Polymorphisme du tetrachloro-1,2,4,5 benzene et du tetrabromo-1,2,4,5 benzene

Combination of three techniques of thermal analysis (hot stage polarising microscope, DSC, Guinier-Lenne) enabled the determination of the polymorphic behaviour of tetra 1,2,4,5-X benzene (X=Cl, Br). Thermal, calorimetric and crystallographic characterizations have been carried out. This study puts forward an interesting problem: theβ phase (P2₁/a, stable at room temperature) of the tetra chlorobenzene has similar arrangement to the two solid piases P2₁/a of tetra bromobenzene. Which one of these two forms is actually isomorphic with tetra chlorobenzene.