Fundamentals of organic chemistry. Chemistry Organic Definition of Organic Chemistry
Organic chemistry arose in the process of studying those substances that were extracted from plant and animal organisms, consisting mostly of organic compounds. This is what determined the purely historical name of such compounds (organism organic). Some technologies of organic chemistry arose in ancient times, for example, alcoholic and acetic fermentation, the use of organic indigo and alizarin dyes, leather tanning processes, etc. For a long time, chemists could only isolate and analyze organic compounds, but could not obtain them artificially, as a result, the belief arose that organic compounds can only be obtained with the help of living organisms. Starting from the second half of the 19th century. methods of organic synthesis began to develop intensively, which made it possible to gradually overcome the established delusion. For the first time, the synthesis of organic compounds in the laboratory was carried out by F. Wöhler ne (in the period 18241828), during the hydrolysis of cyanogen, he obtained oxalic acid, which had previously been isolated from plants, and by heating ammonium cyanate due to the rearrangement of the molecule ( cm. ISOMERIA) received urea, a waste product of living organisms (Fig. 1).
Rice. one. THE FIRST SYNTHESES OF ORGANIC COMPOUNDS
Now many of the compounds present in living organisms can be obtained in the laboratory, in addition, chemists are constantly obtaining organic compounds that are not found in living nature.
The formation of organic chemistry as an independent science took place in the middle of the 19th century, when, thanks to the efforts of chemical scientists, ideas about the structure of organic compounds began to form. The most prominent role was played by the works of E. Frankland (he defined the concept of valency), F. Kekule (established the tetravalence of carbon and the structure of benzene), A. Cooper (proposed the symbol of the valence line that is still used today, connecting atoms when depicting structural formulas), A.M. Butlerov (created the theory of chemical structure, which is based on the position according to which the properties of a compound are determined not only by its composition, but also by the order in which the atoms are connected).
The next important stage in the development of organic chemistry is associated with the work of J. van't Hoff, who changed the very way of thinking of chemists, proposing to move from a flat image of structural formulas to the spatial arrangement of atoms in a molecule, as a result, chemists began to consider molecules as volumetric bodies.
Ideas about the nature of chemical bonds in organic compounds were first formulated by G. Lewis, who suggested that atoms in a molecule are connected by electrons: a pair of generalized electrons creates a simple bond, and two or three pairs form, respectively, a double and triple bond. Considering the distribution of electron density in molecules (for example, its displacement under the influence of electronegative atoms O, Cl, etc.), chemists were able to explain the reactivity of many compounds, i.e. the possibility of their participation in certain reactions.
Accounting for the properties of the electron, determined by quantum mechanics, led to the development of quantum chemistry, using the concept of molecular orbitals. Now quantum chemistry, which has shown its predictive power in many examples, is successfully collaborating with experimental organic chemistry.
A small group of carbon compounds are not classified as organic: carbonic acid and its salts (carbonates), hydrocyanic acid HCN and its salts (cyanides), metal carbides and some other carbon compounds that are studied by inorganic chemistry.
The main feature of organic chemistry is the exceptional variety of compounds that arose due to the ability of carbon atoms to combine with each other in an almost unlimited number, forming molecules in the form of chains and cycles. Even greater diversity is achieved by including oxygen, nitrogen, etc. atoms between carbon atoms. The phenomenon of isomerism, due to which molecules with the same composition can have a different structure, further increases the variety of organic compounds. More than 10 million organic compounds are now known, and their number is increasing by 200-300 thousand annually.
Classification of organic compounds. Hydrocarbons are taken as the basis for the classification, they are considered basic compounds in organic chemistry. All other organic compounds are considered as their derivatives.When systematizing hydrocarbons, the structure of the carbon skeleton and the type of bonds connecting carbon atoms are taken into account.
I. ALIPHATIC (aleiphatos. Greek oil) hydrocarbons are linear or branched chains and do not contain cyclic fragments, they form two large groups.
1. Saturated or saturated hydrocarbons (so named because they are not capable of attaching anything) are chains of carbon atoms connected by simple bonds and surrounded by hydrogen atoms (Fig. 1). In the case when the chain has branches, a prefix is added to the name iso. The simplest saturated hydrocarbon is methane; a series of these compounds begins with it.
