ESR and ENDOR Studies of Cation Radicals Derived from Benzodipyran Compounds. Structure and Dynamic Behavior of Heterocyclic Ring in Tocopherol (Vitamin E)

Abstract

ESR and ENDOR spectra of cation radicals of benzodipyran compounds were measured in CH2Cl2, and the proton hyperfine coupling constants were correctly determined for each radical. From detailed analysis of the temperature dependence of hyperfine coupling of β- and γ-methylene protons in the heterocyclic ring, the equilibrium conformation of the β-methylene group and activation energy for the conformational interconversion have been determined. The structure of the heterocyclic ring was compared with those of α-tocopherol (vitamin E) model previously obtained by X-ray analysis. The result suggests that the solution and crystal conformations of the heterocyclic ring are distinctly different.