ESR and INDO-MO study of radical formation in irradiated crystals of 5,5'-diethylbarbituric acid (barbital)

Journal Article · Thu Nov 01 04:00:00 EST 1979 · Radiat. Res.; (United States)

DOI:https://doi.org/10.2307/3575054· OSTI ID:5642501

Boeyum, R; Sagstuen, E; Henriksen, T

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/sup 0/K. Altogether, five radicals have been identified. At 300/sup 0/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/sup 0/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 the 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 sigma-type nonbonding orbitals on O(4) and O(6). The doublet is due to a radical formed by hydrogen addition to the O(2) position. Upon heat treatment in the temperature range 77 to 295/sup 0/K several radical reactions were observed. Radical II is transformed into radical III at 230/sup 0/K, and this radical is in turn transformed into radical I at 270/sup 0/K. Both reactions seem to be 1:1 conversion processes. Radicals IV and V become unstable at approximately 240/sup 0/K and two unidentified singlet resonances appear. INDO-MO calculations have been used throughout to aid in radical identification and to obtain information about radical conformation.

• Research Organization: Univ. of Oslo, Norway
• OSTI ID: 5642501
• Journal Information: Radiat. Res.; (United States), Journal Name: Radiat. Res.; (United States) Vol. 80:2; ISSN RAREA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400103* -- Radiometric & Radiochemical Procedures-- (-1987)
AZINES
BARBITURATES
CRYSTALS
DRUGS
ELECTRON SPIN RESONANCE
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
HETEROCYCLIC COMPOUNDS
HYPNOTICS AND SEDATIVES
IRRADIATION
LEPTONS
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PYRIMIDINES
RADIATION EFFECTS
RADIATIONS
RADICALS
RESONANCE
SYNTHESIS
TEMPERATURE EFFECTS