Introduction of Polar or Nonpolar Groups at the Hydroquinone Units Can Lead to the Destruction of the Columnar Structure of Pillar[5]arenes

Publication date: Available online 31 May 2019Source: Computational and Theoretical ChemistryAuthor(s): Xiao Wang, Rui-xue Chen, Andrew C.-H. Sue, Han Zuilhof, Adelia J.A. Aquino, Hans LischkaAbstractPillar[5]arenes, a type of novel macrocycles containing di-substituted hydroquinone units linked by methylene bridges in para-positions, have attracted extensive attention in supramolecular chemistry as interesting candidates to be used in the preparation of host-guest complexes. Functionalization by means of rim substitution and sustaining an ordered substituent arrangement on both sides of the rim is important for the development of new pillararene-based materials. In order to achieve this, the rim inversion process of rotating the hydroquinone units through the pillar[5]arenes has to be controlled. In this context we have studied the effect of different types of hydroquinone substituents on the rotational energy profile using density functional theory combined with the hybrid M06-2X functional. The influence of polar (-CH2F, -CH2Cl, -CH2OH, -CH2SH, -CH2NH2) and nonpolar alkyl (-CH3, –CH2CH3, –CH2CH2CH3, -CH(CH3)2, and –CH2CH2CH2CH3) substituents on the on the energy barriers of the rotation mechanism, and different local minima was investigated. The stabilization of the intermediate structures by non-covalent van der Waals and interactions and also by hydrogen bonds constitute a major factor affecting barrier heights. In case of polar substituents, the largest barriers w...

Source: Computational and Theoretical Chemistry - June 1, 2019 Category: Chemistry Source Type: research