 In this video, we'll look at identifying and naming ketones and aldehydes. Ketones and aldehydes look very similar. They both contain the carbonyl group. This is the C double bond O group. The difference lies in where the carbonyl is in the molecule. If it is on the end of a chain, then it's called an aldehyde. If it's anywhere else in the molecule, it's a ketone. We make this distinction because the position of the carbonyl group in the molecule affects the chemical reactions that it can undergo. So you can see that I've drawn the generic ketone here with two R groups coming off it because there's another part of the molecule coming off either side of the carbonyl. Actually, to be properly generic, we should put a little prime on one of the Rs like this to indicate that these two bits sticking off the two Rs could be different. In the aldehyde, because the carbonyl is on the end, the carbon atom needs an extra bond so it has a hydrogen poking off one side. And then on the other side is the rest of the molecule represented here as R. If the molecule is a ketone, then its name ends in OWN. And if it's an aldehyde, it ends in AL. Be careful not to confuse this with the ALL of the alcohols. Now, just a note on drawing stick structures for these guys. For an aldehyde, remember, the carbonyl group is on the end carbon and it has a hydrogen attached. When drawing a stick structure, it's a good idea to draw this end hydrogen out explicitly to remind yourself and other readers that it is an aldehyde. However, it is technically correct to draw an aldehyde like this, leaving the end hydrogen as implicit. So let's try naming this. The longest chain that includes the functional group is five carbons. Don't forget to include the carbon that's part of the carbonyl. So it's based on pentane. But it's an aldehyde, so we're going to call it pentanal. Now we number the chain starting from the aldehyde group and we find that we have three fluoro and four methyl as our substituents. So we put all that together and we alphabetize the substituents and so we get three fluoro, four methyl, pentanal. Good. So now a ketone. You can see from the stick structure that there's a carbonyl group and it has one carbon poking out on either side. So the main chain is this string of three carbons. So this molecule is based on propane. But it's a ketone, so we're going to call it propanone. Now you could specify that the carbonyl group is on the second carbon and call it propan2one. But can you see that for this molecule it actually can't be anything else? If the carbonyl were on either of the other two carbons it would be an aldehyde. So because you've got the ONE on the end and that indicates that it's a ketone you can just get away with calling it propanone. And in fact this compound is more commonly known as acetone. Lastly, how about this? The main chain is a ring with five carbons, so cyclopentane, but it has a carbonyl group stuck on it. It's not on an end carbon. A cycloalkane doesn't have any end carbons. So it's definitely a ketone and not an aldehyde. So we call it cyclopentanone. This example also doesn't need to be numbered. That is, we don't need to call it cyclopentan1one. Can you see why?