Naming Ketones - Online Tutor, Practice Problems & Exam Prep

Ketones are named by modifying the root name of a carbon chain, replacing the "e" with the suffix -one. They have higher priority than alcohols in naming. For IUPAC naming, the ketone's position is indicated (e.g., 2-butanone). Common names involve naming substituents alphabetically followed by "ketone" (e.g., ethyl methylketone). While common names are useful for smaller ketones, IUPAC is preferred for larger, complex structures. Understanding these naming conventions is essential for effective communication in organic chemistry.

Nomenclature

Hey guys. Let's learn how to name ketones. Ketones are going to modify the root name of a carbon chain. You're going to take out the "e" ending of the carbon chain and you're going to replace it with the suffix -one. I know that looks like 1. Please do not say 1. It's pronounced "own" like ketone. In this video, we're not going to discuss the prioritization of all functional groups in terms of numbering locations. But just suffice it to say that ketones are going to have higher priority than pretty much all the groups you learned in Organic Chemistry 1, including alcohol. If you saw an alcohol and a ketone next to each other and you had to figure out which one gets the higher priority with naming and numbering, you would pick the ketone.

When you're assigning common names to ketones, there's IUPAC name and there are common names. When you're assigning common names to ketones, then you're going to name both of the R groups alphabetically and you're going to end with the word ketone. Let me just show you a really quick example of the difference between common and IUPAC. Let's say you have a 4 carbon chain with a carbonyl in the middle. Oh gosh. You can't see that. Sorry about that. Let me move it down a little bit. Much better. In IUPAC, the name of this would be well, it started off as a butane. Now it's going to be a butanone. You have to name the location because I need to know exactly where that ketone is. It could be anywhere. I'm going to name this as a 2-butanone.

In terms of common naming, that would be IUPAC. In terms of common naming, it would be a little different. For the common name, you would just name the substituents in alphabetical order and end with the word ketone. Then it would be ethyl methylketone, almost like it's an ether. Remember that ethers, you can do that as well. You can name both of the substituents and then end with ether. This would be an ethyl methylketone. This common naming system is actually pretty common with a lot of ketones that you'll find in the lab because in the lab, we work with a lot of smaller ketones. But once you get to larger and more complex ketones that have bigger branching groups, the common naming system just becomes impossible to use because now you're going to have to name these huge bulky substituents in common names and it just gets terrible. You should use IUPAC. Definitely use IUPAC for more complex ketones and it's okay to use common names for the easier to name ones, the smaller ketones.

We're going to do 2 examples. I know you guys got this. Let's start off with the first one. Obviously, I don't need the common name for this. I just want the IUPAC name. Go for it.

Name the ketone

All right. What was the longest carbon chain? Well, it turns out that one was a little bit tricky to answer here because we had two of equal length. We had the blue carbon chain that I believe is 6 carbons long. And we had the yellow carbon chain which is also 6 carbons long. Which one did you pick? Does it matter? Yes, it matters. Guys, this goes back to our alkane nomenclature rules from organic chemistry 1. You just need to know that when you have a tie, you're going to go with the one that gives the most substituents. Meaning that if you look at yellow, yellow would only give me one branch, one substituent. Blue would give me two branches, two things coming off. The theory behind this is that the more branches you have, the easier they're going to be to name because they're smaller. It's easier to name something small or a lot of small things than it is to name one big terrible thing. We have the longest carbon chain. It's going to be this guy right here, which means that I have a 2. Hexanone, to be precise, because I'm going to give my priority to the ketone. Now I just need to name my substituents. I have a 3-propyl and I have a 4-methyl. All in alphabetical order, it's going to be 4-methyl-3-propyl-2-hexanone. Easy. Awesome. Let's move on to the next example.

Name the ketone

This one wasn't so bad either. We've got a root carbon ring of a cycloheptane. We just have to figure out where the substituents go and stuff like that. Obviously, my first carbon is going to be the ketone. Ketones have priority over pretty much most groups, but especially alkyl halides and alkanes which don't have any priority at all. Now we just have to determine which direction we number in. Do we number in the red clockwise direction or the blue counterclockwise direction? The answer is red because we're just trying to make the substituents have the lowest numbers possible. None of them have priority.

This turns into a 2-iodo and this is a 3,4,5-trimethyl. Obviously, our cycloheptane becomes cycloheptanone. We can go ahead and put this all together and it would be I comes before M, so 2-iodo-5-methyl-1-cycloheptanone. Just an extra side note here. If you wanted to not include that one and just leave it as no location, that would also be valid. The reason is because we only have one modifying functional group. Notice that you only have one modifier. Since you only have one modifier, it's okay to leave it off as no location because you assume that it's at the first. You absolutely have to put locations if you have 2 or more modifiers. If this became like a cycloheptanone, now you need the locations. I just like to add the locations just to be explicit and both of them would be correct. If you put a one, it's correct. If you didn't put a one, it's also fine. It would just be the methyl and the cycloheptanone together with no hyphens and no dashes and no commas. Awesome guys. So pretty easy stuff. Let's move on to the next topic.

Here’s what students ask on this topic:

How do you name ketones using IUPAC nomenclature?

In IUPAC nomenclature, ketones are named by modifying the root name of the carbon chain. The 'e' at the end of the alkane name is replaced with the suffix '-one'. The position of the ketone group is indicated by a number, which is the lowest possible number assigned to the carbonyl carbon. For example, a four-carbon chain with a ketone on the second carbon is named 2-butanone. The numbering ensures the ketone gets the highest priority over other functional groups like alcohols.

What is the difference between IUPAC and common names for ketones?

The IUPAC naming system for ketones involves modifying the root name of the carbon chain and replacing the 'e' with '-one', along with indicating the position of the ketone group (e.g., 2-butanone). Common names, on the other hand, involve naming the substituents attached to the carbonyl carbon alphabetically followed by the word 'ketone' (e.g., ethyl methylketone). Common names are typically used for smaller ketones, while IUPAC names are preferred for larger, more complex ketones.

Why do ketones have higher priority than alcohols in naming?

Ketones have higher priority than alcohols in naming because the carbonyl group (C=O) in ketones is more reactive and has a greater impact on the chemical properties of the molecule. This higher reactivity and influence on the molecule's behavior make it more significant in the naming hierarchy. Therefore, when both a ketone and an alcohol are present in a molecule, the ketone is given the lower number to reflect its higher priority.

Can you provide an example of naming a ketone with both IUPAC and common names?

Sure! Let's take a ketone with a four-carbon chain and a carbonyl group on the second carbon. The IUPAC name for this molecule is 2-butanone. For the common name, you would name the substituents attached to the carbonyl carbon alphabetically and end with 'ketone'. In this case, the substituents are ethyl and methyl, so the common name is ethyl methylketone.

When should you use IUPAC names over common names for ketones?

IUPAC names should be used over common names for ketones when dealing with larger and more complex molecules. The IUPAC system provides a clear and systematic way to name these compounds, ensuring that the structure and position of the functional groups are easily understood. Common names are more practical for smaller ketones with simple structures, but they become cumbersome and less informative for larger, branched ketones.