racemizálást

Racemization is a process in stereochemistry where a chiral compound, which exists as a pair of enantiomers, is converted into an equal mixture of these enantiomers. Enantiomers are stereoisomers that are non-superimposable mirror images of each other. A 50:50 mixture of two enantiomers is called a racemic mixture or a racemate.

Racemization typically occurs when a chiral center, usually a carbon atom bonded to four different groups, undergoes a reaction that temporarily loses its chirality. This can happen through mechanisms such as inversion or retention of configuration at the chiral center, or through processes where the chiral center becomes planar or achiral for a period before reforming. For example, in some nucleophilic substitution reactions at a chiral center, the reaction intermediate might be planar, leading to attack from either face with equal probability, thus producing a racemic mixture. Another common cause of racemization is the reversible formation of an achiral intermediate from a chiral molecule. If the reaction is reversible and the intermediate is achiral, then upon re-formation of the chiral molecule, both enantiomers are produced in equal amounts.

Racemic mixtures are optically inactive because the rotation of plane-polarized light by one enantiomer is exactly canceled out by the equal and opposite rotation caused by the other enantiomer. This lack of optical activity is a key characteristic distinguishing a racemate from a pure enantiomer. The process of racemization is important in organic synthesis and in biological systems, as it can affect the efficacy and properties of chiral drugs and other biologically active molecules. Separating enantiomers from a racemic mixture, a process called resolution, is often a crucial step in obtaining pure stereoisomers for specific applications.