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Studying for a test? Prepare with these 8 lessons on Alcohols, ethers, epoxides, sulfides.
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Video transcript
In this video, we'll look at the classification and nomenclature of alcohols. So here I have my generic alcohol up at the top. And I have an alkyl group over here on the left. And I have an O-H on the right, which is called a hydroxyl group. Let's look at the classification our alcohol. So if I have a carbon bonded to an O-H, and that carbon is bonded to one other carbon in this alkyl group here, that's said to be a primary alcohol. This carbon over here is bonded to two carbons in those two alkyl groups. So it is therefore a secondary alcohol. And then this carbon over here on the right is bonded to three other carbons. So therefore, it is said to be a tertiary alcohol. Let's take a look at the nomenclature of alcohols. And we'll start with some real simple molecules here. So if I had a molecule that looked like that, and I wanted to name it using IUPAC nomenclature, I want to number my carbon chain to give that O-H the lowest number possible. So therefore, this carbon would get a number one. This carbon would get a number two. And this carbon would get a number three. Now, if that O-H weren't there, then we'd have just a three carbon alkane, which we would call propane. But since we have our O-H there, this is actually an alcohol. Alcohol is going to have the -ol ending. So this is called propanol. So let's go ahead and write propanol here. And the O-H group is coming off of carbon one. So we're going to say that's one propanol like that. How would we classify this alcohol? Well, the carbon right here that is bonded to the O-H, that carbon is bonded to one other carbon right here. So this would be a primary alcohol. So one propanol is a primary alcohol in terms of its classification. Let's look at a similar-looking molecule. Still three carbons, but this time we put the O-H on the carbon in the middle there. So once again, you're going to go ahead and number it. Right. This is carbon one, this carbon two, this is carbon three. This is a three-carbon alcohol. So it's also called propanol. The difference is the hydroxl group is on a different carbon, right? It's now on carbon two. So we're going to write two-propanol here, which is the IUPAC name. This is also called isopropanol, rubbing alcohol, it's all the same stuff. But two-propanol would be the proper IUPAC nomenclature. How would you classify two-propanol? So once again, we find the carbon attached to the O-H. That's this one. How many carbons is that carbon attached to? It's attached to one and two other carbons. So therefore, this is a secondary alcohol. So we have an example of a primary alcohol, and an example of a secondary alcohol here. Let's do a little bit more complicated nomenclature question. And so let's go ahead and draw out a larger molecule with more substituents. So let's put an O-H here. And let's do something like that. And then let's go ahead and do that as well. So give the full IUPAC name for this molecule. So you want to find the longest carbon chain that includes the O-H. OK so you have to find the longest carbon chain that includes the O-H, and you want to give the O-H the lowest number possible. So that's going to mean that you're going to start over here. And make this carbon number one like that. So if that's carbon number one, this must be carbon number two, three, four, five, six, and seven. So we have a seven-carbon alcohol. So seven-carbon alcohol would be heptanol. So we can go and start naming this. Make sure to give us plenty of space here. So we have heptanol. And we know that the O-H is coming off of carbon two. So we can go ahead and write two-heptanol like that. Let's look at the other substituents that we have. Well, what do we have right here coming off of our ring? That's a three-carbon alkyl group. So that would be propyl. So we have three-propyl. So go ahead and write three-propyl in here. And what else do we have? At carbon five, we have two substituents. So we have a chloro group right here. And we have a methyl group right here. And remember your alphabet. Right, so C comes before M. So we can go ahead and put our methyl in there. All right, coming off of carbon five, so that would be five-methyl, like that. And then also coming off five, we have chloro. So five-chloro. Right in here. And that should do it. Everything follows the alphabet rule. So we have five-chloro, five-methyl, three-propyl, two-heptanol for this molecule. What about a problem that includes some stereochemistry? So let's say they give us one where we have to worry about stereochemistry. So let's go ahead and draw another chain out here. So let's see, something like that. And let's make an O-H group going away from us. And then let's go ahead and make this one coming out at us like that. So give the full IUPAC name for this molecule, and you have to include stereochemistry. So once again, find your longest carbon chain that includes your O-H group. And you want to give that O-H the lowest number possible so it takes precedence over things like alkyl groups, and halogens, and double bonds. So we're going to start from the left. So one, two, three, four, five, six, seven, eight, nine like that. So we have a nine-carbon alcohol. So that would be nonanol. And the alcohol is coming off of carbon three. The