# Is an ester or a ketone more acidic?

Two organic chemistry textbooks I've read (by Bruice and by Tandon) say:

Esters are more acidic than ketones, because the resonance between the two oxygen atoms gives less opportunity for the delocalization of the electron pair on the alpha carbon in esters contrary to what happens in ketones.

But, in esters, when the resonance happens between the two oxygen atoms, the oxygen atom gains a positive charge which is highly unstable, given that oxygen is highly electronegative. So, shouldn’t the order of acidity be the other way round?

• Excellent answer (as usual). Just a small addendum: Both cases can be considered a Y aromatic system if you include hyperconjugation from the R groups. Then it is obvious, that in the ester case the $\pi$-system is better delocalised (larger), hence leads to a more stable configuration. Oct 31 '14 at 1:50