Adapting Chiral Gas Chromatography into Existing Undergraduate Laboratories to Emphasize the Importance of Stereochemistry

Owing to the critical role of stereochemistry in biotechnology, medicine, and industry, it must be well represented in undergraduate lab curricula. To achieve these stereochemical laboratory requirements without sacrificing existing lab techniques, we modified two standard laboratory experiments to include chiral GC analysis as follows. (1) The extraction of carvone from spearmint leaves and caraway seeds via steam-distillation or other extraction methods is widely used in laboratories for analyzing the stereochemistry of the extracted products. The experiment was modified to include a GC method using a β-DEX 225 column. This allowed the students to compare the retention times of the spearmint and caraway extracts with those in a racemic mixture and predict their stereochemical configurations (Ror S). (2) The reduction of aldehydes and ketones is another common experiment performed at most institutions. Reduction of acetophenone using sodium borohydride produces a racemic mixture that is observed in the form of two retention times on the chromatogram. Alternatively, reduction using either enantiomer of commercially available Corey–Bakshi–Shibata (CBS) catalysts provides alcohols with higher enantiopurity. Using the GC data, students determined the dominant alcohol enantiomer produced by comparing the retention times of the product enantiomers with that of commercially available enantiopure alcohols. They also used chromatographic data to calculate the enantiomeric excess from their reactions. The experiments also teach students other essential methods, such as inert-atmosphere techniques, thin-layer chromatography, multivendor software analysis, and determining the effects of reaction conditions on product yield and stereochemistry.