Electron spin resonance and ENDOR spectra of radicals formed by the addition of superoxide ions to dimethylformamide

Abstract

Solutions of tetrabutylammonium superoxide in aqueous dimethylformamide (DMF) gave e.s.r. spectra characteristic of partially hydrated superoxide ions (g_max≈ 2.1–2.2). However, in dry DMF, a species with g values characteristic of peroxy radicals (RO₂^˙) was detected (g_x= 2.038, g_y= 2.099 and g_z= 2.002). We suggest that this is the radical ion Me₂NCH(O^–)OO^˙ formed by nucleophilic addition of ^˙O₂^– to the carbonyl group of the amide. This is strongly supported by ¹H ENDOR spectroscopy, which showed hyperfine coupling to one proton (ca. 1–2 G) and weak coupling to two other types of proton (purely dipolar). These are assigned to the C—H amide proton and two types of methyl proton, respectively.