What are structural isomers?

Structural isomers are compounds that share the same molecular formula but differ in the way their atoms are arranged. This difference in arrangement leads to unique structural forms, which can significantly influence the physical and chemical properties of the isomers.

For example, consider butane (C4H10), which can exist as n-butane (a straight-chain form) and isobutane (a branched form). Both have the same number of carbon and hydrogen atoms, yet their molecular structures are different, resulting in distinct properties such as boiling points and reactivity.

The other options do not accurately define structural isomers. Compounds with the same molecular formula but different chemical properties may relate to isomers, but structural isomerism is specifically defined by atomic arrangement. Identical compounds do not represent isomerism at all, while having different molecular formulas indicates that the compounds are simply different, not isomers.