What are structural isomers?

Structural isomers are compounds that share the same molecular formula but differ in the connectivity of the atoms within their structures. This means that while the number and type of atoms are identical, the way those atoms are arranged varies, leading to different chemical properties and reaction behaviors.

For example, consider the molecular formula C4H10. This formula can represent two different compounds: butane and isobutane (or methylpropane). Both have the same number of carbon and hydrogen atoms, but their structures are different due to the arrangement of those atoms. This variation results in distinct physical and chemical properties, demonstrating the importance of structure in determining a compound's characteristics.

The other choices do not accurately define structural isomers. Compounds with the same chemical properties or those producing the same reaction do not necessarily imply isomerism, as chemical properties can vary regardless of isomer status. Similarly, different molecular formulas indicate different compounds altogether, which is not the case with structural isomers, as they must share the same formula. Thus, the definition of structural isomers is best captured by the correct answer.