Homo- and heterolytic X-C bond energies. 1. Homolytic bond energies in common unsaturated organic compounds

It is shown that the homolytic bond dissociation energy (BDE), DH o (X-R), of the X-C bond in allylic, propargylic, benzylic, cyanated, and unsaturated compounds can be estimated by the simple equation DH o (X-R)=DH o -(X-C(CH 3 ) m H 3-m )+E s ΔV nb : where X is a wide variety of univalent atoms or substituents; R is an allylic, propargylic, benzylic, cyanated, or unsaturated group; DH o (X-C(CH 3 ) m H 3 ) are the X-C BDEs in the model saturated compounds; m is the degree of methyl substitution of the group R; E, is the p-m resonance stabilization energy (RSE) of the given conjugated radical R; ΔV nb is the steric compression relief and/or the net change of interactions between nonbonding atoms in the compounds RX and in the radical R and in X resulting from the C-X bond cleavage