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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

Table of contents
24. Carbohydrates


Sugars, saccharides, and carbohydrates are all different words for the same types of molecules. Now that we're all on the same page, let's begin our journey on these fascinating molecules. 



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Hey, everyone, I'm about to take you on a journey through one of the oldest and most elegant fields of organic chemistry and that's the field of sugar chemistry, also known as carbohydrate chemistry. So let's go ahead and get started. Alright, guys. So before we even really get started, I need to tell you one thing. Which is that sugars, sacha rides and carbohydrates are all different words for the same types of molecules. So I'm gonna be using those words interchangeably throughout this course. And you should just think whenever you hear sugar sack, a ride or carbohydrate, those were all describing the same types of molecules. Now, one of those words that you might say often but not really think about too much is carbohydrate. We talk about carbohydrates and nutrition all the time. But when you break the word down to its roots, what you see is that it's actually a hydrate of carbon. That's literally what the word breaks down to. What it's symbolizing. And in chemistry. We know that Ah, hydrate is any atom or molecule that's combined with water. So when we say that a sugar is a carbohydrate, what we're saying is that a sugar is a carbon that's been combined with water. Okay, now there are many sugars out there, but the most basic unit of sugar is called a mono sack. Right? So we're gonna spending ah, lot of time in this course, Uh, just talking about the properties of mono sacrifice before we expand that further into larger sugar's OK, all unmodified mono sacha rights have the same general formula. So no matter what their shape with their size, they always have the same formula. And that's carbon H two and oxygen all to the end, where n is a number greater than or equal to three. Okay, so let's break that down for a second. A few words at a time. So why did I say unmodified unmodified? Because I'm saying this is the way the sugar begins its life. Okay, you could always change a sugar toe, have other atoms on it later, but when it starts off, it's always gonna start off as C H 20 to the end. Now, when you look at this general formula, it describes exactly what I just said about a carbohydrate, which is that a carbohydrate is literally gonna be one carbon that's been combined with one water molecule. So it's cool how it actually breaks down Definitional e like that. Now the last thing is that where N is equal to three or more, all that saying is that your smallest possible sugar is a three carbon sugar. Um, it could be as big as you want, but it has to be at least three carbons. If it's less than three. If it's too, it doesn't really count as a sugar anymore because it just has a very different reactivity. Um, it doesn't. It doesn't behave like other sugars juice. We wouldn't call a to carbon molecule, usually a sugar. Okay, So what else do we need to know about mono? Sack rights were just saying like General Fax right now. Okay, there's an introduction. Mono sack rides can be represented as either straight chains or is rings. So you're going to see that throughout this section? I'm going to be showing them to you as straight chains, and then other times, you're going to see them as rings, and we're gonna explain more why they cycle eyes. Okay, now something you should know is that by definition, a carbohydrate needs to have one oxygen attached to every carbon. To be a carbohydrate, you can't have two oxygen's on one carbon and then zero on the other. That would not be a carbohydrate anymore, so it needs to be a 1 to 1 ratio. Also, an interesting fact about carbohydrates is that they're always gonna have one I HD regardless of their form. Now, remember, guys, what did I HD mean? It meant that you're missing hydrogen is in order to be a saturated molecule. And remember that an HD could either come from a double bond or a ring, right? Not necessarily six member, but a ring. Okay, so that makes sense. According to my, uh, fact about that, they could either be straight chains or rings. That means when it's a ring, it has the one I h. D from the ring, right? And then when it's a straight chain, it must have the one HD from a double bond. So just letting you know you're always gonna have one, no matter what form it's in. Okay, No mano sack rights always begin as either Let's write this down all the hides or key tones. Okay, now, once again, I'm using this word begin because you could always modify that functional group later if you wanted to. Maybe you could change the alga hide into something else. But what I'm saying is that when they begin their life, they always start off as either an alga hide or key tone. Those are your only two possibilities. Okay? And what we do is we call on all the hide sugar and Aldo's and we call a key tone Sugar Akihito's. Okay, so it's pretty easy. Let's look at two examples of mono sack rides. So just looking at the definitions in the facts that I told you we could prove in several different ways that these air mono sack rides. Okay, so first of all, do they have three or more carbons? Yes, I see that they both have. I think six carbons. Eso We're good there. Does it have least I mean, not at least doesn't have exactly one oxygen on every carbon. Yeah, I see that. I see 10 for every carbon. Very