of the heteroatom, in the number of heteroatoms in the cycle. This determines the huge variety of known and annually synthesized compounds of this class. The chemistry of heterocycles is one of the most exciting and important areas of organic chemistry. Suffice it to say that more than 60% of drugs of synthetic and natural origin belong to various classes of heterocyclic compounds.

Natural compounds - compounds, as a rule, of a rather complex structure, often belonging to several classes of organic compounds at once. Among them are: amino acids, proteins, carbohydrates, alkaloids, terpenes, etc.

Polymers- substances with a very large molecular weight, consisting of periodically repeating fragments - monomers.

The structure of organic compounds

Organic molecules are mainly formed by covalent non-polar C-C bonds, or covalent polar bonds of the C-O, C-N, C-Hal type. Polarity is explained by the shift of the electron density towards the more electronegative atom. To describe the structure of organic compounds, chemists use the language of structural formulas of molecules, in which bonds between individual atoms are denoted by one (simple, or single bond), two (double), or three (triple) valence strokes. The concept of a valency stroke, which has not lost its meaning to this day, was introduced into organic chemistry A. Cooper in 1858

Very important for understanding the structure of organic compounds is the concept of hybridization of carbon atoms. The carbon atom in the ground state has an electronic configuration 1s 2 2s 2 2p 2, on the basis of which it is impossible to explain the valency 4 inherent in carbon in its compounds and the existence of 4 identical bonds in alkanes directed to the vertices of the tetrahedron. In the framework of the method of valence bonds, this contradiction is resolved by introducing the concept of hybridization. When excited, s→p electron transition and the subsequent, so-called, sp- hybridization, with the energy of the hybridized orbitals being intermediate between the energies s- And p-orbitals. When bonds are formed in alkanes, three R-electron interact with one s-electron ( sp 3 hybridization) and 4 identical orbitals arise, located at tetrahedral angles (109 about 28 ") to each other. Carbon atoms in alkenes are in sp 2-hybrid state: each carbon atom has three identical orbitals lying in the same plane at an angle of 120 about to each other ( sp 2 orbitals), and the fourth ( R-orbital) is perpendicular to this plane. Overlapping R-orbitals of two carbon atoms forms a double (π) bond. The carbon atoms that carry the triple bond are in sp- hybrid state.

Features of organic reactions

Ions are usually involved in inorganic reactions, such reactions proceed quickly and are completed at room temperature. In organic reactions, covalent bonds are often broken with the formation of new ones. As a rule, these processes require special conditions: a certain temperature, reaction time, certain solvents, and often the presence of a catalyst. Usually, not one, but several reactions take place at once. Therefore, when depicting organic reactions, not equations are used, but schemes without calculating stoichiometry. The yields of target substances in organic reactions often do not exceed 50%, and their isolation from the reaction mixture and purification require specific methods and techniques. To purify solids, as a rule, recrystallization from specially selected solvents is used. Liquid substances are purified by distillation at atmospheric pressure or under vacuum (depending on the boiling point). To control the progress of reactions, separate complex reaction mixtures, various types of chromatography are used [thin-layer chromatography (TLC), preparative high-performance liquid chromatography (HPLC), etc.].

Reactions can proceed very complicatedly and in several stages. Radicals R·, carbocations R + , carbanions R - , carbenes:CX 2 , radical cations, radical anions and other active and unstable particles, usually living for a fraction of a second, can appear as intermediate compounds. A detailed description of all the transformations that occur at the molecular level during a reaction is called reaction mechanism. According to the nature of the gap and the formation of bonds, radical (homolytic) and ionic (heterolytic) processes are distinguished. According to the types of transformations, chain radical reactions, nucleophilic (aliphatic and aromatic) substitution reactions, elimination reactions, electrophilic addition, electrophilic substitution, condensation, cyclization, rearrangement processes, etc. are distinguished. Reactions are also classified according to the methods of their initiation (excitation ), their kinetic order (monomolecular, bimolecular, etc.).

Determination of the structure of organic compounds

Throughout the existence of organic chemistry as a science, the most important task has been to determine the structure of organic compounds. This means to find out which atoms are part of the structure, in what order and how these atoms are interconnected and how they are located in space.

