Figure 4.

(a) Reaction scheme of pairwise addition of p-H₂ to propargyl 1-¹³C-acetate 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-acetate with 5 s p-H₂ bubbling duration. (d) Corresponding thermal ¹H NMR spectrum acquired after relaxation of hyperpolarization (multiplied by a factor of 128). ε_1H = 2090, P_1H = 6.4% (7.2% at 85% p-H₂ fraction) (calculated using signal 4e). (e) ¹³C NMR spectrum acquired after ¹³C hyperpolarization of allyl 1-¹³C-acetate using MFC at 0.15 μT magnetic field with RG = 1. (f) Corresponding thermal ¹³C NMR spectrum acquired after relaxation of hyperpolarization with RG = 203. ε_13C = 580, P_13C = 0.45% (0.74% at 85% p-H₂ fraction). (g) Dependence of conversion of propargyl acetate to allyl acetate on p-H₂ bubbling duration (estimated pseudo-first order rate constant k = 0.124 ± 0.005 s^–1). (h) Dependence of ¹H ALTADENA signal (absolute value) of HP allyl acetate (signal 4e, 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 acetate (signal 4e, red squares) and norbornene (signal 19d, blue circles) on p-H₂ bubbling duration. P_1H for norbornane is not presented because it cannot be estimated reliably due to low conversion of norbornadiene to norbornane. (j) Dependence of P_13C (at 85% p-H₂ fraction) of allyl 1-¹³C-acetate 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).