Ultraviolet Spectra of N -Heterocyclic Systems. I. The Anions of Uracils

Abstract

In aqueous solutions uracil exists predominantly in the diketo form, whereas in alkaline solutions it exists as an approximately 1:1 mixture of two deprotonated forms. The two deprotonated anions show ultraviolet absorptions similar to the anions of 1-methyluracil and 3-methyluracil, and the main contributing canonical structures which give rise to the general absorption feature of the anions are discussed. The peak shifts accompanying N-alkylation or deprotonation may be summarized in a simple empirical rule. Individual ionization constants have also been estimated.The results of uracil can be extended to thymine, uridine, thymidine, and their phosphates. The pesent method can probably be extended to other systems containing two dissociable protons.