Rice. 2. SATURATED HYDROCARBONS
The main sources of saturated hydrocarbons are oil and natural gas. The reactivity of saturated hydrocarbons is very low, they can only react with the most aggressive substances, such as halogens or nitric acid. When saturated hydrocarbons are heated above 450 ° C without air access, C-C bonds are broken and compounds with a shortened carbon chain are formed. High-temperature exposure in the presence of oxygen leads to their complete combustion to CO 2 and water, which allows them to be effectively used as a gaseous (methane propane) or liquid motor fuel (octane).
When one or more hydrogen atoms are replaced by some functional (i.e., capable of subsequent transformations) group, the corresponding hydrocarbon derivatives are formed. Compounds containing the C-OH group are called alcohols, HC \u003d O aldehydes, COOH carboxylic acids (the word "carboxylic" is added to distinguish them from ordinary mineral acids, for example, hydrochloric or sulfuric). A compound may simultaneously contain various functional groups, for example, COOH and NH 2, such compounds are called amino acids. The introduction of halogens or nitro groups into the hydrocarbon composition leads, respectively, to halogen or nitro derivatives (Fig. 3).
Rice. four. EXAMPLES OF SATURATED HYDROCARBONS with functional groups
All hydrocarbon derivatives shown form large groups of organic compounds: alcohols, aldehydes, acids, halogen derivatives, etc. Since the hydrocarbon part of the molecule has a very low reactivity, the chemical behavior of such compounds is determined by the chemical properties of the functional groups OH, -COOH, -Cl, -NO 2, etc.
2. Unsaturated hydrocarbons have the same variants of the main chain structure as saturated hydrocarbons, but contain double or triple bonds between carbon atoms (Fig. 6). The simplest unsaturated hydrocarbon is ethylene.
Rice. 6. UNSATURATED HYDROCARBONS
The most typical for unsaturated hydrocarbons is the addition by a multiple bond (Fig. 8), which makes it possible to synthesize various organic compounds on their basis.
Rice. eight. ADDING REAGENTS to unsaturated compounds by multiple bond
Another important property of compounds with double bonds is their ability to polymerize (Fig. 9.), Double bonds are opened in this case, resulting in the formation of long hydrocarbon chains.
Rice. 9. POLYMERIZATION OF ETHYLENE
The introduction of the previously mentioned functional groups into the composition of unsaturated hydrocarbons, just as in the case of saturated hydrocarbons, leads to the corresponding derivatives, which also form large groups of the corresponding organic compounds - unsaturated alcohols, aldehydes, etc. (Fig. 10).
Rice. ten. UNSATURATED HYDROCARBONS with functional groups
For the compounds shown, simplified names are given, the exact position in the molecule of multiple bonds and functional groups is indicated in the name of the compound, which is compiled according to specially developed rules.
The chemical behavior of such compounds is determined both by the properties of multiple bonds and by the properties of functional groups.
II. CARBOCYCLIC HYDROCARBONS contain cyclic fragments formed only by carbon atoms. They form two large groups.
1. Alicyclic (i.e. both aliphatic and cyclic at the same time) hydrocarbons. In these compounds, cyclic fragments can contain both single and multiple bonds, in addition, compounds can contain several cyclic fragments, the prefix “cyclo” is added to the name of these compounds, the simplest alicyclic compound is cyclopropane (Fig. 12).
Rice. 12. ALICYCLIC HYDROCARBONS
In addition to those shown above, there are other options for connecting cyclic fragments, for example, they can have one common atom (the so-called spirocyclic compounds), or they can be connected in such a way that two or more atoms are common to both cycles (bicyclic compounds), by combining three and more cycles, the formation of hydrocarbon frameworks is also possible (Fig. 14).
