Figure 5.

The ABMM’XX’ spin system in chalcones 1–13 shows a characteristic set of signals corresponding to the B-ring and the olefinic α and β protons. Experimental (top) and simulated (bottom) 500 MHz ¹H NMR signals of Hα (A), Hβ (B; enlargement at linewidth 0.25 Hz; all other simulated spectra are shown at 0.5 Hz linewidth), H2,6 (C), and H3,5 (D) are shown on the left for xanthohumol (1). Each of the peaks (A-D) are generally reported as individual doublets. Long range coupling results in a finer structure visible even at 300 MHz (inset below). The coupling constants (in Hz) shown on the right are within 0.15 Hz of those determined for 4-hydroxychalcones 1-13. Precise values determined for this spin system in 1, 5, and 10 are given in Table 1.