Free Radicals Formed by Exposure of Pyrimidine Solids to Sodium atoms: An Electron Spin Resonance Study.

摘要

Sodium atoms have been deposited on various pyrimidine powders under high vacuum at 77 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 NaCl 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 H2O impurity in the sample, with which the Na atoms combine to release the H atoms. In addition to a resonance with g = 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 eblieved to arise from electrons trapped in interstitial sites or vacancies in the lattice. (Author)