What defines isomers in chemistry?

Isomers in chemistry are defined by compounds that share the same molecular formula but differ in their structural formulae. This means that while the number and types of atoms in an isomer remain constant, the arrangement of these atoms can vary, leading to differing chemical and physical properties. For example, two isomers can have the same molecular formula, such as C4H10, but exhibit different structures (like butane and isobutane), which affect their boiling points, reactivity, and overall behavior in chemical reactions. This concept is crucial in organic chemistry, where even slight changes in structure can result in vastly different molecules with unique characteristics.

In contrast, compounds with different molecular formulas describe entirely different substances, and compounds that are identical in structure do not qualify as isomers since they are essentially the same molecule. Likewise, compounds having the same boiling point may or may not be isomers, as boiling point alone does not provide sufficient information to determine structural differences. Hence, the focus on structural diversity while maintaining the same molecular formula is what distinctly characterizes isomers.