Which of the following species is/are aromatic?

Concept:

Huckel's rule of aromaticity:-

• Conditions for compounds to be Non-aromatic:-
  • Non-aromatic compounds have 4n + 2 or 4n number of π electrons
  • There is no delocalized electron system in that molecule.
  • The system must be non-planar and unconjugated.

​Explanation:-

A. 

• The compound has 6π electrons. It obeys Huckel's (4n+2)π rule for n=1.
• Every member in the ring is sp2 hybridized and thus the molecule is planar.
• The system is conjugated.

Hence, the compound A is aromatic.

B. 

• The compound has 10π electrons. It obeys Huckel's (4n+2)π rule for n=2
• Every member in the ring is sp2 hybridized and thus the molecule is planar.
• The system is conjugated.

Hence, the compound B is aromatic.

C. 

• The compound has 12π electrons.
• Although every member in the ring is sp2 hybridized and thus the molecule is planar.
• The system is conjugated.
• This compound should be anti-aromatic as it contains 12π electrons (obeys 4nπ rule for n=3).

Hence, the compound is anti-aromatic.

Conclusion:-

Hence, only A and B species are aromatic.