The plastic phase of crystalline NaCN has been studied by molecular dynamics simulation. A good agreement with available experimental data has been obtained. A detailed analysis of the translation-rotation coupling has been performed in terms of collective and single-particle motion. Using site symmetry coordinates of the anion and of the surrounding cation cage, we have obtained a picture of the rotational motion of the anions in terms of a cage-aided mechanism. (C) 1997 American Institute of Physics.