stereochemische

Stereochemistry is the branch of chemistry that studies the spatial arrangement of atoms within molecules and the consequences of this arrangement for chemical properties and reactions. It distinguishes stereoisomers—molecules with the same connectivity but different three-dimensional structures. The two major classes are enantiomers, which are non-superimposable mirror images, and diastereomers, which are not mirror images. Stereochemistry also covers conformational isomers, or conformers, arising from rotation about single bonds.

Chirality is a central concept: a chiral molecule lacks an improper symmetry element and has at least one stereogenic center, typically a carbon with four different substituents. The absolute configuration of such centers is denoted R or S by the Cahn–Ingold–Prelog (CIP) rules. For double bonds, E/Z (priority) notation describes substituent arrangement across the double bond.

Determining and predicting stereochemistry relies on various techniques. Optical activity reveals preference for one enantiomer using polarized light. NMR spectroscopy, often with chiral auxiliaries or solvents, can distinguish stereoisomers. X-ray crystallography provides definitive three-dimensional structures, while circular dichroism and vibrational circular dichroism probe chiral environments in molecules.

Historically, stereochemistry emerged from Pasteur’s work on tartrate salts and the work of van’t Hoff and Le Bel on tetrahedral stereochemistry. In modern practice, stereochemistry influences drug design, catalysis, materials science, and agrochemicals, making stereochemical control essential in synthesis and analysis.