NMR study of the conformation of N-(3-pyridinyl)-2-pyridinecarboxamide, N-(3-pyridinyl)acetamide and 2-pyridinecarboxamide

The H-1 NMR spectra of N-(3-pyridinyl)-2-pyridinecarboxamide (1), N-(3-pyridinyl)acetamide (2) and 2-pyridinecarboxamide (3) in CDCl3, (CD3)(2)CO and CD3CN have been measured and analyzed by utilising the correlations in the COSY and HETCOR spectra, chemical shifts and coupling constants. H-1 NMR spectra in dilute solutions (similar to 1 mg ml) and NOE experiments suggest (1) to occur in a single conformation with the 2-pyridyl ring coplanar with the amide plane and the 2-pyridyl nitrogen hydrogen bonded intramolecularly to the N-H. In concentrated solutions of CDCl3 and (CD3)(2)CO, (1) dimerises by cooperative hydrogen bonding. The structure of the dimer was inferred to be similar to that of the adenine-adenine (A-A) base-pair. (C) 1997 Elsevier Science B.V.