An important way that we distinguish between molecules is by identifying isomers of the same
compound—those that have the same molecular formula but different structures. Keep in mind
that isomerism describes a relationship; just as there must be at least two children to have siblings,
two molecules can be isomers to each other, but no molecule can be an isomer by itself.
Throughout this chapter, we will learn how to identify these relationships and describe the
similarities and differences between isomers. Figure 2.1 shows the isomer classes that we will learn
more about and how they are related—feel free to come back to this figure as a reference after you
have read through the more detailed explanations.
Figure 2.1. Structural (Constitutional) Isomers of C 6 H 14KEY CONCEPT
Isomers have the same molecular formula, but different structures.