Dynamics of molecular reorientations: direct determination of rotational angles from two-dimensional NMR of powders

Two-dimensional solid-state deuteron NMR spectroscopy has been applied to study rotational motions in powders. In general, tensorial interactions give rise to powder patterns producing 2D exchange signals with characteristic ridges which manifest the motional mechanism in a model-independent fashion. For deuterons in particular, the angles through which the molecules rotate are read directly from elliptical ridges in the 2D spectrum. Experimental data on the two-site exchange in dimethylsulphone are given as well as theoretical spectra for different types of molecular motion.