Acetate anion destabilization by methyl group

[hariharan venkatasu]

The alkyl group of acetate ion in acetic acid pushes more negative charge inductively toward already negative COO- end destabilize it.In this context I wish to know what actually is destabilization?What happen when acetate ion is destabilized?How the anion is stabilized ultimately? Could you please explain?

 

[shjacks45]

So you are comparing methyl group of acetic acid with Hydrogen of Formic Acid or CO2- of Oxylate? Generally an electron withdawing group like CCl3 (in trichloroacetic acid) pulls negative charge from carboxylic CO2 to the side chain, which allows more Hydrogen ion to detach. Since methyl releases electrons it would make the carboxylic bond with hydrogen stronger. That is methyl makes acetic acid weaker. However an Oxygen, electron withdrawing, makes Carbonic Acid a weak acid, highlighting that electron withdrawing/donating isn't the only criteria. Note that dissociation, acidity, of acetic acid, is in solution with water (The pH definition). Water creates complexes with anions and cation. Rather destabilizing, electron donation allow for more covalent character of acetate compounds eg Copper Acetate.

 

[hariharan venkatasu]

Thank you very much for your reply.But I did not receive reply to my question what actually is destabilization and what happens when acetate ion is destabilized?How stabilization take place ultimately?I request answer for this.

 

[shjacks45]

Destabilization means a carboxylic acid is prone to losing the CO2 group. Acetic acid is stabilized by methyl group. Trichloroacetic acid easily loses CO2 to become CHCl3. The charge on the carboxylic acid portion of acetic acid resonates between the two oxygens. Because methyl lowers the acidity, hydrogen ions are still attached to one of the oxygens, making them different, sorta, because other acetic acid molecules share hydrogen ions. However this does not destabilize as much as change the resonant structures available. In other words the term "destabilize" does not have anything to do with acetate ions.

 

[hariharan venkatasu]

Thank you very much for the answer which does not fully answer my question

 

[hariharan venkatasu]

I am very eager to receive your replies to my earlier questions.Could you please help me?

 

[Borek]

It is all about energy differences between -COOH and -COO^-+H⁺. -COO^- is stabilized by the resonance - if it has lower electron density it is relatively more stable (has a lower combined energy) and the dissociated form is preferred, the higher the electron density the less the energy "gain" and non dissociated form becomes dominant.

Sadly, I feel like this explanation doesn't answer your question "what is destabilization" - as the only exact answer I can think of is "destabilization is making something less stable", which is rather tautological.

 

[hariharan venkatasu]

Thanks a lot for the answer.But my question is what actually happens to the anion?Is there any structural change to the anion?
Sorry for repeating the same problem.

 

[Borek]

No structural change (although with the changing electron density I wouldn't be surprised by some minor changes to the C-O bond lengths and/or the O-C-O angle).

 

[hariharan venkatasu]

Thank you for your answer which clears my doubt to some extent.However I do not understand the first sentence,"It is all about energy differences...and non dissociated form become dominant".Please clarify'

 

[hariharan venkatasu]

I am very eager to see your reply to my last post.I shall be immensely thankful to you if you could post your answer.

 

[Borek]

Sorry, every answer we give you leads only to further questions, as if you had no idea what are the basic principles at work. I strongly suggest you read some general chemistry books where these things are explained. I have no problems helping with details, but full lecture on things that are covered in every chemistry course is out of the question.

 

[hariharan venkatasu]

Thanks a lot for the answer and advice.