Explain the isomerism exhibited by alkenes.

Explanation

2-butene: Geometrical isomerism: `CH_(3)-CH=CH-CH_(3)`
(i) Geometrical isomers are the stereoisomers which have different arrangement of groups or atoms around a rigid framework of double bonds. This type of isomerism occurs due to restricted rotation of double bonds or about single bonds in cyclic compounds.
(ii) In 2-butene, the carbon-carbon double bond is `sp^(2)` hybridised. The carbon-carbon double bond consists of a `sigma` bond and a `pi` bond. The presence of `pi` bond lock the molecule in one position. Hence, rotation around C = C bond is not possible.
(iii)
(iv) These two compounds are termed as geometrical isomers and are termed as cis and trans form. (v) The cis-isomer is the one in which two similar groups are on the same side of the double bond. The trans-isomer is that in which two similar groups are on the opposite side of the double bond. Hence, this type of isomerism is called cis-trans isomerism.