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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: afila2012 on October 07, 2012, 06:38:40 AM

Title: C13 NMR - Spectroscopy
Post by: afila2012 on October 07, 2012, 06:38:40 AM

I am trying to interpret the H1 NMR and C13 NMR spectra to work out the structure of an unknown molecule but I'm having a few problems.

 I have a peak on the C13 NMR at -0.003ppm. This then shows up a tiny bit on the DEPT spectrum. At first I thought maybe just ignore it but on further investigation I'm thinking it must be a carbon in the molecule as we have a large 3 hydrogen peak in the H1 NMR which suggests it would be a methyl group.

Just wondering if anyone knows if it's possible (and can then explain why) for the C on a CH3 group to have a peak at -0.003ppm or if it's some impurities to just be ignored.

Thanks

Title: Re: C13 NMR - Spectroscopy
Post by: discodermolide on October 07, 2012, 08:07:40 AM

-0.003ppm is not very far away from 0ppm.
Surely this is within the thickness of the ink of the recorder?
Is it a -SiMe group? Remembering that SiMe₄ is set at 0ppm.