GENERALIZATION OF AN EMPIRICAL-MODEL FOR BOND-DISSOCIATION ENERGIES

A relationship between homolytic bond dissociation energies (BDEs) of C-X bonds and the electronegativity of X and the degree of methyl subs titution of C has been extended. The range of leaving groups, X, now i ncludes SiH3, GeH3, and PH2 and a variety of C-, N-, and O-centred rad icals. Alkyl groups with ethyl and propyl chains attached to the radic al centre have been incorporated. Steric effects, including those in b ulky silanes, have been treated. The method is believed to be generall y applicable where resonance and ring strain are not significant. BDEs for 73 bonds have been calculated; in the 42 cases where experimental data are available, the average deviation is 0.7 kcal/mol.