Infrared spectra and the molecular conformations of some aliphatic amines

The presence of two CD stretching bands for (CH3)2CDNH2 in dilute CCl4 solution is interpreted in terms of two conformations differing in enthalpy by 0.12 ± 0.02 kcal/mole. The low frequency component is assigned to the thermodynamically more stable conformer with the CD bond trans to the N lone pair. Similar rotational isomerism is observed in CH3CD2NH2 and CD3CH2NH2. Band contours for the NH stretching vibration in some N-alkyl anilines reported previously are also interpreted in terms of rotational isomerism and a change in hybridization of the N atom when the lone pair is trans to an α-CH bond, which results in an increase in vNH and a decrease in vCH.