at the beginning of this lesson. I told you guys that they were gonna be three tests for Chire ality. I've already taught you two of them. One was the Internal Line of symmetry to was finding stereo centers. And now I'm going to teach you the third one. And it turns out that the third one is more of a shortcut than a new rule. So it turns out that this third test has to do on Lee with Di substituted cycle Al Keynes. Okay, what are those? That just basically means a ring that is two identical things coming off of it. Okay. And these happen to be really commonly tested molecules and homework and in exams. So if we can figure out a way to figure these out even quicker, that's going to save us time. In the long run, that's gonna be smart. So these air really just shortcuts. What that means is that for all of these, you could use the other two rules. But if we just memorize these shortcuts, it's just gonna make it even faster for us when we see these. Okay, so I want to go ahead and talk about them There's basically three different types of rings that we deal with on a regular basis. There's what I call Gem Di Substituted Gem is short for the word germinal. And later on, what we're gonna learn about the word genital is that it means two things coming off of the same carbon. Okay, so if you ever see Genital Di substituted, that is always a Cairo. You don't have to give it a test. You don't need toe look for line of symmetry. Nothing. It's just always gonna be a Cairo. And the reason for that is that there's no Cairo center. Okay, if you think about it, both of these are groups here are gonna be exactly the same no matter what. So there's no Cairo center, so this is always gonna be a Kyle. Easy, right? Then let's go off to the other extreme, which is paradise substituted. Now, pair is a word that we're going to use a lot more in or go to, and what it means is across from okay, so basically means or opposite to wow, that just my handwriting is getting worse and worse across from or also opposite to. So basically, if you have to subsistence that are perfectly across from each other. Okay, then. That's also gonna be a Cairo. So this is also something you could just memorize. You don't have to test it. You could just say, Hey, if it's paradise subsided, if they're across for each other perfectly, then it's also gonna be a Cairo. I don't need to test anything. All right now, something to keep in mind they have to be careful about is that this is Onley possible on even numbered rings. Okay, The reason is because if you have, let's say, a five member dring there are no two positions that are perfectly across from each other. This one, ideally, the position that would be across from it would be here. But there's nothing. There's no position there. So there's Onley possible on even members rings like four members six member, eight member and stuff like that. If you have five or seven, it's not gonna work or three. It's not gonna work. All right. So cool. We've already knocked out two huge categories. Gem di Substituted, Paradise substituted. There's always a Cairo. Okay, Well, what about in between In between, we're calling that Middle Di substituted. That just means somewhere in the middle between Jem and somewhere between para basically somewhere in between zero degrees, 180 degrees. Basically, if you're thinking of it as a circle, Okay, well, for these, it's actually gonna depend where the group's heir facing if the group's heir facing sis, then the answer is always gonna be miso a Cairo. And I already showed you as an example of one of these when we did the when I showed you guys the missile compound that I showed you how ring could be a missile complex. Okay, so if there sis is gonna be so a Cairo, if they are trans, then it's always gonna be Cairo. Okay, you don't have to test it. You don't have to do our s anything like that. Just say it's gonna be Cairo for sure.

There is one exception, but there's like a huge disclaimer here that I have to give. Okay, and what this is, is that this happens to be sorry. This happens to be controversial, and I know that that's a really weird word Thio use for organic chemistry because it's like organic chemistry. Like such old science. Like, How could there be controversy about this? It's like, Is this like political? Well, it's It's not like Republicans think one thing and Democrats think another. It's that some professors hence tend to be renegades and think their own things versus what the book says. Okay, so according to your book, this is actually a Cairo. Okay, so according to your book, this exception here of one to cyclo hexane which are going to draw for you, which is actually this right here. Okay, According to your book, this is a Cairo. Okay. So it would fit into this rule that we have right there about if it cysts one to cycle. Heck, saying then it would be a Cairo. Okay, But according to some professors, it's actually Cairo. And I've seen that at the same university, two professors will say two different things, and it really just depends how they're thinking and how they kind of grew up teaching organic chemistry. So let me show you where the controversy lies so that you guys will understand. It Turns out that remember that chair come from, remember that cyclo hexane doesn't exist in a plane or structure. It actually exists as a chair confirmation. So what that means is that I'm just going to draw sis one to cycle. Heck, same. Okay, if I have two groups facing up like this, Okay, it looks like it has a plane of symmetry, right? It looks like it has a perfect plane of symmetry, so this should be a Cairo. But it turns out that what it really looks like is a chair. So what that means is that if they're both facing cysts and if they're 12 apart from each other, then that means that one of them will always be axial, and one of them will always be equatorial. Remember how to figure this out. Basically, they're both want to go to the same face of the ring, so they both only system that you want to. So one of them is gonna be axle on. One of them is gonna be equatorial. Is there a plane of symmetry now? Not really. If you draw it like this, there's no plane of symmetry because if you cut it down the middle, you have two different positions. Okay, so the professors who say that it's Cairo, we'll go buy this argument. We'll say it's Cairo because the positions are different. Now the professors that say that it's a Cairo, which is actually the majority of professors will point to the fact that this is an equilibrium. So what that means is that even though, sure, one of the chairs is Cairo by itself, but it doesn't just exist, as it doesn't just exist as one chair, it exists as an equilibrium of two chairs. Okay, so what that means is that on average, you always have one actual in one equatorial, and they kind of cancel out. So the professors who say that it's a Cairo point to this equilibrium. Okay, Now what's your job? Your job is if you're Professor made a big deal out of this in class or even if maybe they never talked about it all, maybe it would be safe to just go to their office, our and just say Hey, profit. What do you What do you think about 12? Sis? Cyclo. Hexane. Is that Cairo, or is that a Cairo? Because the last thing you want is for this to show up on your test and you don't know which one to pick because you don't know. Okay, now, just you know, either argument is kind of defensible. You could either say you could defend that it's Cairo. You could defend that. It's a carol with these two different arguments. But just, you know, the majority and your book and the majority of people rest in the A Cairo argument. They say that because of this is equal, this is in the equilibrium. Then it's a Cairo over all, even though the structure by itself is Cairo. But like I said, I wouldn't be pointing this out unless I had seen professors test the other way and actually say that it's Cairo. Okay, so this is gonna be kind of up to you guys to just do a little bit of homework with your professor and just say hey, like, is this Kyra Laurie Cairo and then they can let you know. And then you memorize it that way. Are you guys cool it that long explanation. Sorry, but I just want to give you the heads up. But other than that, if it's not that very special case, we're going to go with these rules right here, which is CIS and Trans. That's all you need to know. So what I want you guys to do is for test three. I want you guys to just do these. You answer these next four questions and then we'll go ahead and I'll answer them. All right, so go for it.