Selective formation of radicals in irradiated single crystals: 5,5′-dihydroxybarbituric acid trihydrate

A single crystal ESR study of the title compound shows that the oxy radical RO· is selectively formed in one of the two OH groups attached to the same carbon atom. In relation to this observation, selective formation of radicals in some symmetrical molecules is discussed. It is suggested that a slight deviation from exact symmetry causes highly selective reactions in the crystalline media. Irradiated single crystals offer us a well defined chemical reaction field in which selective reactions take place. Studies from such a view may be of considerable interest in relation to enzymatic activity.