Question: why dmso shows quintet in nmr?
Answer: Why does DMSO show quintet in 1H NMR? ... I learned that dmso peak in 1H NMR caused by proton exchange. So the peak at 2.5 ppm indicates dmso-d5 not d6. Also the dmso which have more exchanged proton like d4 or others can be shown but it is out of normal range.