What is it about?
The HMBC experiment while very widely employed in structure elucidation protocols is at a disadvantage when optimized for very small long-range heteronuclear couplings. At the end of the expeirment, the magnetization is antiphase and when the absolute value spectrum is calculated for presentation the antiphase components can self-cancel preventing the correlation from being observed. LR-HSQMBC, in contrast, is specifically optimized for very long-range heteronuclear correlations. Magnetization is refocused and decoupling can be applied. Hence, while HMBC can "reach out" 3 and only occasionally 4 bonds, in contrast, the LR-HSQMBC experiment routinely affords 4, 5, and often 6 bond correlations. The LR-HSQMBC experiment should be employed AFTER interpreting the HMBC data.
Featured Image
Why is it important?
LR-HSQMBC provides the means of accessing very long-range heteronuclear correlations that cannot be observed using the HMBC experiment.
Perspectives
We have been able to probe very long-range correlations to regions of molecular scaffolds that are devoid of any protons within three bonds, which renders them "transparent" in most cases to being probed with the HMBC experiment. In rigid molecular skeletons 4, 5, 6, and even 7-bond couplings have been observed.
Gary Martin
Merck Research Laboratories
Read the Original
This page is a summary of: LR-HSQMBC: A Sensitive NMR Technique To Probe Very Long-Range Heteronuclear Coupling Pathways, The Journal of Organic Chemistry, April 2014, American Chemical Society (ACS),
DOI: 10.1021/jo500333u.
You can read the full text:
Contributors
The following have contributed to this page
