Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: AMARACHUKWU on May 09, 2018, 06:44:35 AM
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i am a postgraduate student of organic chemistry with little knowledge of characterisation and interpretations of nmr spectra . i need help.
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How did you study this at undergraduate level - e.g. what were your course books, what did you cover (just proton and carbon, or other nuclei as well?)
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just proton and carbon.
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I need help in identifying the molecule
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It is a forum rule that you must show your attempt before we can help you. What are your thoughts?
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That proton nmr is poorly phased. Secondly is this a real reaction where you synthesized something? If so, you should state the starting materials and desired product. It makes interpretation much easier. And it a forum rule that you must give us your attempt.
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Looking again, I don't think this nmr is locked. The peaks are in an unusually downfield part of the spectrum, and poorly resolved. It's in cdcl3 and I see no clean cdcl3 singlet.
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Looking again, I don't think this nmr is locked. The peaks are in an unusually downfield part of the spectrum, and poorly resolved. It's in cdcl3 and I see no clean cdcl3 singlet.
Look at the carbon. I don't think that's CDCl3. Looks like someone locked to the wrong solvent. Maybe CD3OD?
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That proton nmr is poorly phased. Secondly is this a real reaction where you synthesized something? If so, you should state the starting materials and desired product. It makes interpretation much easier. And it a forum rule that you must give us your attempt.
this is a product I got from the isolation of camwood extract. (Baphia nitida) using the traditional column.
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That proton nmr is poorly phased. Secondly is this a real reaction where you synthesized something? If so, you should state the starting materials and desired product. It makes interpretation much easier. And it a forum rule that you must give us your attempt.
this is a product I got from the isolation of camwood extract. (Baphia nitida) using the traditional column.
What solvent did you use to prepare the NMR sample?
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What solvent did you use to prepare the NMR sample?
chloroform
*MOD EDIT - monster quote*
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I have trouble believing there is no alkyl content to this molecule as is implied by the NMR. Thats why I suspect its poorly locked. It just looks like a generally poorly taken NMR. Try asking someone who is experienced in using it to lock and shim it. Also... when you say chloroform, you mean CDCl3 right?
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*MOD EDIT - monster quote*
yes. i just spoke with the lab where the analysis was done and they said thats the much they can do.
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I just can't get your proton, carbon, and IR to jibe. Proton shows broad, polymer-like peaks, all above 5. Carbon shows a bunch of clean singlets, and only about half of them are in the aryl. FTIR shows a peak at 2952 cm-1 which indicates alkyl content, but no carbonyl is seen. However the carbon shows what looks like an ester at 175ppm.
My definitive response to the claim that no one screwed up is that there is no triplet at 77.2 ppm on the 13C NMR, which is characteristic of CDCl3. So ask them to run it again, and this time not be lazy jerks and actually lock and shim it.
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thank you. i will tell them to run it again and get back with thr results
*MOD EDIT - monster quote*
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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
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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.
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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. ::)
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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
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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.
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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