Specifically deuterated molecules may be used to distinguish various NMR signals because deuterium resonates at a different frequency than protium. This approach may be helpful to undergraduate students who synthesize and analyze chalcones that have aromatic and alkene signals with similar chemical shifts. Chalcone synthesis serves as a paradigm of the aldol condensation, a foundational carbon-carbon bond forming reaction that can be used to generate alkenes. Most of the chalcone synthesis experiments in the <i>Journal of Chemical Education</i> rely on starting materials containing benzene, resulting in products containing two aromatic rings. Thus, these molecules have NMR spectra with overlapping aromatic signals and, complicating matters further, the vinyl hydrogens are deshielded into the aromatic region because of conjugation. In this contribution, the possibility is explored that students gain competence and confidence when they are asked to analyze the spectra for a series of specifically deuterated chalcones before being asked to analyze the more complex spectrum of the fully protiated chalcone. Assessment data from both an honors section and a general section of second-year undergraduate organic chemistry will be presented to evaluate the effectiveness of this approach.

Distinguishing aromatic and alkene NMR signals using specifically deuterated chalcones

253rd National Meeting (2017)

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