ABSTRACT
Stereochemistry deals with the topography and transformations of molecules in three dimensions. A chiral molecule is one capable of existence in a pair of non-superposable mirror-image forms. This chapter summarizes the representation and description of basic stereochemistry with special reference to the Combined Chemical Dictionary (CCD). The sequence rule is the universal system of describing absolute configurations. Fischer diagrams follow the convention that the principal chain occupies the vertical position, with the head of the chain uppermost. Extensions of the Cahn–Ingold–Prelog (CIP) rules deals with molecules that are chiral as a whole but contain no chiral centres. E- and Z- are stereochemical descriptors used to describe the configuration about a double bond. d- and l- are older descriptors used to denote the configuration of chiral molecules, especially carbohydrates and α-amino acids. Nowadays, R, S- descriptors are used for all classes of molecule except for the following: carbohydrates, and amino acids.
