Organic compounds. Classes of organic compounds

Organic compounds are most often classified according to two criteria - by the structure of the carbon skeleton of the molecule or by the presence of a functional group in the molecule of the organic compound.

The classification of organic molecules according to the structure of the carbon skeleton can be presented in the form of a diagram:

Acyclic compounds are compounds with an open carbon chain. They are based on aliphatic compounds (from the Greek aleiphatos – oil, fat, resin ) – hydrocarbons and their derivatives, the carbon atoms of which are interconnected in open, unbranched or branched chains.

Cyclic compounds are compounds containing a closed circuit. Carbocyclic compounds in the ring contain only carbon atoms, heterocyclic compounds in the ring, in addition to carbon atoms, contain one or more heteroatoms (N, O, S atoms, etc.).

Depending on the nature of the functional group, hydrocarbon derivatives are divided into classes of organic compounds. Functional group is an atom or group of atoms, usually of a non-hydrocarbon nature, that determine the typical chemical properties of a compound and its membership in a particular class of organic compounds. The functional group in unsaturated molecules is double or triple bonds.

2.2 Principles of chemical nomenclature – systematic nomenclature iupak. Substitute and radical functional nomenclature

Nomenclature is a system of rules that allows you to give an unambiguous name to a compound. At the core replacement nomenclature lies in the choice of the original structure. The name is constructed as a complex word consisting of a root (the name of the parent structure), suffixes reflecting the degree of unsaturation, prefixes and endings indicating the nature, number and position of substituents.

The parent structure (generic hydride) is an unbranched acyclic or cyclic compound in the structure of which only hydrogen atoms are attached to the carbon atoms or other elements.

A substituent is a functional (characteristic) group or hydrocarbon radical associated with the parent structure.

A characteristic group is a functional group associated with or partially included in the parent structure.

Main group– a characteristic group introduced when forming names in the form of an ending at the end of the name when forming names using functional groups.

Substituents associated with the parent structure are divided into two types. Substitutes of the 1st type- hydrocarbon radicals and non-hydrocarbon characteristic groups indicated in the name only in prefixes.

Substitutes of the 2nd type- characteristic groups indicated in the name depending on the precedence either in the prefix or in the ending. In the table below, the seniority of the deputies decreases from top to bottom.

*- The carbon atom of the functional group is part of the parent structure.

The name of an organic compound is composed in a certain sequence.

Determine the main characteristic group, if present. The main group is introduced as an ending in the name of the compound.

Determine the parent structure of the compound. As a rule, the parent structure is taken to be a ring in carbocyclic and heterocyclic compounds or the main carbon chain in acyclic compounds. The main carbon chain is selected taking into account the following criteria: 1) the maximum number of characteristic groups of type 2, designated by both prefixes and suffixes; 2) the maximum number of multiple bonds; 3) maximum chain length; 4) the maximum number of characteristic groups of type 1, designated only by prefixes. Each subsequent criterion is used if the previous criterion does not lead to an unambiguous choice of the parent structure.

The parent structure is numbered in such a way that the highest characteristic group receives the lowest number. If there are several identical senior functional groups, the parent structure is numbered in such a way that the substituents receive the lowest numbers.

The parent structure is called, in the name of which the senior characteristic group is reflected by the ending. The saturation or unsaturation of the parent structure is reflected by suffixes - an,-en,-in, which are indicated before the ending given by the senior characteristic group.

They give names to the substituents, which are reflected in the name of the compound as prefixes and are listed in a single alphabetical order. Multiplying prefixes in a single alphabetical order are not taken into account. The position of each substituent and each multiple bond is indicated by numbers corresponding to the number of the carbon atom to which the substituent is bonded (for a multiple bond, the lower carbon atom number is indicated). Numbers are placed before prefixes and after suffixes or endings. The number of identical substituents is reflected in the name using multiplying prefixes di, tri, tetra, penta and etc.

The connection name is formed according to the following scheme:

Examples of names according to IUPAC substitutive nomenclature:

Radical functional nomenclature has limited use. It is mainly used to name simple mono- and bifunctional compounds.

