Radical formation in salts of pyrimidines. II. Cytosine. HCl crystals

Radicals produced by X-irradiation at 77 K and at 300 K of cytosine. HCl crystals have been analysed by electron spin resonance spectroscopy. Four radicals have been identified: the anion radical of the cytosine molecule, the radical resulting from H-addition at position C6, the radical resulting from H-addition at position O2, and finally a radical resulting from addition of a Cl- to nitrogen N3. Hückel molecular orbital calculations are presented, which support the hypothesis according to which in unsaturated pyrimidines the site of hydrogenation or protonation depends on the state of the molecule.