Question

Which of the following is the smallest aromatic species?

• A. Cyclopropene
• B. Cyclopropenyl cation
• C. Cyclopropenyl anion
• D. Cyclobutadiene

Answer 1

The correct option is B Cyclopropenyl cation

(a) Cyclopropene is non-aromatic because it does not possess conjugation.



(b) Cyclopropenyl cation is aromatic as it follows Huckel's rule $4n+2\pi$ electrons, where $n=0$.


(c) Cyclopropenyl anion is anti-aromatic.

As it contains $4n\pi$ electrons, where $n=1$.
(d) Cyclobutadiene is anti-aromatic.
As it contains $4n\pi$ electrons, where $n=1$.
Hence, the correct option is (b).