EPR Study on Stable Magnesium Complexes of the Phenoxyl Radicals Derived from a Vitamin E Model and Its Deuterated Derivatives

The phenoxyl radical 1*, generated by the reaction of a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H) with 2,2-bis(4-tert-octylphenyl)-1-picrylhydrazyl (DOPPH*), was significantly stabilized by complex formationwith Mg 2 + in deaerated acetonitrile at 298 K. The assignments of the hyperfine coupling constants (hfc) obtained by computer simulations of the observed EPR spectrum of the Mg 2 + complex of 1* (Mg 2 + -1*), were carried out using three deuterated isotopomers of 1*, i.e., 5-CD 3 -1*, 7-CD 3 -1*, and 8-CD 3 -1*, where a methyl group at the C5, C7, or C8 position is replaced by a CD 3 group, respectively. The decreased spin density of the benzene ring in the Mg 2 + -1* complex indicates that delocalization of the unpaired electron in 1* into Mg 2 + by complexation between Mg 2 + and 1* results in the enhanced stability of 1* in the presence of Mg 2 + .