Question

Which of the following species is not aromatic?

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

For a compound to be aromatic,
(i) It should be cyclic
(ii) It should be planar
(iii) It should have extended conjugation
(iv) It should have (4n+2) $\pi$ electrons
Lacking any one of the above requirement, the compound cannot be an aromatic.
(a), (c) and (d) obeys all the conditons, so they are aromatic.
For a compound to be antiaromatic,
(i) It should be cyclic
(ii) It should be planar
(iii) It should have extended conjugation
(iv) It should have (4n) $\pi$ electrons
Lacking any one of the above requirement, the compound cannot be an antiaromatic.
Option (b) has 8 $\pi$ electrons which does obey (4n)$\pi$ rule. Hence, (b) is antiaromatic not an aromatic compound.