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

Abstract

The $^IH$ NMR spectra of N-(3-pyridinyl)-2-pyridinecarboxamide (1), N-(3-pyridinyl)acetamide (2) and 2-pyridinecarbox- amide (3) in $CDCI_3$, $(CD_3)_2CO$ and $CD_3CN$ have been measured and analyzed by utilising the correlations in the COSY and HETCOR spectra, chemical shifts and coupling constants. $^1H$ NMR spectra in dilute solutions $(\sim1 mg \hspace {2mm}ml^{-1})$ 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 $CDCl_3$ and $(CD_3)_2CO$, (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