Challenge your learners to improve their NMR interpretation

Nuclear magnetic resonance (NMR) spectroscopy is a versatile tool used in a wide range of scientific disciplines, including chemistry, materials science, biology and medicine.

Beyond structural elucidation, scientists use NMR spectroscopy to study reaction kinetics, reaction mechanisms and intermolecular interactions. Interpreting NMR spectra is a core skill and consequently an integral component of teaching post-16 spectroscopy.

Students first encounter NMR spectra in secondary school, where they use it to determine the structures of simple organic molecules as part of problem-solving style questions. As an information-rich technique, students can use multiple components of spectra to derive structural information, such as the number, intensity and shape of signals, the chemical shift and J-coupling constants. While often challenging, these questions can develop critical thinking skills.

They identified many common mistakes, possibly reflecting students’ misunderstandings of the basic principles of NMR spectra

The creators of the site organised the problems by complexity. The basic level contains 148 1D spectra (¹H, ¹³C and ¹⁹F) and are appropriate for secondary school students. The advanced level contains 2D spectra. Within the basic and advanced levels, there is further classification: easy, moderate and hard.

In a new paper, the researchers – who developed the site – analysed the success rates of all 200 tasks on NMR Challenge, consisting of more than 428,000 solutions from around the globe, the largest database of responses to NMR assignments. Through this analysis, they identified many common mistakes, possibly reflecting students’ misunderstandings of the basic principles of NMR spectra. The following three case studies summarise the main findings.

Interpreting the findings

Case study 1: when considering isomeric esters, the researchers found students to be competent in using spectral information to recognise molecular fragments, such as a monosubstituted benzene ring, an ethyl chain and the ester group. However, students were less able to use the chemical shift values to identify the connectivity of these fragments.

Case study 2: when considering substitution patterns in disubstituted benzenes, students only recognised para-substituted structures well. The more complex splitting pattern in the ¹H spectrum for ortho- and meta-disubstituted benzenes is the likely cause. However, you can use the number of signals on ¹³C spectra to distinguish homodisubstituted benzenes, which learners rarely considered.

Case study 3: many spectra also included intramolecular interactions, for example the formation of a hydrogen bond between an exchangeable hydrogen atom (for example, OH) and a hydrogen bond acceptor (for example, O in carbonyl). Students often misidentified the increase in chemical shift in the exchangeable hydrogen as they principally used the ¹H NMR spectra for identification and therefore did not draw the correct structures.