Question

Why is cis–trans isomerism common in alkenes?

Answer 1

Cis-trans isomerism is common in alkenes because there is restricted rotation about double bonds.

Explanation:

For example, an alkene such as but-2-ene has two different groups on each alkene carbon.

It can exist as `E-Z` isomers that differ in the positions of the substituents on the double-bonded atoms.

The double bond prevents rotation about the C=C axis.

So the molecule exists as two isomers, with substituents on the same side (cis) or on the opposite side (trans) of the double bond.