Proton and carbon-13 nuclear magnetic resonance studies of substituted pyrimidines. Part 6. Carbon-13-proton coupling constants for some monoprotonated methyl- and amino-pyrimidines

Abstract

J(¹³C,¹H) coupling constants for some monoprotonated methyl- and amino-pyrimidines have been determined by ¹³C n.m.r. spectroscopy. Both the one-bond and long-range coupling constants follow general trends which may be summarized in a few simple rules. Some of these rules differ from those observed for the neutral compounds, due to the effect of monoprotonation. (i) All the one-bond coupling constants increase; taking into account solvent effects, it appears that the increase observed is larger, the closer the carbon atom considered is to the site of protonation. (ii) The three-bond coupling constants ³J(C,H) decrease across the protonated nitrogen.