Stereospecific

Stereospecific describes a chemical reaction or process in which the stereochemistry of the reactant directly determines the stereochemistry of the product. In a stereospecific reaction, each stereoisomer of the substrate yields a distinct stereoisomer of the product, so the outcome cannot be the same for different starting configurations under the same conditions. This is different from stereoselective reactions, where one stereoisomer is formed preferentially from a mixture, but other stereoisomers may still be produced.

Common examples and implications include reactions with true stereospecific control, such as SN2 reactions, which typically invert the configuration at a chiral center, making the process stereospecific. Some eliminations, like certain E2 reactions, are also stereospecific when a required anti-periplanar arrangement governs the outcome. Enzymatic reactions are often stereospecific, producing a single enantiomer or diastereomer of a product due to active-site constraints. In polymer chemistry, stereospecific polymerization can produce polymers with defined tacticity (isotactic or syndiotactic arrangements), affecting material properties. The concept is important in pharmaceuticals and natural product synthesis, where different stereoisomers can have markedly different biological activity or safety profiles.