The far infrared spectra of a number of aliphatic amines have been recorded as dilute solutions in cyclohexane. A characteristic band with center at 225 ± 10 cm<sup>−1</sup> is present in the spectra of aliphatic primary amines with a primary α-carbon atom. On the basis of the deuterium shift this band is assigned to the amino torsion. The effects of branching at the α-carbon, coupling of methyl and amino torsions, and intramolecular association on the frequencies of NH<sub>2</sub> torsions are discussed.
Stephen M. Craven and Freeman F. Bentley, "Far Infrared Group Frequencies. II. Primary Amines," Appl. Spectrosc. 26, 449-453 (1972)