Aromatic triazole foldamers induced by C-H...X (X = F, Cl) intramolecular hydrogen bonding

Article abstract of DOI:10.1021/jo500582c

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.