Azulene () is a non-benzenoid aromatic hydrocarbon. It is highly coloured and has a significant dipo — Aromatic Hydrocarbons Chemistry Question
Question
Azulene ($C_{10}H_8$) is a non-benzenoid aromatic hydrocarbon. It is highly coloured and has a significant dipole moment. This polarity arises from the transfer of an electron from one ring to another, creating a stable aromatic state in both rings. Which of the following ionic resonance structures correctly explains its aromaticity?
Answer: B
💡 Solution & Explanation
Azulene consists of fused five-membered and seven-membered rings. To satisfy Huckel's $(4n+2)\pi$ rule in both rings, an electron is transferred from the seven-membered ring to the five-membered ring. This results in a cyclopentadienyl anion ($6\pi$ electrons, aromatic) and a cycloheptatrienyl cation ($6\pi$ electrons, aromatic), giving the molecule a substantial dipole moment.
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