NMR Structure Elucidation in the Presence of Heteroatoms: An In-Class Activity

In the undergraduate curriculum, the focus of NMR spectroscopy is predominately on molecules containing 1H and 13C as the sole NMR-active nuclei. Teaching students about the impact of NMR-active heteronuclei such as 19F or 31P can be challenging to fit in the undergraduate curriculum, especially if NMR instrumentation and/or a range of compounds are not available. We present an activity to be conducted in class that exposes undergraduates to how heteronuclear NMR spectroscopy can be used to aid in structure elucidation when NMR-active heteroatoms are present. The purpose of the activity is both to expand student understanding of NMR applications as well as further their understanding of the underlying principles of NMR. The activity utilizes a comparative analysis of 1H and 13C NMR spectra of a compound containing no NMR-active heteroatoms with a structurally analogous compound containing I > 0 heteroatoms. Students are tasked with predicting the impact of the heteroatom on the NMR spectrum, followed by the assignment of signals in the actual NMR spectra.