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Topic: nmr interpretation  (Read 10685 times)

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Offline AMARACHUKWU

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Re: nmr interpretation
« Reply #15 on: May 10, 2018, 04:00:57 PM »
here is a second isolate which i sent for nmr and ir analysis. i hope this turns out better than the first isolate. in this case used the libermanns test using acetic acid and conc sulphuric acid 1:1 in an ice bath and it gave a fushia pink/purple coloration which suggests a triterpenoid

Offline wildfyr

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Re: nmr interpretation
« Reply #16 on: May 10, 2018, 06:02:51 PM »
Ask if you can get more useful integrations on the proton NMR, the integrations are junk. I would set the peak at 5.38 to 1H. You have a really lazy NMR guy, this is basic stuff. I still dont' understand why in the carbon NMR the triplet for CDCl3 is not at 77 where it should be.

I think you should talk to a mass spectrometrist, these NMRs simply don't have enough info for an ID if we don't have a starting point structurally. A guess at a triterpenoid from a qualitative and very nonspecific colorimetric test isn't enough. You need molecular weight and O/N/S content to unravel this. MS will also give structural information in the fragments.

Sorry, IDing natural products is an especially challenging art. I'm curious why a postdoc with no analytical experience is being shoved in the deepend like this.

Offline AMARACHUKWU

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Re: nmr interpretation
« Reply #17 on: May 11, 2018, 07:24:30 AM »
MOD Edit -- deleted pointless quote.

.aww... this is not a good news. am an msc student not a phd student. i intend trying till i become grounded in identifying natural products. ill keep trying. but am getting discouraged at this point. ::)
« Last Edit: May 11, 2018, 07:34:08 AM by Arkcon »

Offline kriggy

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Re: nmr interpretation
« Reply #18 on: May 25, 2018, 07:38:39 AM »
Im having hard time believing its run in CDCl3. The carbon looks more like DMSOd6 to me (its septet AND its way more intense compared to the other peaks), however it is referenced wrong it should be at 37ppm give or take.
Your protons look like s#*$ and same goes for COSY.

edit: ok I was talking about the first spectra, didnt see the second ones. They look way better. However, what Im suspecting is that your NMR guy run the spectra in mixture of DMSOD6 and CDCl3 because there are all the characteristic peaks, they are however at wrong positions:
the 43 ppm signal in carbon should be 39 and the 83 should be 79. It was run in DMSO with addition of chloroform which is clear if you look at chemical shift table of solvents
https://www.sas.upenn.edu/~marisa/documents/OrganoMetSolv.pdf (check residual sovlent signal for DMSOD6 and then for chloroform in DMSOD6).
In protons the signal at 5.36 should be 2.5 (its DMSO) and the signal at 10.101 is most likely residual CDCl3

Offline wildfyr

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Re: nmr interpretation
« Reply #19 on: May 25, 2018, 10:57:45 AM »
Why in gods name would someone run it in a mixture of those solvents? It makes the internal standard peak shifts untrustworthy, since 1H CDCl3 won't be exactly at 7.26, DMSO won't be at 3.33 etc etc and same goes for the 13C. If our OP ran a column on this crap I'm sure its soluble in either pure chloroform or DMSO.

This NMR guy should be fired. Any 3rd year organic PhD student could do this. Heck I could train an undergrad in a couple of months to do this basic stuff like looking for bad shimming, checking the solvent table to see if your shifts make sense, and, and integrating the peaks in a manner that is useful.

OP never came back so I hope hes out there fighting the good fight. If you've never done NMR and suddenly have to ID unknown natural products... that is not a good position. Heck even running a column if you don't understand NMR spectra is.... uhh.... pointless?


Edit: OP has logged in in the last 24 hours.
« Last Edit: May 25, 2018, 12:34:27 PM by wildfyr »

Offline kriggy

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Re: nmr interpretation
« Reply #20 on: May 26, 2018, 04:07:44 AM »
I did it few times becaues my sample didnt disolve in CDCl3 so I  pipetted out the solution and dissolved the rest in DMSO but there was still some CDCl3 left so I got two peaks

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