Synthesis and NMR Spectral Analysis of Amine Heterocycles: The Effect of Asymmetry on the 1H and 13C NMR Spectra of N,O-Acetals.

• Autores: James A. Ciaccio, Shahrokh Saba, Jennifer Espinal, Courtney E. Aman
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 84, Nº 6, 2007, págs. 1011-1013
• Idioma: inglés
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• Resumen

  • We describe an undergraduate organic laboratory experiment in which students prepare two structurally similar heterocyclic amines: one achiral, 3-isopropyloxazolidine, 2, and the other chiral, (±)-3-isopropyl-2-(4-nitrophenyl)oxazolidine, 3. These N,O-acetals differ only by the presence of a single ring substituent that introduces asymmetry; thus, each compound has distinct 1H and 13C NMR spectral patterns. Each student prepares 2-(isopropylamino)ethanol, 1, and then the class is divided into two groups: one group prepares 2, and the other group prepares 3. NMR spectroscopy clearly indicates that the nuclei of the methyl groups (and the hydrogens of each methylene) of 2 and 3 are enantiotopic and diastereotopic, respectively. Students must explain why the NMR spectra of 3 have more peaks in the aliphatic region and increased coupling in the 1H spectrum, leading to a discussion of prochirality and topicity of ligands within a single molecule. This operationally straightforward experiment is a meaningful exercise in chemical synthesis and spectral problem solving, and students sample the benefits of collaborative work by dividing up the synthetic and analytical tasks and then sharing their data.