Simple pyrimidines. VIII. The fine structure of isocytosine, thiocytosine, and some isomers

Abstract

The fine structures of 4-amino-6-hydroxy-, 4-amino-6-mercapto-, 4-amino-2-mercapto-, 2-amino-4-hydroxy-, and 2-amino-4-mercapto-pyrimidine are revealed by comparing their ultraviolet spectra and ionization constants with those of their S- and 0-, or N- and S-methyl derivatives. On the evidence here presented they appear to exist largely in aqueous solution as the tautomers containing an amino group, namely: 4-amino-1,6-dihydro-6-oxopyrimidine, 4-amino-1,6-dihydro-6-thiopyrimidine, 4-amino-1,2(and 2,3)-dihydro-2-thiopyrimidine, 2-amino-1,4(and 3,4)-dihydro-4-oxopyrimidine, and 2-amino-1,6-dihydro-6-thiopyrimidine, respectively. Syntheses of hitherto unknown methyl derivatives are recorded.