Homotropenylium cation revisited: POAV and 3D-HMO analysis.

Homoconjugate bonding was characterized as: "... orbital overlap of a type intermediate between sigma and pi", by Winstein over 30 years ago. Nevertheless the concept has remained controversial and the molecular and electronic structure of the homotropenylium cation (1, the prima facle example of this phenomenon), remains in doubt. Previous theoretical calculations, and experimental studies of derivatives of the molecule have produced evidence for two minima on the potential surface, with homoconjugate bond distances, R sub (1,7) = 1.6 and 2.3angstroms.