Figure 7.

Comparison of observed ³J_HαHβ couplings with those predicted by the substituent-specific Karplus equations of Haasnoot et al.⁶⁷ The solid line corresponds to x = y; the dashed line corresponds to values predicted by these same equations after adding Gaussian fluctuations (cf. eq 4) with a standard deviation of σ = 20° to the χ₁ angles reported in Table 1. Note that to a very good approximation, the effect of σ = 20° simply scales the difference in the predicted ³J_HαHβ relative to a value of ca. 6 Hz (Figure S11). The rmsd between observed and predicted ³J_HαHβ values (using the σ = 20° motional model) is 0.75 Hz. ³J_HαHβ values (Table S16) for residues with a single χ₁ rotamer are in red, two χ₁ rotamers in blue, and three rotamers in pink.