O-H is coming off of carbon three. So we have three-nonanol. Like that. So three-nonanol. And let's see, what's our other substituent? Well at carbon six here, we have a two-carbon substituent. So that would be an ethyl group. So let's go ahead and put in our six-ethyl. Go and put that dash in there. So far, we have this six-ethyl, three-nonanol. And we have to worry about stereochemistry. So if they put in wedges and dashes on the problem, you need to think about stereochemistry. And you put those absolute configurations at the beginning of the IUPAC name. So let's figure out the stereochemistry of carbon three, first of all. So this is our chirality center right here, this carbon. And again, you go to the atoms that are directly connected to your chirality center. So that's carbon, carbon, oxygen. Coming off of our chirality center, we also have a hydrogen, which is coming out at us like that. So that would be the lowest priority. So that would get a number four here. So the oxygen has the highest atomic number. So it's going to get a number one. And then we have a longer chain over here for this carbon on the right. So that's going to get a number two, we have a number three. And then the hydrogen would be a number four. So there's a little trick that I covered in an earlier video. So if you ignore the hydrogen, it looks like you're going around this way, it looks like you're going around counterclockwise. So it looks like it's S. But you have this lowest priority group is actually coming out at you. So remember the trick was, if it looks like it's S with those three, just reverse it. And so it must be R. It must have an absolute configuration of R at carbon three. So we'll go ahead and put in here a three R. And then we have to worry about the absolute configuration at carbon six. So at carbon six here, this is another chirality center. Four different substituents attached to it. There's also a hydrogen attached to this carbon, going away from us like that. And let's think about the highest priority. Well, this chain over here on the left is going to get the highest priority. It has the most carbons, it has an oxygen over here. So it's definitely going to be highest priority There are more carbons this one over here on the right. So again, when you assign priority, this is going to get highest one. And then this is going to get a third up here. So this time, you're going around one, two, three, you're going around counterclockwise. But your lowest priority group, which is this hydrogen back here, is going away from you. So this actually is going to be S. So it's counterclockwise. So it's S. Three R, six S. And I went through those kind of fast. So you need to go back and watch some of the earlier videos on absolute configurations if that was a little bit too fast for you. All right. Let's look at cyclic alcohol. So ring systems. Let's look at an alcohol with six carbons in a ring. And then there's an O-H coming off of it like that. So six carbons without the O-H, we would call that cyclohexane. And since this is an alcohol, we would just change that to cyclohexanol. So that's very simple nomenclature. You don't really need a number. But you could write a one there. It's implied if you don't put in. So that would be cyclohexanol. What about something that has a ring system with two hydroxyl groups? So let's say we'll put in some stereochemistry, too. So let's say we have an O-H coming out at us. And let's say we have an O-H going away from us like that. So when you have a situation like this, when you have two alcohols in the same molecule, your prefixes be di. So this is actually a diol. And the nomenclature is based off the cyclohexane molecule. So you would write cyclohexane. And then right after the cyclohexane is where you put the diol. So di meaning two-- two alcohols. You have to specify where those two alcohols are on the ring. So we need to go ahead and number our ring. Let's say this is carbon one. That would make this carbon two, carbon three, and carbon four. So we have alcohols at the one and four positions. So go ahead and write one and four here. And those two alcohols are trans to each other. One is coming out at you. And one is going away from you. So you could go ahead and write trans-one-four-cyclohexanediol. And that's a good IUPAC name. So other types of alcohols. Well, instead of a cyclohexane ring, we could have an alcohol based off of a benzene ring. So we put in our pi bonds like that. And if we have an O-H here, this is a special type of alcohol called a phenol. This molecule is called phenol. And also you'll see this hydroxybenzene portion of the molecule in lots of natural products. So this is actually a very important molecule to recognize, the phenols. Right, let's go ahead and put something on that ring. So let's go ahead and we have our phenol as our base here. And let's go ahead and put a bromine right here. So how would we name that molecule? Well, the base part of the molecule is the phenol molecule. So go ahead and put phenol like that. And then we'll go ahead and number it. So the O-H, this must be carbon one. We want to give our substituent the lowest number possible. So we're going to give this carbon number two. So a bromine coming off of carbon number two. So it's very simple. All you have to do is write two-bromo. So we have two-bromophenol, like that. So that's nomenclature for alcohols, and a special type of alcohol called a phenol.