If the molecule contains one functional group, then the name of the compound is formed from the names of the hydrocarbon radical and the characteristic group:

In the case of more complex compounds, a parent structure with a trivial name is chosen. The arrangement of substituents, which are indicated in prefixes, is made using numbers, Greek letters or prefixes ortho-, meta-, para-.

2.3 Conformations of open-chain compounds

Compounds that have the same qualitative and quantitative composition, the same chemical structure, but differ in the spatial arrangement of atoms and groups of atoms are called stereoisomers. Conformation is the spatial arrangement of atoms in a molecule as a result of the rotation of atoms or groups of atoms around one or more single bonds. Stereoisomers that transform into each other as a result of rotation around a single bond are called conformational isomers. To depict them on a plane, stereochemical formulas or Newman's projection formulas are most often used.

In stereochemical formulas, bonds lying in the plane of the paper are represented by a dash; connections directed towards the observer are indicated by a thick wedge; connections located behind the plane (going away from the observer) are indicated by a shaded wedge. The stereochemical formulas of methane and ethane can be represented as follows:

To obtain Newman's projection formulas, a C-C bond is selected in a molecule; the carbon atom farthest from the observer is designated by a circle, the carbon atom and C-C bond closest to the observer is designated by a dot. The three other bonds of carbon atoms on the plane are displayed at an angle of 120 relative to each other. The stereochemical formulas of ethane can be represented in the form of Newman's projection formulas as follows:

Rotation relative to single bonds in a methane molecule does not lead to a change in the spatial position of atoms in the molecule. But in the ethane molecule, as a result of rotation around the single C-C bond, the arrangement of atoms in space changes, i.e. conformational isomers arise. The minimum angle of rotation (torsion angle) is considered to be an angle of 60. For ethane, thus, two conformations arise, transforming into each other with successive rotations of 60. These conformations differ in energy. The conformation in which the atoms (substituents) are in the closest position, since the bonds obscure each other, is called obscured. The conformation in which the atoms (substituents) are as far apart from each other as possible is called inhibited (anti-conformation). For ethane, the difference in conformation energies is small and equal to 11.7 kJ/mol, which is comparable to the energy of thermal motion of ethane molecules. Such a small difference in the energies of the conformational isomers of ethane does not allow them to be isolated and identified at ordinary temperatures. The eclipsed conformation has higher energy, which is due to the appearance torsional stresses (Pitzer stress) - in interactions caused by the repulsion of opposing bonds. In the inhibited conformation, the bonds are maximally distant and the interactions between them are minimal, which determines the minimum energy of the conformation.

In butane, when rotated relative to the bond between the second and third carbon atoms, an additional beveled conformation ( gauche-conformation). In addition, the eclipsed conformations of butane differ energetically.

The eclipsed (initial) conformation of butane is characterized by maximum energy, which is due to the presence torsion And van der Waals stress. Van der Waals stresses in this conformation arise due to the mutual repulsion of bulky (compared to the H atom) methyl groups that are close together. This interaction increases the energy of the conformation, making it energetically unfavorable. When turning 60 it occurs beveled a conformation in which there are no torsional stresses (the bonds do not obscure each other), and van der Waals stresses are significantly reduced due to the distance of the methyl groups from each other, therefore the energy of the gauche conformation is 22 kJ/mol less than the energy of the eclipsed conformation. With the next rotation by 60, an eclipsed conformation appears, in which, however, only torsional stresses take place. No van der Waals stresses arise between the H atom and the CH 3 group due to the small size of the H atom. The energy of this conformation is 7.5 kJ/mol less than the energy of the original eclipsed conformation. The next rotation by 60 leads to the appearance of a inhibited conformation in which there are no torsion and van der Waals stresses, since the bonds do not obscure each other, and the bulky methyl groups are maximally distant from each other. The energy of the inhibited conformation is minimal, it is 25.5 kJ/mol less than the energy of the initial eclipsed conformation, and 3.5 kJ/mol less than the energy of the oblique conformation. Subsequent rotations result in the eclipsed, skewed, and original eclipsed conformations. Under normal conditions, most butane molecules are in the form of a mixture of gauche and anti-conformers.

