EPR and ENDOR spectroscopy studies on α-aminoanthraquinone radical cations in solution

Abstract

EPR and ENDOR spectra of the radical cations of 1,4-diamino-9,10-anthraquinone, 1,4-bis(methylamino)9,10-anthraquinone, 1,4-bis(ethylamino)-9,10-anthraquinone, 1,4-bis(butylamino)-9,10-anthraquinone and 1,4-bis(hexylamino)-9,10-anthaquinone were measured in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP), with (bis(trifluoroacetoxy)iodo)benzene (PIFA) as oxidizing agent, in the temperature range 260–300 K. The isotropic hyperfine coupling constants (hcc) of the labile amino protons were assigned by deuterium exchange with deuterated trifluoroacetic acid (d-TFA) in HFP as solvent. The results are compared with the radical cations of 1,4-diamino-9,10-anthraquinone and 1,4-bis(methylamino)-9,10-anthraquinone produced in acetonitrile by electrolytic oxidation. A tentative assignment of the hcc constants by MO calculations was made for 1,4-diamino-9,10-anthraquinone. The results indicate that deuteration is restricted entirely to the amino protons and that the obtained radical cation of aminoanthraquinone occurs in the non-protonated form (Q⁺˙).