A new undergraduate organic chemistry laboratory experiment has been developed to assign the absolute configuration of enantioenriched secondary alcohol stereogenic centers using the Competing Enantioselective Conversion (CEC) method. Each group of students is presented with one of three secondary alcohols with an unknown configuration. Students are tasked with (1) determining the absolute configuration of the unknown using the CEC method with thin-layer chromatography and (2) determining which of the three possible secondary alcohol structures match their unknown with the 1H NMR spectrum provided to them.The CEC method uses each enantiomer of a chiral kinetic resolution reagent in parallel reactions to carry out a transformation of the enantioenriched starting material of interest to product. After a given period of time, the reactions are halted and the reaction that has created more product is designated as the fast reaction. The experiment uses thin-layer chromatography as the analytical tool for finding the fast reaction, which is based on recently published research. Students perform a qualitative analysis by viewing the spot density of starting material and product in both reaction lanes on the stained TLC plate. Students then take a picture of the plate with any photo-taking device and perform a quantitative analysis with the free spot-density analysis program ImageJ. Based on a mnemonic, the absolute configuration can be assigned for both the qualitative and quantitative analyses.This experiment, to our knowledge, is the first published protocol for undergraduate students to determine the absolute configuration of stereogenic centers without the preparation of diastereomers and without the use of NMR spectroscopy. In the spring 2013 laboratory course, 1036 students performed the experiment across 58 laboratory sections. Analysis of the resultant student data revealed that 93.6% of students correctly determined the absolute configuration of their unknown.

Use of thin-layer chromatography to determine absolute configuration with the Competing Enantioselective Conversion (CEC) method

248th National Meeting (2014)

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