title: The protonation of the 5-thymyl radical in single crystals of thymine derivatives: e.s.r. and INDO evidence.
abstract: For the 5-thymyl radical, minor couplings additional to beta-protons bonded to C6 and C7 are observed in single crystals of 1-methylthymine. Hyperfine coupling tensors are given of the N3 nitrogen (+3.5/0.0/0.0 G) and of the exchangeable proton (-4.1/-2.5/-0.9 G) bonded to it. In single crystals of thymine . anhydrate, thymine . monohydrate and 5,6-dihydrothymine these additional couplings are unresolved, but are also present. INDO-calculations were performed to reproduce consistently both beta-coupling constants and additional couplings from N3 and H(N3). Comparison of experimental and calculated values to the conclusion that the 5-thymyl radical is protonated at 04 in all single crystals of thymine derivatives investigated.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D003201:Computers; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D011522:Protons; D013941:Thymine / Q000031:analogs & derivatives*; D014498:Uracil / Q000031:analogs & derivatives
chemical_list: D005609:Free Radicals; D011522:Protons; D014498:Uracil; D013941:Thymine