Why must deuterated solvents, such as D2O and CDCl3, be used to prepare NMR samples?

Deuterated solvents are used in NMR samples because they do not interfere with the NMR signal of the compound being analyzed. Regular solvents contain hydrogen atoms that can overlap with the signals of the compound, making it difficult to interpret the NMR spectrum. Deuterated solvents replace these hydrogen atoms with deuterium, which does not produce signals in the NMR spectrum, allowing for a clearer and more accurate analysis of the compound.