Carbon-13 nuclear magnetic resonance spectra in the identification of N-, O or S-methyl derivatives of some tautomeric hydroxy and mercapto nitrogen heterocycles

Abstract

Carbon-13 nuclear magnetic resonance spectroscopy, in contrast to 1H n.m.r. spectroscopy, has been shown to provide a clear distinction in a variety of nitrogen heterocyclic systems between O-methyl and nuclear N-methyl groups. Methoxy groups were found to occur in the range δ�53.20-61.87, nuclear N-methyl groups at 34.29-49.62, and methylthio groups at 12.35-14.55 for the compounds examined in (D)chloroform. Data for N- and O-methyl derivatives of pyridin-2- and -4-ol,* the corresponding pyrimidines, and some sulfur analogues have been compared with those for the unmethylated parent compounds.