By now you should have a pretty good idea of how molecules orient themselves in space in terms of geometry and connectivity. Often, however, there is more than one way a molecule with a certain molecular formula can orient itself. It is important to be able to distinguish different molecules, even if they appear at first to be identical.

There are two major topics you should know in terms of distinguishing similar molecules, which I’m sure you can guess based on the heading. Isomers have the same exact molecular formula but a different arrangement of molecules, often giving them different molecular properties. Chirality has to do with a different orientation around one central, or chiral, atom. This concept is a little tougher to grasp at first, but with practice it should become very familiar.

What to know about Isomers and Chirality

The first thing you’ll need to understand is isomerism. Make sure you understand the different kinds of isomers, specifically diastereomers and enantiomers. Chirality can be a bit trickier, especially when it comes to naming. Understand that a chiral center is an atom with four different substituents branching off of it. You’ll need to know how to name a molecule using the R/S System of naming. This should become second nature with enough practice.


When naming a molecule using R/S, make sure the lowest priority atom/ substituent is in the back, facing away from the viewer. You can still name the molecule if the atom is in front as long as you remember to use the opposite name (i.e. use S instead of R or vice versa).

5 Curated Resources


free, Extensive definitions

This article gives an overview of isomerism and talks about the different kinds of isomers, which will come in handy. Also, it’s got a bunch of links to other articles that go into even more detail in case you struggle with any topics.

This has a summary of all different kinds of isomerism. You probably won’t need to know all of them, but it’s got a handy infographic and some solid examples.


free, Guide

This has links to all different topics regarding chirality, which will be an important subject for the rest of the course.

Introduction to chirality

free, Video Series

Here’s Khan Academy’s overview of chirality. As always, this is a very in depth overview of everything you may need to know about chirality.

R and S Configuration

free, Article

Knowing how to name chiral centers as R or S will be a crucial skill, and this is a solid description of how to do just that.