HYDROGEN BONDING IN THE AMINE HYDROHALIDES: II. THE INFRARED SPECTRUM FROM 4000 TO 2200 CM−1

Abstract

The infrared spectra of a number of amine hydrohalides have been measured in the lithium fluoride region.Hydrogen bonding and the torsional oscillations of the [Formula: see text] groups influence these spectra characteristically. The [Formula: see text] stretching frequencies give broad or fairly broadbands. They are near 3000 cm−1 for aliphatic primary amine salts. The corresponding band lies at somewhat lower frequencies for secondary amine salts and much lower for tertiary ones. The aromatic amine hydrohalides exhibit these bands at lower frequencies than do the aliphatic amine salts of the same order. There is a shift to higher frequencies in the series hydrochloride, hydrobromide, hydriodide.All these spectra contain a number of sharper bands which may or may not coincide with the hydrogen-bonded stretching bands. These are combination bands involving mainly deformation vibrations, and they shift to lower frequencies, throughout the series hydrochloride, hydrobromide, hydriodide.The importance of electrical anharmonicity for the appearance of these bands is stressed.The hydrogen bonds in amine hydrohalides appear to be largely electrostatic in character.