Naming Anhydrides - Online Tutor, Practice Problems & Exam Prep

Anhydrides are carboxylic acid derivatives formed by the condensation of two carboxylic acids. To name an anhydride, alphabetize the two acids and replace "acid" with "anhydride." For symmetrical anhydrides, use the name of one acid followed by "anhydride." For example, ethanoic and propanoic acids yield ethanoic propanoic anhydride. Understanding these naming conventions is crucial for recognizing and working with various acid derivatives in organic chemistry.

Anhydride Nomenclature

Now we're going to learn how to name anhydrides. Anhydrides are a specific functional group that come up a lot in this section and they're one that you might not be very familiar with at all. Let's just back up for a second and talk about what an anhydride is. Basically, an anhydride is a carboxylic acid derivative. Think of it as a carboxylate. But then you've got an acyl group on the other side. Then you've got your carbonyl and R. Another way to think of it is that it's a dicarbonyl with an O in the middle. Whatever you want to think. In terms of naming, the naming of it is going to be visualized in this manner. Basically, when you look at an anhydride, it's actually kind of a combination of 2 carboxylic acids. You could say that maybe this was carboxylic acid 1 and maybe this was carboxylic acid 2. Maybe they came together and made an anhydride. Side note, that's actually how you make anhydrides. You make anhydrides by combining 2 carboxylic acids into an anhydride. That's where the name stems from. What we do is it's really easy. You just alphabetize your 2 different acids, visualize them with the carbon chains. But then instead of ending with the word acid, you would end with the word anhydride.

Another special situation is what happens if your R groups are the same? What happens if both sides of my anhydride are symmetrical? Well, then you don't have to say that it's carboxylic acid 1, carboxylic acid 2 and anhydride. You could just say carboxylic acid 1 anhydride. So just alkanoic anhydride. Why? Because that means that you're assuming that 1 combined with another version of itself to make an anhydride. You're basically saying that this is the anhydride you would yield through the condensation of these 2 carboxylic acids. Let me see. Obviously, just going really I don't want to mess up any questions for you. But this anhydride, I could name it as both the common and the IUPAC. Let's start off with IUPAC. For IUPAC, I would have this would be ethanoic here. And this is propanoic. For IUPAC, let me give myself a little bit more space. For IUPAC, it's going to be ethanoic, propanoic, anhydride, not acid. Don't make that mistake. Common. Common is going to be acetic and propionic. These are the ones you're supposed to memorize. Again, alphabetical order. We're going to get acetic, probionic anhydride. Now you see why it's so important to know those first five for the common names because they can come up with all of these derivatives. That's it. Move on to the question. Let's see if you can get it right and then I'll give you the answer.

Provide the IUPAC name for the molecule

Let's start off with the easier side first, which I believe is this side. This would be benzoic. You really have no excuse not to know that. That's benzoic acid. We know that's what happens when it's on a benzene ring. Now the other side is more complicated because we've got this double bond. How would we name that? With IUPAC, we have a way to do it. Let me show you. For IUPAC, you would call this a 4-carbon carboxylic acid. It's going to be butanoic acid. But there's that double bond. It's in the 3 position. I'm going to turn this into 3-butenoic. That's the coolest thing about IUPAC. Those modifiers that we learned a long time ago still work here. Butenoic, that means I have a double bond in the three position and we're done. Then that would be combining that together, it would be in alphabetical order, benzoic 3-butynoic anhydride. Perfect. So, not so hard. What about common? How would common names change? It turns out that you can't use the butyric modifier; your common names don't work because butyric, that name butyric, wasn't designed to have an "en" in it or an "ol" ending. That's one of the limitations of common names. You can't change them like you can change IUPAC. Do we give up? No. Actually, this is another thing I'm getting at here. This exact substituent actually has a common name all on its own. This is one that you were supposed to know a long time ago from your first few weeks of organic chemistry. Remember that when you're attached directly to a double bond, that's called a vinyl group. But when you're 1 CH₂ away, notice I've got a CH₂ here, that's called an allyl group. Actually, there is a common name for the substituent, and it's a common name you might see on your exam. This would turn into, in the common name, allobenzoic anhydride. Again, don't try to go down the butyric route because butyric, you can't account for that double bond because you can't change the name. You have to use allyl. Awesome, guys. Not that bad. Let's move on to the next question.

Draw the molecule

If you know what you're looking for, this is a really easy question. Formic acid would be again that one carbon carboxylic acid. It would look like this. You could imagine two of these things coming together. We haven't even talked about reactions yet, but two of these things coming together giving me an anhydride is going to look like this. There you have it. That's formic anhydride. Notice that I did not say diformic. It's formic because I'm just assuming that it's reacting with itself. Let's move on to the next topic.

Here’s what students ask on this topic:

What is an anhydride in organic chemistry?

An anhydride in organic chemistry is a carboxylic acid derivative formed by the condensation of two carboxylic acids. It can be visualized as a dicarbonyl compound with an oxygen atom in the middle. Essentially, it is a molecule where two acyl groups are bonded to the same oxygen atom. Anhydrides are important functional groups and are often encountered in various organic reactions and synthesis processes.

How do you name an anhydride using IUPAC nomenclature?

To name an anhydride using IUPAC nomenclature, first identify the two carboxylic acids that form the anhydride. Alphabetize the names of these acids and replace the word 'acid' with 'anhydride.' For example, if the anhydride is formed from ethanoic acid and propanoic acid, the name would be 'ethanoic propanoic anhydride.' If the anhydride is symmetrical, use the name of one acid followed by 'anhydride,' such as 'ethanoic anhydride' for an anhydride formed from two ethanoic acid molecules.

What is the difference between symmetrical and mixed anhydrides?

Symmetrical anhydrides are formed from two identical carboxylic acid molecules, resulting in a single type of acyl group on both sides of the oxygen atom. For example, ethanoic anhydride is formed from two ethanoic acid molecules. Mixed anhydrides, on the other hand, are formed from two different carboxylic acids, resulting in two different acyl groups on either side of the oxygen atom. An example is ethanoic propanoic anhydride, formed from ethanoic acid and propanoic acid.

How do you name an anhydride using common nomenclature?

To name an anhydride using common nomenclature, identify the common names of the two carboxylic acids that form the anhydride. Alphabetize these names and replace 'acid' with 'anhydride.' For example, if the anhydride is formed from acetic acid and propionic acid, the name would be 'acetic propionic anhydride.' For symmetrical anhydrides, use the common name of one acid followed by 'anhydride,' such as 'acetic anhydride' for an anhydride formed from two acetic acid molecules.

What are some examples of anhydrides and their uses in organic chemistry?

Some common examples of anhydrides include acetic anhydride, which is used in the synthesis of aspirin and cellulose acetate, and maleic anhydride, which is used in the production of unsaturated polyester resins. These compounds are valuable in organic synthesis due to their reactivity, particularly in acylation reactions where they introduce acyl groups into other molecules. Anhydrides are also used in the preparation of esters and amides, making them versatile reagents in organic chemistry.