Site of Attack in the Radiolysis of Pyrimidine Compounds

Abstract

PREVIOUSLY reported experiments with thymine in dilute aqueous solutions have shown that the site of attack in radiolysis with cobalt-60 γ-rays depends on the pH (ref. 1). In acid and neutral solutions, the principal attack is on the double bond at the carbon atom remote from the methyl group, with ultimate formation of saturated products^2–5. In strongly alkaline solution the attack is largely at the methyl group, with formation of the unsaturated compound, 5-hydroxymethyluracil, as the principal product. The shift in the site of attack as the pH is increased correlates well with a model based on two changes in the reaction path. At least one of these changes appears to be related to ionization of thymine¹.