THE STRONG INFLUENCE OF THE SOLVENT ON THE ELECTRON-SPIN-RESONANCE SPECTRA OF SEMIQUINONE RADICAL-ANIONS - I - A THEORETICAL INVESTIGATION OF THE HYPERFINE CONSTANTS OF 1,2-BENZOSEMIQUINONE AND 1,4-BENZOSEMIQUINONE BY USING DENSITY-FUNCTIONAL THEORY AND POLARIZABLE CONTINUUM SOLVATION MODELS

The influence of the solvent medium on the isotropic hyperfine constan ts of 1,2- and 1,4-benzosemiquinone is investigated by theoretical cal culations, using B3LYP density functional theory and electrostatic con tinuum solvation models. The computed hyperfine constants are highly s ensitive to the impact of the solvent field, particularly in the case of 1,2-benzosemiquinone where the relative values are completely rearr anged when the dielectric constant of the solvent, epsilon, is increas ed above unity. Consistency with experimental hyperfine data observed in aprotic as well as protic solvents is obtained by appropriate adjus tment of the surface isodensity parameter in the isodensity polarizabl e continuum model (IPCM) of Foresman et al. (C) 1998 Elsevier Science B.V.