Organic Chemistry

Organic Chemistry initially constituted a part of chemistry in general and did not have a special name; later, O. ch. came to mean the chemistry of substances found only in animal and plant organisms. Berzelius defined O. ch. in 1827 as the chemistry of plant and animal substances or substances formed under the influence of vital force. However, very soon the first artificial syntheses of plant and animal substances, carried out from inorganic compounds outside a living organism, appeared. The synthesis of urea by Wohler is considered the first synthesis and dates to 1828; although the synthesis itself was carried out by Wohler in 1824, the proof that the obtained substance was urea was given by him only in 1828. In 1824, Wohler synthesized oxalic acid. These first artificial syntheses initially had no influence on the definition of O. ch. given by Berzelius, which only after 30 years gradually gave way to another. In 1848, Frankland and Kolbe synthesized acetic acid directly from elements; Berthelot, starting from 1853, and then other chemists artificially obtained a number of organic components of animals and plants. At the same time, many substances possessing the properties of organic compounds but not found in either animals or plants were synthesized. Although the name O. ch. no longer corresponded to reality, it has nevertheless been preserved to this day despite the fact that the content of the concept "organic chemistry" has changed sharply, and at present O. ch. is called the chemistry of carbon compounds; organic compounds are carbon compounds.

At the end of the 18th and beginning of the 19th centuries, there was no correct understanding of the composition of organic compounds. Only Berzelius first successfully applied methods of quantitative analysis to organic compounds. Berzelius applied his dualistic theory to organic compounds, according to which organic compounds, like inorganic ones, have a dual composition, but, as Lavoisier also recognized, instead of elements in organic compounds there are radicals that play the role of elements. Gay-Lussac considered sugar as a compound consisting of carbon and water, alcohol as consisting of ethylene and water. In 1823, a phenomenon of extraordinary importance was discovered, which in 1830 received the name isomerism (see). Liebig, investigating fulminating silver, found its composition to be identical with that of silver cyanate, investigated by Wohler, but having different properties than the first salt. Berzelius established the identical composition of tartaric and grape acids, which differ in properties. Facts of this kind received a complete explanation in the theory of the structure of organic compounds, which was preceded by the theory of radicals (see Radicals) and the theory of types. Gay-Lussac noted that the cyan radical, CN, plays in compounds a role as if of an atom. Dumas in compounds called ethyl ones accepted the existence of the ethylene radical, C₄H₄ (theory of ethylene); then alcohol would be expressed as C₄H₄+H₂O, ether as 2C₄H₄ + +NaO. Liebig and Wohler in 1832 published a joint research "on the radical of benzoic acid"; this radical contains oxygen; Berzelius, until then admitting only oxygen-free radicals, now also recognized oxygen-containing radicals. Berzelius considered the benzoyl radical as the oxide of the group C₁₂H₁₀, benzoic acid as the peroxide of this group, ether as the oxide of ethyl (C₂H₅)₂, alcohol as the oxide of the radical C₂H₆. Liebig considered ether and alcohol as derivatives of the ethyl radical, to which he gave a formula doubled compared to the modern one C₄H₁₀; ether as C₄H₁₀O (oxide of ethyl), alcohol as C₄H₁₀.H₂O (hydroxide of ethyl), ethyl chloride as C₄H₁₀Cl₂. Liebig and Regnault pointed to the existence of the acetyl radical C₄H₆; acetaldehyde and acetic acid were considered as the hydroxide and hydroxide of acetyl-C₄H₆O.H₂O and C₄H₆O₃.H₂O. Liebig saw in radicals only some convenience for explaining the formation and decomposition of substances. Berzelius accepted radicals as complex elements and considered them immutable; this opinion was prevailing. For a time it was even thought that the difference between organic and inorganic compounds boiled down to the fact that the former are built from radicals, while the latter from atoms.

