Question

The ring systems having the following characteristics are aromatic.

(i) Planar ring containing conjugated $\pi$ bonds.

(ii) Complete delocalisation of the $\pi$− electrons in ring system i.e., each atom in the ring has unhybridized $p$−orbital, and

(iii) Presence of $(4n+2)\pi$−electrons in the ring where n is an integer $(n=0,1,2,\dots \dots \dots \dots \dots )$ (Huckel rule).
Using this information classify the following compounds as aromatic/nonaromatic

Answer 1

We need to check whether each compound follows the Huckel’s Rule of Aromaticity and the rest of the conditions.


For following the third criteria of Huckel’s rule, the value on ‘n’ on solving this equation of $4n+2$ =
$\pi$ electrons’’, should be $0,1,2\dots \dots i.e$, positive whole integer.






Checklist for Aromaticity

The ring systems having the following characteristics are aromatic:

A) Planar ring containing conjugated $\pi$ bonds.

B) Complete delocalization of the $\pi$ electrons in-ring system i.e., each atom in the ring has unhybridized p-orbital, and

C) Presence of $(4n+2)\pi$ electrons in the ring where n is an integer $(n=0,1,\mathrm{2..})$ [Huckel rule].