Enantiomeric and Diastereoisomeric Relationships: A Practical Approach

Abstract

We describe an experiment in organic chemistry in which the students prepare, purify, and characterize optical isomers. The three optical isomers of the bisoxalamides obtained by the reaction of racemic 1-phenylethylamine with diethyloxalate are separable by flash chromatography into the racemic mixture of (R,R) + (S,S) oxalamides and the (R,S) meso compound. The purified diastereomers are characterized using UV and IR spectra and mp. The mixture may also be quantitatively analyzed by HPLC. The meso isomer and the enantiomers are formed in nearly identical quantities. This observation offers us a means to calculate the optical purity of the starting a-phenylethylamine: the incorporation of an R or S carbon into the oxalamide is assumed to be purely statistical.After resolution of the alpha-phenylethylamines by a previously described procedure and transformation of the enriched R(+) and S(-) amines into the corresponding bisoxalamides, the students determine the diastereomeric composition of their products...