Conformation and Planar Chirality of Pillar[n]arenes

Abstract

The study of the structure and conformational mobility of macrocyclic hosts is very important because these properties dramatically affect their host–guest and self-assembly abilities. Macrocyclic molecules can be divided into two categories according to their conformational mobility: conformationally flexible and fixed macrocyclic compounds. Phenolic units composed of pillar[n]arenes can rotate freely, therefore pillar[n]arenes are designated as conformationally flexible macrocyclic compounds. This chapter deals with the conformational mobility of pillar[n]arenes in the solution state. We also discuss the conformation of pillar[n]arenes in the crystal state. Although the conformational structure in the crystal state is a “snapshot” of one of the conformations of pillar[n]arenes, the structure observed will be the most stable conformation, and this provides useful information about the conformational properties of pillar[n]arenes. In this chapter, we discuss how the substituents on the rims, cavity size and number of rings of pillar[n]arenes dramatically influence the conformational mobility and the most stable structures of pillar[n]arenes in solution and the solid state.