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

💡 Solution & Explanation

For a molecule to be aromatic, it must be cyclic, planar, fully conjugated, and have $(4n + 2)$ $\pi$ electrons (Huckel's rule). Benzene has 6 $\pi$ electrons ($n=1$). The cyclopentadienyl anion has 6 $\pi$ electrons. The cyclopropenyl cation has 2 $\pi$ electrons ($n=0$). The cyclopentadienyl cation has 4 $\pi$ electrons, which fits the $4n$ rule, making it anti-aromatic rather than aromatic.