Design of a combined LED and rapid-injection NMR system for structure elucidations and kinetic analyses

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique often used for structural elucidation of various molecules. The utility of NMR for in situ reaction monitoring is represented by the numerous strategies to conduct chemical reactions inside of the spectrometer, such as rapid-injection (RI-NMR) and LED NMR. In this work, the design of a combined LED and rapid-injection NMR (LED-RI-NMR) apparatus is described and showcased in kinetic studies for three photochemical reactions. The simple design of the LED-RI-NMR system allows for the introduction of both light and reagents into NMR samples for in situ reaction monitoring of reactive intermediates. The distinguishing features of the LED-RI-NMR system described herein include the ability to explore and intercept photogenerated intermediates via RI-NMR and explore the photochemical properties of fleeting intermediates generated by RI-NMR. We demonstrate the versatility of this experimental tool for the kinetic study of organophotoredox cycloadditions, Wolff rearrangements, and azobenzene isomerization reactions.