good. A 1 to 1 ratio. Do I see a t least one I HD on each of these compounds. Well, remember guys that a double bond counts is one HD. So this would be my HD over here. And also remember, from our functional groups section back in Oracle one that C H O is the condensed formula for an alga hide. So what it actually looks like is this. So there's a double bond there as well. That's an alga hide for you. Okay, so, guys, we know these air mono sacha rides and, as you can see, the first one's called Al Dose because it contains an alga hide at the top. The second one contains, is called a key toast because it has a key tone at the second Carbon. Remember that a key tone needs to have our groups on both sides, so you can't put a key tone all the way at the top. It needs to be, at least on the second carbon very good. So easy enough. So far, all the definitions that I gave you at the beginning are checking out. Now let's talk about some more general features. There's so much to learn about carbohydrates, but we have to start with the baby steps. Let's start about talking about naming so mono sack rides can be described both by generic names and by specific names. At this point, you're probably more accustomed to hearing the specific name. So what's a specific name? Glucose. We've all heard of glucose before. It is a name that describes one specific mono sack ride, but we need to know is not only probably a few of those specific names, but we need to know the general categories and those air described by generic names. So how do you name among sugar with a generic name? Well, the first thing you start off with is the Carbonell type. So is it a now the hydra key tone that's going to give you either an alto or a keto prefix? Next, you would go to your carbon chain length and you'd say, How long is the carbon chain? Now here. This is where things get a little tricky. Remember, I said, this is an old fields of organic chemistry, meaning that the naming conventions were devised pre AIPAC before I pack member AIPAC was in 1919. Ah, lot of this sugar chemistry was discovered in the 18 hundreds. So what that means is that a few of the names sound familiar, and a few of them don't really meet convention. So it's pre AIPAC names with an O, sending So, for example, pen toes and Heche sauce. That makes sense. That would be AIPAC, right? Because Pence is the is the prefix for five. Hex is the prefix for six, so that makes sense. But then a four carbon sugar isn't called a beauty tose. As we would expect with AIPAC, it's called a petreaus. Why, it's random guys. Someone named this before AIPAC got started, and then they just stuck with it and then a three. Carbon is called the Triumphs, so just letting you guys know that you're not going to respond, be responsible for all the names upto 20 carbons. As long as you know those four, you're probably OK. Cool. So we'll name or in a little bit. But I want to talk about some stereo chemistry as well. So the total number of stereo I summers possible for a sugar is described by the same formula we used in our Kyra ality section a long time ago to to the end where N is equal to your stereophonic centers. So guys Why is this important? Because sugars, um, are notoriously complicated in terms of their stereo chemistry because they have so many Cairo centers. Okay, remember the guys these air Fisher projections that you're looking at here? Remember, Fisher projections are designed to show you the Chire ality of each atom. So glucose, for example, has how Maney Carol centers. Every single like intersection is a Cairo center. So this would be one. This would be another. This would be another. This would be another. The top one is not Kyra, because this is not for groups. The bottom line is not Carol, because it doesn't have for four different groups. So we have four Cairo centers. So that means just glucose glucose has how many total possible stereo I summers? Well, it would have to to the four, because we're using the four to the end formula. So that means that glucose has 16 possible stereo I summers okay. Such as shows you an example of using the two to the end formula. Okay, Now, once again, guys, I have to preface this by saying this is an old field of organic chemistry, so we're gonna be learning a lot of new terminology that specific two sugars that it doesn't apply to any other types of molecules. And one of those words, that's a new word is an embalmer. So what has an embalmer? So when EP immer guys is a stereo isom er of a mono sack ride that differs at Onley one Cairo carbon. So essentially, what UNEP immer is is it's a diess, Terry. Um, er, remember that die Osteria MERS where, uh, two molecules that were related by having some of the carol centers changed, But not all of them. They were non mere image sterilize summers. So what in a primer is is it's a specific type of dia steri. Um, er that differs at only one Cairo carbon. So how could we look at an example? Well, let's look at one of the EPA rumors of glucose. If all you did was you kept this Carl center the same, you kept this Carl center the same. And you kept this Carl center the same notice that the O. H. Is air all in the same place. But then you move the second Ohh! The C 20 h from the, uh oh, over to uh, that side. That would be an embalmer. And that'll be in September because the die astronomer that differs at only one carbon. Alright, cool guys. So great job. So far, we're just scratching the surface. There's so much more to learn from, uh, mono sack rides, but let's go ahead and do some practice problems.