The initial theory of radicals was based on the recognition of the immutability of the radical; but Dumas, who discovered the phenomenon of metalepsis (replacement of hydrogen in the radical), shook this view (1834-1835), while Laurent on the basis of Duma's rule of substitution gave the theory of substitution or the theory of nuclei; according to this theory, organic compounds after substitution of H in the radical, for example with Cl, do not change their main properties. Dumas denied the analogy between initial and substituted substances. Having opened the struggle against the dualistic theory and the theory of radicals, Duma gave his own theory, the theory of types, close to the theory of nuclei (the oldest theory of types, 1839). The chemical type unites a series of compounds possessing similar chemical properties; these types remain unchanged after substitution of H in the radical with a halogen; for example, acetic acid is of one type with chloroacetic acid, aldehyde with chloral, methane with chloroform. According to Duma, every chemical compound is a whole; the dualistic views of Berzelius were recognized as erroneous; in their place came unitary views; the concept of radicals was abandoned, but Gerard reintroduced it in a modified meaning and under a different name. He gave the theory of residues, atomic complexes remaining after the interaction of two bodies; these residues cannot exist in a free state and combine with each other; the residue according to Gerard is not a real atomic group, but only an abstract concept. On the other hand, the research of Wurtz, Hoffmann (organic derivatives of ammonia) and Williamson (formation and composition of ethers) contributed to the strengthening and development of the theory of types. Supporters of new, unitary views engaged in merging the theory of radicals with the theory of types. Gerard and Laurent gave the theory of types (so-called newest), and Frankland and Kolbe the newest theory of radicals. The theory of types established the following types: H₂, H₂O, H₂S, HCl, NH₃. The type H₂ includes hydrocarbons and metallo-organic compounds, the type H₂O includes alcohols, ethers, aldehydes, acids; H₂S-thio-organic compounds; NH₃-amines, amides, imides; HCl-halogen derivatives, cyanides. Later Kekule introduced mixed types: H₂ and H₂O (this includes benzene sulfonic acid - C₆H₆.SO₂H.O), NH₃ and H₂O (carbamic acid - NH₂.CO.H.O) and a new type CH₄ (this includes CH₃Cl, CHCl₃, CH₃CN). Together with the theory of types thanks to Kolbe (electrolysis of salts of fatty acids) and Frankland (metallo-organic compounds), the theory of radicals also received a strong impetus to development. According to Kolbe, all organic substances are derivatives of inorganic ones, for example, carboxylic acids, aldehydes and ketones are derivatives of carbonic acid, sulfonic acids are derivatives of sulfuric acid. Frankland established the concept of saturation capacity (valence), Kekule, Kolbe determined the valence of carbon and found it equal to 4, which became the starting point of the doctrine of structure, the theory of the structure of organic compounds.

The theory of the structure of organic compounds was given by Kekule, Couper, and Butlerov. All organic compounds according to their structure can be divided into several groups: alicyclic (aliphatic) compounds with an open chain of carbon atoms, and this chain can be straight or branched, with side chains, for example CH₃.CH₂.CH₂.CH₃- CH₃ CH CH₃ normal butane and CH₃-CH-CH₃ isobutane; homocyclic (carbocyclic) compounds with a closed chain of carbon atoms, as in benzene, the first representative of aromatic compounds, and trimethylene, the representative of alicyclic compounds (the structural formula given by Kekule in 1865); heterocyclic compounds with carbon and various other atoms besides carbon in the ring, for example pyridine

