TABLE OF CONTENTS Optical activity (the property of rotating the plane of polarization of light) is characteristic of many organic compounds and of a few inorganic complexes. The determination of the angle of optical rotation is a classical technique of quantitative analysis. More recently, the technique has been extended to structural and stereochemical compounds, and in these the rotatory dispersion (the variation of specific rotation of plane-polarized light with the wavelength of the light) has been found most revealing.
A compound is chiral (the term dissymmetric was formerly used) if it is not superimposable on its mirror image. A chiral compound does not have a plane of symmetry. Each chiral compound possesses one (or more) of three types of chiral elements, namely, a chiral center, a chiral axis, or a chiral plane.
The chiral center, which is the chiral element most commonly met, is exemplified by an asymmetric carbon with a tetrahedral arrangement of ligands about the carbon. The ligands comprise four different atoms or groups. One ligand may be a lone pair of electrons; another, a phantom atom of atomic number zero. This situation is encountered in sulfoxides or with a nitrogen atom. Lactic acid is an example of a molecule with an asymmetric (chiral) carbon.
Two nonsuperimposable structures that are mirror images of each other are known as enantiomers. Enantiomers are related to each other in the same way that a right hand is related to...
