Figure 2.

Partial ${}^{\mathrm{1}}\mathrm{H}$ NMR spectra of the reaction products at a resonance frequency of 400.0 MHz and temperature of 333 K, showing the signals from the ${\mathrm{CH}}_{\mathrm{2}}$ group of I. The hyperpolarized spectrum (blue) was acquired in a gem-PHIP experiment using the pulse sequence in Fig. a, with the intervals ${\mathit{\tau }}_{\mathrm{1}}=\mathrm{90}$  s and ${\mathit{\tau }}_{\mathrm{2}}=\mathrm{90}$  s. The spectrum in black was obtained by waiting 90 s after the conclusion of the experiment and taking the Fourier transform of the NMR signal induced by a single $\mathit{\pi }/\mathrm{2}$ pulse. The spectrum shows an AB peak pattern, with intensity distortions from residual hyperpolarization. The AB spectrum is consistent with a chemical shift difference of $\mathrm{\Delta }\mathit{\delta }=\mathrm{0.197}$  ppm and a two-bond $J$ coupling of ${|}^{\mathrm{2}}J|=\mathrm{16.8}$  Hz. The signal enhancement factor in the gem-PHIP experiment is estimated to be $\sim \mathrm{300}$ , which corresponds to a ${}^{\mathrm{1}}\mathrm{H}$ polarization level of $\sim \mathrm{0.9}$  %.