NMR spectra of pyrimidines effect of substituents on the chemical shift of the para protons in 2- and 5-substituted pyrimidines

Abstract

The chemical shifts of the protons of the pyrimidine ring in the 2 position for a series of 5-substituted pyrimidines and in the 5 position for a series of 2-substituted pyrimidines in solutions in dimethyl sulfoxide were determined. The correlation equations that link the relative chemical shifts with the F and R substituent constants were calculated. The correlation equations were analyzed by comparison with the corresponding correlation equation for a series of monosubstituted benzenes. The reasons for the change in the conductivity of the electronic effects of the substituents via inductive and conjugation mechanisms in the pyrimidine ring as compared with the conductivity in the benzene ring are discussed.