Question

Why isn't cyclopropene aromatic?

Answer 1

Cyclopropene is not aromatic; on the other hand, cyclopropenyl cation, `[C_3R_3]^+` is aromatic.

Explanation:

The requirements for aromaticity are: (i) `4n+2` `pi` electrons; and (ii) that the `pi` electrons be delocalized around a ring. Cyclopropene has `2pi` electrons in the olefin. but these `pi` electrons are localized and are not free to move. Hence cyclopropene is electron precise and not aromatic. On the other hand, for cyclopropenyl cation, the electron count is correct for an aromatic structure, and the `pi` electrons may be delocalized around the ring.