izomerii

Izomerii, or isomers, are compounds that share the same molecular formula but differ in how the atoms are connected or arranged in three-dimensional space. Isomerism arises from the flexibility of chemical bonding and leads to distinct substances with different physical and chemical properties.

Isomerism is commonly divided into two broad classes: structural (constitutional) isomers, where the connectivity between atoms differs, and stereoisomers, where the connectivity is the same but spatial arrangement differs.

Structural isomers include chain isomers (different branching), position isomers (functional groups in different positions), and functional group isomers (different functional groups). For example, n-butane and isobutane (C4H10) are chain isomers.

Stereoisomers include geometric isomers (cis/trans or E/Z) arising from restricted rotation around double bonds or rings, and optical isomers, also called enantiomers, which are non-superimposable mirror images. Enantiomers often have identical physical properties in achiral environments but rotate plane-polarized light in opposite directions and can have different biological activities. Diastereomers are stereoisomers that are not mirror images, such as certain pairs of 2,3-dihalobutane.

Other forms, particularly in coordination chemistry, include linkage isomerism where ligands can bind through different atoms, and conformational isomerism from rotation around single bonds. Understanding isomerism is essential in predicting reactivity, designing drugs, and interpreting spectroscopy.