Foldamer 3a (Figure 9) is consistent with 1a and2a , and the helical pitch is 3.52Å and 3.74 Å.Two three-center hydrogen bonds(N^∗–H−N_Aand N_A−H–N_Q) were formed between the terminal β -pinene-derived pyridyl carboxylic with quinoline oligoamide, the hydrogen bonds length are 2.28 Å and 2.09 Å, the bond angles are 107.9° and 106.8°, respectively. Interestingly, the distribution of N_Q−C_Q−C−N_A shows that angle peaks at ±10°, which is consistent with 2 . That is, three-center hydrogen bonds do improve coplanar of ∠N_Q−C_Q−C−N_A. Next, the investigation was locked at the character of dihedral angle ∠N*−C*−C=O in 3a. Compare with ∠N*−C*−N−H dihedral angle in 1 and2 , rotation of ∠N*−C*−C=O is more difficult than that of ∠N*−C*−N−H. In addition, the electronic delocalization effect was found between bond C=O and pyridine ring of terminal group. The delocalization can be proved by three bonds length. As Figure 11 shows that 3aand 1a has the same bonds N_Q−C_Q, C_Q−C, and C−N_A, but the bonds length of N_Q−C_Q, C_Q−C, and C−N_A are 1.3521 Å, 1.4972 Å and 1.3720 Å in 3a , respectively, which are shorter than those in 1a (1.3698, 1.5529, and 1.4330). Furthermore, the orbital properties of the terminal group also show the delocalization properties of terminal group in3a . The terminal group has contributions in the HOMO orbital of3a , but terminal group has no contribution in the HOMO orbital of 1a (Figure 12). It is worthwhile noting that a metastable state EPP (Q1-Q2 is extended, Q2-Q3 and Q3-Q4 are P helix) has been found in the FEP of 3a (Figure 10), the free-energy ofEPP is about 2.7kcalmol^-1. That is, when the P helix of 3a converts to M helix, it needs cross a metastable state EPP. And the metastable state also results in the big free-energy gap between P- 3a and M-3a , it is the main reason that3a has better helical selection than 1a . Based on the above discussion, we conclude that the electronic delocalization effect influences the selection of helical handedness, and the delivery of chirality in the conjugated chains is easier than in unconjugated system, which corresponds to some experimental results ^[12-15].

Figure 11 . The structure of N_Q−C_Q −C −N_A.Figure 12 The HOMO orbital distribution.