Qualitative reactions to alkenes. Chemical properties and structure of alkenes

What are qualitative reactions to alkenes? In order to answer this question, it is first necessary to understand what is peculiar about the representatives of this class.

Characteristic of the class

First, let's analyze the structure of alkenes. Unsaturated hydrocarbons are compounds having the general formula CnH2n. The structure of alkenes is linear, but in their structure, in addition to a single (simple) bond, there is also a complex (double bond).

Nomenclature

Before describing the qualitative reactions to alkenes, let us dwell on the question concerning their name. The sequence of actions has a similarity to the class of alkanes, but there are also some distinctive parameters, which should be considered separately. To begin with, it is necessary to find the longest carbon chain in the proposed structure, which includes a double bond.

Further, the C atoms are numbered on the side with which the double bond is closer to the beginning of the chain. If there are hydrocarbon radicals in the molecule (other variants of substituents), then their positions are necessarily indicated in figures. In the presence of several identical radicals, use prefixes. Further, the main chain is called using the suffix -ene. An obligatory condition (except for ethylene and propene) is the indication of the position of the multiple bond by the figure.

Variants of isomerism

Qualitative reactions to alkenes are related to the arrangement in the molecules of the double bond. This dependence assumes a more detailed study of the issue of isomerism of unsaturated hydrocarbons. Like other hydrocarbons, there is structural isomerism in alkene molecules. For example, for a substance of composition C4H8, butenes and 2-methylpropene can be represented.

In addition, representatives of this class of unsaturated hydrocarbons have an isomerism of the double bond position. It is from its location that certain chemical properties of a given class depend.

Among the distinguishing types of isomerism, which other representatives of CxNu do not possess, we note geometric (spatial structures). Depending on the rotation of the double bond of the fragments of the alkene molecule, cis and trans isomers can be obtained. Interclass isomerism binds alkenes to cycloalkanes. Such a variety of structures inherent in representatives of the homologous series of ethylene, predetermines their basic chemical properties.

Chemical properties

Qualitative reactions to alkenes are their interaction with aqueous solutions of halogens. They include bromine, iodine, chlorine. As a result of this chemical reaction, the double bond is split, the addition of halogen atoms. As a sign of this interaction, discoloration of iodine (bromine) water is considered. Qualitative reactions to the double bond of alkenes are their interaction with an aqueous solution of potassium permanganate in an acidified medium.

The products of this reaction are sulfates, as well as an organic product. It is the reaction with the oxidant and halogen solution - these are qualitative reactions to alkenes. Hydrogenation to such does not apply, its result will be the production of the corresponding limiting hydrocarbon (alkane). As a prerequisite for their occurrence, there is an increased temperature, as well as the use of a catalyst.

The activity of alkenes is much greater than that of paraffins. The reason is the presence between carbon atoms in the double bond of not too strong bonds.

When any hydrocarbon of CnH2n composition is burned in air oxygen, water vapor, carbon dioxide gas is released, and a sufficient amount of heat is generated. Qualitative reactions to alkenes can be used to isolate these compounds among other substances.

The hydration reaction (water addition) occurs for unsymmetrical alkenes according to the Markovnikov rule. According to him, the hydrogen atom is attached to that carbon, which contains more hydrogen. The hydroxide ion in this case will be attached to carbon at a double bond, at which it is less than H.

In a similar mechanism and rule, alkenes react chemically with hydrogen halide molecules.

The polymerization reaction is also of interest , as a result of which high-molecular compounds are formed. Thus, when ethylene is chosen as the starting monomer for catalytic polymerization, polyethylene is formed, which is a valuable raw material for the chemical industry.

Physical properties

The first representatives of the homologous series of ethylene are gaseous substances that are practically odorless. They are poorly soluble in water, dissolve in organic compounds. There is a direct relationship between the increase in the relative molecular weight and the boiling point (melting), the transition from the gaseous state to the liquid state, to the solid aggregate state.

Conclusion

Where are the representatives of the unsaturated hydrocarbons of the ethylene series used? Ethylene is a valuable raw material for chemical production. From it you can get styrene, vinyl chloride, ethanol, acetic aldehyde, acid, and also dichloroethane. Polymerization of alkenes produces polyvinyl acetate, lubricating oils, and rubbers. On average, the global production of polyethylene is 100 million tons per year. In industrial volumes, propylene is needed for polymer synthesis. In addition, propene is the starting material for the production of oxide, isopropanol, cumene, butyraldehyde, glycerol.

Butins are mainly needed to create polyisobutylene, methyl ethyl ketone, butyl rubber, isoprene. Isobutylene is an excellent chemical raw material for the production of tertiary butanol, butyl rubber, as well as isoprene. It is isobutylene is necessary for the alkylation of phenols in the manufacture of surfactants. Copolymers with butenes are used as a sealant and additives for oils. Higher unsaturated hydrocarbons of a number of ethylene are used not only in the production of polymer materials, but also in the production of higher organic alcohols.