Figure 7.

(a) Reaction scheme of pairwise addition of p-H₂ to propargyl 1-¹³C-pyruvate in CD₃OD followed by polarization transfer to ¹³C nuclei (H_A and H_B are two atoms from the same p-H₂ molecule, cat. = [Rh(NBD)(dppb)]BF₄). (b) Reaction scheme of the competing process of norbornadiene hydrogenation with p-H₂. (c) ¹H NMR spectrum acquired after ¹H ALTADENA hyperpolarization of allyl 1-¹³C-pyruvate with 4 s p-H₂ bubbling duration. (d) Corresponding thermal ¹H NMR spectrum acquired after relaxation of hyperpolarization (multiplied by a factor of 128). ε_1H = 4320, P_1H = 13% (21% at 85% p-H₂ fraction) (calculated using sum of signals 13b and 14b). (e) ¹³C NMR spectrum acquired after ¹³C hyperpolarization of allyl 1-¹³C-pyruvate using MFC at 0.030 μT magnetic field with RG = 1. (f) Corresponding thermal ¹³C NMR spectrum acquired after relaxation of hyperpolarization with RG = 203 (multiplied by a factor of 4). ε_13C = 4340, P_13C = 3.3% (5.4% at 85% p-H₂ fraction). (g) Dependence of conversion of propargyl pyruvate to allyl pyruvate on p-H₂ bubbling duration (estimated pseudo-first order rate constant k = 0.15 ± 0.02 s^–1). (h) Dependence of ¹H ALTADENA signal (absolute value) of HP allyl pyruvate (signal 14b, red squares), norbornene (signal 19d, blue circles) and norbornane (signal 20b+20d, black triangles) on p-H₂ bubbling duration. (i) Dependence of P_1H (at 85% p-H₂ fraction) of allyl pyruvate (signal 13e+14e or the sum of NMR signals 13b and 14b, red squares), norbornene (signal 19d, blue circles) and norbornane (signal 20b+20d or signal 20a, black triangles) on p-H₂ bubbling duration. (j) Dependence of P_13C (at 85% p-H₂ fraction) of allyl 1-¹³C-pyruvate on magnetic field used in MFC experiments (red squares – data points obtained with the 98% ¹³C-enriched precursor, blue circles – data points obtained with the 1.1% ¹³C-enriched precursor).