MCAT Organic Chemistry Review

Isomers

Introduction

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. Flowchart of Isomer Relationships

KEY CONCEPT

Isomers have the same molecular formula, but different structures.