1H and 13C nuclear magnetic resonance and ultraviolet studies of the protonation of cytosine, uracil, thymine, and related compounds

The protonation of the three nucleic acid bases, cytosine, uracil, and thymine, and of related 4-amino-2,6-dimethylpyrimidine and 2-hydroxypyridine has been studied by 1H and 13C nuclear magnetic resonance and ultraviolet spectroscopies mostly in 0.18–18 M aqueous sulfuric acid. The experimental data have been interpreted on the basis of the excess acidity method. The pKn values as well as the assigned protonation sites are discussed and contrasted with other data.