what are constitutional isomers

Constitutional isomers, also known as structural isomers, are specific types of isomers that share the same molecular formula but have different bonding atomic organization and bonding patterns. In other words, they are compounds that differ in connectivity, that is, in the way in which the constituent atoms are connected to one another. For example, butane and isobutane have the same molecular formula, C4H10, but different structural formulas, so they are constitutional isomers. There are several classes of structural isomers, including skeletal isomers, positional isomers (or regioisomers), functional isomers, tautomers, and structural topoisomers. Skeletal isomers are structural isomers that differ in the atoms and bonds that are considered to comprise the "skeleton" of the molecule, while positional isomers are structural isomers that can be viewed as differing only on the position of a functional group, substituent, or some other feature on a "parent" structure. Functional isomers are the constitutional isomers which share the same molecular formula but vary in the manner in which the atoms are connected to each other.