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Why is HMBC superior to LR‐HSQC? Influence of homonuclear couplings J HH′ on the intensity of long‐range correlations
Author(s) -
Bigler Peter,
Furrer Julien
Publication year - 2018
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4762
Subject(s) - homonuclear molecule , heteronuclear molecule , heteronuclear single quantum coherence spectroscopy , chemistry , proton , range (aeronautics) , coherence (philosophical gambling strategy) , nuclear magnetic resonance , physics , two dimensional nuclear magnetic resonance spectroscopy , nuclear physics , quantum mechanics , nuclear magnetic resonance spectroscopy , molecule , stereochemistry , composite material , materials science , organic chemistry
Long‐range heteronuclear single quantum correlation (LR‐HSQC) experiments may be applied as an alternative to heteronuclear multiple‐bond correlation (HMBC) experiments for detecting long‐range correlations but has never enjoyed popularity for that purpose. To the best of our knowledge, the exact reasons have not yet been fully established. For both experiments, it is widely accepted that the evolution of proton–proton homonuclear couplings J HH′ during the polarization transfer delays Δ leads to significant losses, and that the intensity of the observable coherence is zero when J HH′ matches the condition Δ = 0.5/ J HH′ . Here, we analyze the influence of J HH′ on the intensity of long‐range correlations in HMBC and LR‐HSQC spectra. We show that for both experiments long‐range correlations will not be canceled because of homonuclear couplings J HH′ . Our theoretical and experimental results definitely establish and validate the superiority of HMBC‐based experiments among the family of heteronuclear long‐range correlation experiments: (a) the overall cross peak's intensity is higher, and (b) in LR‐HSQC experiments, the intensity of the long‐range cross peaks is additionally influenced in an unwanted way by the magnitude and number of passive homonuclear proton–proton couplings J HH′ .