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Studying for a test? Prepare with these 5 lessons on Alkanes, cycloalkanes, and functional groups.
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Video transcript
- [Voiceover] All the functional groups in this video contain a carbon-oxygen double bond, and we call a carbon-oxygen double bond a carbonyl. So here you can see a carbon-oxygen double bond in this functional group, and here's another one in this functional group, and here's another one down here. For the first functional group this is called an aldehyde, so an aldehyde has an R group on one side of the carbonyl and a hydrogen on the other side of the carbonyl. As an example lets look at this compound. So here is our carbonyl, our carbon-oxygen double bond, and then on this side we have a hydrogen directly bonded to this carbonyl carbon. On the left side we have this R group, so the carbonyl carbon gets a number one, it gets the lowest number possible, and then this carbon would get a number two, this carbon would get a number three, and this carbon would get a number four. So we have a four-carbon aldehyde. So how do we name a four-carbon aldehyde? Well a four-carbon alkane we know is butane, so one, two, three, and four, and we know that this compound is called butane. An aldehyde has an A-L ending, so if you see an A-L ending, that indicates the presence of an aldehyde. So we're gonna lose the E from butane, and add on A-L, so the name of this molecule becomes butanal. Let me write that out here, so this is butanal. Next lets look at a ketone, so a ketone has an R group on one side of the carbonyl, and an R group on the other side of the carbonyl. So for our ketone example lets look at this compound. We're gonna number to give our carbonyl the lowest number possible, so we're gonna start numbering from the left side of our compound, so this would get carbon number one. The carbonyl carbon would be carbon number two. This is carbon number three, this is carbon number four, and this is carbon number five. So we have a five-carbon ketone. A five carbon alkane, let me go ahead and draw out a five-carbon alkane here, this would be called pentane, so that would be pentane. A ketone has an O-N-E ending, so ONE indicates the presence of a ketone. So we're gonna lose the E from pentane, and add ONE. So this would be pentanone, so this is pentanone. We also need to indicate the position of the carbonyls. The carbonyl is at carbon two, so we need to write 2-pentanone, and that's because we could draw another molecule that's pentanone, but this could have the carbonyl at carbon three, so let me go ahead and write that in here, one, two, three. So this compound would be 3-pentanone, and 3-pentanone and 2-pentanone are different molecules, so that's why we need to indicate the position of the carbonyl. For the aldehyde up here, we didn't need to indicate that the aldehyde is at carbon one. That's the only place that it could possibly be. Notice that an aldehyde has this hydrogen directly bonded to the carbonyl-carbon, where as a ketone has, if we look at the carbonyl group right here, we have a carbon on one side, see H 3 on one side in this case, and we have a carbon on this side directly bonded to that carbonyl carbon. So that's the difference between an aldehyde and the ketone, and a lot of students have a hard time telling the difference between an aldehyde and a ketone. Look for this hydrogen directly bonded to the carbonyl-carbon and that's an aldehyde. Next we have a carboxylic acid, so a carboxylic acid has an R group on one side of the carbonyl, and an O-H on the other side. Some students think that this is an alcohol at first, but this is not an alcohol. This O-H is right next to this carbonyl, and that changes the properties. Carboxylic acids have different properties from alcohols. For an example of a carboxylic acid, over here on the right we know that our carbonyl-carbon gets number one, so that's carbon number one. This is carbon number two, carbon number three, and carbon number four. So a four-carbon carboxylic acid. So a four-carbon alkane up here was butane, so we're gonna have OIC acid as our ending, so it would be butanoic acid for the name for this compound. and that's just one of the names, so one of the names for this molecule would be butanoic acid. Alright, probably the most famous carboxylic acid is a two-carbon carboxylic acid, so I can draw it like this really quickly, and this is called acetic acid. Vinegar is just a dilute-solution of acetic acid in water. Alright, our next functional group is called an acyl halide, or you can also call it an acid halide, and you're pretty much talking about acid-chlorides in organic chemistry, and so here is our carbon-oxygen double bond, and then on this side we have an R group, and the right side we have a chlorine. So acyl halides come from carboxylic acid, so this is an example of a carboxylic acid derivative, and an example of an acyl halide on the right here, we have our carbonyl, and then we have our halogen, and the reason I like to call them an acyl halide is this right here on the left, this is an acyl group, and on the right we have our halogen, so this would be acetyl chloride, is one of the names for this, but you can also call them an acid halide. There are carboxylic acid derivatives, so some professors prefer one term, and some professors prefer the other term. Our next functional group is an acid anhydride. So here is our carbonyl, here's the R group, and instead of a chlorine like we had up here we have all of this over here on the right, and so this is an an acid anhydride, or just an anhydride. This is also a carboxylic acid derivative. You can form an acid anhydride from a carboxylic acid, and for the example over here on the right we have acytic anhydrides. Next functional group is called an ester. So an ester is another carboxylic acid derivative. So a carboxylic acid had a hydrogen in this position, but now we have an R group, so we have our carbonyl, we have an O-R, and then we have an R on the left, so that's an ester, and here's an example of an ester over here, so we have an ethyl group instead of a hydrogen, so for acytic acid, let me go ahead and draw acytic acid again. Acytic acid had a hydrogen right here, and now we have an ethyl group, so instantly we know we're talking about an ester, we're not talking about a carboxylic acid. If you wanted to name this ester, you have this ehtyl group, so that would be ethyl, and then this part would be acetate, so ethyl acetate would be the name. Now for the names of all of these, you're gonna get to them later in the course, so it's probably not that important to name these compounds, but it's good to start hearing these things now. And finally, our last functional group is called an amide, atleast that what I call it, but there are several different ways to pronounce this functional group. The dictionary says, atleast my dictionary says, amides, or amids, are the two preferred ways to pronounce this. You'll probably hear amids as one of the most common ways to pronounce this. A lot of professors say amid, and some professors get pretty upset if you don't pronounce this the way that they want. I've heard many more ways to pronounce this functional group too, like amides, and all kinds of things. Use whatever pronunciation your professor wants. That's always the way to do things. Now we have a carbonyl, notice we have a nitrogen right next to the carbonyl-carbon, so nitrogen directly bonded to the carbonyl-carbon, lone pair of electrons on the nitrogen, so that's an amide functional group, or an amid functional group, so these Rs could be hydrogens, you could be talking about hydrogens or you could be talking about alkyl groups, so there's lots of different examples of amides, or amids. On the right is an example, so our carbonyl-carbon gets a number one, so this would be one, this would be number two, this would be number three, this would be a number four, so a four-carbon amide would be butanamides. Let me go ahead and write that down here, so this would be butanamide, or butanamid, depending on how you prefer to pronounce this functional group.