In the pyrrole groups, there can be saturated and unsaturated compounds with multiple bonds: double and triple bonds in acyclic compounds, double bonds in cyclic compounds (in the side chains of cyclic compounds there can also be triple bonds). Numerous syntheses confirmed, developed, and supplemented the theory of the structure of organic compounds. The term "synthesis" was introduced by Williamson in 1850. Particular attention should be paid to the syntheses of methane, acetylene, benzene, hydrocyanic acid, and formic acid, carried out by Wurtz (1853-1879) directly from elements, and also his research on fats, the synthesis of aniline by Zinin (1842) (the proof of the possibility of obtaining aniline from nitrobenzene later formed the basis of one of the largest branches of organic technology - the aniline dye industry). The number of individual classes of organic chemistry rapidly increased, syntheses of amines by Wurtz (1848), Hofmann and others appeared, the first synthesis of a sugar-like substance by Butlerov (1861), the use of organozinc compounds for various syntheses by Frankland, the synthesis of an amino acid by Perkin and Duppa (Perkin, Duppa; 1858). After the synthesis of mauve, the first aniline dye, by Perkin (1856), other artificial triphenylmethane dyes were described by Hofmann, E. Fischer, O. Fischer and others, and syntheses of alizarin by Graebe and Liebermann (Graebe, Liebermann; 1868) and indigo blue by Bayer (Bayer) were published. Clarification of the structure of these important dyes made their industrial synthesis possible. Industrial syntheses of the most diverse dyes appeared - triphenylmethane, alizarin (anthracene), azo dyes, indigo group dyes, indanthrene and many others, creating one of the largest branches of organic technology. The first synthesis of a natural alkaloid (coniine) was carried out by Ladenburg in 1886. With remarkable speed, a large number of individual classes of organic chemistry were obtained by synthesis, each of which has many individual representatives. The clarification of the structure of organic compounds proceeded, of course, not only by synthesis but also by analysis (cleavage) of molecules. Many of the natural organic compounds known at that time were found to be optically active. In 1848-1853, the famous studies of Pasteur on the artificial cleavage of optically inactive racemic substance into two optically active components with opposite signs of rotation and on the reverse synthesis of racemic compound from two such components appeared (see Asymmetric synthesis, cleavage). To explain the optical activity of organic compounds, the theory of structure proved insufficient and required an addition to it in the form of the stereochemical theory of van't Hoff and Le Bel (see Asymmetric carbon, Stereochemistry). From more recent works, the research of Bayer, Wallach and Wagner (90s and later) on the extensive group of terpene compounds, the clarification of the structure of many alkaloids by the work of Konigs, Knorr, Rabe, Pictet, Willstatter and others, the classical works of E. Fischer on the synthesis and study of the structure of carbohydrates, purine bodies should be noted. The latest directions of research in the field of organic chemistry are: clarification of the type of structure of the protein molecule by E. Fischer, Abderhalden, Levene and others; study of the structure of animal and plant pigments by Nencki, Willstatter, H. Fischer, Kuster and others; works of Willstatter on the separation and obtaining of enzymes in as pure a form as possible; synthesis of artificial rubber (a large number of researchers, including S. Lebedev, Vyshvovsky); synthesis of other high-molecular compounds by Staudinger (Staudinger); in the last 14 years, great changes have been made to previous concepts of the structure of polysaccharides (see) by the research of Irvine, Carrer, Pictet, Pringsheim, Hess and others. These studies showed the close connection between the physical and technical properties of starch, cellulose and their chemical structure; in addition, it was discovered that these polysaccharides are built on the anhydride type and their carbon skeleton does not represent a long series of atoms arranged in one chain, but is built from relatively small cells connected to each other by means of probably additional affinity units. This view of the structure of polysaccharides was also transferred to the concepts of the structure of the protein molecule, in which, in addition to long chains of polypeptides, the presence of relatively small cyclic groups of the diketopiperazine type is also admitted (see Proteins). The application of the methods of physical chemistry to organic chemistry gave very important results in clarifying the finest details of structure, especially the application of the refractometric method by Bruhl, further spectroscopy - in the ultraviolet part, X-rayscopy, Raman phenomena. In recent times, the electronic theory of the structure of matter has found application in organic chemistry. Each bond between atoms corresponds to the transition of an electron from one atom to another, which Falk and Nelson propose to denote by arrows: H→C←H, H→C→C→H, H→C≡C→H. A simple bond is carried out by one pair of electrons, a double bond by two, a triple bond by three. For example, Lewis depicts the formulas of methane, ethylene and acetylene as follows: H:C:H, H:C:C:H (two electrons that do not form pairs express residual affinity), H:C:::C:H, or H:C:C:H. In the formula of benzene according to the electronic theory, six carbons are not equivalent, as is usually accepted on the basis of the existence of one monosubstituted: 1, 3, 5-carbons are negative, and 2, 4, 6-mixed (with 3 positive and 1 negative charges). With the development of the electronic theory (Bohr, W. Kossel and others), it is possible to explain the bond in heteropolar compounds quite satisfactorily (see Molecule), but the homopolar bond in molecules of metalloids and in organic compounds is difficult to explain. Research on hexaphenylethane (C6H5)3C-C(C6H5)3 and triphenylmethyl (C6H5)3C+ led some authors (Gomberg, Schmidlin, Chichibabin and others) to the assumption of trivalent carbon, and in some compounds (carbon monoxide CO, isonitriles) of divalent carbon (Nef); in connection with this, the question of the so-called free radicals arose, whose existence in free form was not admitted by classical chemistry. All the diverse organic compounds are divided, as indicated above, into acyclic, homocyclic (among them aromatic) and heterocyclic. In turn, in each of these series, there are distinguished: hydrocarbons, their halogen derivatives, alcohols, ethers (simple and complex), aldehydes, ketones, acids, metallo-organic compounds and others. Among nitrogen-containing compounds - nitro- and amino compounds, azo-, diazo-, hydrazo compounds, nitriles, isonitriles, oximes and others. Further, compounds of mixed function (aldehyde- and ketone-alcohols, carbohydrates, oxy- and amino acids) etc. are known - From the aliphatic saturated hydrocarbons of the general formula CnH2n+2, the first, CH4, is called methane, the second - ethane, C2H6, the third - propane, C3H8, then butane-C4H10, or CH3.CH2.CH2.CH3- normal butane; butane also has an isomer CH3.CH.CH3,

