Question

Unlike most hydrocarbons, azulene ($C_{10}{H}_8$) is highly coloured (deep blue), although its isomer, naphthalene does not have significant zwitter-ionic character, azulene does.
(i) Draw a resonance structure of azulene in which five-membered ring is anionic and the seven-membered ring cationic.
(ii) Can azulene be considered aromatic?

Answer 1

(i) The resonance structure of azulene in which five-membered ring is anionic and the seven membered ring is cationic is given.

(ii) Azulene is an aromatic species as it has (4n+2) pi delocalised electrons. It is a 10 pi electrons conjugated system.