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The article by Mannschreck, Kiessewetter, and von Angerer on the differential interactions between enantiomers and biological receptors (1) is the source for this month’s Featured Molecules. Included in the molecule collection are all of the molecules described in the paper. In many instances we have included structures of multiple optical isomers of the same molecule so that students can not only see the forms that are active, but those that are less active, inactive, or act in an undesirable manner. These molecules will serve as good practice in determining optical configurations, and will also introduce additional forms of isomerism that students may be less familiar with than they are with R and S. Since multiple enantiomers and diastereomers are provided, students may use these molecules, together with an appropriate computational package, to verify that enantiomers have the same energy while diastereomers do not. The tuberculosis drug ethambutol provides an interesting case as both nitrogen atoms are also chiral as well as the two chiral carbon atoms. A calculation on a given structure will include the effect of that nitrogen chirality, although nitrogen inversion is expected to be quite rapid in this molecule. The conformations for the ethambutol molecules that are included here consider all four chiral atoms and are of the form (CNNC). A reasonable computational exercise would be to find the transition state for nitrogen inversion and the barrier height for that process. The supplemental material that is included with the featured article (1) includes a number of molecules that we will add to the collection as time permits. The result, including enantiomers and diastereomers, will be well over 200 additional molecules. A notice will appear in the JCE Featured Molecules column when this new set of molecules is available in JCE Online. 
(S,S)-ethambutol
Students can examine the structures of many drug, pesticide, and fragrance molecules in Jmol or Chime, along with the other molecules in the collection, at the JCE Digital Library Web site. Literature Cited- Mannschreck, A.; Kiesswetter, R.; von Angerer, E. J. Chem. Educ. 2007, 84, 2012.
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