The crystal structure of 4-benzoyl-3-(o-chlorophenyl)-l- ethoxycarbonyl-1a-phenyl-1, 1a, 2, 3-tetrahydro-4H-azirino-[1, 2-a][1, 5]-benzodiazepine was determined by X-ray diffraction method. The result indicates that the conformation of the core skeleton is a twist-boat. The dynamic study was carried out using simulated annealing method. Three typical conformations were found, of which the boat conformation is the most stable one and the aromatic effect was observed.

Key words: DIAZEPAM, CRYSTAL STRUCTURE, CONFORMATION, PHYSICOCHEMICAL CHARACTERISTICS, X-RAY DIFFRACTION ANALYSIS