Rice. fourteen. OPTIONS FOR CONNECTING CYCLES in alicyclic compounds: spirocycles, bicycles and frameworks. The name of spiro- and bicyclic compounds indicate that aliphatic hydrocarbon that contains the same total number of carbon atoms, for example, the spirocycle shown in the figure contains eight carbon atoms, so its name is built on the basis of the word "octane". In adamantane, the atoms are arranged in the same way as in the crystal lattice of diamond, which determined its name ( Greek adamantos diamond)
Many mono- and bicyclic alicyclic hydrocarbons, as well as adamantane derivatives, are part of oil, their general name is naphthenes.
In terms of chemical properties, alicyclic hydrocarbons are close to the corresponding aliphatic compounds, however, they have an additional property associated with their cyclic structure: small cycles (36-membered) are able to open by adding some reagents (Fig. 15).
Rice. fifteen. REACTIONS OF ALICYCLIC HYDROCARBONS, proceeding with the opening of the cycle
The introduction of various functional groups into the composition of alicyclic hydrocarbons leads to the corresponding derivatives alcohols, ketones, etc. (Fig. 16).
Rice. 16. ALICYCLIC HYDROCARBONS with functional groups
2. The second large group of carbocyclic compounds is formed by aromatic hydrocarbons of the benzene type, i.e. containing one or more benzene rings in their composition (there are also aromatic compounds of the non-benzene type ( cm. AROMATICITY). However, they may also contain fragments of saturated or unsaturated hydrocarbon chains (Fig. 18).
Rice. eighteen. AROMATIC HYDROCARBONS.
There is a group of compounds in which benzene rings seem to be soldered together, these are the so-called condensed aromatic compounds (Fig. 20).
Rice. twenty. CONDENSED AROMATIC COMPOUNDS
Many aromatic compounds, including condensed ones (naphthalene and its derivatives), are part of oil, the second source of these compounds is coal tar.
Benzene cycles are not characterized by addition reactions that take place with great difficulty and under harsh conditions; the most typical reactions for them are the substitution reactions of hydrogen atoms (Fig. 21).
Rice. 21. SUBSTITUTION REACTIONS hydrogen atoms in the aromatic nucleus.
In addition to functional groups (halogen, nitro and acetyl groups) attached to the benzene nucleus (Fig. 21), other groups can also be introduced, resulting in the corresponding derivatives of aromatic compounds (Fig. 22), which form large classes of organic compounds - phenols, aromatic amines, etc.
Rice. 22. AROMATIC COMPOUNDS with functional groups. Compounds in which the ne-OH group is attached to a carbon atom in the aromatic nucleus are called phenols, in contrast to aliphatic compounds, where such compounds are called alcohols.
III. HETEROCYCLIC HYDROCARBONS contain in the ring (in addition to carbon atoms) various heteroatoms: O, N, S. Rings can be of various sizes, contain both single and multiple bonds, as well as hydrocarbon substituents attached to the heterocycle. There are options when the heterocycle is “soldered” to the benzene ring (Fig. 24).
Rice. 24. HETEROCYCLIC COMPOUNDS. Their names have developed historically, for example, furan got its name from furan aldehyde furfural, obtained from bran ( lat. furfur bran). For all the compounds shown, the addition reactions are difficult, and the substitution reactions are quite easy. Thus, these are aromatic compounds of the non-benzene type.
The diversity of compounds of this class increases further due to the fact that the heterocycle can contain two or more heteroatoms in the cycle (Fig. 26).
Rice. 26. HETEROCYCLES with two or more heteroatoms.
Just like the previously considered aliphatic, alicyclic and aromatic hydrocarbons, heterocycles can contain various functional groups (-OH, -COOH, -NH 2, etc.), and in some cases the heteroatom in the cycle can also be considered as functional group, since it is able to take part in the corresponding transformations (Fig. 27).
Rice. 27. HETEROATOM N as a functional group. In the name of the last compound, the letter "N" indicates to which atom the methyl group is attached.
