Chapter 3 - Cyclic molecules: Configuration and conformation

Abstract

This chapter deals with configuration and conformation of cyclic molecules. Stereoisomerism in cyclic molecules containing multiple chiral or pseudoasymmetric centres is described with configurational descriptors. The conformational analyses and symmetry of cyclohexane, monosubstituted and disubstituted cyclohexanes are presented in detail. The NMR methods for dynamics of conformational changes and determination of conformational free energy are included. Anomeric effects including its origin are described. Conformational aspects of cyclohexanones, alkylidenecyclohexanes, cyclohexenes and the concepts of allylic A1,2 and A1,3 strains are provided. Small rings including cyclopropane Walsh orbitals, cyclopentanes, cycloheptanes, medium rings and large rings—rotaxanes and catenanes, are introduced. The conformation of fused ring systems—decalins, perhydrophenanthrenes, perhydroanthracenes and steroids, is described. Finally, optical rotatory dispersion (ORD) and circular dichroism (CD) methods for the determination of configuration and conformation of chiral molecules are presented using axial haloketone rule, octant rule and exciton chirality. The CD method for determining protein conformation is included.