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Ether nomenclature

Rules for naming ethers. Created by Jay.

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Video transcript

If we take a look at this ether, notice we have an R group on either side of our oxygen. Like that. And if we wanted to name ethers, there are a couple different ways to do. We'll start off with the common way of naming ethers, which follows the pattern of first naming one of the alkyl groups attached to your oxygen and then naming the other aklyl group. And then, followed by the word "ether." Like that. So alkyl, alkyl, ether. Let's look at an example of common nomenclature. And we'll start with this molecule here. So if I wanted to name this ether, I would first focus in on what sort of alkyl groups do we have attached to our oxygen. We're here in the left. That's a methyl group. And over here on the right, that's an ethyl group. So we need to think about the alphabet rule. And we know that E comes before M, so we're going to write ethyl before methyl. So it will be called "ethyl methyl ether." Like that. So let's do another one. All right. Our goal is to name this ether. And we first, of course, take a look at the alkyl groups that we have attached to our oxygens. So on the left here, we recognize this as being a tert-butyl group. And on the right, we have a methyl group. So in thinking about using the alphabet rule, B comes before M. So the tert-butyl group is going to come before the methyl group in the name. So it should be called "tert-butyl methyl ether." Like that. So the "tert" part isn't a part of the alphabet. Right? You're comparing the "butyl" versus the "methyl." Like that. Now tert-butyl methyl ether might be the correct name-- although, that's probably not what you will hear this molecule called in the laboratory. Usually, you'll hear this called "methyl tert-butyl ether," or "MTBE." MTBE is a very common, organic solvent. It works very well for a number of things. And again, MTBE is what you will hear. But technically, that's not the correct name. Let's look at an ether that has alkyl groups that are the same. So if we have this as our ether, we have two ethyl groups for this one. So we're going to call this "diethyl ether." We're going to use the prefix of "di" here. Now, diethyl ether, of course, is the famous one. This is the one that everyone thinks of when they think about ethers. Let's look at another way to name ethers, and this is the official IUPAC way of naming them. Now, the common way of naming ethers is so common that it's accepted by IUPAC nomenclature. But there is an IUPAC way of doing it for more complicated molecules, and that is to name your ether as a substituent, which we call an "alkoxy." We're going to name ethers as a substituent and then have a parent alkane. So we're going to call these "alkoxy alkanes." Like that. All right. So what you would do is, if you had just this generic ether here like this-- ROR prime-- you would find the larger alkyl group, and that would be your parent name. So let's say the R prime group was my longer carbon chain. That would be my alkane name. Like that. And then, you would name this portion of the molecule as an "alkoxy substituent" on your alkane. So let's look at an example of IUPAC nomenclature. So let's go ahead, and we'll name that first ether that we did a few minutes ago. So the very first one we did. When we're doing common nomenclature, we call this "ethyl methyl ether." So let's go ahead and name it using IUPAC nomenclature here. So what we would do is find the larger group, and that's going to be my parent name. So my larger group would be this over here on the right. And if we were to number that, you could say that's the number 1 and number 2. If you wanted to. You don't really have to for this example. But just to get you thinking about longest carbon chain, that would be ethane right there. So go ahead and write "ethane" as our parent alkane name. And then, what do we have coming off of the ethane portion of the molecule here? So what is R substituent? Well, this is the ether portion. We're going to name it as an "alkoxy." And since we have one carbon to deal with, we know that our root is "meth." And as an "alkoxy," it'd be "methoxy." So the complete IUPAC name for this molecule would be "methoxyethane." Like that. And we don't have to worry about numbers since we have only two carbons on our parent chain here. So "methoxyethane" would be the IUPAC name for this molecule. The common name would be "ethyl methyl ether." Both are acceptable names. Let's do another one where we have a very similar-looking molecule, except, in this case, we're going to add on another carbon there. So if I'm thinking about my parents alkane over here on the right, there would be three carbons for my parent alkanes. So if I wanted to number that, it'd be one, two, and three. A 3-carbon alkene is, of course, propane. So I go ahead and write "propane" right here. And I look