Amidines. Part 28. Influence of substitution at the amidino carbon atom on the sensitivity to substitution at the imino nitrogen atom. pKa Values of N1N1-dimethylbenzamidines

Abstract

Three series (63 compounds) of N¹N¹-dimethylamidines (p-methoxy-, p-nitro-, and p-chlorobenzamidines), each containing the same set of substituents R_x at the imino nitrogen atom, have been synthesized and their pK_a values in 95.6% ethanol (azeotrope) measured. The pK_a values were correlated with σ and σ⁰ constants as well as with the pK_a values of the corresponding primary amines R_xNH₂. It is shown that the sensitivity of the amidine group to substitution at the imino nitrogen atom depends on the substituent in the phenyl ring at the amidino carbon atom. A linear correlation between the slope of the correlation line and the Hammett-type constants of substituents at the phenyl ring at the amidino carbon atom has been found.