Rotation of groups about double bonds are usually restricted due to large torsional strain and it is due to this reason that cis- and trans-isomers have their independent existence. However, certain structural modifications in the compound makes the rotation of groups about double bond possible and hence, for such compound, cis- and trans-isomer exist together in equilibrium.
Identify which of the following compounds has such structural feature and its cis and trans isomers exist together in equilibrium:
Could someone explain the answer step-by-step and the theory behind it?
I think that rotation of groups about a double bond can be possible due to conjugation of double bonds, so the answer should be (A). But I am afraid I haven't completely understood the logic behind it.