EPR SPECTRA AND SPIN DENSITY DISTRIBUTION OF O,S-DIMETHYL 4,4-DITHIOTEREPHTHALATE RADICAL ANIONS

The preparation of O-methyl S-trideuteromethyl 4,4-dithioterephthalate and S-methyl O-trideuteromethyl 4,4-dithioterephthalate is described. The EPR spectra of the corresponding radical anions are measured. Comparison with the spectrum of O,S-dimethyl 4,4-dithioterephthalate radical anions allows the unequivocal assignment of the proton hyperfine structure (proton hfs) coupling constants in the above asymmetric species. Assignment of the arene proton hfs coupling constants is achieved by PM6 and density functional theory MO calculations of the spin density distribution and application of McConnell's relationship a(mu)(H) = -2.4.rho(pi)(mu). The spin density distribution in the asymmetric title compound is compared with those in the radical anions of dimethyl terephthalate and the corresponding symmetric sulfur analogs.