To explain the dramatic increase in 13 C polarization over the original demonstration (2% 13 C polarization, using 50% para-enriched hydrogen) , we consider the key experimental differences. In the previously reported experiments, the hydrogenation reaction took 30 s and was performed by bubbling hydrogen gas into a reaction solution at 50 °C in the high field NMR magnet. In the present case, the reaction was faster (10 s), and was carried out by shaking the sample at 80°C in Earth's magnetic field (~50 µT). Firstly, by using a shorter reaction time in this work, there was less time for spin relaxation to occur. Secondly, it is possible that parahydrogen singlet order is lost due to singlet/triplet mixing occurring on the reaction intermediates ; this destructive process is likely to be more efficient at high magnetic field due to larger chemical shift differences between the parahydrogen protons on the reaction intermediates. Thirdly, longer hydrogenation times may lead to partial degradation of the catalyst, with formation of metal-containing species which may enhance the rate of parahydrogen relaxation. It should also be considered that the reaction solution in the previous work was likely not at 50°C as expected, because the bubbling of roomtemperature hydrogen gas would lower the reaction temperature.