the grouping of hydrocarbon compounds into families (alkanes, alkenes, alkynes, alcohols, carboxylic acids and non-branched esters) based upon similarities in their physical and chemical properties including general formulas, their representations (structural formulas, condensed formulas, Lewis structures), naming according to IUPAC systematic nomenclature (limited to non-cyclic compounds up to C10, and structural isomers up to C7) and uses based upon properties
Structural Isomers are organic molecules with the same molecular formula but a different structural formula. e.g. C4H10 can be butane or methyl propane.
What are Isomers?
You can practice on Khan Academy here.
You can identify if compounds are isomers or not here.