Radiation Abstraction of Hydrogen Atoms in Single Crystals of Thymine

Single crystals of both thymine monohydrate and anhydrous thymine were irradiated at 77°K and the radicals induced were analyzed with ESR spectroscopy. The radical species, formed by abstraction of a hydrogen atom from nitrogen, was studied in detail. Molecular orbital calculations suggest that the abstraction takes place from N(1). The nitrogen and the methyl proton coupling tensors are identical in both crystal systems. The ĝ tensor is axially symmetric (g∥ =2.0032, g⊥ =2.0064) with the axis of symmetry perpendicular to the ring plane. The differences between deuterated and undeuterated thymine monohydrate crystals are also discussed.