Broadband ultrafast 2D NMR spectroscopy for online monitoring in continuous flow

Flow NMR is a powerful tool to monitor chemical reactions under realistic conditions. Here, we describe ultrafast (UF) 2D NMR schemes that make it possible to acquire broadband homonuclear 2D NMR spectra in 90 seconds or less for a continuously flowing sample. An interleaved acquisition strategy is used to address the spectral width limitation of UF 2D NMR. We show how, for a flowing sample, the use of a transverse axis for spatial encoding makes it possible to achieve the very high scan-to-scan stability required for interleaved acquisition. We also describe an optimised solvent suppression strategy that is effective for interleaved acquisition in continuous flow. These developments open the way to online monitoring with flow 2D NMR at high time resolution, as we illustrate with the monitoring of an organocatalysed condensation reaction. 2D NMR spectra with full spectra width are obtained from continuously flowing samples in less than 90 s, using interleaved ultrafast NMR acquisition.

Automated summary

In this study, ultrafast 2D NMR schemes were developed to acquire full spectral width 2D NMR spectra from continuously flowing samples in a short time. By using an interleaved acquisition strategy and an optimized solvent suppression strategy, it was possible to monitor chemical reactions online at high time resolution.