Aromatic Triazole Foldamers Induced by C–H···X (X = F, Cl) Intramolecular Hydrogen Bonding

Aryl-triazole oligomers based on isobutyl 4-fluorobenzoate and isobutyl 4-chlorobenzoate were designed and synthesized. Crystal structure and 1H–1H NOESY experiments demonstrate that the oligomers adopt stable helical conformation, which are induced by C5–H···X–C (X = F, Cl) intramolecular hydrogen bonding between triazole protons and halogen atoms. The stabilities of the folded conformations are confirmed by DFT calculations, which show that each C5–H···F–C planar interaction lowers the energy by ∼3 kcal mol–1 on average, and by ∼1 kcal mol–1 when C5–H···Cl–C bridges are formed. The hydrogen-bonding networks are disrupted in competitive hydrogen-bonding media such as DMSO, generating the unfolded oligomers.