izomerizm

Izomerizm is the phenomenon in chemistry where compounds share the same molecular formula but differ in the arrangement of atoms or in their three-dimensional orientation, leading to different physical and chemical properties. There are two main classes: structural (constitutional) isomers, which differ in the connectivity of atoms, and stereoisomers, which have the same connectivity but differ in spatial arrangement.

Structural isomerism includes chain isomerism (different carbon skeletons, such as n-butane and isobutane, C4H10), position isomerism (same skeleton or functional group at different positions, e.g., butanol isomers), and functional group isomerism (different functional groups with the same formula, such as alcohols and ethers or ketones and aldehydes).

Stereoisomerism covers geometric isomerism and optical isomerism. Geometric isomerism arises around restricted rotation in alkenes or rings, producing cis and trans (or E/Z) forms; for example, cis-2-butene and trans-2-butene have different shapes and properties. Optical isomerism involves chiral centers, yielding enantiomers that are non-superimposable mirror images and may rotate plane-polarized light in opposite directions. Some molecules are achiral despite having stereocenters, or exist as meso compounds.

Conformational isomerism results from rotation about single bonds; these conformers interconvert rapidly at room temperature, as illustrated by eclipsed and staggered forms of ethane.

Isomerism is central to understanding reactivity, physical properties, and biological activity. It is routinely studied with spectroscopy, crystallography, and computational methods, and it has important implications in pharmaceuticals, agrochemicals, and materials science.