at my ether substituent, once again. And I look, and I see how many carbons I have. And there's one on this substituent. So once again, it would be methoxy. So I'll go ahead and write "methoxy" in hear. So "methoxy propane." This time I need to put a number on there. And that group is coming off of carbon, too. So the complete IUPAC name would be "2-methoxy propane," Like that. Let's do a much more complicated one that has a little bit of stereochemistry in it. So if this was the molecule that I was trying to name-- and let's go ahead and put a bromine here like that. All right. So for this one, once again, I have to think about the larger group as my parents name. So if I look at those two alkyl groups, the alkyl group on the left looks like the longest one to me. And I want to number to give my substituents the lowest number possible. So if I look over here on the left, I can see that there are four carbons in my larger substituent. So four carbons is going to be my parent name here. So I'm going to call this "butane." Let's go ahead and start naming it with "butane" right here. So this would be "butane" so far. Now, when I number that butane, I want to give the lowest number as possible to my substituents. So I could start from the left, or I could start from the right. And starting from the right makes more sense because I have a substituent coming off of carbon one. I have a substituent coming off of carbon two. And then, three and four. Like that. If I'm thinking about those two substituents, let's think about how I would name them. Over here on the right, for my alkoxy substituent, this time, there are two carbons in my alkoxy substituent right here. So two carbons would be s, so that would be "ethoxy." And ethoxy is coming off of carbon one. So I can go ahead and write that in here. So "1-ethoxy butane" is what I have so far. And I also have a bromine coming off of carbon two. So it'd be "2-bromo." So I can go ahead and put in "2-bromo-1-ethoxy." And that follows the alphabet. Right? Because B comes before E. So "2-bromo-1-ethoxy butane." And then, we have to worry about the absolute configuration at this carbon right here. So carbon two is a chirality center. So we need to think about how to assign priority to those 4 groups. So if I think about the atoms directly attached to my chirality center-- first, let's go ahead and identify my chirality center. That would be this one right here. Four different groups attached to it because there's also a hydrogen going away from me in space. And I think about atomic numbers. Right? So I have carbon versus carbon versus bromine right here. So bromine, of course, has the highest atomic number. It gets highest priority. Like that. Now, my hydrogen, of course, is going to get lowest priority. So that's priority number 4. And now, I have 2 groups to worry about. I have two carbons to worry about. Let's go ahead and mark those carbons again. So which one of these carbons is going to get higher priority? Well, it's all about what they're attached to. Right? So the carbon on the left is attached to another carbon and two hydrogens. The carbon on the right is attached to an oxygen and two hydrogens. So in terms atomic number, carbon versus oxygen, the oxygen will win. And this substituent on the right would get the highest priority. So this would get a two over here. All the stuff on the right would get a two. And over here on the left, this would be a three. So we have one, two, three going around this way-- going around counterclockwise, which is the s absolute configuration. So this is "(s)-2-bromo-1-ethoxy butane" for the final name. Let's do one more example of naming an ether here. So let's go ahead and look at one that has a ring. And we'll put a double bonds in our ring. Like that. And then, we'll have our ether over here on the right. OK. So if I wanted to name this molecule, I would think about my two alkyl groups and think about which one is the larger one. And of course, all this stuff on the left is going to be my parent name. And then, this is going to be my alkoxy substituent. Like that. So on the left, I know what that molecule is. I know that's called "cyclohexene" from an earlier video. Right? So this is "cyclohexene" as my parent name. I now need to number my ring to give my alkoxy substituent the lowest number possible. All right. So if I wanted to number my ring to give my alkoxy substituent the lowest number possible, I should start here and make that one, two, three and four. Like that. So we think about-- what is that alkoxy substituent? It is an ethoxy substituent because I have two carbons right there. So I have an ethoxy off of carbon four. So this would be "4-ethoxy." And if you wanted to, you could put the 1 in here-- "1-cyclohexene." You could leave it out if you wanted to. So it doesn't really matter. But "4-ethoxy-1-cyclohexane" gives you all the information that you need if you wanted to draw this molecule. So that does it for nomenclature of ethers.