Extracting unresolved coupling constants from complex multiplets by a real‐time J‐upscaled SERF experiment

Abstract

The measurement of small homonuclear coupling constants is often prevented by either their small size and/or overlap with other signal splittings. Here, we present a real‐time method to extract such couplings without interference from other splittings, with a resolution that is beyond conventional NMR spectra. In this real‐time J‐upscaled SERF experiment, homonuclear coupling is removed by slice‐selective pure shift NMR, whereas scalar coupling to only one selected signal is reintroduced by selective refocusing. The remaining couplings are enhanced by real‐time J‐upscaling during interruptions of the FID data acquisition. The resulting spectrum is not only simplified by the restriction of the scalar coupling but also its resolution enhanced. This improved resolution results from a reduction of signal broadening due to magnetic field inhomogeneities from 2 different sources: slice‐selective excitation and the spin‐echo type J‐upscaling element.

CSSF-CLIP-HSQMBC: measurement of heteronuclear coupling constants in severely crowded spectral regions

“…8 A 3D HSQC-HSQMBC approach has also been proposed to address the problem of spectral overlap, 9 as well as a J-scaled CLIP-HSQMBC. 10 In order to overcome this limitation we here propose to apply gradient enhanced proton chemical shi selective ltration (CSSF) 11 as the selection element in the CLIP-HSQMBC method. The ability to very cleanly select an unresolved multiplet in the proton dimension also results in a reduced number of observed correlations in the carbon dimension, thereby reducing the risk of inconvenient overlaps, both direct and folded/aliased, within the sampled carbon spectral width.…”

“… 8 A 3D HSQC-HSQMBC approach has also been proposed to address the problem of spectral overlap, 9 as well as a J -scaled CLIP-HSQMBC. 10 …”