Question

Which of the following(s) will not show geometrical isomerism?

• A.
• B.
• C.
• D.

Answer 1

Answer: (A), (B)

Geometrical isomers has restricted rotation of an atom or groups around the doubly bonded carbon to gives different geometries of a compound. This is also known as Cis-Trans isomerism. This restriction of rotation of double bond is due to the $\pi$ bond because the electrons overlap both above and below the plane of atoms.
Condition for Geometrical isomerism:
Compound should have different group/atom on both side of the double bond. But group across the double bond can be same.
Here compound (a) and (b) has similar group on the one side of the double bond. Hence they don't show geometrical isomerism.
Compound (c) and (d) are the trans and cis isomers of 1,2-Dibromo- 1,2- dichloroethane.
In (c), chlorine and bromine atoms lies on opposite side of the double bond. Hence, it is trans isomer.
In (d), Br and Cl lies on same side of the double bond. Hence, it is a cis isomer.
Therefore, the correct answers are (a) and (b)