Zwitterionic Aromaticity on Azulene Extrapolated to carbo ‐Azulene
Résumé
Azulene 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.