isomerization

Isomerization is a chemical process in which a single molecular formula is rearranged to form a different isomer—an entity with the same number and types of atoms but a different arrangement. Isomers may differ in connectivity (structural or constitutional isomers) or in spatial arrangement (stereoisomers). Within stereoisomerism, common categories include conformational isomers, geometric (cis/trans or E/Z) isomers, and optical isomers (enantiomers and diastereomers). Tautomerization, widely encountered in biology and organic chemistry, is often considered a subclass in which a proton shifts with reorganization of bonds.

Mechanisms: isomerization can proceed by various pathways. Thermal or photochemical energy can drive rearrangements, and reactions may proceed via simple bond rotations, intramolecular shifts, or via catalysts such as acids, bases, or enzymes. Energy barriers determine whether the product is thermodynamically favored or kinetically accessible, producing mixtures or selectively formed products under control of conditions.

Examples: the interconversion between chair conformations of alkanes like butane; cis-trans isomerization around double bonds such as cis-2-butene to trans-2-butene; photoisomerization of azobenzene, used as a molecular switch; retinal isomerization in vision, where light-induced isomerization of a C=C around the polyene chain triggers a signaling cascade.

Significance: isomerization underpins many biological processes (isomerases), materials science (light-responsive compounds), and synthetic chemistry, where control over isomer distribution affects reactivity and properties.