COUPLING OF ACIDITIES AND OXIDATION POTENTIALS TO ESTIMATE HOMOLYTIC BOND-DISSOCIATION ENERGIES AND RADICAL STABILIZATION ENERGIES

The pK(HA) and E(ox)(A-) values of 29 alpha-substituted derivatives of acetone and acetophenone have been compared with those of the parents. The DELTApK(HA) and DELTAE(ox)(A-) values are summed to obtain DELTABDE values, which are equated with the radical stabilization energies (RSEs) of the corresponding radicals. Since the two equilibria defining pK(HA) and E(ox)(A-) are linked to one another, either changes in pK(HA) or E(ox)(A-) may play the major role in deciding the size of the RSEs caused by making the structural change. The largest RSE observed (21 kcal/mol) was for an alpha-R2N substituent, which was caused almost entirely by a change in DELTAE(ox)(A-). But the next largest RSE (10-11 kcal/mol) was for a Ph or a PhS substituent, which was caused largely by a decrease in DELTApK(HA). Similar analyses were made for N-substituent effects on the RSEs of 11 derivatives of acetamide, benzamide, and benzenesulfonamide and for replacing the oxygen atom in the carboxamides by a sulfur atom. Finally, the effects of polyfluorination of hydrocarbons were shown to cause destabilization of the radicals formed by loss of a hydrogen atom from the acidic function.