Single‐Scan Selective Excitation of Individual NMR Signals in Overlapping Multiplets

Peter Kiraly,Gareth A Morris,Mathias Nilsson,Nicolas Kern,Ralph W Adams,Mateusz P Plesniak,David J Procter

doi:10.1002/ange.202011642

Abstract

Abstract2D NMR is an immensely powerful structural tool but it is time‐consuming. Targeting individual chemical groups by selective excitation in a 1D experiment can give the information required far more quickly. A major problem, however, is that proton NMR spectra are often extensively overlapped, so that in practice only a minority of sites can be selectively excited. Here we overcome that problem using a fast, single‐scan method that allows selective excitation of the signals of a single proton multiplet even where it is severely overlapped by other multiplets. The advantages of the method are illustrated in a selective 1D NOESY experiment, the most efficient way to determine relative configuration unambiguously by NMR. The new approach presented here has the potential to broaden significantly the applicability of selective excitation and unlock its real potential for many other experiments.

Highlights

2D NMR is an immensely powerful structural tool but it is time-consuming
Suitable selective pulses for such experiments exist for a wide range of applications[1,3] but have a common limitation: where multiplet structure in proton NMR spectra causes overlap between signals, a single signal cannot be excited without perturbing others
We report a novel approach, a gradient-enhanced multiplet-selective targeted-observation NMR experiment (GEMSTONE), that gives unprecedented selectivity and for the first time allows a single multiplet to be extracted from an overlapped region of many proton signals in a single scan

Summary

Introduction

Experiments often have the capability to provide all the information required for structure elucidation in a fraction, as low as a percent or so, of the 2D experiment time.[2] They use selective pulses to excite a specific signal of interest only. Suitable selective pulses for such experiments exist for a wide range of applications[1,3] but have a common limitation: where multiplet structure in proton NMR spectra causes overlap between signals, a single signal cannot be excited without perturbing others.

Results

Conclusion