Question

Which of the following compounds is not optically active ?

• A.
• B.
• C.
• D. (a) and (b) above.

Answer 1

The correct option is D (a) and (b) above.

(a) is odd cumulene where the terminal groups exist in the same plane so it is optically inactive.

In even cumulenes, having different terminal atoms/groups, two mutually perpendicular π bonds are formed. Hence, the terminal atoms/groups attached to the terminal $s{p}^2$ carbons are in different planes. But both the terminals have a similar groups so it possess plane of symmetry. Hence, (b) is optically inactive.

(c) has chiral carbon because it is attached with 4 different group so it is optically active.