According to Huckel's rule, which of the following cyclic, planar, and fully conjugated species exhi — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Aromaticity requires $(4n+2)\pi$ electrons. The tropylium cation (cycloheptatrienyl cation) has $6\pi$ electrons ($n=1$). The cyclopentadienyl anion has $6\pi$ electrons ($n=1$). The cyclopropenyl cation has $2\pi$ electrons ($n=0$). All three are aromatic. The cycloheptatrienyl anion has $8\pi$ electrons ($4n$, anti-aromatic if planar).