How are oils esters?

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akinaro
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#1
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#1
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?
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Medicineisgood1
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#2
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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?
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akinaro
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(Original post by 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?
This is from the Cgp bookName:  14662426320411945491978.jpg
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Size:  428.1 KB
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anosmianAcrimony
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#4
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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.

Name:  triglyceride.jpg
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anosmianAcrimony
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(Original post by akinaro)
This is from the Cgp bookName:  14662426320411945491978.jpg
Views: 164
Size:  428.1 KB
The chemical in the pink box is a fatty acid, and you're right, it's not an ester. It's a carboxylic acid.
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Medicineisgood1
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#6
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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
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akinaro
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(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
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anosmianAcrimony
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#8
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(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.
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akinaro
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#9
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(Original post by anosmianAcrimony)
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.
Thanks for your help, I get it now 😁
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anosmianAcrimony
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#10
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(Original post by akinaro)
Thanks for your help, I get it now 😁
Great! Glad to be of help.
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haithamnhaque
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#11
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#11
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
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