So now that we understand what a Carl center is and we know how to recognize them on molecules, it's important that we know how to name them. So if you remember back to when I first taught you guys about just simple al que nomenclature, we talked about the AIPAC naming system. And what I told you was that according Toa AIPAC protocol, every single molecule in the universe needs to get its own unique name. That's kind of the point of AIPAC that now we have a systematic way to name every single molecule. Well, now that we've learned about stereo I summers meaning molecules that possess Cairo centers, that means that those sterilized ever since they have different shapes, they're gonna need to be included in the system somehow because they have a distinctive difference. Well, it turns out that all we have to do is we're gonna use the same AIPAC names from before, but we're gonna add just one extra step to account for those Carol centers. And that extra step is called the con angled pre log nomenclature. I know that name blows. So what we're gonna be doing is we're not gonna be using that name so much. That's kind of the technical name that's in your book. I like to just call it the R and s naming system. Okay, you'll understand why it's called RNs in the second. But for right now, just kind of take my word for it that you don't need to say Con angle pre log in class. You could just say R N s and everyone will know what you're talking about. So in order to learn this one extra step, it's actually kind of a five step process. So what we'll be doing this will just be I'll be teaching you one step at a time with the molecule so that you can apply it and see exactly how how to use that rule. Okay, so let's go ahead and get started with our first step

All right. So our first step starts off pretty easy. What it states is that you're gonna have to assign priorities to the four atoms on a carol center based on their atomic mass in the periodic table. So let's break that down a little bit more. First of all, notice that I underlined four atoms. Why specifically is it the number four? Because, remember, the definition of a Kyle center was any atom that has four different groups. So what I'm basically just saying here is that you find those four different groups and you give them priorities. How? Based on their mass in the periodic table. Okay, so let's just go ahead and look at this molecule to kind of get started with this rule. First of all, do you guys were you guys able to find? And Adam here? That would count as a carl center, because that's always gonna be the first step. Locate your carl center. So do you see one? Maybe an Adam. That's four different. Yeah. You found it. It's this one right here. Remember, I can use a star to represent a carol center. Awesome job. Notice that that carbon has four completely different atoms coming off of it. It has oxygen, nitrogen, hydrogen. What's that stick? Obviously, that would be a carbon. Okay, Perfect. So you've got four different atoms. This is definitely a Tyrell center. So we've got the first step down. The second step is that we need to assign priorities based on the periodic table. This might be the point of the video that you want to pause and grab a periodic table and then rush back over here. But we could also use this to remember our big seven. So remember that the Big seven is just a method to remember some of the most important Adams on the periodic table. Remember that the way you do this is we just draw literally a big seven, okay? And then you split the big seven into seven boxes, and then we would just fill these out in order of the atoms on the upper right hand side of the periodic table. So remember that we always start off with Carvin, okay? And then we go to nitrogen oxygen flooring. Now we're in the halogen, and we have to go down. So be flooring, chlorine roaming iodine. That's our Big Seven. Okay? Obviously, this isn't comprehensive, but it's a great reference point, even for all the other atoms on the periodic table. Okay, so now I'm just gonna trust you guys that either you're looking at the big seven that I just drew or you have a periodic table. Let's go ahead and assigned priorities. So my first question to you is which one will get the highest priority out of these four different atoms? Which one is the highest? According to atomic mass, it has to be the oxygen, right, Because we said that we have four different atoms. Oxygen, nitrogen, hydrogen, carbon. Okay, so this is gonna be my number one priority because it has the highest weight on the periodic table. Okay, I don't have any of the heavier atoms. So now, if that's number one, which one is number two? Number two has to be nitrogen because it's a little bit lighter. So it's going to get my two. Which one's number three has to be carbon. So, carbons. My number three and just you guys know if you ever see a hydrogen, that's always gonna be your four. Okay? Because nothing is lighter than hydrogen, right? So you could always just draw for there immediately if you just wanna get good at it. Okay, so that was the first step, guys, it's just look at your periodic table. If you need to draw your big Seven and go ahead, compare priorities. Not so bad, Right? Let's move on to the next step.

