Isotope effects on the equilibrium of p-benzoquinone and its radical anion: ab initio and DFT studies

Abstract

The isotope effect on the equilibrium between p-benzoquinone and its radical anion has been quantitatively estimated using Hartree-Fock (3-21G, 6-31G^∗ and 6-31+G^∗∗ basis sets) as well as pure and hybrid density functional methods (BP86 and B3LYP with 6-31G^∗ and 6-31+G^∗∗ basis sets). Equilibrium constants involving ²H, ¹³C, ¹⁷O and ¹⁸O isotopes have been calculated. At all levels, the deuterium isotope effect is substantial, while heavy atom isotope effects are small. The trend remains the same even when the presence of a counterion (Na⁺) is taken into account explicitly in the calculations. These conclusions differ qualitatively from an earlier experimental study.