Isolation and Stereochemistry of Optically Active Selenonium Imides

Optical resolution of racemic diaryl selenonium-N-toluene-4‘-sulfonimides (rac-1a−d) by liquid chromatography using an optically active column yielded optically pure selenonium imides. The absolute configuration around the selenium atom of (−)-2,4,6-tri-tert-butyldiphenylselenonium N-toluene-4‘-sulfonimide [(−)-1a] was determined to be S by X-ray crystallographic analysis, and those of the other optically active selenonium imides were determined on the basis of their specific rotations and CD spectra. The kinetics of racemization by pyramidal inversion of the optically active selenonium imides (+)- and (−)-1b and 1d were studied. The results indicated that the activation energy for the racemization of optically active selenonium imides was greater than those for sulfonium imides

Bistable Polymorphs Showing Diamagnetic and Paramagnetic States of an Organic Crystalline Biradical Biphenyl-3,5-diyl Bis(<i>tert</i>-butylnitroxide)

Bistable Polymorphs Showing Diamagnetic and Paramagnetic States of an Organic Crystalline Biradical Biphenyl-3,5-diyl Bis(tert-butylnitroxide

Solid State Optical Activity of Dichalcogenides: Isolation by Chiral Crystallization and Determination of Absolute Configuration

Optically active diphenyl dichalcogenides were isolated in bulk for the first time by chiral crystallization. The absolute configuration of the P-helical enantiomer of diphenyl disulfide was determined by X-ray crystallography. On the basis of this determination and considering the similarities of the Cotton effects of diphenyl diselenide and ditelluride, the absolute configuration of optically active diphenyl dichalcogenides could be assigned. Furthermore, stereochemistry of chiral crystallization could be controlled by using an optically active crystal as a seed crystal