Determination of Molecular Structures of Free Radicals from ESR Parameters

Abstract

The method to determine the molecular structures of free radicals on the basis of the experimental ESR parameters and theoretical ones calculated by the INDO-UHF method was described. The functional, which involves the differences between experimental and theoretical values for the g-factors and the anisotropic and isotropic hyperfine coupling constants, was minimized to obtain the ESR parameter-optimized molecular structure. The method was applied to 12 free radicals, HCO, CF₃, NF₃⁺, CO₂^-, NO₂, H₂NO, (CH₃)₂C0⁺, CH₂CHCH₂, CH₂OCH₂⁺, C₂F₄, C₆H₅, and SiH₃Cl^-, and the calculated molecular structures were compared with the energy-optimized structures and the experimental ones. Better agreement with experiment was obtained in the ESR parameter-optimized structures. The proposed method shows efficiency and appropriateness to the elucidation of radical structures from the anisotropic informations on the g-factors and hyperfine coupling.