Which of the following monocyclic conjugated species explicitly satisfies the criteria for being ant — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Anti-aromaticity occurs in cyclic, planar, fully conjugated molecules that contain exactly $4n$ $\pi$ electrons ($n = 1, 2, 3...$). Cyclobutadiene is a 4-membered planar ring with 2 conjugated double bonds, yielding 4 $\pi$ electrons ($n=1$). Thus, it is highly unstable and anti-aromatic. The tropylium cation (6 $\pi$), cyclopentadienyl anion (6 $\pi$), and benzene (6 $\pi$) all possess $4n+2$ $\pi$ electrons ($n=1$) and are aromatic.