Plastic crystals (PCs) are promising materials with piezo-, ferroelectric, magnetic- and barocaloric properties. Recent discoveries of colossal barocaloric effects suggest they could have important applications in solid-state cooling. Recently we observed colossal barocaloric properties (≥100 J kg-1 K-1) under moderate pressures (<1 kbar) in [(CH3)3(CH2Cl)N]FeCl4 and [(CH3)3(CH2Cl)N]GaCl4. The properties of these materials, along with similar PCs, result from combinations of changes in the long-range structural symmetry and local molecular orientation. But the link between structure and properties is not clear. Thus, here we examine the dynamic structural changes occurring as a function of temperature and pressure to accompany calorimetric measurements and determine the precise chemical-structure mechanisms behind the functional properties. This study will provide vital information for developing effective property engineering strategies.