The development of organic chemistry in the 19th century was characterized by the establishment of the fundamental laws governing the structure of organic compounds. The theory of chemical structure, formulated by Butlerov, became the cornerstone of this science. It postulated that the properties of organic compounds are determined by the arrangement of atoms in their molecules and the nature of the chemical bonds between them. This theory was supported by numerous experimental observations, including the phenomenon of isomerism, where compounds with the same molecular formula exhibit different properties due to different structural arrangements. The concept of valence, or the combining capacity of atoms, was crucial in understanding how carbon atoms could form stable chains and rings, leading to the vast diversity of organic compounds. The development of structural formulas provided a visual representation of molecular architecture, allowing chemists to predict and explain chemical reactions. The work of Kekulé on the structure of benzene, with its cyclic arrangement of carbon atoms and alternating double bonds, was particularly significant. The discovery of new classes of organic compounds, such as hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, and their derivatives, expanded the scope of organic chemistry. The synthesis of these compounds from simpler substances, often from inorganic materials, demonstrated the unity of chemistry and the interconnectedness of all substances. The development of analytical techniques, such as elemental analysis and the determination of molecular weights, provided the necessary data to establish the composition and structure of organic compounds. The study of organic reactions led to the understanding of reaction mechanisms, including substitution, addition, elimination, and rearrangement reactions. The concept of functional groups, specific groups of atoms within molecules that are responsible for characteristic chemical reactions, became a central organizing principle in organic chemistry. The classification of organic compounds based on their functional groups allowed for systematic study and prediction of their properties. The development of organic chemistry was also influenced by advances in other scientific disciplines, such as physics and biology. The discovery of the electron and the development of quantum mechanics provided new insights into the nature of chemical bonding, leading to the electronic theory of valence. This theory explained how atoms share electrons to form stable molecules, providing a deeper understanding of organic structure and reactivity. The application of spectroscopic techniques, such as infrared and ultraviolet spectroscopy, allowed for the determination of molecular structure and the identification of functional groups. The study of organic chemistry continued to evolve throughout the 19th century, laying the foundation for the rapid developments of the 20th century. The synthesis of complex natural products, such as sugars, alkaloids, and steroids, demonstrated the power of organic synthesis and the ability of chemists to mimic nature. The development of industrial organic chemistry led to the production of dyes, pharmaceuticals, plastics, and other synthetic materials, transforming society and the economy. The 19th century was a period of remarkable progress in organic chemistry, establishing it as a central discipline in the chemical sciences and paving the way for future discoveries.

