37.4.4—Need for deuterated solvents, e.g. CDCl ₃,

A deuterated solvent such as CDCl₃ replaces most solvent hydrogen atoms with deuterium, which is not detected in ordinary proton NMR in the same way. This prevents a huge solvent ¹H signal masking the sample.

The solvent must dissolve the sample and be sufficiently non-reactive. Small residual protonated-solvent peaks can still appear and should not be mistaken for the compound.

Dissolving an organic sample in CDCl₃ allows its proton signals to be observed while the deuterated solvent also provides a lock signal for the instrument.

Deuterated does not mean proton-free in an absolute sense; residual solvent peaks and exchangeable protons may remain visible.