stereoisomerit

Stereoisomerit, or stereoisomers, are compounds that share the same molecular formula and the same connectivity of atoms but differ in the three-dimensional arrangement of those atoms in space. This difference in spatial arrangement can lead to distinct physical, chemical, and biological properties even though the atoms are connected in the same way.

Two main categories describe stereoisomerism. Configurational isomers cannot interconvert without breaking and reforming covalent bonds; they include enantiomers and diastereomers. Conformational isomers (conformers) interconvert by rotations about single bonds and often do so rapidly at ordinary temperatures, without bond breaking.

Enantiomers are non-superimposable mirror images, typically arising from a stereocenter (a carbon atom attached to four different groups). They have identical physical properties in achiral environments but interact differently with chiral environments and rotate plane-polarized light in opposite directions. The absolute configuration at a stereocenter is assigned using the R/S system according to CIP rules. A mixture containing equal amounts of enantiomers is called a racemate and is usually optically inactive.

Diastereomers are stereoisomers that are not mirror images of each other. They include many pairs with different relative configurations and, in some cases, cis/trans (geometric) isomers around restricted rotation, such as in alkenes or cyclic systems. For example, certain diastereomeric forms of tartaric acid differ in both physical properties and biological activity.

Meso compounds are a special class of diastereomers that contain multiple stereocenters but are achiral due to an internal plane of symmetry. Stereoisomerism is a fundamental concept in stereochemistry, influencing reactivity, spectroscopy, and the behavior of molecules in biological systems.