O-H BOND STRENGTHS AND ONE-ELECTRON REDUCTION POTENTIALS OF MULTISUBSTITUTED PHENOLS AND PHENOXYL RADICALS - PREDICTIONS USING FREE-ENERGY RELATIONSHIPS

General equations for the empirical determination of relative O-H bond strengths and one-electron reduction potentials of multisubstituted phenols and phenoxyl radicals are derived. The derivations are based on data from direct and indirect measurements of phenolic O-H bond strengths, and one-electron reduction potential measurements using electrochemical and radiation chemical methods. The resulting equations are DELTAD(O-H) = -1.97 + 29.87 SIGMAsigma+ (kJ mol)-1 and E-degrees = 0.79 + 0.34 SIGMAsigma+ (V vs. NHE) where SIGMAsigma+ is the sum of the Brown substituent values (sigma(o)+ = 0.66 sigma(p)+, sigma(m)+ and sigma(p)+). The conditional relationship sigma(o)+ = 0.66 sigma(p)+ is also derived in this work.