The experimental data clearly indicate the presence of highly mobile guest species. Sample cooling gives rise to characteristic line shape effects that can be attributed to a slow-down of the rotational motion. Additional 2H NMR measurements were performed on the plastic crystal 1,4-diazabicyclo[2,2,2]octane where highly mobile species were observed. A quantitative analysis of the experimental data is achieved by appropriate computer simulations taking into account various molecular motions for each studied system. The analysis of these theoretical data give rise to the kinetic parameters that are in the order of related systems.