The Student Room Group
Original post by nisha.sri
Is it only in the C13 NMR where all the nitrogen etc... disappear ? Does it happen in proton nmr too ? Also what effect do this have if this is added ?


Nope. D2O only has an effect on proton NMR spectra. OH and NH groups don't have carbon in them, so they wouldn't show up on the 13C spectra at all, as they don't have carbon environments.

Adding D2O (also known as a 'D2O shake') is useful, as it removes the peaks on the proton NMR spectra which could be caused by OH and NH groups - this is because these groups aren't split and could appear anywhere along the spectra.

Naturally, a normal hydrogen atom has an odd mass number, so it has a property called 'spin', meaning it can be detected by proton NMR. A deuterium atom (an isotope of hydrogen) has an even mass number, so it doesn't have spin, hence isn't detected by proton NMR. So, adding D2O makes peaks 'disappear' since the added deuterium replaces the hydrogen atoms in OH and NH groups, hence they're not detected afterwards.

A chemist would typically do a first NMR run, add D2O, and then do a second NMR run. The chemist would then compare both spectra to see which peaks aren't there anymore, as this indicates OH or NH groups.
(edited 5 years ago)
Reply 2
Original post by username2312801
Is it only in the C13 NMR where all the nitrogen etc... disappear ? Does it happen in proton nmr too ? Also what effect do this have if this is added ?

In nuclear magnetic resonance (NMR) spectroscopy, the disappearance of signals related to certain nuclei, such as nitrogen, is more commonly associated with carbon-13 (C13) NMR rather than proton (H1) NMR.

1.

C13 NMR:

2.

In C13 NMR, the signal for nitrogen, along with signals for other heteronuclei like oxygen, sulfur, etc., usually doesn't appear. This is because carbon-13 NMR primarily focuses on the carbon-13 isotope, which is the stable isotope of carbon and the one commonly used in C13 NMR spectroscopy.

3.

H1 NMR:

4.

In proton NMR, signals for hydrogen atoms, including those in functional groups like amines (containing nitrogen), are observed. Nitrogen does not directly give rise to a signal in proton NMR unless it is part of a hydrogen-containing functional group.

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