Question

Choose the correct statement for the given compounds

• A. (a) is aromatic whereas (b) is non-aromatic.
• B. Both (a) and (b) are aromatic.
• C. (a) is non-aromatic whereas (b) is aromatic
• D. Both (a) and (b) are anti-aromatic.

Answer 1

The correct option is C (a) is non-aromatic whereas (b) is aromatic

For structure (a) :
[8]-Annulene


For structure (a) the no of $\pi e^{-}$ are 8 i.e has $\left(4n\right)\pi e^{-}$. So it should be anti-aromatic.
Since, anti-aromatic compounds are the least stable, so it becomes non-planar (i.e tub shaped as shown ) and hence it is non-aromatic . So, this compound is non-aromatic.
In structure (b)
Naphthalene:
It is planar , has conjugation, and 10 $\pi e^{-}$ i.e. it follows huckel rule $(4n+2)\pi e^{-}$
It is aromatic compound.