Stereochemii

Stereochemii, or stereochemistry, is the branch of chemistry that studies the three‑dimensional arrangement of atoms in molecules and how this spatial arrangement affects physical properties, reactivity, and interactions with other substances, including biological systems. The subject distinguishes between different spatial arrangements that have the same connectivity of atoms.

Stereoisomers are compounds with identical bonds but different orientations in space. Enantiomers are pairs that are non‑superimposable mirror images; they often display opposite optical activity. Diastereomers are stereoisomers that are not mirror images. Some molecules contain stereogenic elements, such as chiral centers (usually a carbon atom bonded to four different groups) or elements of axial, planar, or helical chirality. A related concept is meso compounds, which are achiral despite having stereogenic centers.

Nomenclature follows several conventions. Absolute configuration at a stereocenter is designated R or S using CIP priority rules. Double bonds are labeled E (opposite) or Z (together). Older cis/trans terms describe relative orientation around a bond but can be ambiguous in some cases.

Stereochemical analysis employs experimental and computational methods. Optical activity and polarimetry measure how chiral compounds rotate plane-polarized light. NMR spectroscopy, often with chiral reagents, and X-ray crystallography elucidate three‑dimensional arrangements. Chiral chromatography separates enantiomers, and computational methods help predict stereochemical outcomes.

Applications span organic synthesis, pharmacology, and materials science. Stereoselective or stereospecific reactions produce predominantly one stereoisomer. Inorganic chemistry recognizes optical isomerism in coordination complexes. Polymers exhibit tacticity, affecting material properties. The history includes Pasteur’s resolution of tartrate enantiomers and the development of CIP rules by Cahn, Ingold, and Prelog.