In the case of 13 C1-allyl pyruvate, although coherent redistribution of PHIP is also operative, the observed oscillations are less distinct than in the case of maleic acid (Fig. .b). The likely reason is the presence of a multitude of coupled nuclei participating in the polarization transfer process, which leads to averaging of coherent oscillations of the detected C polarization. Thus, instead of strong modulations, only a smooth buildup of the 13 C polarization is observed during the first 200 ms of evolution at ULF followed by some oscillations around the average polarization level. We measured P( 13 C) = 3.3 % in an experiment with an evolution period 𝜏 𝑈𝐿𝐹 = 0.2 s, which is even lower than the maximal value of 3.5 % for the fixed field experiment. No detectable C signal enhancement was obtained for 13 C2-allyl pyruvate during experiments with coherent polarization transfer.