Conformation Regulation of Trisresorcinarene Directed by Cavity Solvation

This compound is a synthetic macrocycle comprising three pivaloyl-protected resorcinarene units connected by six pentylene chains. We conducted a conformational study using ¹H-NMR, X-ray diffraction (XRD), and computational analyses. The macrocycle adopts two conformers, one open, the other closed. The ratio of the open to closed forms depended on the solvent used. Only the open form existed in [D₈]toluene, both forms coexisted in [D₆]benzene, and the closed form was the major conformer in [D₁]chloroform. The benzene-solvated open form observed in the solid state suggests that cavity solvation by solvent molecules directs the open form. The open form was the major or only conformer in [D₁₀]o- and [D₁₀]m-xylene and [D₁₂]mesitylene, whereas the closed form was the major conformer in [D₆]acetone. The open and closed forms were equally populated in [D₁₀]p-xylene, suggesting that the size, shape, and dimensions of the solvent molecules most likely influenced the conformation of the protected trisresocinarene.