title: Free radicals formed by exposure of pyrimidine solids to sodium atoms: an electron spin resonance study.
abstract: Sodium atoms have been deposited on various pyrimidine powders under high vacuum at 77 degrees K and the electron spin resonance spectra of the resulting free radicals have been observed. Generally, the spectra show that the electron of the Na goes into a molecular orbital of the pyrimidine ring and the Na+ ions become attached to a carbonyl oxygen of the resulting pyrimidine anion. In 5-fluorouracil and 5-chlorouracil, however, the halogen is evidently abstracted by the Na to form NaF or NaC1 and the neutral uracil radical. Thymine shows evidence for H-addition radicals as well as the Na+-[thymine]-complex. The H source for the addition radicals may be an H-2-0 impurity in the sample, with which the Na atoms combine to release the H atoms. In addition to a resonance with g equals 2.00 from the pyrimidine anion radical, broad resonances with g greater than 2 were observed for 5-bromouracil, 5-chlorouracil and 5-iodouracil, as well as for alloxan and cytosine. These resonances, generally unstable at room temperature, are believed to arise from electrons trapped in interstitial sties or vacancies in the lattice.
mesh_terms: D000496:Alloxan; D001976:Bromouracil; D003596:Cytosine; D004578:Electron Spin Resonance Spectroscopy; D005472:Fluorouracil; D005609:Free Radicals; D011743:Pyrimidines; D012964:Sodium; D013941:Thymine; D014498:Uracil / Q000031:analogs & derivatives
chemical_list: D005609:Free Radicals; D011743:Pyrimidines; D001976:Bromouracil; D014498:Uracil; D000496:Alloxan; D003596:Cytosine; D012964:Sodium; D013941:Thymine; D005472:Fluorouracil