Kekule Valence Structures Revisited. Innate Degrees of Freedom of PI-Electron Couplings

摘要

For individual Kekule valence structures we consider the smallest possible number of placements of CC double bonds such that a Kekule structure is fully determined. The number may be viewed as special weighting scheme for individual Kekule valence structures. Alternatively its reciprocal indicates the degree of a long-range order in a Kekule structure. Contributions from individual Kekule valence structure add to a novel structural invariant F, the innate degree of freedom associated to a conjugated system. We find that F correlates well with the molecular resonance energy. 8 refs., 3 figs. (ERA citation 11:036447)