Reactions of organic chemistry. In contrast to the reactions of inorganic chemistry, where ions interact at a high rate (sometimes instantaneously), molecules containing covalent bonds usually participate in the reactions of organic compounds. As a result, all interactions proceed much more slowly than in the case of ionic compounds (sometimes tens of hours), often at elevated temperatures and in the presence of substances accelerating the process - catalysts. Many reactions proceed through intermediate stages or in several parallel directions, which leads to a marked decrease in the yield of the desired compound. Therefore, when describing reactions, instead of equations with numerical coefficients (which is traditionally accepted in inorganic chemistry), reaction schemes are often used without specifying stoichiometric ratios.The name of large classes of organic reactions is often associated with the chemical nature of the active reagent or with the type of organic group introduced into the compound:
a) halogenation introduction of a halogen atom (Fig. 8, first reaction scheme),
b) hydrochlorination, i.e. exposure to HCl (Fig. 8, second reaction scheme)
c) nitration introduction of the NO 2 nitro group (Fig. 21, second direction of the reaction)
d) metallization introduction of a metal atom (Fig. 27, first stage)
a) alkylation introduction of an alkyl group (Fig. 27, second stage)
b) acylation introduction of the acyl group RC(O)- (Fig. 27, second stage)
Sometimes the name of the reaction indicates the features of the rearrangement of the molecule, for example, cyclization ring formation, decyclization ring opening (Fig. 15).
A large class is formed by condensation reactions ( lat. condensatio - compaction, thickening), in which new C-C bonds are formed with the simultaneous formation of easily removed inorganic or organic compounds. Condensation accompanied by the release of water is called dehydration. Condensation processes can also take place intramolecularly, that is, within a single molecule (Fig. 28).
Rice. 28. CONDENSATION REACTIONS
In the condensation of benzene (Fig. 28), the role of functional groups is played by C-H fragments.
The classification of organic reactions is not strict, for example, shown in Fig. 28 The intramolecular condensation of maleic acid can also be attributed to cyclization reactions, and the condensation of benzene to dehydrogenation.
There are intramolecular reactions that are somewhat different from condensation processes, when a fragment (molecule) is split off in the form of an easily removable compound without the obvious participation of functional groups. Such reactions are called elimination ( lat. eliminare expel), while new connections are formed (Fig. 29).
Rice. 29. ELIMINATION REACTIONS
Variants are possible when several types of transformations are jointly realized, which is shown below by the example of a compound in which different types of processes occur upon heating. During thermal condensation of mucic acid (Fig. 30), intramolecular dehydration and subsequent elimination of CO 2 take place.
Rice. thirty. CONVERSION OF MUCKIC ACID(obtained from acorn syrup) into pyromucous acid, so named because it is obtained by heating mucus. Pyrosmucus acid is a heterocyclic compound furan with an attached functional (carboxyl) group. During the reaction, C-O, C-H bonds are broken and new C-H and C-C bonds are formed.
There are reactions in which the rearrangement of the molecule occurs without changing the composition ( cm. ISOMERIZATION).
Research methods in organic chemistry. Modern organic chemistry, in addition to elemental analysis, uses many physical research methods. The most complex mixtures of substances are separated into constituent components using chromatography based on the movement of solutions or vapors of substances through a layer of sorbent. Infrared spectroscopy transmission of infrared (thermal) rays through a solution or through a thin layer of a substance allows you to establish the presence of certain fragments of a molecule in a substance, for example, groups C 6 H 5, C \u003d O, NH 2, etc.Ultraviolet spectroscopy, also called electronic, carries information about the electronic state of the molecule; it is sensitive to the presence of multiple bonds and aromatic fragments in the substance. Analysis of crystalline substances using X-rays (X-ray diffraction analysis) gives a three-dimensional picture of the arrangement of atoms in a molecule, similar to those shown in the above animated figures, in other words, it allows you to see the structure of the molecule with your own eyes.
The spectral method nuclear magnetic resonance, based on the resonant interaction of the magnetic moments of nuclei with an external magnetic field, makes it possible to distinguish atoms of one element, for example, hydrogen, located in different fragments of the molecule (in the hydrocarbon skeleton, in the hydroxyl, carboxyl or amino group), as well as determine their proportion. A similar analysis is also possible for the nuclei C, N, F, etc. All these modern physical methods have led to intensive research in organic chemistry - it has become possible to quickly solve those problems that previously took many years.
