13C n.m.r. spectra of 2‐substituted pyrimidines

Abstract 13C n.m.r. chemical shifts and carbon‐proton coupling constants of 2‐substituted pyrimidines are reported. The carbon chemical shifts are correlated with π‐electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH2, OCH3 and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon‐proton coupling constants do not correlate with the electronegativity of the substituents. Carbon‐proton coupling constants and proton‐proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon‐proton coupling constants in 2(1H)‐pyrimidinone and 2(1H)‐pyrimidinethione which accompany anion and cation formation are reported.