Explain why rotation about carbon-carbon double bond is hindered ?

Explanation

Carbon -carbon double bond consists of a `sigma and a pi` bond. The `pi` bond is formed by lateral overlap of unhybridised p-orbitals of two carbon atoms above and below the plane of the carbon atoms . If an attempt be made to rotate one of the C-atoms of the double bond with respect to the other , the p-orbitals will no longer overlap ,thereby causing fission of the `pi` bond. since breaking of a `pi` bond requires considerable amount of energy , which is not available at room temperature, so rotation about carbon -carbon double bond is hindered.