Naming Esters - Online Tutor, Practice Problems & Exam Prep

Esters are named using two components: an alkyl group and a carboxylate. The alkyl group is derived from the alcohol, while the carboxylate comes from the corresponding carboxylic acid, minus the hydrogen. For example, ethyl acetate can also be referred to as ethyl ethanoate. Understanding this nomenclature is crucial for identifying esters in organic chemistry, as they play significant roles in various reactions and applications, including Fischer esterification and acyl transfer reactions.

Ester Nomenclature

In this page, we're going to learn how to name esters. Esters are actually one of the hardest functional groups to name, and that's because ester is one of the only functional groups where the name of the functional group is not found anywhere in the nomenclature. Meaning that if you have an ester, you're not going to actually see the name "ester" anywhere. What is the name? Well, it turns out that an ester is named of two components. Imagine that you've got an ester. Remember that the general structure is COOR. What they consider is that everything on this side is an alkyl group. You name this as an alkyl group. And then the way that they name the other side is they think, well, this looks a lot like carboxylic acid but without the H. What do you call it when a carboxylic acid is missing its H? You call it a carboxylate. It's an alkyl carboxylate. That is how we name it as an alkyl carboxylate. You have to determine what that name is going to be.

I'll do a worked example here and then I'll let you guys go to do it yourself. Here we've got an ester, obviously, and we have an alkyl group and a carboxylate. The way we would name this is the alkyl group is ethyl, a 2 carbon chain. The carboxylate could be named in 1 of 2 ways. It could be named as the common name which would be a 2 carbon chain which would be acetic acid which would be acetate because acetate is the negative anion, or that's in the common name. Or it could be named as ethanoate because it's ethanoic acid, so that would be IUPAC. Both of these would be correct. You'll hear ethyl acetate. You'll hear ethyl ethanoate. Obviously, acetate is way more common. You hear that everywhere. Ethyl acetate would be the name of that structure there.

Let's go ahead and move on to this practice problem. Let's see if you can get it right.

Name the structure

I would have accepted 2 answers for this question. If you did common, that's fine. If you did IUPAC, that's also fine. My alkyl group in this case is cyclopentyl, a cyclopentyl group. Then my carboxylate in common would be valerate. In IUPAC, it would be pentanoate. Both of these are correct. I'm going to put here cyclopentyl valerate or cyclopentyl pentanoate. Again, see how tricky this is: if you didn't take the time to learn it, you might not recognize that this is an ester on an exam because it doesn't have the word "ester" in it. It's like, who thought of that? Someone really messed up. See if you guys can go ahead and draw the one below.

Draw the molecule

What I would do is I would start off with the general structure of an ester. First of all, how do I even know what functional group this is? Obviously, it's on the ester page. You're thinking ester. But what if you saw this on an exam in the middle of a bunch of other stuff? What you could think is that you've got an alkyl group and formate is a carboxylate. When you see alkyl and carboxylate together, that suggests it's an ester. Once you've made that connection, draw your general structure of an ester. I'm going to draw OR and R. Now all I need to do is really just plug and chug. I take the R groups from my name and replace them. The isopropyl part, does that part go on R₁ or R₂? What do you guys think? R₂. That means that's my alkyl group. I'm going to write it like this: I have isopropyl. Formate, what type of carboxylic acid is formate? Formic acid is a one-carbon carboxylic acid, meaning that this is actually an H because the one carbon comes from the carbonyl, so this is your structure, isopropyl formate. Awesome, guys. Let's move on.

Here’s what students ask on this topic:

How do you name an ester in organic chemistry?

To name an ester in organic chemistry, you need to identify two components: the alkyl group and the carboxylate. The alkyl group is derived from the alcohol part of the ester, while the carboxylate comes from the carboxylic acid part, minus the hydrogen. For example, in ethyl acetate, 'ethyl' is the alkyl group from ethanol, and 'acetate' is the carboxylate from acetic acid. The IUPAC name for ethyl acetate is ethyl ethanoate. Understanding this nomenclature is crucial for identifying esters in various reactions and applications.

What is the general structure of an ester?

The general structure of an ester is represented as RCOOR', where R and R' are alkyl or aryl groups. The ester functional group consists of a carbonyl group (C=O) attached to an oxygen atom, which is also bonded to another carbon atom. This structure is derived from a carboxylic acid (RCOOH) by replacing the hydrogen atom of the hydroxyl group (-OH) with an alkyl or aryl group (R').

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

Common names for esters are often derived from the names of the parent alcohol and carboxylic acid. For example, ethyl acetate is derived from ethanol and acetic acid. In contrast, IUPAC names follow a systematic approach: the alkyl group from the alcohol is named first, followed by the name of the carboxylate derived from the carboxylic acid. For instance, ethyl acetate's IUPAC name is ethyl ethanoate, where 'ethanoate' comes from ethanoic acid (acetic acid).

Why is ester nomenclature considered challenging in organic chemistry?

Ester nomenclature is considered challenging because the name 'ester' does not appear in the compound's name. Instead, esters are named based on two components: the alkyl group from the alcohol and the carboxylate from the carboxylic acid. This dual-component naming system requires a good understanding of both alcohol and carboxylic acid nomenclature. Additionally, esters can have both common and IUPAC names, adding another layer of complexity.

Can you provide an example of naming an ester using both common and IUPAC names?

Sure! Let's take the ester formed from methanol and butanoic acid. The common name for this ester is methyl butyrate, where 'methyl' comes from methanol and 'butyrate' comes from butanoic acid. The IUPAC name for the same ester is methyl butanoate, where 'butanoate' is derived from butanoic acid. Both names are correct, but the IUPAC name is more systematic and widely used in scientific literature.