Isomerism is a phenomenon in chemistry where two or more compounds have the same molecular formula but different structural arrangements or spatial orientations, resulting in distinct chemical and/or physical properties. Isomers are compounds that share the same number of atoms of each element but have different connectivity or arrangement of atoms within their molecules.

There are different types of isomerism:

1. Structural Isomerism: Also known as constitutional isomerism, this type of isomerism arises when compounds have the same molecular formula but different connectivity of atoms. Structural isomers can be further classified into various subtypes:
   • Chain Isomerism: Isomers have different carbon chain arrangements.
   • Positional Isomerism: Isomers have the same carbon chain but different functional group positions.
   • Functional Group Isomerism: Isomers have different functional groups.
   • Tautomeric Isomerism: Isomers exist in dynamic equilibrium due to the shifting of protons (tautomers).
2. Stereoisomerism: Stereoisomers have the same molecular formula and connectivity of atoms but differ in spatial arrangement. Stereoisomerism is further divided into:
   • Geometric (Cis-Trans) Isomerism: Occurs in compounds with restricted rotation around a bond, leading to different spatial arrangements.
   • Optical Isomerism (Enantiomerism): Compounds are non-superimposable mirror images of each other, resulting in chiral molecules.
3. Conformational Isomerism: This type of isomerism involves different spatial arrangements due to rotations around single bonds. Conformational isomers are usually rapidly interconvertible at room temperature.

Isomerism has significant implications for the properties and behavior of compounds. Isomers can have distinct physical properties (such as boiling points, melting points, and solubility) and different chemical reactivity. Understanding isomerism is crucial in areas such as drug design, materials science, and the study of complex chemical reactions.