Figure 3.

(a) Single scan ¹³C NMR spectrum of free C (δ 116.7, 15.5 μL) in the presence of 1 (10 mg) and pyridine-d₅ (3.75 μL). Hyperpolarization transfer was completed in a PTF of 0.5 G. The inset trace shows the corresponding methyl ¹³C-region, magnified 128 times relative to the main trace. The antiphase multiplet at 117.8 ppm is due to the quaternary ¹³C signal of bound C in 3. (b) Experimental (upper) and theoretically calculated (lower) ¹³C NMR spectra of the quaternary signal of C after hyperpolarization in a PTF of 0.5 G; (c) ¹³C field plot of C after hyperpolarization transfer using 1 over the PTF range of 0.5 to 140 G at intervals of 20 G collected experimentally (left) and theoretically calculated (right).