Figure 2.

Schematic illustrations of ¹H–¹³C HETCOR spectra (right) for four different structural fragments (left) and the derived constraints. Structures (a) and (b) contain an “open” conformer. Structures (c) and (d) contain a “closed” conformer. Blue dotted lines are sufficiently short C–H distances between C_M and H_O to generate peaks in the spectra. Orange dotted lines are too long to generate peaks. After applying the constraints with a threshold distance of X = 3.5 Å, we see that the absence of a peak in fragment (a) is the only unambiguous constraint.