Optical Induction in Chiral Crystals. IV. The Correlation between the Absolute Conformation of 4,4'-Dimethylchalcone and the Absolute Configuration of Its Dibromide

Article abstract of DOI:10.1107/S0567740881005979

The structure and absolute configuration of the enantiomer of 4,4'-dimethylchalcone dibromide (C17H16Br2O) formed in excess in a gas/solid bromination reaction of a single crystal of 4,4'-dimethylchalcone have been determined at 85 K.The crystals are orthorhombic, space group P2₁2₁2₁, with a=35.167(4), b=5.544(1), c=7.915(1) Angstroem, Z=4.Refinement of the two possible enantiomers gave R=0.0489, 0.0618; R_w=0.0323, 0.0436 for a total of 1806 observed reflections.The succesful determination of the chirality of the conformation of the reactant (the absolute conformation) made it possible, for the first time, to correlate the absolute configuration and optical rotation of the product and the conformation of the achiral, optically inactive, olefinic reactant in a chiral crystal.This correlation supports the proposed reaction mechanism involving a bromonium ion intermediate.The striking similarity of the packing arrangements of the product and reactant may explain the exclusive crystallization of crystals of one-handedness in excess, when minute quantities of the former are added to solutions of the latter.