Some sections of organic chemistry have emerged as large independent areas, for example, the chemistry of natural substances, drugs, dyes, and the chemistry of polymers. In the middle of the 20th century the chemistry of organoelement compounds began to develop as an independent discipline that studies substances containing a S-E bond, where the symbol E denotes any element (except carbon, hydrogen, oxygen, nitrogen and halogens). Great progress has been made in biochemistry, which studies the synthesis and transformations of organic substances occurring in living organisms. The development of all these areas is based on the general laws of organic chemistry.
Modern industrial organic synthesis includes a wide range of different processes these are, first of all, large-scale production oil and gas processing and the production of motor fuels, solvents, coolants, lubricating oils, in addition, the synthesis of polymers, synthetic fibers, various resins for coatings, adhesives and enamels. Small-tonnage industries include the production of medicines, vitamins, dyes, food additives and fragrances.
Mikhail Levitsky
LITERATURE Karrer P. Organic chemistry course, per. from German, GNTI Himlit, L., 1962Cram D, Hammond J. Organic chemistry, per. from English, Mir, M., 1964
"Structural chemistry" is a conditional term. We are talking about the level of development of chemical knowledge, in which a special role is played by the concept of "the structure of a chemical compound", as well as the structure of molecules.
F. Kekule connected the structure of molecules with the concept of the valency of an element or the number of units of its affinity. On this basis, the structural formulas of organic chemistry arose and the term "organic synthesis" appeared.
At this time, aniline dyes were synthesized on the basis of the simplest carbohydrates. Then new substances were taught (drugs, explosives, etc.).
The defining idea of the concept of chemical structure was the theory of chemical structure by A.M. Butlerov (1861). A characteristic, non-classical concept was the idea of isomerism and its relationship with the structure of substances and the typology of molecules. Butlerov was the first to clearly formulate the definition of chemical structure as a way of chemical bonds in a molecule and in chemical compounds. He also introduced the concept of the energy intensity of chemical bonds. Thus, with the help of structural theory, the systematics of organic compounds developed.
The introduction by J. van't Hoff (1874) of stereoscopic structural models was also important.
Modern structural chemistry uses the cooperative interaction of classical chemical models of matter and the typology of molecules (atomic-molecular, geometric both in two and three dimensions, with a non-classical electronic model) and relies on the interaction of classical and quantum chemistry. Quantum-mechanical ideas about the types of chemical bonds in intersection with the angular geometry between them and the geometry of the electron density distribution are of particular importance. A special role in the formation and development of structural chemistry was played by physical methods for studying the structure of organic and inorganic compounds and, above all, X-ray diffraction analysis, optical, X-ray and electron spectroscopy, neutron diffraction, etc.
According to modern concepts, the structure of molecules is the spatial and energy ordering of a quantum mechanical system consisting of atomic nuclei and electrons. Organic compounds are structural formations from organic molecules. The main role in the structure of organic compounds belongs to carbon, which builds complex cyclic, branched, linear chains, involving other chemical elements in them, primarily hydrogen.
The structure of inorganic compounds is interconnected with the chemistry of solid and liquid crystal bodies, which intersects with quantum physics. The structure is given by the quantum mechanical interaction of atoms in inorganic molecules, atoms of chemical elements and (or) inorganic molecules in inorganic compounds.
S. I. LEVCHENKOV
BRIEF OUTLINE OF THE HISTORY OF CHEMISTRY
Textbook for students of the Faculty of Chemistry of the Russian State University
5.2. STRUCTURAL CHEMISTRY
The emergence of structural chemistry
In the first half of the 19th century, a fundamentally new concept of chemistry was born - structural chemistry, based on the premise that the properties of a substance are determined not only by its composition, but also by its structure, i.e. the order of connection of atoms and their spatial arrangement. The very first structural representations necessarily arise together with Dalton's atomism. Developing ideas about how to combine "simple atoms" into "complex atoms", Dalton pursued only one goal - to create a theory to explain the empirically discovered stoichiometric laws. Nevertheless, the symbols of chemical elements chosen by Dalton themselves suggested, when depicting complex atoms, the choice of a certain order of connecting atoms to each other. However, the question of the order of connection of atoms was postponed for quite a long time, since chemists did not have any facts indicating the influence of the method of connection of atoms on the properties of a substance. The chemical symbolism of Berzelius made it possible to circumvent this issue, although Berzelius's electrochemical theory still considers some problems ("adhesion forces", "juxtaposition", etc.), which later became fundamental questions of structural chemistry.
