Bisresorcinarenes 1a−d were obtaine

Bisresorcinarenes 1a−d were obtained in excellentyields, and 1e was finally obtained in 50% yield. X-ray diffractionanalysis showed that 1a and 1b adopted helical conformations,whereas the two resorcinarenes of 1c−e were in parallelorientations in which the clefts of the aliphatic chains entrappedone or two solvent molecules. The conformational study revealedthat the helix interconversion between the (P)- and (M)-helicalconformers depended on the length of the aliphatic chains. 1a hadthe largest energetic barrier to helix interconversion, while in 1b,its more flexible aliphatic chains lowered its energetic barriers.The P/M interconversion of 1a was coupled with the clockwise/anticlockwise interconversion of the interannular hydrogenbonding of the two resorcinarenes. The large negative entropic contributions indicate that the transition state is most likelymore ordered than the ground states, suggesting that the transition state is most likely symmetric and is solvated by watermolecules. Calculations at the M06-2X/6-31G(d,p) level revealed that the more stable (P)-conformation has clockwiseinterannular hydrogen bonding between the two resorcinarenes