 So let's have another look at our naming rules. Now that we have this extra information about functional groups and their suffixes, we need to update our rules. There are two amendments that we need to make. First, when you find and name the longest carbon chain, it must have the functional group in it. This could mean that it isn't actually the longest possible carbon chain. The second amendment is that when you number the main chain, the functional group must be given the lowest possible number. So let's use this molecule as an example. First, we look for the longest chain that has the functional group in it. And that would be this one with five carbons. So the root of the name is going to be pent. And the functional group is an alcohol. You can see the OH group there. So the end of the name will be ol. So we call the main part of the molecule pentanol. Note that we still put the an in the middle. This indicates that all the bonds are single. If the molecule had a double bond, we could amend this to pentanol. Okay, but we're not finished yet. We need to indicate where the alcohol group is. And we also need to add the substituent. So we number the chain in such a way as to give the functional group the lowest possible number. In this case it's easy. So we have to number the chain so that the OH group is attached to carbon number one. So that makes it pentan-one-ol. Notice that we separate the numbers and letters by hyphens when writing a name. And the substituent is a two carbon chain so it's called ethyl. And it's on carbon number two. So the complete name is two ethyl pentan-one-ol. In the following videos we'll go through more examples of how to name molecules containing each of the different kinds of functional groups.