A proton magnetic resonance investigation of solid mono-, di-, tri- and tetra-methylammonium chlorides

Abstract

The proton magnetic resonance spectrum has been measured over a wide temperature range for polycrystalline mono-, di-, tri-, and tetramethylammoniumn chlorides, which are found to exhibit a diversity of ionic motions. Only the dimethylammonium ion exhibits spectral narrowing by rotational tunnelling of the methyl groups at 4°K. At higher temperatures the other three ions exhibit methyl group reorientation. The monomethylammonium ion also shows reorientation of the N +H 3 group, the dimethylammonium ion reorients about its diad axis, and the trimethylammonium ion about its triad axis. The tetramethylammonium ion exhibits quasi-isotropic reorientation. None of the compounds shows diffusional narrowing at the highest temperatures of measurement.