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 (4n+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

6πe-

Huckel rule obeyed

Aromatic

B.

No

No, Incomplete (sp3 hybrid carbon)

6πe-

Non-aromatic

C.

Yes

Yes

 6πe-(4n+2+lone pair e-) Huckel rule verified

Aromatic

D.

Yes

No

4πe-

Anti-aromatic

E.

Yes

Yes

Huckel rule obeyed

Aromatic

F.

Yes

Yes

2πe- Huckel rule verified n=0

Aromatic

G.

Yes

No

8πe- Huckel rule not verified

Non-aromatic