A level carboxylic acids

How do carboxylic acids become delocalised. Where does the shared electron come from, could someone please explain it.

Reply 1

How do carboxylic acids become delocalised. Where does the shared electron come from, could someone please explain it.

Hello Slugzie(:!

This is just a brief and simple explanation; I hope it is sufficient for you.

Carboxylic acids, such as acetic acid (CH3COOH), have a delocalisation due to the carbonyl group (C=O) and the hydroxyl group (OH).
The carbonyl group has a polar bond with a positive partial charge on the carbon atom and a negative partial charge on the oxygen atom, while the hydroxyl group is slightly polar with a positive partial charge on the hydrogen atom and a negative partial charge on the oxygen atom.
In the resonance structure, the carbonyl group delocalises, allowing the carbon and oxygen atoms to share electrons. The hydroxyl group is also delocalised, with electrons shared between the hydrogen and oxygen atoms.
The carbon atom has a full external energy level, while the oxygen atom has a partially full external energy level.
When they bond, the oxygen atom shares its lone electron pair with the carbon atom, forming a covalent bond.
In the resonance structure, the shared electrons delocalise, meaning that they do not reside on a single atom. Instead, they get shared between several atoms.

Supplement: Resonance
Each oxygen atom of the carboxylate ion carries only half of the negative charge due to the equal distribution of the negative charge between the two oxygen atoms.

Bye,
Sandro

(edited 7 months ago)

Reply 2

Nitrotoluene

Original post by Nitrotoluene

Hello Slugzie(:!
This is just a brief and simple explanation; I hope it is sufficient for you.
Carboxylic acids, such as acetic acid (CH3COOH), have a delocalisation due to the carbonyl group (C=O) and the hydroxyl group (OH).
The carbonyl group has a polar bond with a positive partial charge on the carbon atom and a negative partial charge on the oxygen atom, while the hydroxyl group is slightly polar with a positive partial charge on the hydrogen atom and a negative partial charge on the oxygen atom.
In the resonance structure, the carbonyl group delocalises, allowing the carbon and oxygen atoms to share electrons. The hydroxyl group is also delocalised, with electrons shared between the hydrogen and oxygen atoms.
The carbon atom has a full external energy level, while the oxygen atom has a partially full external energy level.
When they bond, the oxygen atom shares its lone electron pair with the carbon atom, forming a covalent bond.
In the resonance structure, the shared electrons delocalise, meaning that they do not reside on a single atom. Instead, they get shared between several atoms.
Supplement: Resonance
Each oxygen atom of the carboxylate ion carries only half of the negative charge due to the equal distribution of the negative charge between the two oxygen atoms.

Bye,
Sandro

Hello Slugzie(:!
I would like to know if you have at least read my reply. Receiving feedback or a simple thank you can be gratifying.
Don't consider me an arrogant person.

Krgds,
Sandro

(edited 7 months ago)

Reply 3

scimusic

Hi try here https://www.science-revision.co.uk/A2_carboxylic%20acids.html

and https://www.chemguide.co.uk/organicprops/acidmenu.html#top

and also here https://chemrevise.org/wp-content/uploads/2015/10/6-1-3-revision-guide-carboxylic-acids-and-esters.pdf

Reply 4

Slugzie(:

Original post by Nitrotoluene

Hello Slugzie(:!
This is just a brief and simple explanation; I hope it is sufficient for you.
Carboxylic acids, such as acetic acid (CH3COOH), have a delocalisation due to the carbonyl group (C=O) and the hydroxyl group (OH).
The carbonyl group has a polar bond with a positive partial charge on the carbon atom and a negative partial charge on the oxygen atom, while the hydroxyl group is slightly polar with a positive partial charge on the hydrogen atom and a negative partial charge on the oxygen atom.
In the resonance structure, the carbonyl group delocalises, allowing the carbon and oxygen atoms to share electrons. The hydroxyl group is also delocalised, with electrons shared between the hydrogen and oxygen atoms.
The carbon atom has a full external energy level, while the oxygen atom has a partially full external energy level.
When they bond, the oxygen atom shares its lone electron pair with the carbon atom, forming a covalent bond.
In the resonance structure, the shared electrons delocalise, meaning that they do not reside on a single atom. Instead, they get shared between several atoms.
Supplement: Resonance
Each oxygen atom of the carboxylate ion carries only half of the negative charge due to the equal distribution of the negative charge between the two oxygen atoms.

Bye,
Sandro

Thank you, I'm not really sure what resonance is

Reply 5

Nitrotoluene

Original post by Slugzie(:

Thank you, I'm not really sure what resonance is

Ciao Slugzie(:!

