Caractérisation du polymorphisme du méthyl-2 naphtalène

2-Methylnaphthalene presents three crystalline forms. The high-temperature form I (T > 292 K) is monoclinic. Its structure is disordered and characterized by a statistical molecular entity which is centrosymmetric. Form III has a very narrow existence range: 289.0-292.0 K. Nevertheless, its X-ray powder diffraction pattern has been accurately obtained. The low-temperature form III' (T < 289.5 K) is monoclinic. All the observed transitions are first order. No form II, corresponding to a unidirectional substructure of form I, has been found here, contrary to the cases of 2-chloro- and 2-bromonaphthalene. The JCPDS Diffraction File Nos. are 34-2000, 34-1999 and 34-1998.