Distinguishing Vinylic and Aromatic 1H NMR Signals Using Selectively Deuterated Chalcones

• Courtney A. Gehman ^[1] ; Eric R. Hantz ^[1] ; Christian S. Hamann ^[1]
  1. [1] Albright College

     Albright College

     City of Reading, Estados Unidos

     
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 98, Nº 7, 2021, págs. 2323-2332
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • 1H NMR spectroscopy is a molecular characterization technique that is ubiquitously used in research and teaching laboratories alike. Strategic deuteration of molecules is a commonly employed technique in the deconvolution of 1H NMR signals. Here this approach is applied in a second-year chemistry course in which students synthesize 4-methoxychalcone using the Claisen–Schmidt variant of the foundational aldol reaction. The 1H NMR spectrum is complicated by a crowded aromatic and alkene region due in part to extensive conjugation through the two phenyl groups surrounding an α,β-unsaturated ketone. This report demonstrates that students gain competence and confidence in making 1H NMR assignments when presented with a curated set of selectively deuterated chalcones rather than the corresponding spectrum of the fully protiated chalcone. While deuteration does not resolve all of the challenges associated with interpreting this spectrum, it is an invaluable tool to complement chemical shifts (including the predictive nature of resonance structures), integration, and spin–spin splitting. A proposed lecture is presented that is timed to correlate with the performance of the chalcone synthesis lab. Assessment data collected before and after the lecture and then again on the final exam point to the effectiveness of this approach.