Effect of Br···O\nBonding on the Chiral\nAssembly of Brominated Amides in the Crystalline Phase

A cyclic\ntriamide of 2,5-dibromo-4-ethylaminobenzoic acid, which\nhas a fixed axial chirality, was prepared in racemic and enantiopure\nforms. The structures of the corresponding crystals and homochiral\nmolecular assembly formation were analyzed from the viewpoint of intermolecular\ninteractions. Although the packing arrangements in the two types of\ncrystals were similar, the packing difference suggested the importance\nof the CO···Br–C contact for the chiral\nassembly. A statistical analysis of amides with the above contact\nrevealed a correlation between the molecular assembly type (hetero-\nor homochiral) and the contact angle of adjacent molecules interacting\nthrough CO···Br bonding. Specifically, in the\nabsence of aryl groups, the O···Br–C angles\ncloser to 180° facilitated the assembly of molecule pairs into\na chiral arrangement. In contrast, the opposite trend was observed\nin the presence of one or more aryl groups. Furthermore, the chiral\nand racemic crystals displayed different preferences for the CO···Br\nangle, indicating its importance in determining crystal chirality.\nOur approach extended the scope of the previously reported method\nand demonstrated its applicability to compounds with other skeletons.