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.