While doing the NMR analyses of some polymer samples sometime I have observed that the integral ratios of some polar protons (Exchangeable protons) don't matches with the integral ratios of aliphatic protons! Does this happen really or I am doing any mistakes? If so, then is there any particular reason?
I have used DMSO-d6 solvent for the analyses.
Thanks but what about the integration ratio? Specifically in case for polymer?
Yes the integration ratio should change. For example some exchangable protons could disappear from spectrum (i.e. integration=0) in water solvent. So I would expect exchangables to have integration values that differ from expected value.
No ive just observed it in my own experience and it is a pretty well established phenomenon. I imagine a book on NMR basics would mention this.
Also if you use a (partly) deuterated solvent with exchangeable hydrogens, each site for fast enough exchangeable hydrogens will be occupied by the same proportion of protons and deuterium, reducing the apparent integral of your proton signal. So that may depend on the presence of trace water in your DMSO solvent.
Another point : it may happen that large signals, common foor exchangeable protons, are more tricky to accurately integrate than sharp signals, of non exchangeable ones.
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