Electron spin resonance studies. Part XXXIV. The use of the aci-anion from nitromethane as a spin trap for organic radicals in aqueous solution

Abstract

The aci-anion CH₂:NO₂^– has been used as a spin trap for a variety of organic radicals, which have been generated in aqueous solution by reactions effected by the hydroxyl radical or the sulphate radical anion, SO₄·^–. The resulting species have been identified by their e.s.r. parameters, confirmation being obtained where necessary by independent generation of the species from the appropriate nitro-compound and a one-electron donor (·CMe₂·OH). Of especial value in the analysis, splitting is observed not only from the (β-) methylene protons in RCH₂NO₂·^– but also in almost all cases from γ-protons and, in some cases, from δ-protons; further, ∂_N and ∂_H(β-CH₂) are significantly dependent upon structure. For radicals of the type CXYZ·CH₂·NO₂·^–, the splittings of the two β-methylene protons are unequal, evidently as the result of the chirality of the neighbouring carbon atom. In some cases information has been obtained about the mechanisms of reaction, as in comparison of the reactions of ·OH and SO₄·^– with carboxylate ions and of those of 2-chloro- and 2-iodoethanol with ·OH.