The emergence of structural chemistry should apparently be associated with the discovery of the phenomenon of isomerism. In 1825, Johann Justus von Liebig discovered that the elemental composition of fulminic acid corresponds exactly to the composition of cyanic acid, which Friedrich Wöhler had obtained the year before. Repeated analyzes carried out by Wöhler and Liebig unambiguously established the existence of substances that are identical in composition but differ in properties. Continuing work with cyanic acid, Wöhler, by evaporating a solution of ammonium isocyanate, obtained in 1828 an isomeric organic substance, urea. In 1830, J. Ya. Berzelius found that grape and tartaric acids also have the same composition, but differ in properties. Berzelius proposed the term for the discovered phenomenon "isomerism"(from the Greek ισοζ μερον - equal measure). It soon became clear that this phenomenon is extremely common in organic chemistry. The composition of organic substances includes a relatively small number of elements - carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus (the so-called organogenic elements) - with a huge variety of properties. That is why, throughout almost the entire 19th century, structural concepts were in demand, primarily in organic chemistry. It should be emphasized, however, that the concepts of "structural chemistry" and "organic chemistry" should not be categorically equated.
The solution to the problem of the structure of organic substances was based on the ideas of Berzelius about radicals- polar groups of atoms (not containing oxygen) that can pass from one substance to another without change. Back in 1810-1811. Joseph Louis Gay-Lussac and Louis Jacques Tenard showed that cyanide radical CN behaves like a single atom (moreover, very similar to a chlorine or bromine atom). The concept of radicals, which is in good agreement with the electrochemical theory of Berzelius, made it possible to extend this theory to organic substances.
Creation of theories of structural chemistry
Theory of complex radicals arose and began to be actively developed by many chemists after the work of Liebig and Wöhler "On the radical of benzoic acid", published in 1832. Liebig and Wöhler showed that the grouping of atoms C 14 H 10 O 2 (the correct gross formula is C 7 H 5 O) in the chain of transformations of benzoic acid (benzaldehyde - benzoic acid - benzoyl chloride - benzoyl cyanide) behaves as a whole - like a kind of "organic atom". The theory of complex radicals quickly gained almost universal acceptance. In 1837, in the generalizing article "On the Current State of Organic Chemistry", one of the authors of which was Liebig, it was argued that the study of complex radicals is the main task of organic chemistry, since "cyan, amide, benzoyl, ammonia radicals, fats, alcohol and its derivatives form the true elements of organic nature, while the simplest constituents - carbon, hydrogen, oxygen and nitrogen - are found only when organic matter is destroyed. The number of described radicals increased rapidly. The theory of complex radicals proceeded from the assumption that radicals are capable of independent existence, although chemists have not been able to isolate them. Berzelius wrote about this: "The reason why we cannot isolate the radicals ... is not that they do not exist, but that they combine too quickly."
coordination chemistry
For quite a long time, the theory of valency was applied mainly to organic compounds. However, rather soon, structural concepts were also in demand in the chemistry of complex compounds. The theoretical concepts of this branch of inorganic chemistry were formed on the basis of studying the properties of complexes obtained by the interaction of transition metal salts with ammonia. The first step towards coordination chemistry was ammonium hypothesis Thomas Graham (1840), who saw an analogy between the interaction of ammonia with acids and with metal salts; according to this hypothesis, the metal took the place of one of the hydrogen atoms in the ammonium ion. Graham's hypothesis was developed in 1851 by Hoffmann, who suggested that the hydrogen atom in the ammonium radical can be replaced by another ammonium radical.
