What are isomers defined as in chemistry?

Isomers are defined as compounds that have the same molecular formula but differ in their structural arrangements. This means that while the number and types of atoms in the compounds are identical, the way those atoms are connected or arranged can vary significantly.

This structural variation can lead to different physical and chemical properties, even though the molecular formula remains constant. For example, butane and isobutane both have the molecular formula C4H10, but their structures differ: butane is a straight-chain alkane, while isobutane has a branched structure. This difference in structure can result in distinct boiling points, densities, and reactivities, highlighting the importance of structural arrangement in defining isomerism.

The other options do not accurately capture the definition of isomers as they refer to characteristics that are not specific to the concept of isomerism. Compounds that react similarly or have identical physical properties do not necessarily qualify as isomers, as these traits can be shared by different compounds altogether. Similarly, the mention of different molecular formulas is contrary to the definition of isomers, which must share the same molecular formula.