The Fine Structure of Cytosine

Abstract

The ionization constants and ultraviolet spectra of cytosine, of its appropriately methylated derivatives, and of related compounds are used to indicate that its pre- dominant tautomeric form in aqueous solution is 4-amino-1,2-dihydro-2-oxopyrimidine. This is in sharp contrast to its recent formulation as a zwitterion on the grounds of its nuclear magnetic resonance spectrum.