O–H bond strengths and one-electron reduction potentials of multisubstituted phenols and phenoxyl radicals. Predictions using free energy relationships

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Abstract
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 ΔD(O–H)=–1.97 + 29.87 ∑σ+(kJ mol)–1 and E°= 0.79 + 0.34 ∑σ+(V vs. NHE) where ∑σ+ is the sum of the Brown substituent values (σo += 0.66 σp +, σm + and σp +). The conditional relationship σo += 0.66 σp + is also derived in this work.