Compounds containing a guest molecule included in a host structure, like clathrates have attracted a lot of interest. It is important to understand the interactions between a guest molecule and a host structure in order to explain in which way the guest molecule changes the structural and dynamical characteristics of the host. The study of free rotations in the host structure provides a new and exciting method of investigating these interactions. Inelastic neutron scanering directly yields information on the dynamics of the molecule whereas from neutron diffraction on orientationally disordered molecular crystals the time averaged density distribution. which is a consequence of the underlying dynamic, is obtained. The analysis of low temperature data requires a complete quantum-statistical treatment of the problem. Modern computing methods permit both pieces of information to be coupled together with advance. Thus we will evaluate a complete quantum statistical description of the orientational disorder present in these compounds.