My compound (quercetin) contains 10 proton and supposed to shows 10 different chemical shift. but the HNMR only shows 8 peaks which is shows 8 different chemical shift. can anyone help me with this question please.
Quercetin contains 5 phenolic OH-groups, including at least two quite acidic and highly exchangeable ones (near carbonyl group). They also can form H-bonds with this carbonyl. Perhaps that’s the reason. Moreover, OH groups, as Erkan has mentioned, are very often not displayed in NMR spectra at all (that depends on their acidity, solvent, water and acid impurities, etc.). I just assume that you have not missed these protons because they are located under broad signals of solvent (e.g. DMSO) or water J
Well said. One additional possibility is that you actually do not have the compound you think you have. It could instead be a structural analog of the compound you think you have. The third possibility is that the exchangeable proton is an unexpectedly broad peak, which when exchanged with any deuterated solvent peaks could easily not be detected at all. So changing to a solvent which more slowly exchanges with the exchangeable proton can have you see it.
Once you've gone through all the excellent points above, if you're still not seeing what you think you should, check a known standard as a control to insure the instrument/setup is working properly.
I agree with Dr. Walter Schmidt ideas and others. and some times we have overlapping of pikes.
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