The role of triplet repulsion in alkyl radical addition to a π-C-O bond and alkoxy radical addition to a π-C-C bond

The experimental activation energies of the R-. + O = (CRR2)-R-1 and RO. + CH2 = CHR1 addition reactions are analyzed within the framework of the parabolic model of the bimolecular addition reaction. The activation energy also depends on the dissociation energy of the forming C-O bond and on the reaction enthalpy: the higher the dissociation energy, the higher the activation energy. The empirical relationship r(e)/D-e = 0.97 x 10(-13) m kJ(-1) mol is found for H-., Cl-., Br-., R-., and RO. radical addition to multiple C=C and C=O bonds (r(e) is the distance between the peaks of the intersecting parabolic curves). This is due to the effect of the triplet repulsion on radical addition. The interaction of polar groups and the steric effect also influence the activation energy.