What are the qualitative reactions to alkenes? In order to answer this question, you must first understand what is the peculiarity of the representatives of this class.
Class feature
First, let us 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 characterizing the qualitative reactions to alkenes, let us dwell on the question concerning their name. The sequence of actions is similar to the class of alkanes, but there are some distinctive parameters that should be considered separately. First you need to find the longest carbon chain in the proposed structure, which includes a double bond.
Further, C atoms are numbered from the side on which the double bond is located closer to the beginning of the chain. If hydrocarbon radicals (other variants of substituents) are present in the molecule, then their position must be indicated with numbers. In the presence of several identical radicals, clarifying prefixes are used. Next, they call the main chain itself, using the suffix –en. A prerequisite (except for ethylene and propene) is to indicate the position of the multiple bond with a digit.
Variants of isomerism
Qualitative reactions to alkenes are associated with the arrangement of a double bond in the molecules. Such a dependence suggests a more detailed study of the issue of isomerism of unsaturated hydrocarbons. Like other representatives of hydrocarbons, in the molecules of alkenes there is a structural isomerism. 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 position of the double bond. It is on its location that some chemical properties of this class depend.
Among the distinctive types of isomerism that other representatives of SchNu do not possess, we note geometric (spatial structures). Depending on the double bond rotation 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 determines their basic chemical properties.
Chemical properties
Qualitative reactions to alkenes are their interaction with aqueous solutions of halogens. These include bromine, iodine, chlorine. As a result of such a chemical reaction, the cleavage of the double bond occurs, the addition of halogen atoms. The bleaching of iodine (bromine) water is considered as a sign of this interaction. Qualitative reactions to the double bond of alkenes are their interaction with an aqueous solution of potassium permanganate in an acidified environment.
The products of this reaction are sulfates, as well as an organic product. It is the reaction with the oxidizing agent and the halogen solution that is the qualitative reaction to alkenes. Hydrogenation is not one of those, its result will be the receipt of the corresponding saturated hydrocarbon (alkane). The mandatory conditions for their course are elevated temperature, as well as the use of a catalyst.
Alkenes are much more active than paraffins. The reason is the presence of not too strong bonds between the carbon atoms in the double bond.
When burning any hydrocarbon of CnH2n composition in air oxygen, water vapor, carbon dioxide are released, as well as the formation of a sufficient amount of heat. Qualitative reactions to alkenes can be used to isolate these compounds from other substances.
The hydration reaction (water addition) occurs for asymmetric alkenes according to the Markovnikov rule. According to it, the hydrogen atom joins that carbon, which contains a greater amount of hydrogen. In this case, the hydroxide ion will attach to carbon at the double bond, at which it is less than N.
According to a similar mechanism and rule, alkenes enter into a chemical reaction with hydrogen halide molecules.
Of interest is the polymerization reaction, as a result of which macromolecular compounds are formed. So, when ethylene is selected as the initial monomer during 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, soluble in organic compounds. There is a direct correlation between an increase in relative molecular weight and boiling (melting) temperatures, the transition from a gaseous state to a liquid, solid state of aggregation.
Conclusion
Where are representatives of unsaturated hydrocarbons of a number of ethylene used? Ethylene is a valuable raw material for chemical production. Styrene, vinyl chloride, ethanol, acetic aldehyde, acid, and dichloroethane can be obtained from it. During the polymerization of alkenes, polyvinyl acetate, lubricating oils, and rubbers are formed. On average, world 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 manufacture of oxide, isopropanol, cumene, butyric aldehyde, glycerol.
Butins are mainly necessary for the creation of polyisobutylene, methyl ethyl ketone, butyl rubber, isoprene. Isobutylene is an excellent chemical raw material in the manufacture of tertiary butanol, butyl rubber, as well as isoprene. Isobutylene is necessary for the alkylation of phenols in the manufacture of surfactants. Copolymers with butenes are used as a sealant and oil additives. Higher unsaturated hydrocarbons of a number of ethylene are used not only in the production of polymeric materials, but also in the production of higher organic alcohols.