Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Wald_ron on October 06, 2011, 03:34:04 PM
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Why does DEPT not show Carbons without any Hydrogens on it? Are they simply lost in the Noise?
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No, they won't show because of the method used to obtain a DEPT spectrum.
13C spectra, if they were taken in the same manner 1H spectra were taken, would show enormous couplings between the carbon and any protons on it. This would make spectra difficult to read. Instead, the proton range is irradiated to decouple the protons from the carbons, collapsing the expected multiplets back into singlets. Very strong singlets due to the polarization transfer, which is why even in a normal 13C spectra, the quaternary carbons have very weak signals compared to protonated ones.
In a DEPT spectra, the irradiation is tuned to give a specific tip angles for the protons, and the spectra collected in the carbon range. Only the carbons which have protons and can exhibit polarization transfer will show, and different tip angles will cause different arrangements to show.
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The various DEPT-sequences are used for distinguishing CH, CH2 & CH3 from one another. DEPT-spectrum usually
doesn't have any peaks for the quaternary carbons.
[Note: fledarmus was quicker than me, but I'll post this anyway]
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Thank you :)