NO2CH2COOH vs benzoic acid acidity

[510586]

Advertisement - Members don't see this ad

How come NO2ch2cooh is more acidic? Its electron withdrawing no2 makes it acidic, but doesn't benzoic acid have resonance which is higher priority in cardio?

 

[100%permwinner]

Both acids have carboxylic acid functional group so when the carboxyl proton gets removed, the negative charge on the oxygen anion can only delocalize to the adjacent O bonded to the same C (in these two molecules). The kind of electron withdrawing group matters. NO2 is more electron withdrawing than phenyl by induction, because N and O are more electronegative than C. This will weaken the O-H bond in NO2CH2CO2H further, making its carboxyl proton more easy to remove.

 

[510586]

Both acids have carboxylic acid functional group so when the carboxyl proton gets removed, the negative charge on the oxygen anion can only delocalize to the adjacent O bonded to the same C (in these two molecules). The kind of electron withdrawing group matters. NO2 is more electron withdrawing than phenyl by induction, because N and O are more electronegative than C. This will weaken the O-H bond in NO2CH2CO2H further, making its carboxyl proton more easy to remove.

Oh OK thank you very much. For some reason I thought the benzene delocalizes it but that's only in stuff like phenols. So it wouldn't be possible for something like this to happen?

 

[100%permwinner]

Oh OK thank you very much. For some reason I thought the benzene delocalizes it but that's only in stuff like phenols. So it wouldn't be possible for something like this to happen?

That's not relevant to your question about acidicity. This image shows benzoic acid is a meta director. If you draw out all possible resonance structures, you will see positive charges on ortho and para positions.

 

[510586]

That's not relevant to your question about acidicity. This image shows benzoic acid is a meta director. If you draw out all possible resonance structures, you will see positive charges on ortho and para positions.

Doesn't more resonance increase the acidity because it stabilizes the anion though? which is why benzoic acid is more acidic than say normal carboxylic acids?

 

[100%permwinner]

Doesn't more resonance increase the acidity because it stabilizes the anion though? which is why benzoic acid is more acidic than say normal carboxylic acids?

Higher acidicity implies its conjugate base is more stable, equilibrium favors deprotonation more. Resonance does increase the stability of conjugate base (i.e. carboxylate after deprotonation). The main point is the negative charge on the oxygen can delocalize to as many atoms as possible through resonance. Phenol is a great example. If you draw out resonance structures of deprotonated benzoic acid, you will find it is not possible to delocalize the lone pair electrons on the negatively charged oxygen to carbon atoms in the ring (i.e. making carbon negatively charged).

 

[510586]

Higher acidicity implies its conjugate base is more stable, equilibrium favors deprotonation more. Resonance does increase the stability of conjugate base (i.e. carboxylate after deprotonation). The main point is the negative charge on the oxygen can delocalize to as many atoms as possible through resonance. Phenol is a great example. If you draw out resonance structures of deprotonated benzoic acid, you will find it is not possible to delocalize the lone pair electrons on the negatively charged oxygen to carbon atoms in the ring (i.e. making carbon negatively charged).

ohh ok I get it now. Thank you for your help!

 

[510586]

Woops meant to post this to DAT discussions sorry.