The classification of organic compounds became increasingly sophisticated as more compounds were discovered and studied. The distinction between aliphatic and aromatic compounds, based on their structural and chemical properties, proved to be fundamental. Aliphatic compounds, which include alkanes, alkenes, and alkynes, are characterized by open-chain structures, while aromatic compounds, such as benzene and its derivatives, contain ring structures with delocalized electrons. The study of heterocyclic compounds, which contain atoms other than carbon in their ring structures, expanded the diversity of organic chemistry. These compounds, including pyridine, thiophene, and furan, exhibited unique properties and reactivities. The development of stereochemistry, concerned with the three-dimensional arrangement of atoms in space, became crucial in understanding the properties of organic compounds. The discovery of optical isomerism, where compounds exist in forms that rotate plane-polarized light in opposite directions, highlighted the importance of molecular geometry. The concept of chirality, or handedness, in molecules became central to stereochemistry, with the asymmetric carbon atom being a key feature. The study of reaction mechanisms revealed the step-by-step processes by which chemical reactions occur, providing insight into the factors that influence reaction rates and products. The development of catalysis, both homogeneous and heterogeneous, became essential for many organic reactions, allowing for the acceleration of reactions and the selective formation of products. The study of organic chemistry also had significant implications for other scientific fields. The development of biochemistry, concerned with the chemistry of living organisms, relied heavily on the principles of organic chemistry. The study of enzymes, vitamins, hormones, and other biological molecules provided insights into the molecular basis of life. The development of medicinal chemistry, focused on the design and synthesis of drugs, became a major application of organic chemistry. The discovery of new drugs, such as antibiotics and analgesics, revolutionized medicine and improved human health. The development of polymer chemistry, concerned with the study of large molecules composed of repeating units, led to the production of synthetic materials such as plastics, fibers, and rubbers. These materials transformed industry and daily life, providing new materials with diverse properties and applications. The study of organic chemistry continued to evolve throughout the 20th century, with new techniques and theories being developed to understand the structure and reactivity of organic compounds. The development of spectroscopic methods, such as nuclear magnetic resonance (NMR) and mass spectrometry, allowed for the detailed analysis of molecular structure. The development of computational chemistry, using computers to model and predict chemical behavior, provided new tools for understanding organic chemistry. The study of organic chemistry remains a dynamic and evolving field, with new discoveries and applications being made continually. The principles of organic chemistry continue to be essential for understanding the molecular world and for developing new materials and drugs that benefit society.

