Structural isomerism, also known as constitutional isomerism, is a type of isomerism where compounds have the same molecular formula but different arrangements of atoms. This results in distinct structural connectivity, which can lead to differences in chemical and physical properties. Structural isomers have different chemical names and often exhibit varied reactivity due to their different functional groups or bond arrangements.

There are several subtypes of structural isomerism:

1. Chain Isomerism: In chain isomerism, compounds have the same molecular formula but different arrangements of the carbon skeleton. This can involve branching, straight chains, or even cyclic structures.
2. Positional Isomerism: Positional isomerism arises when the same functional group is attached to different positions in the carbon chain. This is commonly seen in compounds with substituents like alkyl groups or halogens.
3. Functional Group Isomerism: This type of isomerism occurs when compounds have the same atoms but different functional groups. For example, compounds with the same molecular formula may differ in whether they have an alcohol, ether, or ketone functional group.
4. Tautomeric Isomerism: Tautomeric isomers are compounds that exist in dynamic equilibrium due to the shifting of protons. They are interconvertible by a proton shift, resulting in different arrangements of atoms.
5. Ring-chain Isomerism: This type of isomerism occurs in cyclic compounds. One isomer has a ring structure, while the other isomer has an open chain.
6. Ring Position Isomerism: In cyclic compounds, the location of a functional group on the ring can change, leading to ring position isomerism.

Each type of structural isomerism contributes to the diversity of organic compounds and their properties. Different structural isomers often have distinct physical characteristics, boiling points, melting points, and chemical reactivity. Understanding the concept of structural isomerism is essential in organic chemistry and has implications in fields such as drug development, materials science, and chemical synthesis.