37.4.5—O-H and N-H proton exchange with D2O

Exchangeable O–H and N–H protons can be replaced by deuterium when D₂O is added. Because deuterium is not normally observed in a proton NMR spectrum, the corresponding signal disappears or weakens.

Compare spectra before and after adding D₂O. A disappearing broad signal supports an O–H or N–H assignment, but it does not by itself distinguish the two.

An alcohol spectrum with a broad signal that vanishes after D₂O treatment provides evidence for an O–H proton.

Do not expect ordinary C–H peaks to disappear; their hydrogens do not exchange rapidly with D₂O under the test conditions.