Table 3.

Amide-rotation velocity in the model compounds.^a

compound	kcis-to-trans, Hz
	in D2O, ε 80.1 (310 K)	in CD2Cl2, ε 8.9 (298 K)	in C6D6, ε 2.3 (298 K)
	0.033 ± 0.002	0.033 ± 0.002b	0.043 ± 0.004
1	0.041 ± 0.004	0.187 ± 0.003	0.463 ± 0.034
2	0.087 ± 0.009	0.220 ± 0.016	0.556 ± 0.027
3	0.131 ± 0.008	0.690 ± 0.019	2.44 ± 0.07
4	0.060 ± 0.006	0.265 ± 0.007	0.855 ± 0.031

^aMeasured by ¹H and ¹⁹F EXSY NMR. Few spectra with different mixing times were measured. The exchange rate values were calculated from various exchange resonances and averaged. Their root mean deviation from the mean value is provided. The k values were converted to the energy barriers using the Eyring equation. The error in E^≠ takes into account the standard deviation in the k values, and does not take into account the temperature calibration error. ^bThe value is for CDCl₃, ε 4.8.