Competing Hydrogen-Bond Polarities in a Dynamic Oligourea Foldamer: A Molecular Spring Torsion Balance

Symmetrical oligourea foldamers were made from meso cyclohexane-1,2-diamine and desymmetrised by incorporating terminal functional groups (carbamates, ureas or thioureas) with differing hydrogen-bonding capacities. Irrespective of solvent, the foldamers populate a dynamic equilibrium of two alternative screw-sense conformers whose relative population is determined by the competing hydrogen-bonding properties of the terminal groups, dictating the foldamer's global hydrogen-bond directionality. Intermolecular association of these dynamic foldamers with achiral anionic guests (acetate or phosphate, but not neutral hydrogen-bonding solvents) leads to inversion of the conformational preference, as strong intermolecular hydrogen bonding induces reorganization of the intramolecular hydrogen-bond network. The foldamers behave as a molecular torsion balance whose conformational preference is governed by competing hydrogen-bond pairing.