Electron spin resonance study and theoretical calculations of some methoxybenzene radical cations

Abstract

Reaction of methoxybenzene derivatives with phenyliodine(III) bis(trifluoro-acetate), PIFA, yielded the corresponding radical cations, which were observed and characterized by ESR and visible spectroscopies. The application of this methodology to this kind of compound has allowed well-resolved ESR spectra to be obtained of the one-electron oxidized compounds, thus determining the hyperfine coupling constants of the cation radical when the solvent was 1,1,1,3,3,3-hexafluoropropanol (HFP). The requirements of the substitution pattern of the aromatic ring have been studied. In contrast, it was not possible to obtain the ESR spectra of N,N-dialkylaniline radical cations in the same reaction conditions. The ESR spectra obtained corresponded to non-identified secondary reaction products. The spectral resolution obtained by application of this method has been compared with that obtained when the radical cations were generated by in situ electrochemical oxidation.Semiempirical calculations have allowed the coupling constants to be assigned to the magnetic centers in the radical cation. The spin densities obtained from these calculations have been correlated with bibliographic data on the reactivity of radical cations under nucleophilic attack.