Structural isomerism refers to the phenomenon where two or more compounds have the same molecular formula but differ in the arrangement of atoms or groups within the molecule. This difference in arrangement can result in distinct chemical and physical properties for each isomer.

Explanation:
Structural isomerism can be further classified into various types, such as chain isomerism, functional group isomerism, tautomeric isomerism, ring-chain isomerism, and position isomerism. These types of isomerism occur due to differences in the connectivity or location of atoms within the molecule.

1. Chain isomerism:
In chain isomerism, the carbon skeleton of the molecule differs. This can occur due to branching or the presence of different functional groups along the carbon chain. For example, consider the isomers of butane: n-butane and isobutane. In n-butane, the carbon chain is linear, whereas in isobutane, the carbon chain is branched.

2. Functional group isomerism:
Functional group isomerism occurs when compounds have the same molecular formula but different functional groups. For example, ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3) are functional group isomers. Ethanol contains the hydroxyl (OH) functional group, while dimethyl ether contains an ether (O) functional group.

3. Tautomeric isomerism:
Tautomeric isomerism involves the interconversion of isomers by the migration of a hydrogen atom and the rearrangement of double bonds. This phenomenon is commonly observed in keto-enol tautomerism. For example, in the case of acetaldehyde, it can exist as both the keto form (CH3COH) and the enol form (CH2=CHOH).

4. Ring-chain isomerism:
Ring-chain isomerism occurs when a compound can exist as both an open-chain and a cyclic structure. For instance, glucose can exist as both an open-chain form and a cyclic hemiacetal form.

5. Position isomerism:
Position isomerism arises when functional groups or substituents are located at different positions on the carbon chain. For example, 1-propanol (CH3CH2CH2OH) and 2-propanol (CH3CHOHCH3) are position isomers.

In conclusion, structural isomerism refers to the isomerism that arises due to differences in the arrangement of atoms or groups within the molecule. It is different from stereoisomerism, which involves the spatial arrangement of atoms or groups within the molecule.

Isomers which differ only in the arrangement of atoms within the molecule without any reference to the spatial arrangement (stereoisomerism) are known as structural isomers, and the same phenomenon is called structural isomerism.