When moving from inorganic to organic chemistry, one can see how the classification of organic and inorganic substances differs. The world of organic compounds has a variety and many options. The classification of organic substances not only helps to understand this abundance, but also provides a clear scientific basis for their study.

The theory of chemical structure was chosen as the basis for class distribution. The basis of the study of organics is work with the largest class, which is usually called the main class for organic substances - hydrocarbons. Other representatives of the organic world are considered as their derivatives. Indeed, when studying their structure, it is not difficult to notice that the synthesis of these substances occurs by replacing (replacing) one, and sometimes several hydrogen units in the hydrocarbon structure with atoms of other chemical elements, and sometimes with entire radical branches.

The classification of organic substances took hydrocarbons as a basis also because of the simplicity of their composition, and the hydrocarbon component is the most significant part of most known organic compounds. Today, of all the known organics related to the world, compounds built on the basis have a significant predominance. All other substances are either in the minority, allowing them to be classified as exceptions to the general rule, or are so unstable that their production is difficult even in our time.

Classification of organic substances by dividing them into separate groups and classes allows us to distinguish two large organic classes of acyclic and cyclic compounds. Their very name allows us to draw a conclusion about the type of structure of the molecule. In the first case, it is a chain of hydrocarbon units, and in the second, the molecule is a ring.

Acyclic compounds can have branches or form a simple chain. Among the names of these substances you can find the expression “fatty or aliphatic hydrocarbons”. They can be saturated (ethane, isobutane, or unsaturated (ethylene, acetylene, isoprene), depending on the type of bond of some carbon units.

The classification of organic substances belonging to cyclic compounds implies their further division into the group of carbocyclic and the group of heterocyclic hydrocarbons.

Carbocyclic “rings” are made up of carbon atoms only. They can be alicyclic (saturated and unsaturated), and also be aromatic carbocyclic compounds. In alicyclic compounds, the two ends of the carbon chain simply join together, but aromatic compounds have a so-called benzene ring in their structure, which has a significant effect on their properties.

In heterocyclic substances, atoms of other substances can be found; nitrogen most often performs this function.

The next component that affects the properties of organic substances is the presence of a functional group.

For halogenated hydrocarbons, one or even several halogen atoms can act as a functional group. Alcohols obtain their properties due to the presence of hydroxo groups. For aldehydes, a characteristic feature is the presence of aldehyde groups, for ketones - carbonyl groups. Carboxylic acids differ in that they contain carboxyl groups, and amines have an amino group. Nitro compounds are characterized by the presence of a nitro group.

The variety of types of hydrocarbons, as well as their properties, is based on a very different type of combination. For example, the composition of one molecule may include two or more identical, and sometimes different, functional groups, determining the specific properties of this substance (glycerol).

A table that can easily be compiled based on the information presented in the text of this article will provide greater clarity for considering the issue (classification of organic substances).

There are several definitions of what organic substances are and how they differ from another group of compounds - inorganic. One of the most common explanations comes from the name "hydrocarbons". Indeed, at the heart of all organic molecules are chains of carbon atoms bonded to hydrogen. There are also other elements called “organogenic”.

Organic chemistry before the discovery of urea

Since ancient times, people have used many natural substances and minerals: sulfur, gold, iron and copper ore, table salt. For the entire existence of science - from ancient times to the first half of the 19th century - scientists could not prove the connection between living and inanimate nature at the level of microscopic structure (atoms, molecules). It was believed that organic substances owe their appearance to a mythical life force - vitalism. There was a myth about the possibility of raising a human “homunculus”. To do this, it was necessary to put various waste products into a barrel and wait a certain time for the vital force to arise.

A crushing blow to vitalism was dealt by the work of Weller, who synthesized the organic substance urea from inorganic components. Thus, it was proven that there is no vital force, nature is one, organisms and inorganic compounds are formed by atoms of the same elements. The composition of urea was known before Weller’s work; studying this compound was not difficult in those years. The very fact of obtaining a substance characteristic of metabolism outside the body of an animal or human was remarkable.

