Zwitterionic Aromaticity on Azulene Extrapolated to carbo‐Azulene

Abstract

AbstractAzulene is stabilized by “zwitterionic aromaticity”, what about its ring carbo‐mer? The greater dipole moment of the latter is oriented in the opposite direction, while providing an enhanced zwitterionic aromatic character. Comparison of local aromaticity indices for the two rings, with 5 and 7 C−C bonds in azulene or C−C2−C edges in carbo‐azulene, allows analysis of the quasi‐independent influence of size on the π‐electronic properties of these aromatic bicyclic molecules exhibiting quasi‐identical shapes and π‐resonance schemes between their common set of sp2C−H vertices. The electrostatic features of such dipolar hydrocarbons are also analyzed by comparison with their respective radical cation and anion, and with their apolar bicyclic isomer, naphthalene and carbo‐naphthalene.