Alcohol, Aldehyde, Ketone Acidity

[MedPR]

Stable base = weak base, right? And weaker conjugate base = stronger acid (comparatively). So, since a carboxylate ion is more stable than an alkoxide ion, the corresponding carboxylic acid is more acidic than the corresponding alcohol.

It makes sense to me that a carboxylate ion is more stable than an alkoxide ion because of resonance and electron delocalization and all that. Cool.

However, I'm not understanding why an alcohol is more acidic than a similar ketone/aldehyde. I'm thinking the reason alcohol is more acidic than aldehyde is due to the electron donating alkyl group in the alkoxide ion (whereas in the aldehyde there is only a hydrogen), thus increasing basicity.

For ketone anions, I understand that there is electron donation by the alkyl groups (even moreso than in alkoxide ions), but why doesn't the pi bond and resonance stabilize it enough to make it a weaker base than alkoxide?

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[ljc]

Because an O-H bond is easier to break than a C-H bond, even with resonance.

 

[lkthlttr]

Stable base = weak base, right? And weaker conjugate base = stronger acid (comparatively). So, since a carboxylate ion is more stable than an alkoxide ion, the corresponding carboxylic acid is more acidic than the corresponding alcohol.

It makes sense to me that a carboxylate ion is more stable than an alkoxide ion because of resonance and electron delocalization and all that. Cool.

However, I'm not understanding why an alcohol is more acidic than a similar ketone/aldehyde. I'm thinking the reason alcohol is more acidic than aldehyde is due to the electron donating alkyl group in the alkoxide ion (whereas in the aldehyde there is only a hydrogen), thus increasing basicity.

For ketone anions, I understand that there is electron donation by the alkyl groups (even moreso than in alkoxide ions), but why doesn't the pi bond and resonance stabilize it enough to make it a weaker base than alkoxide?

Even with the resonance stabilization, a substantial portion of the negative charge is still going to rest on the carbon atom (the alpha carbon to the carbonyl) which is much less stable than the case of the alcohol where the negative charge lies on the more electronegative oxygen.