Crystal structure, conformation, and absolute configuration of (?)-menthyl-p-bromophenylglyoxylate

Abstract

The crystal and molecular structure of (—)-menthyl-p-bromophenylglyoxylate has been studied by x-ray diffraction techniques using diffractometer data. Crystals of this compound are triclinic:a= 10.152(3),b=19.661(3),c = 9.220(3) A, α = 92.45(2), β = 102.74(4), γ = 93.11(4) °, andZ = 4. The structure was refined by least squares toR = 0.064. All 88 hydrogen atoms were determined from electron density difference maps. The significant structural features are the following: (i) the four molecules are conformationally different from one another; (ii) the two > C=O groups of the glyoxylate are twisted with respect to each other across the central C-C bond by angles ranging from 92 ° to 111 °; (iii) the phenyl group is coplanar with the proximal > C=O group; and (iv) all four molecules exhibit a conformation in which the axial hydrogens on the cyclohexane rings eclipse the closer keto oxygen. The absolute configuration was determined by the anomalous dispersion method and is (1R, 3R, 4S).