Isomeeri

Isomeeri, or isomerism in chemistry, is the phenomenon where compounds share the same molecular formula but differ in the arrangement of atoms, leading to distinct properties and behaviors. Isomerism highlights how structure influences function in chemical systems.

There are two broad categories: structural (constitutional) isomers and stereoisomers. Structural isomers differ in how atoms are connected (connectivity). Examples include chain isomers, such as n-butane and isobutane (both C4H10), and position isomers where a functional group or double bond occupies different positions along the carbon skeleton. Functional group isomers are compounds with the same formula but different functional groups, such as ethanol (C2H6O) and dimethyl ether (C2H6O).

Stereoisomers have the same connectivity but differ in spatial arrangement. Geometric (cis/trans) isomerism occurs in restricted rotations around double bonds or rings, affecting properties like boiling points and reactivity. Optical isomerism arises from chirality, producing enantiomers that are non-superimposable mirror images; diastereomers are stereoisomers that are not mirror images. Conformational isomerism (conformers) results from rotation about single bonds and can interconvert readily at room temperature, influencing reactivity and interactions.

Applications of isomerism are broad. In pharmaceuticals, different isomers can have markedly different efficacy or safety. In materials science and fragrances, isomeric forms can yield distinct physical properties and scents. Analytical techniques such as NMR, IR, UV-vis spectroscopy, and X-ray crystallography help identify and distinguish isomers, often complemented by chromatography.

Etymology derives from Greek isos “equal” and meros “part.” Isomeeri underlines the significance of molecular arrangement in chemistry and related fields.