Question

Which of the following molecules, in pure form, is (are) unstable at room temperature ?

(a) A

(b) B

(c) C

(d) D

Solution

Order of stability is Aromatic > Non aromatic > Anti Aromatic.

Compound B and C are anti aromatic compounds because they have 4n number of pi electrons conjugating in the ring. Compound A is non-aromatic because it as a sp^3 hybridised carbon (non planar) while the the compound D is aromatic ( 4n + 2) pi electrons conjugating in a planar ring.