Atoms and structure play unexpected role in optical rotation

Abstract

The creators of a theoretical method that computes a molecule's absolute stereochemistry now say they can determine the role each atom or group of atoms plays in a molecule's optical rotation angle—and the results can be unexpected. The rotation angle of plane-polarized light as it's shined through chiral molecules is one of the key ways of distinguishing stereoisomers from each other. But although quantum mechanics has long explained the link between optical rotation angle and structure, a reliable method for performing the requisite cumbersome calculations remained elusive until recently. Earlier this year, however, chemistry professors David N. Beratan and Peter Wipf and graduate student Rama K. Kondru, all at the University of Pittsburgh, were able to predict the absolute stereochemistry of hennoxazole, a complex marine natural product. They correlated the molecule's absolute stereochemistry with an optical rotation angle, thus confirming which stereoisomer was which (C&EN, March 2, page 9). Now they'...