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This is a 1H NMR spectrum of plasma treated methyl alpha D-glucopyranoside.

Now I'm having problems trying to read the spectra and interpreting if there are any changes to it. What I suspected would happen during plasma treatment is that the methoxy group would break off, leaving it or replacing it with any other possible ROS or RNS. I don't know how to identify the methoxy groups present or to read those peaks to see if there are other possible structural changes.

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The usual approach to determining change by NMR following a reaction or procedure is to compare your final spectrum to your starting sample's spectrum, run with identical parameters. That is, look at the spectrum you ran before your plasma treatment and look for changes in peak position and intensity. Within Topspin (which your spectrum here has been processed with) this is very easy to do; you can run a dual display and overlay your spectra on the screen, and even compute a difference spectrum.

Of course, if you are having problems assigning the final spectrum, you should again go back to the spectrum of your starting material and compare to the assignments you made for that. That will make it easy to identify which parts of the molecule have undergone some change. Of course, you might expect that you haven't had complete clean conversion, and there may be a number of products constituting only partial conversion. Otherwise, you are potentially having to characterise a completely new molecule.

You do have the spectrum for your starting material, don't you?

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  • $\begingroup$ I didn't run a control sample NMR, but seeing as the spectrum should be the same, I obtained one from SBDS. When I'm comparing them they don't really look alike. I can see some differences between the two, my problem is that I am unable to identify and label those differences. I understand that due to different parameters (different solvent, different nmr machine) would make the peaks ppm shift, but I don't think it is that significant. Do you know at which ppm hydroxy and OMe groups would appear on the spectrum? $\endgroup$ – damnit55 May 7 '17 at 22:21
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    $\begingroup$ Yes I do, but you will need to show some evidence of your own efforts to assign and rationalise the spectrum. What can you deduce from the spectrum? Where would you expect the -OH/-Me peaks to come? Your sample looks like it may have been run in D2O; the SBDS is in dmso. Why don't you expect the differences to be significant? I think they probably would be, especially if you are having trouble with assignments to begin with. As it stands, you are essentially asking for someone to assign your spectrum for you. This is not a forum for others to do your work for you. $\endgroup$ – long May 7 '17 at 22:51
  • $\begingroup$ I understand that. Yeah this sample was done D2O solvent, as it can be seen from the peak at 4.693 ppm. I have very basic knowledge when it comes to NMR and can only work out structures of simple alkanes or alkenes. This is a good bit over my head. Peak at 3.2741 ppm indicates OMe group as far as I understand. I don't know about the OH group peaks showing in the spectra. Yeah, the SBDS is in dmso, but as far as I understand the only difference is in peak shift. Fact that different solvent was used shouldn't interfere with the spectrum, if the molecule is the same. cont. $\endgroup$ – damnit55 May 7 '17 at 23:48
  • $\begingroup$ cont. Most of the spectrum between my sample and the spectrum on SBDS looks the same except for the multiplet at ~3.5ppm. Hence why I was asking about OH groups, so that I can rule it out as one of the options for it. I can't think of a reason for that multiplet there. My experiment was basically to try and cleave off OMe group, by using plasma generated species. I could identify that, but getting second oppinion on it doesn't hurt. As I mentioned before, I really have close to none experience in reading NMR spectras, hence why I am asking for help, tp figure out if there are other changes. $\endgroup$ – damnit55 May 7 '17 at 23:56

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