Polymorphisme Cristallin des Sept Premiers Termes de la Serie des 4,4′-Di-n-alcoxyazoxybenzenes—I—Enthalpimetrie Differentielle—Spectroscopie Raman (Modes de Reseau)

Abstract

Abstract A crystalline polymorphism has been detected in the seven first members of the homologous series 4,4′-di-n-alkoxyazoxybenzenes (n = 1 to 7) by D.S.C and Raman spectroscopy. In the case of the compounds n = 1,3,4,5, the crystalline polymorphism is characterized in the high temperature phase by a statistical disorder of the azoxy group, the molecules being pseudo-centrosymmetrical. Besides, for n = 3 and 5, con-trarily to n = 1 and 4, an important increase of the molecular volume due to conformational changes appears at the transition. As for the members n = 2, 6 and 7, the crystalline systems of the two solids are practically similar.