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unexpected NMR results for a morpholine-based amide

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Babcock_Hall:
https://organicchemistrydata.org/hansreich/resources/nmr/?index=nmr_index%2F13C_shift#cdata84

Good Morning,

We made (EtO)2P(O)CH2C(O)N(-CH2CH2OCH2CH2-), where the amide is the morpholine group.  As expected, four of the carbon atoms showed coupling to phosphorus.  There are two signals, 47.3 ppm and 42.4 ppm, that I believe to be -NCH2- groups.  Given that there is restricted rotation around the amide (-NC(O)-) bond, seeing two peaks is understandable (see link for a couple of examples).  However, the peak that I assigned to -OCH2- at 66.7 ppm is the only signal in this region other than the CH3CH2[/sub]O- peak, which is one of the doublets.  I am a little puzzled why restricted rotation would affect one carbon atom and not the other.

Later I may post a little bit about the H-1 spectrum as well.

rolnor:
To see the effect off restricted rotation the atom needs to get two different environments magneticaly, mayby one off the atoms does not have this?

Babcock_Hall:
A colleague of mine suggested something similar, which is that the difference in the two environments of the CH2O groups may be small enough to put these two nuclei into the fast-exchange regime.  I need to refresh my memory on chemical exchange to make sure that I understood correctly.

rolnor:
Its at least possible, can you maybe cool the probe? Or look at proton-nuclei?

Babcock_Hall:
I just looked at the H-1 NMR.  The 8 hydrogen atoms of the morpholine group form a multiplet centered near 3.68 ppm.  It looks like a triplet in which each of the three signals is further split into two or three signals.

When I went to Hans Reich's site, I found a few examples of amides in which the two carbon atoms directly attached to the nitrogen atom had C-13 chemical shift differences around 2-3 ppm.  I have not searched extensively for morpholine-containing compounds specifically.

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