1969 Volume 89 Issue 3 Pages 302-309
^1H-nuclear magnetic resonance spectra of 38 kinds of chloro- and fluoro-substituted pyrimidine derivatives at 60 Mcps in deuterated dimethyl sulfoxide, with tetramethylsilane as internal standard, were obtained and examination was made on the relationship between chemical shifts and electron densities computed by simple LCAO-MO method. More or less parallel relationships were found to exist between chemical shifts of 2- and 5-position ring protons and electron densities of carbon atoms at positions 2 and 5, respectively, as well as between 2- and 4-amino protons and 5-methyl protons and electron densities of 2- and 4-amino groups and 5-methyl groups, respectively. It was revealed that electronic influence of substituents on the 5-position proton was larger than that on the 2-position proton. The nuclear magnetic resonance signals of 5-position protons of fluoropyrimidines occurred in higher magnetic field than those of the corresponding chloropyrimidines, which was ascribed to the larger tendency of fluorine atom to donate electrons to the conjugate system than chlorine atom. Examination was made also on the assignment of proton signals of non-equivalent amino groups of 2, 4-diamino-6-chloropyrimidine and 2, 4-diamino-6-fluoropyrimidine, and those in higher magnetic field were assigned to 2-amino protons and those in lower magnetic field to 4-amino protons.
