Mass Spectrometry in Organic Synthesis: Claisen–Schmidt Base-Catalyzed Condensation and Hammett Correlation of Substituent Effects

Abstract

Undergraduate laboratories generally teach an understanding of chemical reactivity using bulk or semimicroscale experiments with product isolation and subsequent chemical and spectroscopic analysis. In this study students were exposed to mass spectrometry as a means of chemical synthesis as well as analysis. The ionization method used, paper spray, is rapid and can be coupled with online analysis (by mass spectrometry) or off-line analysis (e.g., thin layer chromatography). Chemical synthesis in the course of paper spray ionization takes advantage of the accelerated reaction rates associated with changes in pH and reagent concentrations. Such changes arise from solvent evaporation from charged microdroplets. In these experiments students contrasted paper spray techniques with traditional bulk synthetic methods for the Claisen–Schmidt base-catalyzed condensation. From mass spectral data obtained during the laboratory session, students were able to model electronic effects of substituents on reaction rates. Experimental procedures tailored to the undergraduate organic teaching laboratory are provided.