So when we use the term chirality, this is just a property of molecules in which mirror images of molecules are nonsuperimposable. If you go back and take a look at my videos on isomers, you'll see where I did this analogy with these dogs. So here this dog is looking in the mirror. In the mirror it sees its mirror image. Now if you were to take that dog out of the mirror and slide it over this dog, they wouldn't match up. They wouldn't line up. That's because if we slip this dog over out of the mirror, this spot here would not line U exactly because the spot is over here. Lining this dog U over here would mean that its spot would be on this side. This means that they are mirror images of each other.
Now optical isomers. Optical isomers are also called enantiomers. These are chiral molecules, and they possess one or more chiral centers. Now what the heck is a chiral center? Well, a chiral center is where a carbon is connected to four unique groups. And if you don't have four unique groups, then you're classified as being a chiral. So if we take a look here at this molecule on the left, it is a chiral. And it's a chiral because if we take a look, this carbon is connected to what? An OH an NH2, but then it's connected to two CH3's. It is not connected to four different or unique groups.
The molecule on the right is chiral because this H is connected to what in OH and NH2 and H and a CH34 unique groups. So this carbon here is chiral. Now, chiral molecules we say are optically active, so that's why we say optical they're optical stereoisomers. That's because they're optically active. All that means is that they rotate plane polarized light. In this level of chemistry, you won't have to worry too much about that at all. That's reserved more for real organic chemistry when you take orgo one and or go 2. But for right now, just realize they're called optical isomers because they rotate plane polarized light.
So this is the definitional explanation of that, right? So just remember when we're talking about chirality, we're talking about mirror images. We're talking about a carbon atom within a molecule connected to four different or unique groups.