The infrared spectra and structure of acetamide and acrylamide

The far-IR vapour phase spectra of acetamide and acrylamide are reported and several transitions in the amido “inversion” vibration are identified. The potential energy curves governing the vibration are deduced from the experimental data and are found to have a single broad minimum for both molecules, implying that the amido hydrogens are copianar with the N-CO atoms, but that the resistance to their out of plane displacement is small. The band contours found in the mid-IR spectrum of acrylamide suggest that the cis orientation of the two double bonds about the C-C single bond is favoured over the trans orientation; indeed no evidence of the latter has been found.