Further studies of intramolecular motions in crystalline ammonium bromides by CP/MAS NMR

Abstract

A series of nine compounds consisting of dimethyl, trimethyl and ethyldimethyl ammonium bromides in which the other alkyl group contains a (2-phenyl)ethyl moiety were synthesised and studied by CP/MAS NMR. The results of dynamic NMR studies on the solids suggest that there is a dramatically wide range of molecular motions occurring in this simple series of compounds. A combination of dynamic line shape analyses and T_1ρ measurements reveals the considerable extent of intramolecular group motions including rotations of trimethylammonium, ethyldimethylammonium and phenyl groups. Rates of rotation and activation parameters for these molecular motions are derived where appropriate.