Isomerism is a phenomenon in which two or more compounds have the same molecular formula but different structural arrangements of atoms. These compounds are called isomers. In organic chemistry, isomers can be classified into two main types: structural constitutional isomers and stereoisomers.1. Structural constitutional isomers: These isomers have the same molecular formula but differ in the connectivity of atoms. They can be further classified into chain isomers, position isomers, and functional group isomers.2. Stereoisomers: These isomers have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of atoms. Stereoisomers can be further classified into enantiomers, diastereomers, and geometric isomers cis-trans isomers .To determine the isomerism of a molecule in organic chemistry, you need to analyze the molecular formula, connectivity of atoms, and spatial arrangement of atoms in the molecule.Example of two isomers: Pentan-2-ol and Pentan-3-olMolecular formula: C5H12OPentan-2-ol:CH3-CH2-CH OH -CH2-CH3Pentan-3-ol:CH3-CH2-CH2 OH -CH2-CH3Key differences:1. Connectivity of atoms: In Pentan-2-ol, the hydroxyl group -OH is attached to the second carbon atom, while in Pentan-3-ol, the hydroxyl group is attached to the third carbon atom. This difference in connectivity makes them position isomers, which are a type of structural isomers.2. Physical properties: Due to the difference in the position of the hydroxyl group, these isomers may exhibit different physical properties, such as boiling points, melting points, and solubility.3. Chemical properties: Although both isomers have similar chemical properties due to the presence of the hydroxyl group, their reactivity may differ slightly depending on the position of the hydroxyl group in the molecule.