Historically, the existence of optical isomers was first identified by Biot (1) in the early 1800s and Pasteur later confirmed his work (2) in 1848. In order to explain the phenomena of optical activity, van't Hoff (3) and separately, Le Bel (4) introduced the concept of the asymmetric carbon atom to explain the source of optical rotation.

However, the first serious attempts that were made to rationalize the absolute stereochemistry of optical isomers were made by Emil Fisher (5) for which he was awarded the Nobel Prize. In his work, Fisher predicted that the (+)-isomer of glyceraldehyde was the D-isomer and arbitrarily assigned the sterochemical structure shown in figure 1.

Ultimately, Fisher s assumption was proved correct by Bijovet (6) employing X-ray crystallographic measurements. Interest in sterochemistry was not exceptional at first, but there was steady progress in the field during the twentieth century until the advent of the Thalidomide disaster. This unfortunate incident resulted in a tremendous increase in sterochemical research and, with the introduction of stringent legislation to prevent any reoccurrence of the tragedy, this, almost frenetic activity in stereochemistry, continues today.

A Short Preface to Basic Stereochemistry

A discussion on stereochemistry is not strictly relevant to a book on chiral gas chromatography but, for the effective practice of the technique, some basic stereochemistry must be known, The analyst will need to be familiar with the fundamental concepts, definitions and conventions currently in use, in order to understand the nature of the separation, the physical chemistry involved in the solute/phase distribution and the unique nature and interactive behavior of the stationary phases available.

The isomers of a substance, that only differ in the spatial arrangement of their atoms, are called stereoisomers.

Stereochemistry is the study of the three-dimensional structure of stereoisomers. Certain stereoisomers that differ in their capacity for rotating the plane of polarized light that passes through them, are considered optically active or chiral and these isomers are termed enantiomers. A simple explanation of optical activity is as follows.