The next step was chain theory, proposed in 1869 by Christian Wilhelm Blomstrand and improved by Sophus Mads Jørgensen. In the Blomstrand-Jørgensen theory, for some elements, a valency higher than usual was allowed, as well as the possibility of the formation of chains by atoms of nitrogen, oxygen and other elements. The experimentally established difference between the acid residues that make up the complex was explained by the different way of their binding - directly to the metal or to the end of the chain. For example, for ammonia complexes of the composition CoCl 3 6NH 3, CoCl 3 5NH 3 and CoCl 3 4NH 3, from solutions of which three, two and one equivalent of chlorine are deposited with silver nitrate, respectively, Jörgensen assumed the following structure:
However, the Blomstrand-Jörgensen theory could not explain, for example, the existence of two isomeric complexes of the composition CoCl 3 ·4NH 3 - praseosalts (green) and violeosalts (violet).
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
|
Functional groups |
Connection class |
|
|
designation |
title |
|
|
F, -Cl, -Br, -I |
halogen derivatives of hydrocarbons |
|
|
hydroxyl |
alcohols, phenols |
|
|
carbonyl |
aldehydes, ketones |
|
|
carboxyl |
carboxylic acids |
|
|
amino group |
||
|
nitro group |
nitro compounds |
|
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, -an 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.
Organic chemistry is the science of organic compounds and their transformations. The term "organic chemistry" was introduced by the Swedish scientist J. Berzelius at the beginning of the 19th century. Prior to this, substances were classified according to the source of their production. Therefore, in the XVIII century. There were three types of chemistry: "plant", "animal" and "mineral". At the end of the XVIII century. the French chemist A. Lavoisier showed that substances obtained from plant and animal organisms (hence their name "organic compounds"), unlike mineral compounds, contain only a few elements: carbon, hydrogen, oxygen, nitrogen, and sometimes phosphorus and sulfur. Since carbon is invariably present in all organic compounds, organic chemistry has been occupied since the middle of the 19th century. often referred to as the chemistry of carbon compounds.
The ability of carbon atoms to form long unbranched and branched chains, as well as rings and attach other elements or their groups to them, is the reason for the diversity of organic compounds and the fact that they greatly outnumber inorganic compounds in number. About 7 million organic compounds are now known, and about 200 thousand inorganic compounds.
After the works of A. Lavoisier and until the middle of the XIX century. chemists conducted an intensive search for new substances in natural products and developed new methods for their transformation. Particular attention was paid to the determination of the elemental composition of compounds, the derivation of their molecular formulas, and the determination of the dependence of the properties of compounds on their composition. It turned out that some compounds, having the same composition, differ in their properties. Such compounds were called isomers (see Isomerism). It has been observed that many compounds in chemical reactions exchange groups of elements that remain unchanged. These groups were called radicals, and the doctrine that tried to present organic compounds as consisting of such radicals was called the theory of radicals. In the 40-50s. 19th century attempts were made to classify organic compounds according to the type of inorganic ones (for example, ethyl alcohol C2H5-O-H and diethyl ether C2H5-O-C2H5 were assigned to the type of water H-O-H). However, all these theories, as well as the determination of the elemental composition and molecular weight of organic compounds, have not yet been based on a solid foundation of a sufficiently developed atomic and molecular theory. Therefore, in organic chemistry there was a discrepancy in the methods of recording the composition of substances, and even such a simple compound as acetic acid was represented by different empirical formulas: C4H404, C8H804, CrH402, of which only the last one was correct.
Only after the creation of the theory of chemical structure by the Russian scientist A. M. Butlerov (1861) did organic chemistry receive a solid scientific basis, which ensured its rapid development in the future. The prerequisites for its creation were the successes in the development of atomic and molecular theory, ideas about valency and chemical bonding in the 50s. 19th century This theory made it possible to predict the existence of new compounds and their properties. Scientists have begun the systematic chemical synthesis of organic compounds predicted by science that do not occur in nature. Thus, organic chemistry has become to a large extent the chemistry of artificial compounds.
In the first half of the XIX century. Organic chemists were mainly engaged in the synthesis and study of alcohols, aldehydes, acids, and some other alicyclic and benzoic compounds (see Aliphatic compounds; Alicyclic compounds). From substances not found in nature, derivatives of chlorine, iodine, and bromine were synthesized, as well as the first organometallic compounds (see Organoelement Compounds). Coal tar has become a new source of organic compounds. Benzene, naphthalene, phenol and other benzenoid compounds, as well as heterocyclic compounds - quinoline, pyridine, were isolated from it.
