Structural isomerism, or constitutional isomerism (per IUPAC), is a form of isomerism in which molecules with the same molecular formula have bonded together in different orders, as opposed to stereoisomerism. There are multiple synonyms for constitutional isomers.
Three categories of constitutional isomers are skeletal, positional, and functional isomers. Positional isomers are also called regioisomers. Tautomers are subcategory of functional isomers.
1 Skeletal isomerism
2 Position isomerism
3 Functional group isomerism
4 Isomer counting