Stereoisomers themselves are further divided into two types. We have our geometric stereoisomers and our optical stereoisomers. With geometric stereoisomers, these are molecules with different spatial arrangements around a double bond. Optical isomers, on the other hand, are molecules that are non-superimposable mirror images of each other.

Now when we say nonsuperimposable, these mirror images cannot be placed one over the other. So just imagine you have a dog and this dog is looking into a mirror. This mirror image of itself would mean that these two dogs are optical stereoisomers. If we were to take this dog and take it out of the mirror and try to slide it over this dog here, we would see that they don't perfectly line up because if you slide it all the way over to the left, we have this spot here.

So when you slide it over, it would appear over here, but that doesn't match up with this dog where the spot is on this side. Now this and this would more or less match up with this and this. But again, it's this portion here. When you slide it over the other dog, that would not match up. That makes these two optical stereoisomers of each other.

And remember, the fastest way to look at it is to look at two molecules. Imagine there's a mirror between them. The molecule on the left, when it looks into the mirror, does it see the molecule on the right? If it does, that means they're optical stereoisomers of each other. That's the easiest way to understand this type of stereoisomer. We've talked about these two additional types of stereoisomers. Click on the next video and let's take a look at an overall chart.