Nomenclature – Carboxylic Acids and Their Derivatives

00:02 In terms of nomenclature, the names are given by replacing the “–e” at the end of the corresponding alkene with the appropriate suffix. So, let us take a look, for example, at acid or acyl chlorides. In this particular example, as you can see, what we have is a chlorine group directly attached to the carbonyl carbon. In terms of the number of carbons we have, we have ethyl, do we not? And so, therefore, this will be known as ethanoyl chloride. Sometimes in common parlance, it is called acetyl chloride and is a very common reagent when acetylation reactions need to be carried out.

00:40 Let us look at the longer chain and slightly more complicated acid chloride, shown on the right hand side of the screen. Here, you can see the longest chain consists of 4 carbons.

00:51 Therefore, it must be a butanoyl chloride of one description or another. Note also, the numbering goes as before, the order of priority is the carbon which bears the oxygen, oxygen having a larger mass than the carbon it takes priority and we count backwards along the longest chain: 1, 2, 3, 4. Therefore, our 2 methyl substituents are in the 2 position and the full IUPAC name for this molecule would be 2,2-dimethylbutanoyl chloride.

01:23 Now, let us talk about anhydrides. Anhydrides have these rather interesting structure where we effectively have the joining of two carboxylic acids in the absence of water. Hence, the name acid anhydride, so in other words, acids with their water removed. In this particular case, all of these assuming they are uniform would take the name of the alkane group with the “-e” removed and would be “-ioc” and then anhydride.

01:54 So, in this scenario, because we have two ethanoyl or ethanoic systems coming together, it would be an ethanoic anhydride. If, indeed, we had a third carbon on each of those, it would be propionic anhydride. The common name for ethanoic anhydride is acetic anhydride and you will sometimes see that on bottles of chemicals.

02:18 Now, I want to talk to you about carboxylic esters and esters are very important, not just in terms of a, from a medical perspective, in terms of product development, but also, for example, in the flavours that you get in things like wine and odours and so forth that are derived from complex arrangements of carboxylic esters.

02:41 The nomenclature for an ester is shown here. Here, we start off with the idea that the names must be alkyl alkanoate which means that when you look at Methylethanoate, we find the part of the molecule which contains the carboxylate part i.e. that has the CH3 directly attached to the carbon, could be a CH2 or a CH, but is directly attached to the carbonyl carbon. That is your “-oate” part.

03:10 So, in this case, we have a CH3 and then a carbon, therefore, it is ethan; it must be ethanoate. The alkyl part is derived from the alkyl or aryl chain which is directly attached to the oxygen. So, looking at the right hand side of that molecule methylethanoate, you can see that there is a CH3 group. This is methyl and therefore, the name for this compound is methylethanoate.

03:37 Have a look at the molecule in the right hand side and see if you can apply those rules to determine the name of that molecule. Let us work through it.

03:50 If you actually have a look at what contains a carboxylate moiety, our carbon double bonded oxygen, we count backwards: 1, 2, 3, 4, 5 through our longest possible chain. This gives us the core structure, if you like, pentanoate. And now, what we have to do is see the length of the chain that’s directly attached to the oxygen, the alkoxy part, counting along from the oxygen: 1, 2, 3, we have 3 carbons on the right hand side and therefore, our underlying structure, without any further substituents, is propylepentonoate. This gives us the basic structure.

04:29 The substitution in the pentonoate chain is correlated by knowing that we go from 1, 2, 3, 4, 5 all the way through the alkanoic part of that molecule. And so, therefore, the methyl groups are in the 2 and 4 positions respectively, thus giving us the name 2,4-dimethyl-propylpentonoate.

04:48 Now, let’s look at the final class and this is a particularly important class because as we will see in Module IV, amides and esters pervade every element of drug development and drug design, if not least, from a product perspective. Amides consist of a carboxyl group to which carbonyl… carbonyl carbon and NH2 or NR2 group is attached. So, let’s have a look at some of this nomenclature.

05:22 Here we have a very simple, so called, primary amide, there aren’t many of them. This is ethyl amide. This is because the carboxyl part which forms the initial… the initial part or initial prefix for the nomenclature, it contains two carbons: ethyl amide, otherwise known as acetylamide or acetamide.

05:44 Now, let’s have a look at something a little bit more complex on the bottom right hand side. This does look a bit more complex, but the reality is quite straightforward. Let us look at the underlying amide, let’s have a look at the longest chain in the system, okay? So, if we count back from our carboxyl group like we did for our ester, we see that we have 3 carbons as our longest chain. So, this means that we are talking about a propanamide that is the longest chain, that is the underlying carboxyl part of it. But, wait, not only do we have substitution along that propanamide ring, but we also have substitution directly on the nitrogen. Hence, the term N,N-trimethyl… N,N,2-trimethylpropanamide because we are saying, by that nomenclature, that we have 2 methyl groups attached to the N and we also have a methyl group in the 2 position on the propane chain. If we didn’t have those 2 methyl groups on that nitrogen, it would just be 2 methylpropanamide, but because we have those 2 methyl groups on that nitrogen, we have to designate where they are.

07:00 Right. Okay. So, nomenclature summary because that was a lot to get through. If we look here at functional group carboxylic acid, in all cases, we change the “-e” at the end of the alkene… alkane to the “-ioc” acid, the “-oyl” chloride, the “-oic” anhydride, the alkyl “-oate” or indeed, the amide depending on whether we are dealing with a carboxylic acid, an acyl chloride, an anhydride, a carboxylic ester or an amide itself.

07:34 So, this is the nomenclature summary. And so, when you see these names, you should be able to relate them directly to the basic structure of that functional group and this is important because understanding the basic structure of that functional group means you will know how it will react with other things and this is what we are going to go on to now.