isobutane; the names of isomers are formed from the name of the normal hydrocarbon with the prefix "iso"; further representatives of hydrocarbons received names based on the number of carbon atoms, with numerals taken from Greek: pentane, C₅H₁₂, hexane, C₆H₁₄, heptane, C₇H₁₆, octane, C₈H₁₈; the name of the next hydrocarbon is taken from Latin, nonane, C₉H₂₀; decane, C₁₀H₂₂; the next hydrocarbon bears a Greco-Latin name: undecane, C₁₁H₂₄; further names come from the Greek language. The number of isomers increases sharply with the number of carbon atoms: C₅H₁₂ has 3 isomers, C₁₃H₂₈ has 802 isomers. Unsaturated hydrocarbons of the general formula C_nH_2n are named according to the radical of the corresponding saturated compound with the ending "ene", ethylene, C₂H₄; the hydrocarbon C₆H₁₀ is called amylene (corresponding radical - amyl, C₅H₁₁); the first representative of hydrocarbons of the general formula C_nH_2n-2 is called acetylene, C₂H₂. Halogen derivatives are named according to the radical (see Alkyl Hal) with the addition of an adjective from the name of the halogen, for example CH₃Cl - methyl chloride, C₂H₅Br - ethyl bromide. Alcohols receive names either according to the radical with the addition of the word "alcohol", e.g. C₂H₅.OH - ethyl alcohol, or (Kolbe nomenclature) as derivatives of methyl alcohol, CH₃OH, called carbinol, with the addition of the corresponding radical, e.g.: CH₃.CH₂OH - methyl carbinol, (CH₃)₂CH.OH - dimethyl carbinol. Similarly, according to Kolbe nomenclature, acids are designated as derivatives of acetic acid, e.g.: (CH₃)₂CH.COOH - dimethylacetic (otherwise valeric) acid. To indicate the position of the substituent in substituted acids (amino-, halo-, hydroxy-acids, etc.), letters of the Greek alphabet are used, counting the carbon atoms from the one adjacent to the carboxyl group, denoted as α-C; so for example CH₂Br.CH₂CH₂.COOH is called β-bromovaleric acid. This method of designation is also applied to substituted compounds of other classes of organic chemistry. Aldehydes are named according to the acid into which they are oxidized, e.g. CH₃.CHO - acetaldehyde; ketones are named according to the radicals with the addition of the word "ketone", e.g. CH₃.CO.C₂H₅ - methyl ethyl ketone. Aromatic compounds are named after the first representative of aromatic hydrocarbons - benzene, C₆H₆; C₆H₅.CH₃ - methyl benzene (toluene), C₆H₅.NO₂ - nitrobenzene, C₆H₄(NO₂)₂ - dinitrobenzene, C₆H₃(NO₂)₃ - trinitrobenzene. The position of substituent groups is denoted by prefixes: ortho-, meta-, para- (o-, m-, p-) for disubstituted and by adjectives: "symmetrical", "unsymmetrical" (asymmetrical) and "adjacent" (vicinal), or s, as, v for trisubstituted. In o-compounds the substituent groups are adjacent, ¹/²; in m-compounds they are separated by one position, ¹/³; in p-compounds they are separated by two positions, opposite each other, ¹/⁴; the arrangement of substituent groups in trisubstituted compounds is seen from the following schemes: v- as- s- Along with these names, there are many empirical, technical, and pharmaceutical names, such as chloroform, iodoform, wood and alcohol, acetone; organic acids bear almost exclusively empirical names, such as formic, acetic, valeric, oxalic, succinic, malic, tartaric, citric, lactic, etc. Also empirical names are carbohydrates (glucose or grape sugar, also dextrose, levulose or fructose, also fruit sugar, cane, barley (maltose), milk (lactose) sugar; starch, cellulose). In the aromatic series there is a very large number of empirical and technical names (toluene, xylene, picric acid); terpenes (pinene, sylvestrene, limonene, etc.) are named empirically. The huge number of organic compounds, the abundance of names, and their diversity and inconsistency forced chemists to raise and resolve the question of a more strict scientific nomenclature of organic compounds. At the international meeting of representatives of chemical societies in Geneva in 1892, the nomenclature of organic compounds (Geneva or scientific nomenclature) was developed. According to this nomenclature, the usual names are retained for normal saturated hydrocarbons of the aliphatic series; isomers are named according to the hydrocarbon without a side chain with the addition of the name of the side chain radical and the number of the carbon atom to which the side chain is attached, starting the numbering of carbon atoms from the atom of the main chain closest to the side chain; e.g.,

CH₃

_

_

CH₃.CH₃.CH₃.

.CH₃ will be 2-methylbutane,

i | CH₃ CH₃ .CH₂.CH₃-2,3-dimethylbutane; if two side chains are attached to the same carbon atom, then both have the same number, which is repeated in the name, e.g. CH₃.C(CH₃).CH₃ will be 2,2-dimethyl-

CH₃ propane. Halogen derivatives of saturated hydrocarbons are named similarly to the previous example, for example CH₃.CHCl.CH₃ will be 2-chloropropane, CH₃.CCl₂.CH₃ -2-chloro-2-methyl-

