Hey guys. Let me teach you how to name aldehydes. So, 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 for alcohols, you take out the 'e' and replace the 'e' of the alkane with the suffix 'ol'. So then ethane would become ethanol. It's the same thing with aldehydes except 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. Ethanal would be a 2 carbon aldehyde. You have to be careful about how you say those vowels because they are pretty similar to each other.
Now, it turns out that there is one major difference between aldehydes and other functional groups, and it has to do with the definition of what an aldehyde is. If you think about it, aldehydes are by definition terminal carbonyl. 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 number. You would never say that something is a one-ethanol. Why? Because the carbonyl has an H on it. Remember, aldehydes have an H on them, so that means it's by definition on the end of the chain, so you don't need to name the location. Instead of saying one-hexanal, you just say hexanal because there is no possibility of having 2 or 3 hexanal. Why? If it was a 2 or 3, now it would be inside the chain, and that’s called a ketone, so 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 a 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 5-membered ring. When that happens, then the aldehyde gets a special name because it's a substituent. As a substituent, it receives the name carbaldehyde. It's not "does," and 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, a branch off of that root chain. Then you do have to give it a location because I need to know where on that chain it is, and you have to call it carbaldehyde instead of aldehyde to indicate that it is now substituent. If you're a little bit lost, don't worry about it. We're going to do 2 examples and 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.
