Racemic

Racemic refers to a mixture that contains equal amounts of two enantiomers, which are non-superimposable mirror images of a chiral molecule. A racemate, or racemic mixture, has a 1:1 ratio of the enantiomers and is typically optically inactive because the rotations caused by each enantiomer cancel each other out. The term racemic derives from the historical concept of racemic acid, studied in the 19th century in relation to tartaric acid from grapes.

Enantiomers have identical physical properties in an achiral environment, such as melting point, boiling point, and solubility, but they interact differently with plane-polarized light and with other chiral substances. As a result, a racemate shows no net optical rotation, whereas the individual enantiomers rotate plane-polarized light in equal magnitude but opposite directions. The composition of a mixture is often described by enantiomeric excess (ee), defined as the absolute difference between the amounts of the two enantiomers, expressed as a percentage.

Racemization is the process by which one enantiomer converts into its mirror image, potentially converting an enantiopure sample into a racemate. Separation of racemates, or resolution, is a central task in chiral chemistry. Classical resolution techniques exploit diastereomer formation with a chiral counteragent to produce separable compounds, while modern methods include chiral chromatography and enzymatic or catalytic approaches that favor one enantiomer.

Racemic mixtures have significant implications in pharmaceuticals and chemistry, since enantiomers can differ in biological activity and side effects. The study of racemization and resolution informs drug development, synthesis, and the understanding of how chirality influences function.