How are oils esters?

I'm really confused. I don't get how oils are esters when they have the same functional group as carboxylic acid. Can someone explain how they are esters?

Reply 1

Medicineisgood1

Hi, do you have a picture of the oil? If so you should see that it has a double bond O and one single O bond, and no OH group. This is where the ester bond is. If you have a picture could you upload it?

Reply 2

akinaro

Original post by Medicineisgood1

This is from the Cgp book

Reply 3

anosmianAcrimony

Usually when we talk about oils we're talking about triglycerides, which are composed of three fatty acid molecules each ester bonded to a single glycerol molecule. Fatty acids are very long aliphatic chains with a carboxylic acid group at one end; they can also have double bonds within the chain. Glycerol could also be described as propan-1,2,3-triene, if that makes any sense.

So the overall structure of a triglyceride is as pictured. I've pointed out the ester bonds.

Reply 4

anosmianAcrimony

Original post by akinaro

This is from the Cgp book

The chemical in the pink box is a fatty acid, and you're right, it's not an ester. It's a carboxylic acid.

Reply 5

Medicineisgood1

Yeah anosmian is definitely correct about the triglycerides which will come up during AS biology, but in that picture it is clearly a COOH acid

Reply 6

akinaro

Original post by anosmianAcrimony

The chemical in the pink box is a fatty acid, and you're right, it's not an ester. It's a carboxylic acid.

But if it's a carboxylic acid then how is it an oil when oils are esters? Sorry if I'm not getting this

Reply 7

anosmianAcrimony

Original post by akinaro

But if it's a carboxylic acid then how is it an oil when oils are esters? Sorry if I'm not getting this

Not all oils are esters. Triacylglycerols and fatty acids are both considered oils, but fatty acids are just carboxylic acids, not esters. It's the long aliphatic chain that makes something an oil, not the ester group.

Reply 8

akinaro

Original post by anosmianAcrimony

Thanks for your help, I get it now 😁

Reply 9

anosmianAcrimony

Original post by akinaro

Thanks for your help, I get it now 😁

Great! Glad to be of help.

Reply 10

haithamnhaque

I read that they are esters because they are made by reacting glycerol (an alcohol) with fatty acids. And the equation for esters is alcohol+acid----> ester + water