Conformation of the dimethylamino-group in benzene, pyridine, pyrimidine, and cytosine derivatives. 13C Chemical shift studies of ortho-methyl substitution effects

Abstract

The ¹³C n.m.r. spectra of several dimethylamino-derivatives of pyridine, pyrimidine, and 2-oxopyrimidine with and without C-o-methyl groups have been obtained. Analysis of the chemical shifts of C-methyl and amino N-methyl carbon atoms as well as C(Me) and C(NMe₂) ring carbon atoms indicates a progressive twist of the dimethylamino-group in hindered derivatives from a planar conformation in the 2-oxopyrimidine compound to the most twisted one in the benzene derivative.