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Determination of heteronuclear long-range H,X coupling constants from gradient-selected HMBC spectra

✍ Scribed by Wieland Willker; Dieter Leibfritz

Publisher
John Wiley and Sons
Year
1995
Tongue
English
Weight
539 KB
Volume
33
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

A gradient‐selected J‐HMBC experiment is presented. Coherence selection with magnetic field gradients results in HMBC spectra in which t~1~ noise is very low or completely eliminated. This makes it possible to detect unequivocally very small (<2 Hz) long‐range H,X coupling constants. With a slight modification, the HMBC experiment can be used for the quantitative measurement of these couplings. The signal amplitude of spectra with increasing coupling evolution time Ο„ shows the characteristic sin (Ο€J~XH~Ο„) dependence. By fitting a sine curve to the experimental data or by performing a 3D J‐resolved HMBC experiment, accurate ^n^J~XH~ coupling constants are obtained. This method is especially useful for estimating coupling constants between protons and unprotonated heteronuclei, e.g. quaternary carbons, ^15^N nuclei in labelled prolines or ^31^P in organophosphates.

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