Question

Which of the following compound is non aromatic:

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

In option (a), the structure is cyclic, planar, 6 electron's system ($4\pi \stackrel{-}{e}{}^{\prime }s+2\stackrel{-}{e}$ from only one lone pair)(only one lone pair required for delocalisation). It follows (4n+2) rule (n=2). $4\pi \stackrel{-}{e}{}^{\prime }sand2\stackrel{-}{e}$ from lone pair are in complete delocalisation or in resonance, hence aromatic.

In option(b), the structure is cyclic, planar, 6$\pi \stackrel{-}{e}{}^{\prime }s$ system but not in conjugation, hence non-aromatic.

In option(c), the structure is cyclic, planar, 6$\stackrel{-}{e}{}^{\prime }s$ system ($4\pi \stackrel{-}{e}{}^{\prime }s+2\stackrel{-}{e}$ from one negative charge) follows (4n+2) rule, hence aromatic.

In option(d), the structure is cyclic, planar 2$\pi \stackrel{-}{e}{}^{\prime }s$ follows (4n+2) rule, hence aromatic.

So the correct answer is option(b).