The experimental and computational study on the IR spectra and structure of pyridine-3-carboxamide (nicotinamide)-d0 and -d2

The structure and force field of pyridine-3-carboxamide (nicotinamide)-d0 and -d2 have been studied by IR spectra, ab initio and density functional calculations. According to the energy analysis, the E-conformer is more stable than the Z-one. This result is in agreement with the correlation analysis performed (experimental vs theoretical IR frequencies), that indicates the same conformer is prevalent in CHCl3/CDCl3 solutions, as well as in the solid state. Both ab initio and DFT force field calculations give good descriptions of the IR spectra of nicotinamide-d0 and -d2 studied, and fairly good ones for the corresponding isotopic shifts. The theoretical bond lengths and angles are in excellent agreement with those determined experimentally by electron and neutron diffractions. According to the calculations, the carboxamide group holds a negative electric charge and the Mulliken charge transfer between it and the β-pyridyl ring is 0.30 e−.