True power of 1D NMR

An interesting case study of a correct structure assignment for aquatolide appeared in JOC. It’s interesting from several points of view. First, it nicely shows how one can effectively use reach information from free induction decay (FID), which is lost (or masked) in Fourier-transformed spectra. Second, it emphasizes importance of data sharing and demonstrates crucial role of ‘research parasites‘ in scientific ecosystem. Third, the paper has seven-point manifest in the conclusions section.

The introduction sets the stage for the rest of the paper with quite a bold quote:

The present study demonstrates that practically everything the chemist needs to know for a correct structural elucidation process is contained in the proton NMR FIDs.
And then in the subsection entitled “Consequences of Incomplete Correlation Maps” the authors are grumbling a lot about insufficient attention of researchers and journals to a thorough analysis of 1D 1H NMR spectra (‘The mother of all NMR experiments’ ©). Later in “Intelligent Use of HNMR Observations” they show what was wrong with the old structure of aquatolide and how one should pay more attention to discrepancies in experimental vs. predicted chemical shifts and Js. The scrupulous 1.5-page long Hemingway-style description of the spectrum in “Full HNMR Interpretation of Aquatolide” rounds up the “1D” part of the paper and in authors’ words “provides a model treatment of 1H homonuclear NMR data, which should be reported for even apparently straightforward structural assignment”.

multiplets
I fell in love with these snobby ‘”Multiplets”‘

In general, it looks like the actual structure of aquatolide was just a decoration for authors to write their “1D HNMR manifesto”. Seriously people, no cheating with 2D, play around with apodization and do the full autopsy on your 1Ds first! I wonder what would they say about 2DJ NMR.

Confirmation employing 2D data sets is appropriate after the 1D spectrum has been  thoroughly examined and can focus on issues that are otherwise not fully resolved.
From the practical side, the authors suggest a nice and clear graphic method of assigning coupling constants, Quantum interaction and linkage tables (QuILTs). It is applicable to 1D as well as 2D spectra and could be indeed a good standard for reporting NMR spectra instead of (or together with) text transcripts and actual pictures of spectra used nowadays.
Surprisingly enjoyable read 🙂

 

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Author: Slava Bernat

I did my PhD in medicinal chemistry/chemical biology of G protein-coupled receptors and then explored some chemical biology of non-coding RNA as a postdoc. Currently I'm working in a small biotech company in San-Francisco Bay area as a research chemist. I'm writing about science, which catches my attention in rss feed reader and some random thoughts or tutorials.

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