Plastic phases are characterized by a positional ordering of the molecular centers of mass while molecules are rotating in a hindered way. Therefore these phases are characterized by a disorder only in orientation. This kind of phases shows the same features appearing in glass forming liquids, and are thus excellent model systems to understand the role played by orientational disorder in liquids. We propose to measure two plastic phases associated to two molecules one displaying a dipolar moment and the other one being non-polar. Since the centers of mass of both phases display a BCC symmetry, any effect will be solely due to differences in rotational dynamics.