Question Video: Naming an Ester From Its Structural Formula Chemistry

Which of the following names does the ester shown have? [A] ethyl benzoate [B] phenyl benzoate [C] propyl benzoate [D] phenyl propanoate [E] benzyl methanoate

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Video Transcript

Which of the following names does the ester shown have? (A) Ethyl benzoate, (B) phenyl benzoate, (C) propyl benzoate, (D) phenyl propanoate, or (E) benzyl methanoate.

The question asks us to name an ester. This is the general displayed formula for an ester. This R group, which represents the rest of the molecule, can be an alkyl group, an aryl group, or a hydrogen atom. And this R group can be an alkyl group or an aryl group.

Now that we know what an ester looks like, we need to know how to name it. The first step in naming an ester involves splitting the molecule at the CO single bond and reverting it to its parent molecules, which are the molecules used to make the ester. Esters can be formed by reacting a carboxylic acid and an alcohol. To find out which carboxylic acid was used to make the ester, we add a hydroxy group or OH to the carbonyl carbon. And to find out which alcohol was used to make the ester, we add a hydrogen atom to the oxygen from the other part of the ester molecule.

We have now found the molecules used to make the ester. Our next step in the ester-naming process is to name this carboxylic acid and alcohol. Once we have the name of the carboxylic acid and alcohol, we can start naming the ester. To find the first part of the ester’s name, we take the first part of the alcohol’s name and add the suffix -yl. To find the second part of the ester’s name, we take the first part of the carboxylic acid’s name and add the suffix -oate.

Now that we know how to name an ester, let’s look at the ester given in the question. First of all, we need to split the molecule at the CO single bond and revert the ester to its parent carboxylic acid and alcohol molecules. To find which carboxylic acid was used to make the ester, we add a hydroxy group to the carbonyl carbon. And to find out which alcohol was used to make the ester, we add a hydrogen atom to the oxygen in the other part from the ester molecule. We now have the parent molecules. These are the molecules that were used to make the ester.

Our next step is naming the carboxylic acid and alcohol. The carboxylic acid has a carboxylic acid functional group bonded to a benzene ring. To name this molecule, we take the benz- from benzene. And as it is a carboxylic acid, we add the end -oic acid, giving us the name benzoic acid. The alcohol contains three carbon atoms, giving us the prefix prop-. They are singly bonded, giving us an-, and of course it contains the alcohol functional group, giving us the suffix -ol. Therefore, the name of the alcohol is propanol.

For the next part of the ester-naming process, we take the first part of the alcohol’s name, which is prop-, and we add the suffix -yl, giving us the name propyl. Finding the second part of the ester’s name involves taking the first part of the carboxylic acid’s name, which is benz-, and adding the suffix -oate. This gives us the name benzoate.

So the answer to the question “Which of the following names does the ester shown have?” is (C) propyl benzoate.

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