In recent years, photochemistry has experienced a “golden age”, rapidly advancing the field of organic synthesis. The exploration of photochemical reactivity led to a greatly expanded chemical space that is synthetically accessible. However, practical applications of photochemistry to achieve robust synthetic processes on an industrial scale were sparse due in large part to a mechanistic complexity of photochemical reactions and a lack of adequate tools to investigate those.
NMR has long been a very useful and powerful tool to monitor chemical reactions and to investigate their mechanisms. LED-based NMR illumination device first introduced in 2013 [1] as a simple and powerful tool to obtain valuable and rich kinetic and structural insights into photochemical reactions.
Using a similar setup, Merck NMR group developed a series of applications of LED-NMR to monitoring and studying of the photochemical reactions. Applications included NMR actinometry [2] to measure quantum yield of the reactions, comprehensive mechanistic investigations of the role of the photocatalysts [3], detecting and elucidating unstable reactive intermediates in situ [4] and troubleshooting photochemical reactions to enable the development of a robust 100+ kg scale flow photochemical reaction [5]. In this presentation we will demonstrate these applications and discuss the details of LED-NMR experiments. In addition, we will discuss the experimental setup, which is simple, affordable and could be easily employed in any lab equipped with an NMR spectrometer.
1. Feldmeier, C., Bartling, H., Riedle, E., and Gschwind, R.M.; J. Magn. Reson. 2013, 232, 39-44.
2. Ji, Y., DiRocco, D.A., Hong, C.M., Wismer, M.K., and Reibarkh, M.; Org. Lett. 2018, 20, 8, 2156–2159.
3. Lehnherr, D., Ji, Y., Neel, A.J., Cohen, R.D., Brunskill, A.P.J., Yang, J., Reibarkh, M.; J. Am. Chem. Soc. 2018, 140, 42, 13843–13853.
4. Ji, Y., DiRocco, D.A., Kind, J., Thiele, C.M., Gschwind, R.M., and Reibarkh, M.; ChemPhotoChem, 2019, 3, 984–99.
5. Ji, Y., Bottecchia, C., Lévesque, F., Narsimhan K., Lehnherr, D., McMullen, J.P., Dalby, S.M., Xiao, K.-J., and Reibarkh, M.; J. Org. Chem. 2022, 87, 4, 2055–2062.