Accurate Estimation of the One-Electron Reduction Potentials of Various Substituted Quinones in DMSO and CH3CN

The one-electron reduction potentials of 116 important p- and o-quinones in DMSO and CH3CN were predicted for the first time by using the B3LYP/DZP++ method and the PCM cluster continuum model. The calculated gas-phase electron affinities and one-electron reduction potentials agree well with the available experimental observations, respectively. The study showed the one-electron reduction potentials of the 116 quinones range from -0.949 to 1.128 V in DMSO and from -0.904 to 0.971 V in CH3CN. The one-electron reduction potentials of p-quinones are generally smaller than those of the o-quinones by about 0.132 V. For quinones with aromatic properties, 2-substituted-1,4-naphthquinones have the largest one-electron reduction potentials, followed by substituted-1,4-anthraquinones and then by substituted-9,10-anthraquinones. The study also showed that the one-electron reduction potentials of quinones in DMSO are linearly dependent on the sum of the Hammett substituent parameters sigma(p): E-NHE(p-Q/p-Q(center dot-)) = 0.45 Sigma sigma(p) - 0.194(V) and E-NHE(o-Q/o-Q(center dot-)) = 0.45 Sigma sigma(p) - 0.059(V). Combined with the hydride affinities of quinones in the former paper [Delta G(H)-(A)(p-Q) = -16.0 Sigma sigma(p) - 70.5 (kcal/mol) and Delta G(H)-(A)(o-Q) = -16.2 Sigma sigma(p) - 81.5 (kcal/mol)] and the one-electron reduction potentials of quinones estimated in this work, we obtained the homolytic bond dissociation energies of the hydroquinone anions (QH(-)) and found that these thermodynamic parameters also have linear correlations against the sum of the Hammett substituent parameters sigma(p) if only the substituents have no larger electrostatic inductive force and no large steric hindrance: BDE(p-QH(-)) = 5.05 Sigma sigma(p) + 63.18 (kcal/mol) and BDE(o-QH(-)) = 5.33 Sigma sigma(p) + 71.30 (kcal/mol). Knowledge about the redox potentials of the quinones should be of great value for the understanding of the nature of chemical reactions of quinones, the designing of new electronic materials of quinones, and the examining of biological activities of quinones.