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Stereochemical and conformational exchanges in N,N'-di(2-pyridyl)formamidines: An X-ray and (1)H NMR study.

The solid state structure of N,N'-di(2-pyridyl)formamidine displays a four-hydrogen-bonded dimer. In solution, two isomers are observed, one of which is selected and amplified either by crystallization or by adding protons. Solution state analysis of N,N'-di(2-pyridyl)formamidines reveals the presence of the uncommon Z formamidine isomer, which equilibrates with the E-isomer with an activation energy of 90 kJ mol(-1) in CDCl(3).