![Sample our Medicine, Dentistry, Nursing & Allied Health journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/5944/TOC-Subject-Sample-2021-Medicine-Dentistry-Nursing-Allied-Health.jpg"})
Summary
Radical formation in single crystals of 1,3-dimethyluracil by X-irradiation has been studied by electron spin resonance at 9·5 GHz. This crystal contains no hydrogen bonds. Only Van der Waals forces are present. Accordingly, after X-irradiation at 300 K, the only radicals observed are those resulting from the excitation path: the H-addition radical at C5 and an H-abstraction radical from a methyl group.
Irradiation with light of λ > 400 nm induces the transformation of the C5-addition into the C6-addition radical. INDO calculations indicate that the C6-addition radical is protonated at O4. Since this crystal does not contain N-H or O-H bonds, this protonation can only occur through proton-abstraction from a C-H bond of a neighbouring molecule by the carbonyl group. The presence of short contacts between C6 and O4 is taken to suggest that the abstraction occurs at C6.