Chemistry of amidines. Part 3. Analysis of conformation about the N′-pyridyl bond in N′-(2-pyridyl)formamidines

Abstract

A conformational analysis of a series of N,N-dimethyl-N′-(2-pyridyl)formamidines and their conjugate acids using the ¹H NMR nuclear Overhauser effect shows that they exist preferentially in the conformation in which the pyridine and the imino nitrogen lone pairs are anti. For compounds having electron-donating substituents the syn conformation becomes important on protonation.