Ncert Exercises & Solutions

The ring systems having the following characteristics are aromatic.

(a). Planar ring containing conjugated $π$ bonds.

(b). Complete delocalisation of the $π$ -electrons in the ring system i.e., each atom in the ring has unhybridised p-orbital, and

(c). Presence of $(4 n + 2) π$ -electrons in the ring where n is an integer (n=0,1,2,...) [Huckel rule].

Using this information, the number of aromatic compounds are:

1. 2
2. 4
3. 5
4. 3

	Compound	Planar Ring	Complete delocalization of -electron	Huckel rule electron	Aromatic or non-aromatic
A.		Yes	Yes	$6 {πe}^{-}$ Huckel rule obeyed	Aromatic
B.		No	No, Incomplete (sp³ hybrid carbon)	$6 {πe}^{-}$	Non-aromatic
C.		Yes	Yes	$6 {πe}^{-}$ (4n+2+lone pair e^-) Huckel rule verified	Aromatic
D.		Yes	No	$4 {πe}^{-}$	Anti-aromatic
E.		Yes	Yes	Huckel rule obeyed	Aromatic
F.		Yes	Yes	$2 {πe}^{-}$ Huckel rule verified n=0	Aromatic
G.		Yes	No	$8 {πe}^{-}$ Huckel rule not verified	Non-aromatic