Acidity of Alcohols vs. Aldehydes & Ketones??

[eager2bMD]

Can someone please explain to me why alcohols are more acidic than both aldehydes and ketones?
From my rationalization, I would think it would be the other way around because the more acidic molecule will be the one whose conjugate base is most stable. The carbonyl group on aldehydes and ketones is electron-withdrawing, which would stabilize the negative charge better, so wouldn't this make their conjugate bases more stable and thus make aldehydes and ketones more acidic?
If somebody could please tell me where my logic is wrong, I would realllly appreciate it! Thanks!!!

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[Bruinsfinalfour]

Can someone please explain to me why alcohols are more acidic than both aldehydes and ketones?
From my rationalization, I would think it would be the other way around because the more acidic molecule will be the one whose conjugate base is most stable. The carbonyl group on aldehydes and ketones is electron-withdrawing, which would stabilize the negative charge better, so wouldn't this make their conjugate bases more stable and thus make aldehydes and ketones more acidic?
If somebody could please tell me where my logic is wrong, I would realllly appreciate it! Thanks!!!

Your logic is wrong in that if you de-protonate an aldehyde/ketone...you are left with an ionic carbon atom...which you should know is extremely unstable. When you de-protonate an alcohol, you are left with an ionic oxygen atom which is much more stable (bigger, more electronegative)

 

[eager2bMD]

Thanks Bruins! By focusing on little details, I completely neglected the most basic principles. Thanks for the help!

 

[nm825]

Your logic is wrong in that if you de-protonate an aldehyde/ketone...you are left with an ionic carbon atom...which you should know is extremely unstable. When you de-protonate an alcohol, you are left with an ionic oxygen atom which is much more stable (bigger, more electronegative)

I too had the same question regarding why alcohols are more acidic. Isn't this guy's answer partially wrong though. O- is not bigger than C-; it's smaller because it has a higher Zeff, right? The real reason is just that O is more electronegative than C and this more willing to take on excess electrons, right?

 

[enervate]

I too had the same question regarding why alcohols are more acidic. Isn't this guy's answer partially wrong though. O- is not bigger than C-; it's smaller because it has a higher Zeff, right? The real reason is just that O is more electronegative than C and this more willing to take on excess electrons, right?

Both of your questions are correct although the difference between the atomic radii of oxygen and carbon is nothing like the difference between oxygen and sulfur. That is to say, the difference in atomic radius has, as you implied, little bearing upon the stability of either anion.