So when we use the term chirality, this is just a property of molecules in which mirror images of molecules are non superimposable. 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 we 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 up exactly because the spot is over here lining this dog up 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 anant tumor. These are c 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 and NH two, but then it's connected to two ch threes, it is not connected to four different or unique groups. The molecule on the right is Cairo because this H is connected to what Noh in NH two an H and ach 33 uni uh four unique groups. So this carbon here is Cairo. Now chiral molecules we say are optically active. So that's why we say optical, they're optical stereo isomer. 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 Orgo two. But for right now, just realize they're called optical isomers because they rotate plane polarized light. So this is a 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.
2
example
Chirality Example 1
Video duration:
1m
Play a video:
Here in this example, question, it says identify the following molecule as Cairo or a chiro. Now, here's a huge hint when it comes to chiral centers, remember the carbon must be connected to four unique groups. But if you are a double bonded or triple bonded carbon, it's not possible if we take a look at this double bonded carbon, for instance, carbon must make four bonds. It's making 123 bonds that we see that fourth bond is that invisible hydrogen? Now, how many groups would that carbon be connected to 123 can't get to four. So if you have a double bond or a triple bond for carbon, it can't be Cairo. So that means we're ignoring all these carbons within this benzene ring. And we're focusing on this carbon here and this carbon here. The carbon on the far right. It's making one bond. So it has three hydrogens. We don't see definitely not Cairo, but this carbon here, it's making 123 bonds that we see. So it has one hydrogen that's invisible. So what groups is it connected to? Well, it's connected to this hydrogen, this oh group, this entire benzene. And then this ch three group, how many unique groups is that that's four unique groups? Which means that this carbon here is a chiral carbon, which means the molecule overall would be chiral. So here we're gonna say the following molecule is a chiro molecule.
3
Problem
Problem
Identify chiral centers in the provided optical isomers.
A
B
C
D
4
Problem
Problem
Identify molecule(s) capable of rotating plane polarized light.
A
A and D
B
B and C
C
A and C
D
C and D
E
A, C, and D
5
concept
Drawing Enantiomers Concept 2
Video duration:
2m
Play a video:
In this video, we're gonna talk about the methods we can use in drawing in an an tumor. Now, when drawing in an tumor of a chiral molecule, there are two methods available. Now with method one, we're gonna draw an image the molecule sees in the mirror. So let's just imagine this blue dotted line here is our mirror and this molecule is looking into it, it would see back its own reflection. Now, what would this look like? Well, we still have this carbon here in the center, you would see this NH two still at the top. And what else would it see? Well, it's looking in the mirror. So it see these two over here looking back at it. So we'd have the H with still the dash wedge bond and we'd have our ch three group. So we'd have it like this. Remember we wanna show the connection between the carbon carbons. So it's best to draw it this way. And then we'd have the oh back here, this new image that I've just drawn is the mirror image of my original molecule or it's enantiomer. Remember enim is the mirror image. Now, this one method one is a little bit tricky because you have to look into the mirror and you have to draw it kind of like backwards. An easier method would be method two with method two, all you'd have to do is you change your solid wedge to a dashed wedged and your dash wedge to a solid wedged on the chiral center, you keep the molecule in place the way it is. So here carbon would still be here. This NH two would still be here, this 08 would still be over here. And all we're doing here is we're inverting the bonds. So now this dashed bond becomes a wedged bo and it has the H now and then this wedge bond becomes a dashed bond and it has ach three connected to it. In this method, we keep the molecule stationary in the same spot and we're just changing the bonds that show spatial orientation, right. So we could call this the inversion method for method two, right. So these are the two different ways we can draw the anatomy of our original chiral molecule.
6
example
Drawing Enantiomers Example 2
Video duration:
1m
Play a video:
So here it says drawing is for each given chiral molecule using method one. All right. So here we're going to imagine this is our mirror and our molecule looks into it when it does it seize back its own reflection. So here we have our carbon, you would see this oh back in the mirror, we still have this metal group here. And then we have these two in the back, make sure you're showing the connections correctly carbon to carbon. And then here connected to the H. So this would be the anatom or mirror image of our original molecule. For the second one, we imagine there's a mirror here. We'd have these two carbons still connected to each other and we're looking at our reflection in the mirror. So we'd have that H there. We'd have this here and this age here. And in the back, we have this age still here, this br here in the back. And then finally our NH two here. So this would represent our second mirror image or second ener for this chiro molecule in option two, right? So this is how you would show both of our mirror images or enum of our original chiral molecules.
7
Problem
Problem
Provide the enantiomer using method 2. (Hint: chiral center is circled in red.)
A
B
C
D
8
Problem
Problem
Predict enantiomer for thalidomide compound given below.