Azulene () 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

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?

Prashant Kotian · Accepted Answer

Correct answer: B. Azulene consists of fused five-membered and seven-membered rings. To satisfy Huckel's rule in both rings, an electron is transferred from the seven-membered ring to the five-membered ring. This results in a cyclopentadienyl anion ( electrons, aromatic) and a cycloheptatrienyl cation ( electrons, aromatic), giving the molecule a substantial dipole moment.

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