1H and 13C NMR spectral studies of conformation of some N-(2-pyridinyl)-3-pyridinecarboxamides

Article abstract of DOI:10.1016/S0022-2860(98)00365-2

The ¹H and ¹³C NMR spectra of N-(2-pyridinyl)-, N-(4-methyl2-pyridinyl)-, and N-(6-methyl-2-pyridinyl)-3-pyridinecarboxamides (1-3, respectively) and 3-pyridinecarboxamide (4) in different solvents have been analysed using COSY, HETCOR, chemical shift and coupling constant correlations. The conformations of 1-4 have been obtained by utilizing the NMR spectra, NOE experiments and MINDO/3 calculations. In dilute solutions, the 2-pyridyl ring is coplanar with the amide group while the 3-pyridyl ring is apparently not. Compounds 1-3 dimerize through cooperative hydrogen bonding in concentrated CDCl₃ solution (approximately 0.1 M) and the structure of the dimer resembles some of the DNA base-pairs. Hydrogen bonding between N-H and the solvent molecules hinders dimerization in (CD₃)₂CO and CD₃CN.