Deuterated DMSO, also known as dimethyl sulfoxide-d<sub>6</sub>, is an isotopologue of dimethyl sulfoxide (DMSO, (CH<sub>3</sub>)<sub>2</sub>S=O)) with chemical formula ((CD<sub>3</sub>)<sub>2</sub>S=O) in which the hydrogen atoms ("H") are replaced with their deuterium ("D") isotope. Deuterated DMSO is a common solvent used in nuclear magnetic resonance spectroscopy (NMR).
Deuterated DMSO is produced by heating DMSO in heavy water (D<sub>2</sub>O) with a basic catalyst such as calcium oxide. The reaction does not give complete conversion to the d<sub>6</sub> product, and the water produced must be removed and replaced with D<sub>2</sub>O several times to drive the equilibrium to the fully deuterated product.
DMSO is a good solvent for many organic compounds. Because deuterated DMSO does not contain any <sup>1</1</sup>H atoms, it produces no peaks in <sup>1</sup>H-NMR and as a result is commonly used as a solvent for NMR experiments. Commercially available deuteriated DMSO is not isotopically pure. The residual DMSO-d<sub>5</sub> produces a <sup>1</sup>H-NMR signal observed at 2.50 ppm, which appears as a quintet (J<sub>HD</sub>=1.9Hz). In <sup>13</sup>C-NMR, the chemical shift of DMSO-d<sub>6</sub> is 39.52 ppm, and appears as a septet.
Deuterated DMSO is used as a reagent for the introduction of a trideuteromethyl group (CD<sub>3</sub>) onto organic structures.