So Step two deals with a really common issue that we face with RNs naming, which is that sometimes you're gonna be comparing your atoms and you have a tie because two of them have identical atomic weights. Well, what do you do in that situation? Well, if you do have a tie between your atomic weights or then we're going to do is we're gonna compare the next set of atoms that they're both attached to and basically have a playoff system. OK, in the playoff system, we look at the next immediate atoms that they're both attached to. And then we compare those atomic weights and you say, Well, which of these is bigger? Which of these is heavier and that's gonna be the winner. So let's go ahead and apply this to an example. First of all, I really hope that you guys can identify the carnal center here. Yeah, so you should be getting a little bit better at this. It's their That's it. Okay. And now we have to figure out. First of all, are there any issues with step one in terms of are we able to name these priorities easily? Okay, so let's kind of just do the first step, which you just figure out what all the atoms are. Well, I noticed that right away I have an issue because two of the atoms that are attached to my Carl center are the same. I haven't oxygen and oxygen. Okay, now, if I compare both of those in the periodic table, I'm obviously gonna get equal atomic masses. So that means I'm definitely enough to use a playoff there, no matter what. But let's continue. Maybe the other atoms, we can figure out what order there in. Well, this is a carbon, because that's a carbon group in our group and e t look that up on the periodic table, you're not gonna find it, because that stands for Ethel. That really just stands for ch two ch three. I've got another two way tie. Guys, I've got another to a tie between this carbon and this carbon, so I'm definitely having some issues with rule number one. Okay, now, there is one thing that we could do even before this playoff system. What I can safely say is that my oxygen are going to get positions one and two and my carbons are going to get positions three and four, right? Because oxygen's air bigger than carbon. Okay, that's just common sense. But I don't know which order they're gonna be in in order to figure out the order after his playoffs. So let's do the oxygen playoff first. This is for spots one and two. So this will be my red oxygen. This will be my blue oxygen. Okay, So what is my oxygen attached to the red one? It's attached immediately to an age. What is the blue oxygen attached to you that's immediately attached to M E? What is m e stand for? That's a method group. Okay, so method group is CH three, so it's attached to a C. Okay, so in the playoff system, I look at what's in the bracket. Okay? It's almost like March madness or something, but it's just a lot more boring, and you can't win money from it. Unfortunately, at least I haven't developed that that way to make money yet. Um, s O. But which one is gonna win inside of that bracket? It's gonna be the carbon because carbon is heavier than hydrogen. Right? So we've got a clear winner. This is my number one. And this is like number two. Okay. Makes sense So far, both my oxygen's beat my carbons, but the metal beats the h. So let's move on to the carbons. So I'm gonna do the same thing, and you're gonna do, like, a color system. This will continue to be my blue carbon. I'll make this one green. Okay, So what I want to do is that notice that for oxygen, oxygen is only touched A One more thing. But carbon always has three bonds, so I'm gonna draw all three. So for my blue one, what are the three additional bonds besides the Kyle Center? Because you never go backwards. You only go forwards. What are the three atoms that that carbon is attached to? Well, it's attached toe one carbon on one side. Let's just say that that is the left side. It's attached to another carbon on the right side. And then it's also attached to an H that wasn't drawn. So I'm gonna draw that. I'm gonna put that here. So that's what's in my bracket there. Those are the three additional atoms attached to the carbon. Not look at green. Okay, So, green. Once again, I'm not gonna look at the Kyle center. I'm just gonna move forward. Green is attached to well, to h is because it's ch two and then ch three. It's also attached to this carbon here because obviously it's a chain, right? So it needs to be attached. What we tend to do for bracket is we put biggest Adam's first. So instead of writing, this is h h C. I would actually write this as C h h. And it just makes it easier to compare the brackets and see who wins. So now I know that I had a tie between the carbons. If I move into the bracket, is there a winner? Well, if you look at the first Adam, there's still a tie. They're both attached to carbon. But if you look at the second set, this is where your winner is determined. Okay. Came down to the wire. It was a close game, but I'm sorry, Green, you lost. All right. So that means that my blue is gonna be number three and my green is going to be the biggest loser at number four. And see how we systematically did that with a playoff system. Okay, so that's all there is to it. We'll practice it more. Don't worry, but those are the basics.

Step three is pretty straightforward. It just says if you're using the playoff system and you run into a double bond or triple bond, the double bond is going to count twice and a triple bond is going to count three times. So I think the easiest way to relate to this is just to do an example. So archival center is where right here. And let's kind of figure out those four different atoms that we've been doing so far. So we have an H. So obviously, we can already tell what priority that's gonna be right out of the four numbers. Which one is it gonna be for automatically? Good job. Okay, But these other three, let's figure out I've got carbon. I've got carbon. Oh, man, I have a three way tie, guys. So remember that if we have a tie where the atoms don't have different atomic weights, we have to use the playoff system. But now, on top of that, I have a slightly more complicated situation because some of these carbons have double bonds on them. So let's figure out how to do the bracket playoff system like before. So let's do I'd say the easier one first, which is the blue carbon. So the blue carbon, I would say, What are the three atoms that are attached to it? Well, I definitely have to. H is coming off of it and have another carbon. So I'm gonna put in order of atomic mass carbon h h. So that wasn't so bad. We're used to doing that. Now let's look at the red one. The red carbon is a little bit tricky because the red carbon noticed it only has one h coming off of it, and it has a carbon over here. But notice that it's double bonded to that carbon. So basically, we're gonna count that as two separate bonds. Why? Because we need to account for all three bonds of the carbon makes so to me. Ah, double bond to carbon. Is Justus good as to bonds to carbon? So I'm gonna put carbon carbon. So those both of those counts as the double bond and hydrogen. And then finally, I've got green, which is even a little bit crazier because notice that green is actually attached to two carbons, but one of them is single bonded, and one of them is double bonded. So you guessed it. You're just gonna add that up together? The green is attached toe all carbon C C C. Two from the double bond, one from the single bond. Does that make sense and noticed that I'm always moving forwards? I'm never moving backwards towards the Carl center. So now that we've applied that double bond rule, of course, this would also apply with triple bonds. I just don't have one drawn. Okay. What are our priority is gonna be? Well, green is gonna be number one Read would be number two Blue would be number three. Okay, so I'm just gonna write thes here, one to three and then obviously or hydrogen is number four.

