Deuteron‐Decoupled Singlet NMR in Low Magnetic Fields: Application to the Hyperpolarization of Succinic Acid**

The reaction of unsaturated substrates with hydrogen gas enriched in the para spin isomer leads to products with a high degree of nuclear singlet spin order. This leads to greatly enhanced NMR signals, with important potential applications such as magnetic resonance imaging (MRI) of metabolic processes. Although parahydrogen-induced polarization has the advantage of being cheap, compact, and mobile, especially when performed in ultralow magnetic fields, efficiency is lost when more than a few protons are involved. This strongly restricts the range of compatible substances. We show that these difficulties may be overcome by a combination of deuteration with the application of a sinusoidally modulated longitudinal field as a well as a transverse rotating magnetic field. We demonstrate a six-fold enhancement in the C-13 hyperpolarization of [1-C-13, 2,3-d(2)]-succinic acid, as compared with standard hyperpolarization methods, applied in the same ultralow field regime.