The translational and orientational disorder of some liquids can be frozen if they are cooled down quick enough, giving rise to a Structural Glass (SG). But for some molecular compounds molecules displaying pseudo-globular shape can rotate around the equilibrium positions of a crystalline lattice, the quenching can lead to the so called Orientational Glass (OG), in which the orientational disorder is frozen while the long-range translational order still persists. That is the case of some simple halogen-ethane compounds. In addition, the existence of conformational disorder (trans and gauche conformers) which can hybridize with sound modes in both the OG and the ordered low-temperature phases makes relevant the study of the anomalous enhanced vibrational density of states in the low-frequency spectral range over the predicted one by Debye for the low-temperature ordered solid phase.