Theory of A. M. Butlerov

The role of the Russian school of chemists in the development of science studying organic substances is great. Entire eras in the development of organic synthesis are associated with the names of Butlerov, Markovnikov, Zelinsky, and Lebedev. The founder of the theory of the structure of compounds is A. M. Butlerov. The famous chemist in the 60s of the 19th century explained the composition of organic substances, the reasons for the diversity of their structure, and revealed the relationship that exists between the composition, structure and properties of substances.

Based on Butlerov’s conclusions, it was possible not only to systematize knowledge about already existing organic compounds. It has become possible to predict the properties of substances not yet known to science and to create technological schemes for their production in industrial conditions. Many ideas of leading organic chemists are being fully realized today.

The oxidation of hydrocarbons produces new organic substances - representatives of other classes (aldehydes, ketones, alcohols, carboxylic acids). For example, large volumes of acetylene are used to produce acetic acid. Part of this reaction product is subsequently consumed to produce synthetic fibers. An acid solution (9% and 6%) is found in every home - this is ordinary vinegar. The oxidation of organic substances serves as the basis for the production of a very large number of compounds of industrial, agricultural, and medical importance.

Aromatic hydrocarbons

Aromaticity in molecules of organic substances is the presence of one or more benzene nuclei. A chain of 6 carbon atoms closes into a ring, a conjugated bond appears in it, therefore the properties of such hydrocarbons are not similar to other hydrocarbons.

Aromatic hydrocarbons (or arenes) are of great practical importance. Many of them are widely used: benzene, toluene, xylene. They are used as solvents and raw materials for the production of drugs, dyes, rubber, rubber and other products of organic synthesis.

Oxygen-containing compounds

A large group of organic substances contains oxygen atoms. They are part of the most active part of the molecule, its functional group. Alcohols contain one or more hydroxyl species -OH. Examples of alcohols: methanol, ethanol, glycerin. Carboxylic acids contain another functional particle - carboxyl (-COOOH).

Other oxygen-containing organic compounds are aldehydes and ketones. Carboxylic acids, alcohols and aldehydes are present in large quantities in various plant organs. They can be sources for obtaining natural products (acetic acid, ethyl alcohol, menthol).

Fats are compounds of carboxylic acids and the trihydric alcohol glycerol. In addition to alcohols and linear acids, there are organic compounds with a benzene ring and a functional group. Examples of aromatic alcohols: phenol, toluene.

Carbohydrates

The most important organic substances of the body that make up cells are proteins, enzymes, nucleic acids, carbohydrates and fats (lipids). Simple carbohydrates - monosaccharides - are found in cells in the form of ribose, deoxyribose, fructose and glucose. The last carbohydrate on this short list is the main metabolic substance in cells. Ribose and deoxyribose are components of ribonucleic and deoxyribonucleic acids (RNA and DNA).

When glucose molecules are broken down, energy is released that is necessary for life. First, it is stored during the formation of a kind of energy carrier - adenosine triphosphoric acid (ATP). This substance is transported in the blood and delivered to tissues and cells. With the sequential elimination of three phosphoric acid residues from adenosine, energy is released.

Fats

Lipids are substances of living organisms that have specific properties. They do not dissolve in water and are hydrophobic particles. The seeds and fruits of some plants, nervous tissue, liver, kidneys, and the blood of animals and humans are especially rich in substances of this class.

The skin of humans and animals contains many small sebaceous glands. The secretion they secrete is brought to the surface of the body, lubricates it, protects it from moisture loss and the penetration of microbes. The layer of subcutaneous fat protects internal organs from damage and serves as a reserve substance.

