stereochemi

Stereochemi, commonly referred to as stereochemistry, is the branch of chemistry that studies the three-dimensional arrangement of atoms in molecules and how this spatial organization affects properties, reactivity, and biological activity. It examines stereoisomers, which have the same connectivity but different spatial arrangements, including enantiomers and diastereomers, and the factors that control their formation and interconversion.

Key concepts include chiral centers, stereocenters, and prochiral substrates. Absolute configuration is described by the Cahn–Ingold–Prelog rules as R or S, while geometric isomerism around double bonds is described as E or Z. Configurational isomers differ in arrangement and cannot interconvert without bond breaking, whereas conformational isomers arise from rotation about single bonds and may rapidly interconvert. Enantiomers are non-superimposable mirror images with identical physical properties in achiral environments but opposite optical activity; diastereomers are stereoisomers that are not mirror images.

Determining stereochemistry relies on methods such as NMR spectroscopy, chiroptical techniques like polarimetry and circular dichroism, and X-ray crystallography when crystals are available. The concept of stereoselectivity describes the preferential formation of one stereoisomer over another in a chemical reaction, including enantioselectivity and diastereoselectivity. Approaches to achieve asymmetry include asymmetric synthesis with chiral catalysts or auxiliaries, and resolution methods to separate enantiomers from racemic mixtures.

Stereochemistry has broad applications in chemistry and biology. In pharmaceuticals, the activity and metabolism of drugs often depend on stereochemistry; in agrochemicals, flavors, fragrances, and materials design. The field advances with developments in catalysis, computational methods, and analytical techniques for determining and exploiting stereochemical outcomes.