Hexacyclinol - NMR spectra vs plain images
Hexacyclinol - NMR spectra vs plain images
I’m sure that many of you are aware of the infamous controversy over the total synthesis of Hexacyclinol . There are a plethora of arguments, from the purely synthetic chemical point of view to the spectroscopist perspective, which both put in doubt the veracity of aforementioned total synthesis. You can find, at the end of this post, a list of references that may be of interest on this subject. In this particular post, I would like to comment on several interesting aspects from an NMR standpoint. In the original article’s “supporting information”, one can find the spectra of Hexacyclinol and derived compounds. I believe that the key to the controversy here lies in the fact that these spectra are found solely as plain images, that is, all the relevant spectral information that could have provided more conclusive proof over the authenticity or not of the total synthesis of this compound is lost. Let’s consider for example, the image of the Hexacyclinol spectrum: http://2.bp.blogspot.com/-O9qaiExyYC.../s400/Hexa.jpg I have cut the central vertical area of the image in order to visualize the highest intensities as well as the smallest ones together. The objective is to simply appreciate with clarity the level of 13C satellites intensities in the case of the CHCI3 signal. The level is indicated by the red horizontal line which would correspond, approximately to an intensity of 32, that is, a ~0.55% of the intensity of the CHCI3 signal. At first glance, one cannot observe such signals from the 13C satellite. Is this a conclusive reason to assume that this spectrum is really a fake, that is, a spectrum that was created synthetically? Of course, I’d say it is not conclusive but it could be an indication. In principal, I would say that the SNR of this spectrum seems good enough for the 13C signals to be observed; not only in the CHCI3 area but rather that they cannot be observed in any part of the spectrum. I can only come up with two reasons that justify the absence of those signals:
In summary, it is very difficult to reach conclusive results working with plain images. Once the spectra have been acquired, transforming them into images only result in an irreversible loss of important information. I believe that publishers should oblige authors to submit spectra/original FID’s (including all the files with additional metadata) to avoid any type of loss of relevant information. References:
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