Effect of Temperature and Solvent on the Structure of Amide Cavitands

Conformational changes of amide cavitands A – C were investigated at varied temperatures and in several solvents. While cavitands A and B , with comparatively smaller substituents such as Et and ⁱPr, were always in vase conformation in non‐polar solvents such as CDCl₃, CD₂Cl₂, (D₈)THF, and C₆D₆, their thermoswitching (vase to kite) was observed in polar solvents such as (D₇)DMF and (D₆)DMSO or in the presence of acid (TFA) and H‐bonding inhibitor (TFE). Intra‐ and interannular H‐bonds of A and B were clearly observed by low‐temperature ¹H‐NMR spectra in CDCl₃. No conformational change of cavitand C with bigger substituent (^tBu) was observed under any tested temperature range and in polar or non‐polar solvents; C was always in the kite conformation.