Knowledge Bank

The planarity or non-planarity of the isolated formamide molecule was matter of controversy for fifteen years, until the correct $interpretation1$ of the far-infrared spectrum finally established that the molecule, including the amino hydrogens, is indeed planar in the vapor phase. In the present work, the far-infrared vapor-phase spectra of two other simple amides, acetamide (and some deuterated analogues) and acrylamide (propenamide) are reported. Transitions between the lowest three energy levels of the symmetric out-of-plane wagging vibration of the amino hydrogen atoms are assigned for each molecule and the potential energy function governing this vibration is calculated. The co-planarity of the amino hydrogens with the heavy atoms in these molecules is firmly established.