R. Boyum, E. Sagstuen, T. Henriksen
Nov 1, 1979
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Abstract
Single crystals of 5,5′-diethylbarbituric acid (barbital) were irradiated with 4.0-MeV electrons and studied by ESR in the temperature range 77 to 300 K. Altogether, five radicals have been identified. At 300 K the only stable radical is formed by abstraction of an ethyl group from C(5). That radical has been identified by Haak and Benson (J. Chem. Phys. 55, 3693-3697 (1971)). At 77 K at least four other radicals are formed. At high doses (above 5 Mrad) the dominating one (radical II) is formed by a hydrogen abstraction from one of the methyl groups. Radical III, which appears in a small concentration at this temperature, is formed by abstraction of one of methylene protons in the ethyl groups. At low doses (below 5 Mrad) a singlet (radical IV) and a doublet (radical V) became accessible for study. It is suggested that the singlet, exhibiting a large g-value variation, is due to a cation radical with the spin density shared between two σ-type nonbonding orbitals on O(4) and O(6). The doublet is due to a r...