Question

Among the following, the optically inactive compound is :

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

As $N$ is involved in conjugation with the benzene ring, its hybridisation changes from $s{p}^3$ to $s{p}^2$ and in this way, it becomes planar. Hence, its chirality is lost once it becomes a planar structure.

Compound (c) is a even cumulene.
In even cumulenes, two mutually perpendicular π bonds are formed. Hence, the terminal atoms/groups attached to the terminal $s{p}^2$ carbons are in different planes. These terminals represent arrangement like $s{p}^3$ hybridised chiral centre. Since, the terminals are of different atoms it does not possess any plane or centre of symmetry. Hence, the molecule is optically active.

Compound (b) and (d) has a chiral centre so they are optically active.

Hence, (a) is correct.