What is optical isomerism?

Optical isomerism is a form of stereoisomerism that arises due to the presence of non-superimposable mirror images.

Optical isomerism is a fascinating aspect of stereochemistry, a sub-discipline of chemistry that deals with the spatial arrangement of atoms in molecules. It is a type of isomerism where the isomers, known as optical isomers or enantiomers, are mirror images of each other, much like your left and right hands. These isomers are non-superimposable, meaning they cannot be placed on top of each other and give the same molecule.

The phenomenon of optical isomerism is due to the presence of a chiral centre in a molecule. A chiral centre, often a carbon atom, is one that is bonded to four different groups. This arrangement allows for two different ways these groups can be arranged in space, leading to two different isomers.

Optical isomers are named so because they interact with plane-polarised light in a unique way. When plane-polarised light passes through a solution of an optical isomer, the plane of polarisation is rotated. The direction and degree of this rotation is a characteristic of the particular isomer. One isomer will rotate the light in a clockwise direction (dextrorotatory), while the other will rotate it in an anticlockwise direction (levorotatory).

This property of optical isomers has significant implications in many areas, particularly in the field of biochemistry. Many biological molecules, such as amino acids and sugars, exhibit optical isomerism. The two isomers can have very different biological activities. For example, one isomer of a drug may be beneficial, while the other may be harmful.

Understanding optical isomerism is crucial in the design and synthesis of pharmaceuticals, as well as in the study of biological systems. It's a complex but fascinating area of chemistry that combines spatial reasoning with chemical knowledge.