What are structural isomers?

Structural isomers are defined as compounds that share the same molecular formula but differ in the way the atoms are arranged or bonded to each other. This variation in connectivity leads to different properties, physical characteristics, and sometimes different functional groups. For example, the molecular formula C4H10 can represent both butane and isobutane, which have distinct structures and, consequently, different boiling points, densities, and chemical behaviors.

The other options do not accurately capture the definition of structural isomers. Compounds with identical structural formulas would not be considered isomers, as they are the same compound, not different arrangements. The term “interconvert” relates more to conformational isomers or tautomers rather than structural isomers, which are fixed in their connectivity. Lastly, compounds with the same molecular mass but different elements do not pertain to structural isomers, as isomerism is specifically about different arrangements of the same atoms, not different types of atoms altogether.