What is Optical Isomerism in Organic Chemistry?

Optical isomerism is a type of stereoisomerism where molecules have the same molecular formula and sequence of bonded atoms (constitution), but they differ in the three-dimensional orientations of their atoms in space. This phenomenon occurs due to the presence of a chiral center, which is usually a carbon atom bonded to four different groups.

For example, consider lactic acid. It has two optical isomers (enantiomers) because the central carbon atom is attached to four different groups: -OH, -COOH, -CH₃, and -H. These two enantiomers are mirror images of each other and cannot be superimposed.

Enantiomers have identical physical properties except for the direction in which they rotate plane-polarized light. One enantiomer will rotate light in a clockwise direction (dextrorotatory, denoted as '+') and the other in a counterclockwise direction (levorotatory, denoted as '-').