Tamara I. Vakulskaya, Lyudmila I. Larina and Alexander V. Vashchenko
Some natural flavonoids and their synthetic nitro-derivatives have been investigated by polarography and EPR spectroscopy under electrochemical reduction in acetonitrile, DMF, DMSO and 1,2-dimetoxyethane. All studied compounds, apart from flavanone, which accepts two electrons at once, are reduced on the first stage with one-electron transfer. Nevertheless, the primary radical anions were detected by the EPR spectroscopy only for 4′-nitroflavone. Radical anions of other flavonoids are quickly dimerized. The analysis of the temperature dependence of the superfine interaction constants and broadening lines in EPR spectra of 4′-nitroflavone radical anions has shown that the distribution of spin density is due to both the change of medium polarity and rotation of the nitrophenyl moiety.