The 1H NMR spin system of the prenyl unit in xanthohumol (1) exhibits multiple long-range coupling. Simulated (sim) and experimental (expt) 500 MHz 1H NMR spectra of the prenyl signals in 1 are shown. Precise δ and J values determined for 1 are given in Table 1. A H2″, B CH2-1″ (simulation linewidth above 0.8 Hz; below 0.5 Hz), C Me-4″, D Me-5″. Linewidth in simulated spectra shown for signals A, C, and D is 0.5 Hz. *
2J coupling not observed; geminal coupling between the 1″ methylene protons was observed only in the 8-prenylated flavanones, 15 and 17 (see Figure 4B). The coupling constants are within 0.1 Hz of those determined for compounds containing this same moiety (2, 7, 8, and 14-17).