Visualizing Unresolved Scalar Couplings by Real-Time J-Upscaled NMR

Scalar coupling patterns contain a wealth of structural information. The determination, especially of small scalar coupling constants, is often prevented by merging the splittings with the signal line width. Here we show that real-time J-upscaling enables the visualization of unresolved coupling constants in the acquisition dimension of one-dimensional (1D) or multidimensional NMR spectra. This technique, which works by introducing additional scalar coupling evolution delays within the recording of the FID (free induction decay), not only stretches the recorded coupling patterns but also actually enhances the resolution of multiplets, by reducing signal broadening by magnetic field inhomogeneities during the interrupted data acquisition. Enlarging scalar couplings also enables their determination in situations where the spectral resolution is limited, such as in the acquisition dimension of heteronuclear broadband decoupled HSQC (heteronuclear single quantum correlation) spectra.