Friday, May 23, 2008

NMR prediction on ChemSpider

As Tony recently mentioned, there is a new button on ChemSpider to predict H NMR spectra based on the web service:

To give it a spin I am posting the experimental spectrum of Ugi product UC-150D underneath the predicted one.

This is going to be extremely helpful and yet another reason for using ChemSpider in active chemistry research. However, this tool does not replace the need for understanding how to interpret NMR spectra.

First, two of the predicted peaks - the phenanthrene H at 8.5 ppm and the benzylic H at 5.7 ppm - are off by almost half a ppm. Second, the algorithm does not take into account the diastereotopic nature of the methylene group centered at 4.8 ppm. This is predicted to be a singlet but appears, as expected, as a pair of doublets.

With this new tool there is a danger that students might think that they don't need to learn the finer details of NMR analysis since the predicted spectrum just pops up so conveniently. I hope people will report on what they find to be most and least reliable as they work on real problems.

The beauty of ChemSpider is that both the theoretical and experimental spectra can be stored in the same record. Yet another reason to continue to routinely upload our spectra.


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