Question

Which of the following is an aromatic compound?

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

Answer 1

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

Structure (a) is non planar due to the presence of $s{p}^3$ hybridised carbon and also there is lack of conjugation. Hence this sturucture is non-aromatic.
In structure (b):
It is cyclic and has a planar structure with all carbon atoms $s{p}^2$ hybridised.
It has $10\pi e^{-}$, i.e. follows $(4n+2)\pi e^{-}$huckel rule
and has conjugation.
So, it is an aromatic compound.
In structure (c)
Nitrogen's lone pair does not take part in resonance, so it is not counted in $\pi$ electrons .
Number of $\pi e^{-}=10$. It follows $(4n+2)\pi e^{-}$ huckel rule and has conjugation.
It is also a planar structure.
It is an aromatic compound.
So (d) is the correct option.