Monosaccharides - Drawing Fischer Projections - Video Tutorials & Practice Problems
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In order to best visualize sugars we will be using Fischerprojections, devised by EmilFischer himself. The great thing about using these projections is that it will allow us to easily notice chirality centers.Â
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Monosaccharides - Drawing Fischer Projections
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Let's talk about how to properly draw Matsuzaka rides using a representation that was designed specifically for sugars. And that representation is called the Fisher Projection. So guys, in 18 91 email Fisher, who's one of the most prolific organic chemists of the 19th century. He's essentially the guy that discovered carbohydrates and discovered carbohydrate chemistry. He devised a representation called Fisher Projections, specifically for the purpose of depicting carbohydrates. So even though you've learned about Fisher projections previous to this topic, this is really the reason he designed them. It was so that he could better understand and better illustrate the Chire ality of sugars. Okay, now it's gonna be really important. Because of this. It's gonna be very important that we understand how toe go from bond lines of Fisher using with with sugars and also how to go from Fisher tube online. Okay, now, one thing that you need to know right away is that the way that you're supposed to align your mono Sacha ride. Your Fisher projection is with the most oxidized carbon, the most oxidized Adam on the top of your Fisher projection. So here what you see is that I have this mano Sacha, right? That's represented on the left as just a bond line, and it ZMA more difficult to deal with the mono sack right in that form, it's much more difficult to illustrate the Cairo ality to compare it to another one. So in all Fisher said, why don't I draw them like this? That's going to make them so much easier compared to each other because you just see all the o. H is you can compare a which is much easier this way. And what you see is that this top carbon would be considered more oxidized because it has two bonds toe. Oh, and this bottom one would be considered less oxidized because it only has one bond to hope. Okay, so you always put the most oxidized part on the top. Okay, so this is d ribose. We've talked about ribose already before, but now you know that that's actually what the bond line looks like. Okay, so bond lines of Fisher is the first essential tool that you need. Okay. So similar to our lessons in or go one. Remember that whenever we wanted to turn a bond line into a fissure, we used this, uh, Johnny patented method called the Caterpillar Method. Right. And what the Caterpillar method taught us is that what we want to do is we want to rotate all the bonds so that you have essentially, like the back of a caterpillar. So where does the caterpillar come from? I think of this as being a caterpillar, and this is like its face. It's just like happy chewing on a leaf or something. And then those things at the top are like the hairs on the back of the caterpillar so you can go back and learn about the Caterpillar method there. But I'm just gonna remind you guys that what the Caterpillar methods says is that every substitute Wint that's already facing up stays the same. So when you notice is that carbon to stays exactly the same, the O. H. Is faced towards the back here and it's still faced towards the back. But in order to make the other substitutions face up in order in order to rotate them to the opposition, you also need to rotate the legend dash information. So that means that two wrote in order to rotate this oh wish to face up. I need to face it towards the back on carbon one. And on three. I need to face it towards the back as well, Because it rotated. Okay, then, once you have it lined in that way, you could easily draw your fisher projection. Because then all you need to do is look at it. Think. Okay in the front. What do I c I c h h h So that would be this one. This one. This one. And that would be on this side and then on the back. What do I see? Ohh, Ohh! Ohh. And that would be back here. Okay, so that is the most sure fire way to get it right. Okay. Now, alternatively, once you get good at this method, what you'll notice is that all you really have to do is a shortcut. Is swapped the stereo chemistry of all downward facing alcohol's. Okay, So what that means is that if I wanted to kind of take a shortcut and bypass the caterpillar and go straight to the fisher, how could we do that? Let's see. Can we actually do this? Well, what you'd say is here's my eyeball. Right. I'm looking at it this way. Okay? And what I see is that on the two carbon I haven't always faced away from me. Okay, this one right here, I'm gonna make it yellow. So I would already put it faced away from me on this side as if my eyeball was looking at this one. Okay, so I would say, Well, it's faced away those to red eyeballs air in the same position, just with different representations. So it's faced away. Now on the red eye ball on the left, it looks like those o. H is air faced towards me. So it looks like I should put them on this side of the Fisher projection, but no, they're faced downwards, so if it's down, you have to flip it. So those 20 H. Is on one and three. They look like they're going to face this way. But I actually, because their face downwards, I have to swap them to this side, meaning that this one here and this one here, even though they're both towards me towards the eyeball, I have to draw them away from me because they swapped. Okay, So let's, uh, kind of just a little shortcut. The downward facing positions you would swap. Cool. Now let's go from Fisher Tobe Online. So from Fisher Tobe online the most against surefire way, the most reliable way to convert it would be to use a reverse caterpillar. So that would say, Hey, we've got this molecule. This is what it looks like from my eyeball here. What would the caterpillar look like? Well, the caterpillar would be a straight back with positions 12 and three and everything that's closest to the eyeball. You can't really see the whole eyeball. Sorry. I'm gonna draw it again. It's better. I think so. Everything that's closest to the eyeball should be on a wedge. So that would be this group here. This group here should be here and here. Right? And everything that's far from the eyeball should be on a dash, So that should be this one here. Okay, so that is the reverse caterpillar. I just made a caterpillar. Now, how do I turn this into a bond line? What? Turns out that when you do that, you're going to get two possible answers. They're both the same molecule, but they're just rotated differently because It just depends. If I'm starting off with a zigzag that starts going up or a zigzag that starts going down, you're gonna get to different possibilities. Okay, so let's start off with the one that is going up. Okay, so the one that's going up, what I would do is I would just draw this Alba height exactly the same. And I would say that this is positioned 12 three And then this is your C H 20 h. Are you guys find with that? This C H 20 H. Is this guy right here? Okay. Similarly, over here, my Alba head would now face up, so this would be positioned 123 And then this is my C H 20 h where it's just based down now. Okay, Now how would we actually drawing the O. H. Is will notice You would Onley need to flip the ones that are faced down now. So when the first one which positions can stay exactly the same, Which positions are still facing up one and three. So what I could do is I could draw one as a wedged po each and I could draw three as a dashed Ohh. Why? Because those were the same exact positions that they were in in the Caterpillar. By the way, I'm not going to draw H is because they could be implied right now on to two was facing downwards. So now I need to flip it, meaning that too should actually have a dash o h. And now I'm done with that molecule. It's done Cool. Awesome. Now let's see how it would differ with the second one. So what? The second one? Which position stayed the same in terms of their still facing up? Now it's too so too. I can face the same direction. It should be an ohh that's wedged now one in three because of the way I drew my zigzag Now one in three have to be changed. So now one would be a dash Ohh! And three would be a wedged. Oh, age! Okay, so, guys, even though these two molecules look very different there, the same exact molecule And both of these answers would be correct answers on a test. Your professor would give you full credit for both of them. The reason I drew both of them is because if I drew the first one, and usually the second one, I'm gonna get so many questions of Johnny is mine, the same as yours. So I wanna make sure to draw both ways. Just that. You know, you're always gonna get to different looking answers, but both of them are the same if you just use the correct rules. All right, So now we know how Thio draw Fisher projections and how toe also kind of undrawn them and go back to the bond line. Let's go ahead and do some practice related to Fisher projections.
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Problem
Problem
Convert the following monosaccharide into its Fischer representation. Is it a D or L-isomer?
A
B
C
D
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Problem
Problem
Convert the following monosaccharide into a bondline representation.
A
B
C
D
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