stereoisomeria

Stereoisomerism, sometimes referred to as stereoisomeria, is the branch of stereochemistry concerned with isomers that have the same molecular formula and connectivity but differ in the three-dimensional arrangement of atoms in space. These differences arise from restricted rotation about bonds or the presence of chiral centers, leading to distinct spatial arrangements that cannot be superimposed on each other.

The principal divisions are enantiomerism and diastereomerism. Enantiomers are pairs of non-superimposable mirror images, usually centered on one or more stereocenters with four different substituents. They share many chemical properties but rotate plane-polarized light in opposite directions and interact differently with chiral environments, such as biological systems. A racemate contains equal amounts of both enantiomers; the degree of imbalance is called enantiomeric excess.

Diastereomers are isomers that are not mirror images. They may be formed when a molecule has two or more stereocenters, or from restricted rotation giving geometric isomers. Epimers are a subset of diastereomers that differ at one stereocenter; anomers are cyclic isomers differing at the anomeric center.

Geometric isomerism describes cis/trans (or E/Z) arrangements around carbon–carbon double bonds or within cycloalkanes where rotation is hindered. These isomers can have markedly different physical properties and reactivities.

Conformational isomerism refers to different spatial arrangements that interconvert by rotations about single bonds. If interconversion is rapid at room temperature, these are often not distinguished as separate isomers.

Determination of stereochemistry commonly uses NMR spectroscopy, chiroptical methods, X-ray crystallography, and, in practical terms, resolution through chiral chromatography.