σ-π Conjugation: occurrence and magnitude

Abstract

Charge-transfer spectra of aryl-CRz-Metal(X)n systems have been used to study the nature and extent of C-Metal hyperconjugation. Effects of changes in X, changes in R, and changes of the metal (C, Si,'Ge, Sn, Pb, Hg, B, etc.) on the extent of cr-Jt conjugation as weil as effects of rotation about the aryl-C bond have been determined. The dependence of cr-Jt conjugation upon electron deficiency is discussed and a general theory for the extent of hyperconjugation is presented.