It was found that spontaneous isomerization takes place between three isomers of a pillar[5]arene (P5)-based pseudo[1]rotaxane. The isomerization process could be monitored by 1H NMR spectra in polar solvent and the geometric configurations of the three isomers were further evaluated by theoretical calculations. In the threaded forms, the alkyl side chain might be preorganized by intramolecular N–H⋯O bonds between the urea group of the side chain and the methoxy group of the P5 and further stabilized by multiple interactions, including H-bonding, C–H⋯π interactions, and the steric effect of the N-Boc moiety. These cooperative interactions greatly enhance the stability of the threaded form in polar solvent, and endow it with very special self-inclusion behavior.
研究发现,基于五柱[5]
芳烃(P5)的准[1]轮烷的三种异构体之间存在自发异构化现象。在极性溶剂中可以通过氢核磁共振谱图监测异构化过程,并通过理论计算进一步评估了三种异构体的几何构型。在穿线形式中,侧链中
脲基与P5的甲氧基之间的分子内N-H...O键可能预组织烷基侧链,并通过多重相互作用进一步稳定,包括氢键、C-H...π相互作用以及N-Boc基团的位阻效应。这些协同作用大大增强了极性溶剂中穿线形式的稳定性,并赋予其特殊的自包含行为。