Chemistry of amidines. Part 1. Determination of the site of initial protonation in N′-pyridylformamidines

Abstract

A series of substituted N,N-dimethyl-N′-pyridylformamidines has been synthesised and the pK_a values of the conjugate acids have been measured in water at 25 °C. Consideration of the pk_a values shows that initial protonation is predominantly on the imino nitrogen of the amidine system rather than on the pyridyl nitrogen. The effect of the protonation on the ¹H and ¹³C NMR spectra of the amidines is discussed.