There are several methods for solving these problems.

elemental analysis consists in the fact that the substance is decomposed into simpler molecules, by the number of which it is possible to determine the number of atoms that make up the compound. This method does not make it possible to establish the order of bonds between atoms. Often used only to confirm the proposed structure.
Infrared spectroscopy (IR spectroscopy) and Raman spectroscopy (Raman spectroscopy). The method is based on the fact that the substance interacts with electromagnetic radiation (light) of the infrared range (absorption is observed in IR spectroscopy, and radiation scattering is observed in Raman spectroscopy). This light, when absorbed, excites the vibrational and rotational levels of the molecules. The reference data are the number, frequency and intensity of vibrations of the molecule associated with a change in the dipole moment (IC) or polarizability (CR). The method allows you to establish the presence of functional groups, and is also often used to confirm the identity of a substance with some already known substance by comparing their spectra.
Mass spectrometry. A substance under certain conditions (electron impact, chemical ionization, etc.) turns into ions without loss of atoms (molecular ions) and with loss (fragmentation, fragmentary ions). The method allows you to determine the molecular weight of a substance, its isotopic composition, and sometimes the presence of functional groups. The nature of the fragmentation allows us to draw some conclusions about the structural features and recreate the structure of the compound under study.
Nuclear magnetic resonance (NMR) method is based on the interaction of nuclei with their own magnetic moment (spin) and placed in an external constant magnetic field (spin reorientation), with variable electromagnetic radiation in the radio frequency range. NMR is one of the most important and informative methods for determining the chemical structure. The method is also used to study the spatial structure and dynamics of molecules. Depending on the nuclei interacting with radiation, there are, for example, the method of proton resonance PMR, NMR 1 H), which allows you to determine the position of hydrogen atoms in a molecule. The 19 F NMR method makes it possible to determine the presence and position of fluorine atoms. The 31 P NMR method provides information on the presence, valence state, and position of phosphorus atoms in a molecule. The 13 C NMR method makes it possible to determine the number and types of carbon atoms; it is used to study the carbon skeleton of a molecule. Unlike the first three, the last method uses a minor isotope of the element, since the nucleus of the main 12 C isotope has zero spin and cannot be observed by NMR.
Method of ultraviolet spectroscopy (UV spectroscopy) or electronic transition spectroscopy. The method is based on the absorption of electromagnetic radiation in the ultraviolet and visible regions of the spectrum during the transition of electrons in a molecule from the upper filled energy levels to vacant ones (excitation of the molecule). Most often used to determine the presence and characteristics of conjugate π-systems.
Methods of analytical chemistry make it possible to determine the presence of certain functional groups by specific chemical (qualitative) reactions, the fact of which can be fixed visually (for example, the appearance or change in color) or using other methods. In addition to chemical methods of analysis in organic chemistry, instrumental analytical methods such as chromatography (thin-layer, gas, liquid) are increasingly used. A place of honor among them is occupied by chromatography-mass spectrometry, which makes it possible not only to assess the degree of purity of the obtained compounds, but also to obtain mass spectral information about the components of complex mixtures.
Methods for studying the stereochemistry of organic compounds. From the beginning of the 80s. the expediency of developing a new direction in pharmacology and pharmacy associated with the creation of enantiomerically pure drugs with an optimal ratio of therapeutic efficacy and safety has become obvious. Currently, approximately 15% of all synthesized pharmaceuticals are represented by pure enantiomers. This trend was reflected in the appearance in the scientific literature of recent years of the term chiral switch, which in Russian translation means “switching to chiral molecules”. In this regard, methods for establishing the absolute configuration of chiral organic molecules and determining their optical purity are of particular importance in organic chemistry. The main method for determining the absolute configuration should be considered X-ray diffraction analysis (XRD), and optical purity - chromatography on columns with a stationary chiral phase and NMR using special additional chiral reagents.

The connection of organic chemistry with the chemical industry

The main method of organic chemistry - synthesis - closely links organic chemistry with the chemical industry. Based on the methods and developments of synthetic organic chemistry, small-tonnage (fine) organic synthesis arose, including the production of drugs, vitamins, enzymes, pheromones, liquid crystals, organic semiconductors, solar cells, etc. The development of large-tonnage (basic) organic synthesis is also based on the achievements of organic chemistry. The main organic synthesis includes the production of artificial fibers, plastics, processing of oil, gas and coal raw materials.