Concept: Concept: Anhydride Nomenclature4m
Now we're going to learn how to name anhydrides. Anhydride are a specific functional group that come up a lot in this section. They’re one that you might not be very familiar with at all. Let’s just back up for a second to talk about what is an anhydride.
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 two carboxylic acids. You could say that maybe this was carboxylic acid 1 and maybe this was carboxylic acid 2, and maybe they came together and made an anhydride. Side note, that’s actually how you make anhydrides. You make anhydrides by combining to carboxylic acids into an anhydride. That's where the name stems from.
What we do is it’s really easy. You just alphabetize your two 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? Then you don't have to say that it's carboxylic acid 1, carboxylic acid 2. Anhydride, you could just say carboxylic acid 1 anhydride. It’s just alkynoic anhydride. Why? Because that means that you're assuming that one combined with another version itself to make an anhydride. You're basically saying that this is the anhydride you would yield through the condensation of these two carboxylic acids.
Let me see. That’s 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, this would be ethanoic here and this is propanoic. For IUPAC, it’s going to be ethanoic, propanoic anhydride, not acid. Don’t make that mistake. Common. The 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 propionic 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.
Concept: Example 1: Provide the IUPAC name for the molecule3m
Alright guys, let's start off with the easier side first, which I believe is this side. So, this would be benzoic and you really have no excuse not to know that, that's a benzoic acid, we know that's what happens when it's on a benzene ring, perfect. Now, the other side is more complicated because we've got this double bond so how do we name that? Well, with IUPAC we have a way to do it. So, let me show you. So, for IUPAC you would call this a 4 carbon carboxylic acid. So, it's going to be butanoic acid, butanoic, right? But there's that double bond, it's in the 3 position. So, I'm going to turn this into 3 butenoic and that's the cool thing about IUPAC guys, those modifiers that we learned a long time ago still work here. So butenoic, that means I have a dual bond in the 3 position and we're done. So, then that would be, combined that together it would be, in order, alphabetical order, benzoic, 3-butanoic anhydride, perfecto, okay? So, not so hard.
Now, what about common, how would common change? Well, guys it turns out that you can't use like butyric in this case, wouldn't work here, because I got a double bond and anytime you have a 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 or common names, you can't change them like you can change IUPAC. So, do we give up? no, actually this is another thing I'm getting at here, this actually 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 one CH2 away. Notice I've got a CH2 here, that's called an Allyl group. So, actually they're in a common name for the substituent and it's a common name you might see on your exam. So, this would turn into, in a common name it would be allyl benzoic anhydride, okay? 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, okay? Awesome guys. So, not that bad, let's move on to the next question.
Concept: Example 2: Draw the molecule1m
So guys, if you know what you're looking for this is a really easy question, formic acid would be, again that one carbon carboxylic acid so it look like this. So, you could imagine that two of these things coming together, right? We haven't even talked about reactions yet but two of these things coming together, giving me an hydride, is going to look like this, there you have it, it's formic anhydride, so notice that I did not say diformic, it's formic because I'm just assuming that it's reacting with itself. Awesome. So, it's move on to the next topic.