CH₃ propane, CH₂Cl.CH₂Cl-1,2-dichloroethane. Alcohols receive the ending "ol", which is attached to the root of the name of the corresponding hydrocarbon; in addition, the number of the carbon atom at which the OH group is attached is added, e.g. CH₃OH-methanol, C₂H₅.OH-ethanol, CH₃CH₂CH₂CH₂OH--propanol-1, CH₃CH₂CH₂OH-2-methylpropanol-2. Aldehydes received the ending "al", attached to the name of the hydrocarbon with the same number of carbon atoms, e.g. HCHO-methanal, CH₃.CHO-

|

-2-methylpropanal. H₃C Ketones receive similarly the ending "on"; in addition, the number of the carbonyl carbon is added, counting from the beginning of the chain, for example CH₃.CO.CH₃ will be propanone, CH₃.CH₂.CO.CH₂.CH₃-pentanone-3. The names of acids are adjectives from the names of hydrocarbons with the same number of carbon atoms, with the addition of the word "acid", e.g. H.COOH-methanoic acid, CH₃.COOH-ethanoic acid; in the presence of side chains, the position of the side chain and carboxyl is indicated, for example CH₃CH₂CH₂COOH _ I

will be 2-methylbutanoic acid C8. Dibasic acids have the prefix 'di' before the word 'acid', for example COOH.CH2.COOH-propanedioic acid, etc. Unsaturated ethylene hydrocarbons are named after the saturated ones with the ending 'ene' and with the addition of the number of the carbon after which the double bond is located, for example CH2:CH2-ethene, CH3.CH:CH.CH3-butene-2; acetylene hydrocarbons have similar names with the ending 'yne'; for example CH≡CH-ethyne, CH3.C≡C.CH3-butyne-2. Benzene is called benzene according to the Geneva nomenclature; toluene-methylbenzene, di- and tri-substituted have the numbers of the carbons at which the substituent groups are located in addition to the name of the hydrocarbon; for example symmetrical trinitrobenzene-1,3,5,NO2 NO2 NO2. Terpenes are named according to the terminology proposed by Baeyer; for example limonene,CH3 CH3 CH2 =10 /A CH CH : called 9 CH2 CH2 D 1,8-mentadiene (A denotes a double bond, the numbers 1,8 indicate the position of the double bonds).* Thanks to the rapid development of synthetic reactions and the large number of scientific workers in organic chemistry, the number of organic compounds has grown extremely and currently exceeds 250,000. This multitude of the most diverse organic compounds has been studied and classified so successfully that it is one of the most coherent scientific disciplines. Organic chemistry is in close connection with other branches of natural science: inorganic chemistry, physical chemistry, colloid chemistry, * For the nomenclature of carbohydrates in connection with the latest data on their structure, see Kramer M., Sugars and their derivatives, L., 1930; Shorygin P., Chemistry of carbohydrates, M.-L., 1927. crystallography. For medicine, organic chemistry has extremely important significance both due to its closest relation to biological chemistry and thanks to the flourishing development of pharmaceutical chemistry, a large part of the products of which belongs to the field of organic chemistry. With the current development of culture and industry, organic chemistry has a very significant influence on the most diverse aspects of human life: nutrients, fabrics, writing paper, coal dyes, fragrant substances, sweet substances, photographic reagents, etc.-these are compounds of organic chemistry. Organic chemistry has enormous significance in military affairs, since almost all explosives and a significant part of poisonous substances are products of organic chemistry. Modern organic technology is planned in such a way that, while in peacetime engaged in the production of medicinal substances, dyes, artificial silk, etc., it can be immediately reorganized for the needs of military chemistry with the beginning of the war. In the 20th century, catalytic and pyrogenetic reactions have been widely developed both in laboratory and factory practice, to which belong: improved methods of coking, cracking process, liquefaction of solid fuel, synthesis of methyl alcohol from water gas, synthesis of rubber, conversion of coal into ethyl alcohol, acetic acid, acetone and many other processes. Laboratory of organic chemistry, see. Chemistry.

V. Gulevich, I. Yaychnikov.