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Nomenclature and properties of amides

Video transcript
Voiceover: Another carboxylic acid derivative is the amide functional group, and you'll hear many different ways to pronounce this functional group. I usually say "[am-ide]," but I've heard "[am-ids]," or "[ay-mides]," or, however you want to say it. To me, it's not really that big of a deal; it seems to be more where you're from, in terms of how you pronounce it. So if our goal is to name this two-carbon amide over here on the right, let's start with the two-carbon carboxylic acid, over here on the left. So we have two carbons, and if you think about the IUPAC name, so two carbons, this would be ethanoic acid, to name the corresponding amide, we're going to drop the ending. So we're going to drop the "oic acid," and add on "amide." So, let's go ahead and write that. So, we would drop the "oic acid," and add on "amide," so "ethanamide," or "ethanamid," is what you could call this molecule over here, on the right. Of course, most people don't call this "ethanoic acid"; most people call this "acetic acid." So, if we think about naming this derived from acetic acid, let's go ahead and write that down, if we drop the ending this time, we don't have an extra "o." so we just have this "ic," so we're gonna drop the "ic acid," and add "amide" onto that, so we would make "acetomide," if we think about over here, or, "acetomid," however you want to say it. So, once again, think about dropping the ending, and adding "amide" on. So acetomide is an example of a primary amide, so this is a primary amide, and the way I like to think about this, is this nitrogen here is bonded to only one carbon, the carbon right here, so that makes this primary. If you wanna think about naming this one down here, this time, the nitrogen is bonded to two carbons, the carbon in our carbon EEL, and also this carbon over here. And so, this one is an example of a secondary amide, a nitrogen bonded to two carbons. If we think about the parent carboxylic acid, so over here, one, two, three carboxylic acid, three carbons in this carboxylic acid. So the IUPAC name would be "propanoic acid," so let's go ahead and write out "propanoic acid." We're gonna use this as the base for the amide on the right. So, once again, we're gonna drop the "oic acid" ending, just like we did up here, and so we drop the "oic acid" ending, and add on "amide," so we have "propanamide," so let's go ahead and write that. So over here on the right, we would have propanamide, or propanamid, like that. And then, that takes care of, if you will, this portion of the molecule. Now we still have this methyl group, right here, to worry about, and that methyl group is coming off of this nitrogen here, so the methyl group coming off of this nitrogen. And the way we show that, is to put an "N" here, and then a "methyl," so "N-methyl-propanamide," tells us that we have a methyl group coming off of the nitrogen in our amide, and, so that's how it's done. Alright, let's look at some more examples, so two more examples for amides right here, and let's see how to name them. Let's start with the one on the left: So, for this one, if I think about the carboxylic acid, it'd be a one, two, three, four; so four-carbon carboxylic acid; the IUPAC name is "butanoic acid." So, we drop the "oic acid" part, and add on "amide," so it'd be "butanamide." So let's go ahead, and write that in. So this would be, "butanamide." And then, we have to think about what else is attached to this nitrogen, here. So, the nitrogen in our amide right here, has a methyl group here, and another methyl group here, so two methyl groups. So this time, we're gonna write, "N, N-dimethyl," so we have two methyl groups; each one of those methyl groups is attached to that nitrogen, so "N, N-dimethyl-butanamide" would be the name for this molecule. In terms of classifying it, so in terms of classifying this amide here, this would actually be a tertiary amide, because this nitrogen is attached to one, two, three other carbons, and so it's a tertiary amide. Alright, let's look at naming one more, so this one over here, on the right. And if I think about the carboxylic acid, from which this is derived, so you have to use your imagination a little bit, so if I think about this portion, instead of the nitrogen here, if I had an OH, that would be benzoic acid. So I'm just gonna go ahead, and write that right here. So, "benzoic acid." We know we're gonna drop the ending, we're gonna drop the "oic acid" part, and add "amide," so it'd be "benzamide." So let's go ahead and write that. So it has our parent name here, so we would have "benzamide" here. And then, let's think about what else we have: we have a nitrogen, and we have a methyl group, one methyl group bonded to that nitrogen, and then we have another methyl group over here on the ring. So let's go ahead, and number the ring, and see where our other methyl group is. So our other methyl group, if we number our ring, this would be carbon one, if we think about this as being like benzoic acid. So if we're numbering our ring, this would be carbon one, and then carbon two, carbon three, and carbon four. So we have a methyl group at carbon four, and we also have a methyl group coming off of our nitrogen. So this time, we're going to write, let me go ahead and write here, this'll be "N, 4-dimethyl," so we have "N, 4-dimethyl-benzamide," as our name for this molecule. So, notice the difference. So here we have a methyl group, on our nitrogen, right here, and we have a methyl group coming off of carbon four, so that's where our dimethyl comes from. For this one, we have N, and another N, because both of our methyl groups are coming off of the nitrogen in the example on the left, and so it's just useful to contrast these two molecules, when we're thinking about nomenclature. In terms of physical properties of amides, let's look at a little diagram here, showing acetamide. So we have our amide right here, and physical properties, in terms of what state of matter is this, acetamide is actually a solid, at room temperature and pressure, and so this is a solid. It has a lot of hydrogen bonding: so, we could think about some hydrogen bonding here, we could think about some hydrogen bonding here; there are lots of opportunities for hydrogen bonding. So partial negative oxygen, partial positive hydrogen, bonded to this nitrogen, which is withdrawing some electron density from this hydrogen. So, lots of opportunities for hydrogen bonding. Acetamide is solid at room temperature, and so its melting point turns out to be, approximately 82 degrees Celsius, so that's its melting point; its boiling point is actually much higher, so, somewhere around 221 degrees, so higher. This is actually the melting point, and the boiling point being much higher, due to the very strong inter-molecular forces that are present between amide molecules. In terms of solubility of amides in water, small amides are definitely soluble. So if I think about water coming along. Let's go ahead a draw water in here. Water is a polar molecule: so partial negative, partial positive. So like dissolves like: this polar amide will dissolve in polar water, you can think about some hydrogen bonding going on right here, so like dissolves like. And there's also a resonance property to amides, so I won't get too much into resonance, but there's a lone pair of electrons on this nitrogen, which can move into here, pushing these electrons off onto the oxygen, giving you a plus one formal charge on your nitrogen, and a negative one formal charge one your oxygen. And so, amides can be polar as well; this also can explain the solubility of acetamides in water here. So small amides can be soluble in water, but of course, as we've been discussing in these videos, as you increase this R group, as you increase the number of carbons, if you turn this into an R group, the more carbons you have, the more non-polar [unintelligible] you have, so you would decrease the solubility of amides as you do that. So, we'll talk much more about the resonance structure for amides in future videos, because it is extremely important for things like reactivity, and chemical reactions