Amidines. Part 15. Influence of substitution at imino and amino nitrogen atoms on pKa values of N1-methyl-N1N2-diarylacetamidines

Abstract

A series of 19 unreported N¹-methyl-N¹N²-diarylacetamidines containing two different substituents at the phenyl rings have been synthesized and their pK_a values in 95.6% ethanol (azeotrope) measured. The pK_a values have been correlated with σ° constants of the two substituents. The influence of substitution at either of the nitrogen atoms on basicity and on the regression coefficient is discussed, and it is shown that the pK_a values of N¹N²-diarylamidines can be predicted with satisfactory accuracy on the basis of the dual-substituent (planar) Hammett equation.