Fig. Timing diagrams for (a) hydrogenation followed by a conventional field sweep for polarization transfer; (b) hydrogenation followed by polarization transfer using a STORM pulse; (c) hydrogenation under simultaneous WOLF+STORM fields, followed by polarization transfer using a STORM pulse. In (a) para-enriched hydrogen is bubbled through the sample for a duration τ B in the presence of a static bias field (B 0 ) along the laboratory frame z-axis. During the period τ T the field is linearly increased from 0 µT to a target value Bsweep. In (b) the linear field sweep is replaced by the application of a rotating magnetic field generated by two orthogonal transverse coils. The amplitude of the transverse rotating field is given by B STORM . In (c) the bubbling period is conducted under the simultaneous application of a small bias field B bias , a transverse rotating field of amplitude B STORM and an oscillating longitudinal field of amplitude B WOLF . The singlet-to-magnetization polarization transfer is initiated by turning off the longitudinal WOLF field, while retaining the rotating transverse STORM field. In all three cases, the sample is transferred to a high-field NMR apparatus immediately after the polarization transfer, followed by a π/2 pulse and signal acquisition on the 13 C channel. tests this hypothesis by applying simultaneous WOLF and STORM pulses during the hydrogenation interval, in order to suppress singlet-triplet mixing in the product molecules. At first this seems counter-intuitive, since a lone STORM pulse induces singlet-to-magnetization polarization transfer from the proton pair to the 13 C nucleus, as demonstrated in protocol (b). Such a process would be undesirable during the slow hydrogenation reaction, since the premature transfer of singlet order to 13 C magnetization would lead to a loss of spin order, when summed over all reacting molecules. However, as discussed in the supplementary material, the superposition of a resonant STORM pulse with a suitably chosen WOLF pulse suspends the polarization transfer until the hydrogenation is complete, while preserving the deuterium-decoupling properties of the STORM pulse, and also suppressing singlet-triplet mixing effects during hydrogenation.