Monosaccharides can be described by both generic names and specific names.


Generic naming involves: 

  • Carbonyl type (i.e. aldo— )
  • Carbon Chain Length (Pre-IUPAC) with –“ose” ending (i.e. –triose, -tetrose, –pentose, -hexose, etc)

Provide the generic name for the following monosaccharide.


How many possible stereoisomers AND epimers exist for the following aldopentose? Draw all of the possible epimers. 


Identifying Types of Stereoisomers

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identify and label all of the possible stereo I summers of Aldo Tetro sauce, um, as an anti MERS dia stereo MERS or EP Immers of each other. Cool. So let's go ahead and start off with the new definition, which is a bombers. And then we'll move on to the other definitions that we know from the Cairo ality section of this textbook. So which ones here would be embalmers of each other? Remember, FMR has to defer at Onley one carbon, so these two would be a plumber's. Everything that I'm gonna put with Blue Arrows is gonna be in September. So I'm gonna put here blue is equal toe Palmer. Cool. So those would be bombers, these would be a plumber's oops. And that's actually pretty much it. Those are the only FMR is that we see now. What does it mean to be an Indian team? Er, remember that in Oh, that's not how you spell that. Remember that in any anti Um, er has all of the carol centers changed so you can't have any of the same. They have toe have changed completely so well, some financing MERS that I see are these. That's in Indian team because I see that the 20 H is used to face to the right and now they faced with left. I also see that these are Indian teamers. Cool e think I see another FMR guys e c Samora Palmer's? So what else was in a primer here? This is an EP immer, right? Because what I notice is that here, these two are the same. But in the top, they changed, right? So those were embalmers as well. And it looks like these a two d are also related as farmers. Cool. So there might be more relationships, guys, I'm gonna keep looking at them as we keep going through this. Okay? So I don't see any more in the A teamers, though. So I'm gonna move on to the next definition, which is dying Hysteria MERS. So which of these air die astronomers? Actually, guys, every September, by definition, is a dye astrium Er so it's gonna be all the same arrows as farmers. Yeah, Now you might be saying Okay, Johnny. Well, if they're the same thing, why? We have two different words for the same thing. Well, guys, this molecule happens toe the definitions of die. Astronomers and farmers happen to be the same because it's so small. But if it was bigger, you would actually have die. Astronomers they're not Emerse. Okay, In this case, since there's only two Carl centers, they happen to line up perfectly. But if you had three Carl centers, then it would be possible to have a di Astrium or that isn't Epivir, that it changed at one position and it would be possible to have a die Astrium or that is not nippy more because it changed it to different positions. Okay, so just so you know, um, in this case, they happen to have the same definition, but they won't always. I don't see any other relationships that we missed. So I think this question is over with good job. Let's move on to the next video