R and S of Fischer Projections

Now that we're pretty familiar with Fisher projections, it turns out that there's gonna be a new way to determine r and s for them. The reason is because converting these structures to bond line and then figuring out our n s would be part of my French a bitch. All right, So we want to do is we want to figure out an easy way to figure out our s. And there actually is. There's a shortcut that we can use. So I want to go ahead and show you guys that now. All right, so this is basically the way it works. We wanna determine the location of the lowest priority group. Okay, What I mean by location is we want to figure out Is it vertical or is it horizontal? Okay, if and the lost party group is always gonna be four. So basically, I just want to know where is for okay. If four is vertical. Okay. If forest faced vertical, then the Chire ality is exactly as it looks. I'm just going to go from 1 to 3. I'm gonna draw that arrow, and that's gonna be it. Okay. Whereas if four is horizontal. Okay, then the Cairo ality is just gonna be flipped. So whatever you draw, you're just gonna take the opposite sign. Alright, so here I have two examples. This would be an example where h is vertical. So notice that my fourth priority group is vertical, so that means that it's gonna be as it looks. So I'm just gonna say 1 to 2 to three, it's going in A s direction. So that's actually gonna be the final answer. The final answer for this carols center. It would just be s. Does that make sense so far? Now, let's look at this next one. Here's my Carl Center. Fouras, you can see is now horizontal. So I mean, that's going to be flipped. So once again, I'm gonna do 1222233 toe one. It looks like s but it's actually gonna be our because the fact that it's horizontal now keep in mind for Fisher projections. I'm never swapping group, so I'm not swapping out one in four or anything like that. All I'm doing is I'm just taking the Chire ality and I'm flipping it. If it happens to be horizontal or I'm keeping it if it happens to be vertical. So in some ways, this is actually easier than what we learned for the other compounds. And when you have a very big Fisher projection that has a lot of Carl Centers, you're gonna be thankful that you have this method. You could just go really, really fast and figure it out. Okay, So I want you guys to do now is go ahead and determine the absolute configurations. Meaning they are in the S for this Fisher projection using this formula and using this format, and then when you're done, I'll go ahead and show you guys how to do it.

Alright, guys. So this wasn't an easy problem. This is actually a pretty complicated problem if you got it right. Power to you. Okay, but this is not easy. So first of all, here's my first Carol center, and I need to recognize what the's substitutes are. I need to figure out priorities. So my first priority obviously has to be my oxygen because oxygen is the higher atomic weight. But then what I have here is carbon, and I'll say, That's my blue carbon, my red carbon and my blue carbon. Okay, Which one's going to get higher? Priority? Well, in order to understand this, I need to know what the C H O functional group is. Do you guys remember what that is? I hope you guys remember That is an alga hide. So what? That actually looks like I'm just gonna scratch this out is like this double bond. Oh, and h Okay, that's what C H o means I told you guys when I talked about was functional groups. They have to memorize that. Okay, so there you go. That's your That's one functional group. The other one is a carbon with the chlorine and oxygen So if you can't immediately tell which one is gonna win, you have to do the playoff system. And if you do the playoff system, what you would find is that the sea that's in blue would be attached to an O and O and an H, whereas the sea that's in red would be attached to a C, l and O and A C. Okay, so which one is gonna win? Just the one that has the heaviest atom on it. So read has toe win because red has a c l on it. So this is gonna be too. Then this one's gonna be three. And then finally, this will be my four. Okay, so that was a little bit tricky. Okay, Now I'm going to say okay. Is my four vertical or horizontal? It is. Horizontal is that means whatever I draw has to get flipped, so I'm gonna go ahead and go. 122223321 This looks counterclockwise, but really, this is gonna be clockwise. Okay, so that's my first one. That was a lot of work. Let's move on. Okay, so let's go into this next Karl center. So for this next one. I have that. This is gonna be my one because chlorine is heavier than oxygen. This is my to then I have three and four. Which is this blue carbon and this green carbon. Okay, so which one is gonna win there once again? I mean, this one, you just have to do playoffs. So I'm gonna do blue. That's see, what is that attached to you? It's attached to an O. It's attached to a C, and it's attached to an h. Now let's go down to the screen. The green one is attached to an O it's attached to a C and it's attached to an h. So which one's gonna win? I actually don't have a winner yet. They're both the same. So what happens if I get to now I play off and they're both the same. Have to keep going down the longest carbon chain. All right, so that means that now I'm actually going to go to each carbon that it was attached to. So notice that this blue was attached to another carbon. That's this carbon. Now I'm going to say, What are the three things that that carbon is attached to. Well, we already did. This one. It's attached toe. Oh! Oh, and age. The reason I'm counting twice is because that is an alga hide. So it has a double bond. Oh, I'm going to do the same thing for this. See, this has to do with this sea. So this sees attached to what it's actually touched to Justin. Oh, and in H and H. Why is that? Because it's a C H 20 Okay, so now do we have a winner? Yes, we dio. Now we have a winner. This one has to be three, and this one has to be four. So it's gonna be three on. It's gonna be four. Okay, So that one Like I said, this is just a really tricky question. So now is my fourth priority. Vertical or horizontal? It is vertical. Okay, So what that means is that I'm just gonna draw this exactly how it looks. 1222233 toe one. It looks like an s. And it is an s. Okay, proof. So now let's go into this last one. Yeah. This last one would have. This is my one. This is my four. And we already did this before. In terms of we know, the Cielo is gonna be better. Sissons, My two, this is my three is my lowest priority. Horizontal or vertical? It's horizontal. So I'm gonna flip whatever I get 1 to 2, 2233 toe one. It looks like an s, but actually it's an are okay. And those are my three Cairo centers. Now, I know this seems like it took forever, but it wasn't because of the it wasn't because of actually figuring out the rotation. The part that took a long time is that this just was a hard problem in terms of figure out priorities. So no matter what strategy you used, this is going to take forever. Okay, It's gonna take a while, but I think that what you're going to notice is that using the horizontal and vertical thing is going to save you as a lot of time and just you know, you can't There actually is no alternative if you don't want to use this horizontal vertical thing. The Onley other alternative to get it right every time is to convert it completely. The bond line and then do it from there, and that's just like I said, That's a bitch. That's a massive bitch that would take forever. So this is gonna be a lot easier. Hopefully, save you guys a lot of time, right? So let's go ahead and move onto the next topic.