Diene hydrocarbons (diolefins, alkadienes, dienes) are saturated hydrocarbons in the structure of which there are two double bonds. Given the chemical structure, alkadienes are divided into three types: Type I - diolefins with cumulated bonds (CH2CCH2); Type II - alkadienes with conjugated (conjugated) bonds; double bonds in the diene structure are separated by a single bond (22); Type III - dienes with isolated bonds (2222).
Diene hydrocarbons: general description
Of the three types of dienes, type II alkadienes are of greatest interest to the chemical industry. Using electron diffraction, it was found that the double bonds in the butadiene molecule between C1 and C4 are longer than in the ethylene molecule.
Diene hydrocarbons: isomerism
For these organic compounds , two types of isomerism are characteristic - spatial (stereoisomerism) and structural. The first type is the isomerism of the structure of the hydrocarbon chain, which can be straight or branched. The second type of isomerism is due to the spatial localization of atoms and atomic groups near double bonds. Thus, trans and cis isomers of dienes are formed. For example, for a diene with the molecular formula C5H8, there are three structural isomers:
CH2CHCHCH2CHCH2; CH2C (CH3) CHCH2; CH3CHCHCCH2.
Diene hydrocarbons: nomenclature
Two nomenclatures are used for the name of dienes - historical (for example, divini, alen) and IUPAC (International Union of Theoretical and Applied Chemistry). According to the IUPAC nomenclature, the corresponding alkene diene is first called, in the name of which the suffix "an" is replaced by "diene", after which the numbers indicate the location of double bonds in the hydrocarbon chain. The numbering of the hydrocarbon chain is carried out so that the numbers have the least value. The above diene formulas according to the IUPAC nomenclature will be called as follows: 1,4-pentadiene; 2-methyl-1,3-butadiene; 1,3-pentadiene.
There are a number of industrial and laboratory methods for the synthesis of dienes. The main ones are the depolymerization of natural rubber (dry distillation), the method of catalytic dehydration of alkanes, the method of dehydration of monohydric saturated alcohols.
Butadiene is a valuable raw material for the production of synthetic rubbers (butadiene-nitrile, butadiene, styrene), as well as perchlorovinyl. Isoprene is a substance with a characteristic odor. Isoprene was first obtained from natural rubber by dry distillation. Isoprene is also obtained by dehydration of isopentane. Used to obtain synthetic rubbers, medicinal and aromatic substances.
Rubber is an elastic and very strong material of organic origin, which is obtained from natural raw materials (natural rubber) and synthetic methods (synthetic). The basis of rubber are diene molecules with conjugated double bonds. In the process of processing this material with sulfur and heating (vulcanization), rubber is formed. Rubbers are a very important raw material for the production of tires and tubes, insulation strips, rubber gloves, shoes and other items used in industry, farming, everyday life, medicine and veterinary medicine.
Ethylene hydrocarbons in their structure have one double bond. Sometimes these compounds are called olefins, since lower gaseous alkenes, reacting with chlorine or bromine, form oily compounds that are insoluble in water.
Acetylene hydrocarbons (alkynes) are compounds that contain one triple bond. Of the all alkynes, acetylene, which is obtained by the interaction of calcium carbide with water, is of the greatest importance. This gas is used in autogenous welding and metal cutting. Acetylene is a valuable raw material for the production of ethylene, ethyl alcohol, acetaldehyde, vinylacetylene, acetate, benzene, trichloroethane, acrylonitrile.