Squirrels

Proteins make up more than half of all organic substances in the cell; in some tissues their content reaches 80%. All types of proteins are characterized by high molecular weights and the presence of primary, secondary, tertiary and quaternary structures. When heated, they are destroyed - denaturation occurs. The primary structure is a huge chain of amino acids for the microcosm. Under the action of special enzymes in the digestive system of animals and humans, the protein macromolecule will break down into its component parts. They enter cells where the synthesis of organic substances occurs - other proteins specific to each living creature.

Enzymes and their role

Reactions in the cell proceed at a speed that is difficult to achieve under industrial conditions, thanks to catalysts - enzymes. There are enzymes that act only on proteins - lipases. Starch hydrolysis occurs with the participation of amylase. Lipases are needed to break down fats into their constituent parts. Processes involving enzymes occur in all living organisms. If a person does not have any enzyme in his cells, this affects his metabolism and overall health.

Nucleic acids

Substances, first discovered and isolated from cell nuclei, perform the function of transmitting hereditary characteristics. The main amount of DNA is contained in chromosomes, and RNA molecules are located in the cytoplasm. When DNA is reduplicated (doubling), it becomes possible to transfer hereditary information to germ cells - gametes. When they merge, the new organism receives genetic material from its parents.

The classification of organic compounds is based on the theory of chemical structure of A. M. Butlerov. Systematic classification is the foundation of scientific nomenclature. Thanks to it, it became possible to give a name to each previously known and new organic substance, based on the existing

Classes of organic compounds

They are classified according to two main characteristics: localization and number of functional groups in the molecule and the structure of the carbon skeleton.

The carbon skeleton is a part of a molecule that is quite stable in various chemical reactions. Organic compounds are divided into large groups, taking into account organic matter.

Acyclic compounds(biofatty compounds or aliphatic compounds). These organic compounds in the molecular structure contain a straight or branched carbon chain.

Carbocyclic compounds- these are substances with closed carbon chains - cycles. These biocompounds are divided into groups: aromatic and alicyclic.

Heterocyclic natural organic compounds- substances in the structure of whose molecules there are cycles formed by carbon atoms and atoms of other chemical elements (Oxygen, Nitrogen, Sulfur) heteroatoms.

The compounds of each series (group) are divided into classes of various organic compounds. The belonging of an organic substance to one class or another is determined by the presence of certain functional groups in its molecule. For example, classes of hydrocarbons (the only class of organic substances that lack functional groups), amines, aldehydes, phenols, carboxylic acids, ketones, alcohols, etc.

To determine whether an organic compound belongs to a series and class, a carbon skeleton or carbon chain (acyclic compounds), a cycle (carbocyclic compounds) or a core is isolated. The presence of other atomic (functional) groups in the molecule of the organic substance is then determined, for example, hydroxyl - OH, carboxyl - COOH, amino group, imino group, sulfhydride group - SH, etc. The functional group or groups determine whether a biocompound belongs to a certain class and its main physical and chemical properties. It should be said that each functional group not only determines these properties, but also influences other atoms and atomic groups, simultaneously experiencing their influence.

When replacing the Hydrogen atom in molecules of acyclic and cyclic hydrocarbons or heterocyclic compounds with various functional groups, organic compounds are obtained that belong to certain classes. We present individual functional groups that determine whether an organic compound belongs to a certain class: hydrocarbons R-H, halogen derivatives of hydrocarbons - R-Hal, aldehydes - R-COH, ketones - R1-CO-R2, alcohols and phenols R-OH, carboxylic acids - R-COOH , - R1-O-R2, carboxylic acid halides R-COHal, R-COOR, nitro compounds - R-NO2, sulfonic acids -R-SO3H, organometallic compounds - R-Me, mercaptans R-SH.

Organic compounds that have one functional group in the structure of their molecules are called organic compounds with simple functions; two or more are called compounds with mixed functions. Examples of organic compounds with simple functions include hydrocarbons, alcohols, ketones, aldehydes, amines, carboxylic acids, nitro compounds, etc. Examples of mixed-function compounds include hydroxy acids, keto acids, and the like.

A special place is occupied by complex bioorganic compounds: proteins, proteids, lipids, nucleic acids, carbohydrates, the molecules of which contain a large number of different functional groups.