So finally, in Step four, we're gonna learn how to name these guys. So step four starts off by saying that if your last priority group is in the back, I'm not even gonna read the rest yet. Let's just define that first part. The last prayer to group is always gonna be which group? Group number four. So it's actually just redefine that as four. That's the easiest way to say it. So if four is in the back now, what does the back mean in three D structures, that always means a dash. So this is actually starting off by saying that if four is on the dash, Okay, then we're gonna trace a path from the highest priority to the lowest priority. Okay, Now, what that literally means is that we're gonna draw arrows from my number one priority to my number two and from my number two priority to my number three. Okay, but remember, there's so that's from highest to lowest. Remember, there's four groups. What happens to number four? Do I also drawn arrow to that one? No, because you're always gonna ignore group number four because it's on the dash. Okay, since it's in the back of the molecule. I don't look at it. I only look at groups 12 and three. So now I trace that path. And if that path happens to look like a clockwise path, meaning, does it look in the direction that oclock would move in? Okay. Now for this, you're gonna need to know what an analog clock looks like. I know that for maybe some of you younger folks, maybe you're not used to seeing those too often, but we're just gonna have to stretch ourselves a little bit. Clockwise rotation is going to get in our letter, okay? And a counterclockwise rotation is gonna get a s letter. Hence the name R N s. Okay, so let's just use bring out that down. That example that we did before those priorities are gonna be the exact same priorities. And let's see if we can assign an R or A s to this carol center. Okay, so those priorities should be correct. This is my Carl center. So now the first thing I have to ask myself is Is my number four on the dash? Perfect. It is. So that means I can use this rule. So this next rule says I draw arrows from one to to from 2 to 3 and then finally back from 3 to 1. What about number four? I ignore it because it's in the back. I don't want to use number four. So is this a clockwise rotation or a counterclockwise rotation? This is clockwise, folks. And since it's clockwise, this is going to be considered in our ice. Um er okay, so we haven't learned how to incorporate this into the full name yet, but this is considered in our awesome right. Awesome. So let's go ahead and move on to step number five.

step Number four is really easy to use, but it has a major limitation, which is that it on Lee works if you're number four is on the dash. And guess what your professor is often going to give you molecules where your number four is not on the dash. It might be on the front, or it might be on the side. Why would he do such a thing? Obviously, to make your life harder. Okay, so in that case, you're gonna have to move down to step five. Which step five is kind of like your contingency plan. Okay, If you're number four, last priority group is not in the back, Which I'm sorry to tell you is most of the time. Okay, Then we're gonna have to make an adjustment because it turns out that the method we use for step four is actually the easiest way to figure this out. But my number four needs to be on the dash in order to use it. So we're gonna do is we're gonna cheat a little bit, and we're going to swap number four with whatever is on the dash already. Okay. Meaning that whatever numbers on the dash. Let's say it's two or three. We're going to redraw those numbers and swap them so that we can pretend like number four is on the dash. Even though it really isn't on the dash. We're just gonna pretend now there's no free lunch were cheating here. I just told you, this is like a game of make believe. We're gonna pretend like the four is on the back, even though it isn't. So. In order to make up for that, we're gonna have to swap whatever sign we get to make up for the fact that we swapped the groups. Okay, so this is really easy. It just means that if you trace your path and it looks like our you're actually gonna give, it s if it looks like an s, you're actually going to give it an arm. Okay, so let's go ahead and do an example where we bring down the priorities from before and see how it works out. Remember that this was number one. Number two, number three and number four. Okay, so is my number four on the dash. No, it's not. It's actually in the front. So what are we going to do well in order to use the system from before. I have to swap out the rule. Says the number four has to swap with whatever's on the dash. What's on the dash? One. Okay. Now I wanna warn you guys against other methods of doing this. Some online tutorials, like YouTube, whatever or even your professor will sometimes tell you to redraw the molecule with this pretend switch. I think that's really unnecessary. And that's really confusing. It's a lot easier just to swap out the numbers. Okay, So I'm gonna scratch out for we know that that's moving to the back. We're gonna scratch out one, you know, that's swapping, and I'm going to redraw just the numbers, Okay? Now that my four is in the back, I can ignore it, and I can draw my path. So my path goes. 122223321 Remember that? I ignore four. What does that look like to you? It looks like an arm. Okay. Is this actually gonna be are? No, Because I had to swap that group in the beginning, so I'm actually going to consider this to be an s is, um er okay. And that's the final answer. So this really isn't that hard. You just have to remember to swap it the end to make up for the fact they swapped at the beginning. Okay, great. Let's move on to an example.