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NMR spectra with very broad peaks

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tomek:
What is the source of those very broad peaks in proton NMR? I have always attributed them to the presence of paramagnetic impurities (eg. oxygen) or adventitious inorganic salts in the sample. What is the most common source of these peaks in your opinion? I include one such spectrum for illustration (notice the broad 4 ppm peak).

Babcock_Hall:
Exchange broadening is another reason why some peaks are broad.  My recollection is that the water peak in DMSO is usually broad.  What is your solvent?

Corribus:
Broadened OH or NH can show up in this region. Adding a drop of D2O can help.

tomek:
The solvent in this case was DMSO. But the peak is too broad for it to be coming from HDO and the chemical shift is 4 ppm. All protons from a molecule are accounted for. This is an extra peak. In some other cases I have observed extremely broad and flat peaks.

Corribus:
If there is any trace water in your DMSO and your analyte has any OH or NH (or other functional group capable of hydrogen bonding), proton exchange with the trace water can significantly broaden the NH or OH peak. This is why adding a small amount of D2O can help.

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