An ESR analysis of a heathyphen;stable radical in ggr;hyphen;irradiated single crystals of 1hyphen;methylthymine

摘要

Free radicals formed in ggr;minus;irradiated single crystals of 1minus;methylthymine were studied by ESR spectroscopy. In addition to the known C6minus;hydrogen adduct radical, a second radical is formed which is very stable for short periods at 200deg;C, as well as being present in the crystals at room temperature before high temperature annealing. Computer simulation was used as an aid to identifying this radical, which is 1minus;methylminus;5minus;methyleneuracilminus;10minus;y1, formed by net hydrogen abstraction from the methyl group. Certain ESR spectral features suggest molecular packing disorder about an axis constructed along C6 and N3. The principal values for proton hf couplings perpendicular to both the CH bond and the unpaired electronrsquo;sporbital direction, along the Cminus;H bond and along theporbital direction, respectively, in gauss, are: H1(24.5, 8.1, 15.4); H2(H2minus;C10par;Hminus;C6)(24.8, 6.9, 15.4); HC6(14.0, 5.2, 10.5); and thegtensor values parallel and perpendicular to theporbital direction are, respectively, 2.0018 and 2.0027.