Molecular Properties of Caffeine Explored by NMR: A Benchtop NMR Experiment for Undergraduate Physical-Chemistry Laboratories

NMR is a fundamental part of any undergraduate chemistry degree, and training students how to measure and interpret NMR spectra is essential for postgraduate research or chemistry-based careers. Traditionally, the undergraduate laboratory experience with NMR is restricted to sample submission for NMR analysis, which is typically conducted by a technician. However, instant access to NMR instrumentation is now possible because of the development of benchtop NMR spectrometers. These can be placed on the lab bench alongside other spectroscopic equipment. The simplicity of operation and variety of experiments available allows the development of new undergraduate experiments across organic-, inorganic-, and physical-chemistry laboratories. Here we describe a new experiment for undergraduate physical-chemistry laboratories that incorporates relaxation measurements to understand the behavior of caffeine in a variety of conditions. The experiment uses the T ₁ and T ₂ experiments available on most benchtop spectrometers, which can be processed using a variety of software packages. The experiment, performed in the third year of a 4 or 5 year Bachelor's or Master's degree, follows a five-lecture unit on NMR spectroscopy as part of a third undergraduate chemistry course. It can be conducted in pairs or groups of three in three 3 h laboratory sessions, but it can be tailored to reduce the required time. The experiment allows students to become proficient users of a new piece of equipment, incorporate taught theory, and handle data in different platforms and software packages. Allowing students hands-on access to NMR instrumentation gives them a complementary experience to their NMR lectures and offers a unique way to inspire a new generation of chemists.