Fig. 3: The possible conformations of the imine adducts of isophthalaldehyde derivatives bearing different central substituents between the two imine units.
From: The sharp structural switch of covalent cages mediated by subtle variation of directing groups
These different central substituents include (A) H, (B) OH, (C) alkoxy (OR) unit, and (D) ester (OCH2COOC2H5) chain. Hydrogen bonding interactions occurs between the central substituents and the two imine units on both sides, which are marked with red dashed lines. OH favors the exo-endo conformation, while the OR unit favors exo-exo one. In the case of the ester, both exo-exo and exo-endo are stable conformations, driven by hydrogen bonding with different modes. These relatively stable conformations are encircled with red rectangles. (E) Two conformations of an imine compound, including syn (right) and anti (left). The syn conformer is more favored than the anti one due to smaller steric hindrance in the former conformer.
