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Introduction to CH-acidic Compounds

Hydrogen-Deuterium Exchange

Due to the acidity of the α hydrogens of enolizable carbonyl compounds, the α hydrogen may easily be exchanged for deuterium (H/D exchange). H/D exchange may, for instance, occur when the carbonyl compound is treated with heavy water ( $D_{2} O$ ). The exchange can be detected through ¹H NMR, as deuterium does not produce a signal in ¹H NMR. As the exchange proceeds relatively rapidly, the α hydrogen of enolizable carbonyl compounds cannot be detected through ¹H NMR if $D_{2} O$ is used as a solvent. Whenever a carbonyl compound is treated with a large excess of $D_{2} O$ , for instance, if it is dissolved in $D_{2} O$ , virtually all α hydrogens of the carbonyl compound are exchanged. A large excess of $D_{2} O$ is essential, since H/D exchange is an equilibrium reaction.