It is shown that the homolytic bond dissociation energy (BDE), DH-degrees(X-R), of the X-C bond in allylic, propargylic, benzylic, cyanated, and unsaturated compounds can be estimated by the simple equation DH-degrees(X-R) = DH-degrees(X-C(CH3)mH3-m) + E(s) + DELTAV(nb) : where X is a wide variety of univalent atoms or substituents; R is an allylic, propargylic, benzylic, cyanated, or unsaturated group; DH-degrees(X-C(CH3)mH3-m) are the X-C BDEs in the model saturated compounds; m is the degree of methyl substitution of the group R; E(s) is the p-pi resonance stabilization energy (RSE) of the given conjugated radical R; DELTAV(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.