In the second half of the XIX century. hydrocarbons, alcohols, acids with a branched carbon chain were synthesized, the study of the structure and synthesis of compounds important in practical terms (indigo, isoprene, sugars) began. The synthesis of sugars (see Carbohydrates) and many other compounds became possible after the advent of stereochemistry, which continued the development of the theory of chemical structure. Organic chemistry of the first half of the 19th century. was closely associated with pharmacy - the science of medicinal substances.
In the second half of the XIX century. there has been a strong alliance between organic chemistry and industry, primarily aniline dye. Chemists were tasked with deciphering the structure of known natural dyes (alizarin, indigo, etc.), creating new dyes, and developing technically acceptable methods for their synthesis. Yes, in the 70s and 80s. 19th century applied organic chemistry.
Late XIX - early XX century. were marked by the creation of new directions in the development of organic chemistry. On an industrial scale, the richest source of organic compounds, oil, began to be used, and the rapid development of the chemistry of alicyclic compounds and the chemistry of hydrocarbons in general (see Petrochemistry) was associated with this. Practically important catalytic methods for the transformation of organic compounds appeared, created by P. Sabatier in France, V. N. Ipatiev, and later N. D. Zelinsky in Russia (see Catalysis). The theory of chemical structure has deepened significantly as a result of the discovery of the electron and the creation of electronic ideas about the structure of atoms and molecules. Powerful methods of physicochemical and physical studies of molecules were discovered and developed, primarily X-ray diffraction analysis. This made it possible to find out the structure, and therefore, to understand the properties and facilitate the synthesis of a huge number of organs! ical connections.
From the beginning of the 30s. 20th century in connection with the emergence of quantum mechanics, computational methods appeared that made it possible to draw conclusions about the structure and properties of organic compounds by calculation (see Quantum chemistry).
Among the new areas of chemical science is the chemistry of organic derivatives of fluorine, which have gained great practical importance. In the 50s. 20th century the chemistry of price compounds arose (ferrocene, etc.), which is a connecting link between organic and inorganic chemistry. The use of isotopes has firmly entered the practice of organic chemists. As early as the beginning of the 20th century. freely existing organic radicals were discovered (see Free radicals), and subsequently the chemistry of non-polyvalent organic compounds was created - carbonium ions, carbanions, radical ions, molecular ions (see Ions). In the 60s. completely new types of organic compounds were synthesized, such as catenanes, in which individual cyclic molecules are linked to each other, similar to the five intertwined Olympic rings.
Organic chemistry in the XX century. acquired great practical importance, especially for oil refining, polymer synthesis, synthesis and study of physiologically active substances. As a result, such areas as petrochemistry, polymer chemistry, and bioorganic chemistry emerged from organic chemistry into independent disciplines.
Modern organic chemistry has a complex structure. Its core is preparative organic chemistry, which deals with the isolation from natural products and the artificial preparation of individual organic compounds, as well as the creation of new methods for their preparation. It is impossible to solve these problems without relying on analytical chemistry, which makes it possible to judge the degree of purification, homogeneity (homogeneity) and individuality of organic compounds, providing data on their composition and structure in an isolated state, as well as when they act as initial substances, intermediate and end products of the reaction. For this purpose, analytical chemistry uses various chemical, physicochemical and physical research methods. A conscious approach to solving the problems facing preparative and analytical organic chemistry is provided by their reliance on theoretical organic chemistry. The subject of this science is the further development of the theory of structure, as well as the formulation of relationships between the composition and structure of organic compounds and their properties, between the conditions for the occurrence of organic reactions and their speed and the achievement of chemical equilibrium. The objects of theoretical organic chemistry can be both non-reacting compounds and compounds during their transformations, as well as intermediate, unstable formations that occur during reactions.
Such a structure of organic chemistry was formed under the influence of various factors, the most important of which were and remain the demands of practice. It is precisely this that explains, for example, the fact that in modern organic chemistry the chemistry of heterocyclic compounds is developing rapidly, closely related to such an applied direction as the chemistry of synthetic and natural drugs.
