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 2 H , 13 C , 17 O and 18 O 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.