Try reading these lecture notes on 'resonance'; you might gain a clearer insight into this intricate chemistry subject, here: Resonance
Please confirm that the link has opened correctly.

Thank you in advance.
Krgds,
Sandro

Reply 6

UtterlyUseless69

Original post by Slugzie(:

Thank you, I'm not really sure what resonance is

Don’t worry about it - it’s not something you are expected to learn for A level.

You also aren’t required to know that there is delocalisation in the carboxylic acid group.

Reply 7

SonicNChemistry

Original post by Nitrotoluene

Hello Slugzie(:!
This is just a brief and simple explanation; I hope it is sufficient for you.
Carboxylic acids, such as acetic acid (CH3COOH), have a delocalisation due to the carbonyl group (C=O) and the hydroxyl group (OH).
The carbonyl group has a polar bond with a positive partial charge on the carbon atom and a negative partial charge on the oxygen atom, while the hydroxyl group is slightly polar with a positive partial charge on the hydrogen atom and a negative partial charge on the oxygen atom.
In the resonance structure, the carbonyl group delocalises, allowing the carbon and oxygen atoms to share electrons. The hydroxyl group is also delocalised, with electrons shared between the hydrogen and oxygen atoms.
The carbon atom has a full external energy level, while the oxygen atom has a partially full external energy level.
When they bond, the oxygen atom shares its lone electron pair with the carbon atom, forming a covalent bond.
In the resonance structure, the shared electrons delocalise, meaning that they do not reside on a single atom. Instead, they get shared between several atoms.
Supplement: Resonance
Each oxygen atom of the carboxylate ion carries only half of the negative charge due to the equal distribution of the negative charge between the two oxygen atoms.

Bye,
Sandro

Wow that sounds very interesting and a nice introduction to Carboxylic Acids. I won't be starting this topic untill Sunday I think but care if I add this to my organic chemistry notes? I have a question about Carboxylic Acids; what properties make them weak acids? Carboxylate are square planar then?

(edited 7 months ago)

Reply 8

TypicalNerd

Original post by SonicNChemistry

They are planar, but not square planar. Square planar shapes are anything where the molecule is flat but bonded to 4 groups at right angles to each other. Trigonal planar would be a better description, but since the C-C and C-O bonds don’t repel equally, it isn’t a perfectly trigonal planar geometry.

The acidity can be explained in terms of how stable the conjugate base is compared to the conjugate acid. Bog standard carboxylic acids are generally weak acids as there isn’t really anything to stabilise the conjugate base besides resonance within the carboxylate functional group. Substituted ones with things like alcohol groups and amines may be well stabilised by the inductive effect and internal hydrogen-bonding. This is beyond A level, however, so I wouldn’t stress about adding any of it to your notes.

Reply 9

SonicNChemistry

Original post by TypicalNerd

They are planar, but not square planar. Square planar shapes are anything where the molecule is flat but bonded to 4 groups at right angles to each other. Trigonal planar would be a better description, but since the C-C and C-O bonds don’t repel equally, it isn’t a perfectly trigonal planar geometry.
The acidity can be explained in terms of how stable the conjugate base is compared to the conjugate acid. Bog standard carboxylic acids are generally weak acids as there isn’t really anything to stabilise the conjugate base besides resonance within the carboxylate functional group. Substituted ones with things like alcohol groups and amines may be well stabilised by the inductive effect and internal hydrogen-bonding. This is beyond A level, however, so I wouldn’t stress about adding any of it to your notes.

I guess the molecular drawing looked slightly ambiguous 🤔
So increasing the Hydrogen bonding within and inducing dipole-dipole removes electrons from the conjugate base decreasing the Pka?
I added it anyway just for knowledge. Today I've literally just started reading reactions of the Carbonyl group with Ketones and Aldehydes. And I have to do a bit of standard deviation and variance before I leave the house 😂.

(edited 7 months ago)

Reply 10

TypicalNerd

Original post by SonicNChemistry

Internal hydrogen bonding can stabilise the conjugate base, lowering the pKa (see lactic acid vs propanoic acid as an example).

Inductive effects can be responsible for increased acidity. They do indeed help to better spread the electron-density across the conjugate base, which stabilises it more and thus incidentally lowering the pKa of the acid.

Understanding this is generally a concept first formally taught at university, but I have seen 2-mark past A level questions where they have asked about the effect of substituting an alkyl hydrogen for a group like -Cl or -OH on the acidity of a carboxylic acid.

Just in case you ever get one such exam question

(edited 7 months ago)