stereoisomers

Stereoisomers are compounds that have 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 arrangement arises because rotation about certain bonds is restricted, so the molecules cannot be superimposed by simple rotation.

Stereoisomers are commonly divided into enantiomers and diastereomers. Enantiomers are non-superimposable mirror images of each other and have identical physical properties except for the direction in which they rotate plane-polarized light and how they interact with other chiral systems. Diester! Correction: diastereomers are not mirror images of each other and typically have different physical properties. A subset of diastereomers includes geometric isomers, such as cis/trans or E/Z isomers, which arise around restricted bonds like carbon–carbon double bonds or around ring junctions.

Stereocenters, often carbon atoms bonded to four different groups, give rise to configurational stereoisomers. For a molecule with n stereocenters, up to 2^n stereoisomers are possible, though internal symmetry can produce meso compounds that reduce the number of distinct isomers. Mesos are achiral despite having stereocenters because of an internal plane of symmetry.

Identification and separation of stereoisomers involve optical activity and techniques like chiral resolution, formation of diastereomeric derivatives, or chiral chromatography. The stereochemistry of a molecule can profoundly influence its chemical reactivity, physical properties, and biological activity, making the study of stereoisomers essential in chemistry and pharmacology.