Aldehyde Nomenclature

Concept: Concept: Nomenclature

4m
Video Transcript

Hey guys! Let me teach you how to name aldehydes. Like many other functional groups, aldehydes are going to be modifying the root name of the carbon chain. Take for example alcohol. We know that alcohol is you take out the e and you replace the e of the alkane with the suffix -ol. Then ethane would become ethanol. It’s the same thing with aldehydes. We’re just going to change one letter. It's going to be the suffix -al.
That actually could be a little confusing because those suffixes sound really similar. Ethanol would be an alcohol. Ethanol would be a two-carbon aldehyde. You have to be careful about how you say those vowels because they are pretty similar to each other.
It turns out that there is one major difference between aldehyde and other functional groups. It has to do with the definition of what an aldehyde is. If you think about it, aldehydes are by definition terminal carbonyls. They’re always at the end of the chain. What that means is that we don't need to number them the same way we would number other functional groups. In fact, it does not receive a location. You would never say that something is 1-ethanal. Why? Because the carbonyl has an H on it. Remember, aldehydes have an H on them. That’s means that by definition on the end of the chain so you don’t need to name the location.
Instead of saying 1-hexanal, you just say hexanal because there’s no possibility of having 2 or 3 hexanal. Why? If it was a 2 or 3, that would be inside of the chain and that’s called a ketone. It becomes a different functional group if it’s internal. But if it’s terminal, then it’s an aldehyde and we don't need to name the location. We just assume it’s at one of the ends.
There are going to be some times where you're not able to put the aldehyde inside of the root and it has to stick off. A good example of this is ring. We’re going to do a naming example in a second. Whereas you notice the aldehyde is not part of the root chain because the root chain is going to be this five-membered ring. When that happens, then aldehyde gets a special name because it’s a substituent. As a substituent, it receives the name carbaldehyde. It does receive a location. If you're able to put it into the root chain, then the root is going to be -al and there’s going to be no location because you assume it’s at one of the ends.
However, if you're not able to put the carbonyl, the aldehyde in your root chain, let’s say that it’s a substituent. It’s a branch off of that root chain. Then you do have it give it a location because they need to know where on that chain is it and you have to call it a carbaldehyde instead of an aldehyde to indicate that it is now a substituent.
If you’re a little bit lost, don't worry about it. We’re going to do two examples. By the end of these two examples, you’re going to have a pretty good idea of what's going on. Go ahead and try the first one. Name it according to the rules that I told you and then I’ll give you the answer