Of course, the distribution of dihedral angle ∠NQ CQ C−NAand ∠CQ−CQ−NA−C can make a distinction between the chirality of 2a and 2b . From Figure 7, it can be seen that the angle peaks of ∠NQ−CQ−C−NA at ±10° for (P)-2a /(M)-2b . The angle peaks of ∠NQ−CQ−C−NA for2a/2b are less than that in 1a/1b , it due to two three-center hydrogen bonds O–H−NA and NQ–H−NA improve the coplanar of ∠NQ−CQ−C−NA(Figure 8). Based on above analysis, it shows that atomic chirality is the main factor on the helical selection of β -pinene-derived pyridyine
Figure 7. The three-center hydrogen bond in 2b. Figure 8. The frequency of occurrence for NQ−CQ−C−NA in2a and 2b
substituted foldamer at C-terminal, and hydrogen bond just enhance the stable of foldamers 2a/2b . However, the experimental found that the N-terminal substituted foldamers have better helical selection than C-terminal substituted foldamers. What is the intrinsic reason?
2.3Helix-handedness bias ofβ‑pinene-derived pyridyl carboxylic acid-substituted oligomers 3a/3b at N-terminal