isomerizm

Isomerizm is a term in chemistry describing phenomena where two or more compounds share the same molecular formula but differ in the arrangement of atoms or in their three-dimensional orientation. Isomers can have markedly different physical and chemical properties, despite identical composition. Isomerizm is typically categorized into structural (constitutional) isomerism and stereoisomerism, with a further distinction to conformational isomerism within the latter.

Structural isomers differ by connectivity: atoms are linked differently. This includes chain isomerism (different carbon skeletons, for example n-butane and isobutane), positional isomerism (different position of a functional group), functional group isomerism (different functional groups with the same formula, for example glucose and fructose), and ring–chain isomerism. Because of these differences, structural isomers can have distinct reactivity and properties.

Stereoisomerism covers isomers with the same connectivity but different spatial arrangement. Geometric isomerism around carbon–carbon double bonds (E/Z or cis/trans) is common, as in 2-butene. Optical isomerism arises from chiral centers, yielding enantiomers—non-superimposable mirror images—and diastereomers, which are not mirror images. Enantiomers can have different biological activity and physical properties; racemic mixtures contain equal amounts of both enantiomers. Conformational isomerism, another aspect, results from free rotation about single bonds, producing different conformers such as staggered and eclipsed forms in alkanes like ethane. At room temperature these interconversions are rapid, often averaging properties.

Significance of isomerizm lies in predicting reactivity, spectroscopy, pharmacology, and biology. Not all molecules exhibit all types, and energy barriers or symmetry considerations determine how easily isomers interconvert or can be isolated.