CONJUGATION IN RADICAL CATIONS OF BENZENE, ETHYLENE, AND ACETYLENE DERIVATIVES - NONUNIVERSALITY OF THE RESONANCE PARAMETERS OF GROUP-14 ORGANOELEMENT SUBSTITUENTS

The first vertical ionization potentials I-1 of molecules RpiX (X = Ph , H2C=CH, and HC=C) depend on the joint influence of the inductive, re sonance, and polarizability effects of substituents X, which are chara cterized by parameters sigma(I), sigma(R)(+), and sigma(alpha), respec tively. The mechanism of conjugation in radical cations formed upon io nization of RpiX is changed as compared to neutral RpiX molecules, whi le the substituent X becomes polarized. The conjugation and polarizabi lity effects are strenthened in the sequence Ph < H2C=CH < HC=C as R-p i changes from Ph to H2C=CH and HC=C. The sigma(R)(+) parameters of Si -, Ge-, and Sn-containing substituents X are dependent on the type of R-pi but are connected by linear dependences in the series of benzene, ethylene, and acetylene derivatives.