most acidic proton

[dentalwhiz]

In a given molecule, a ketone is given on one end, an aldehyde on the other. The answer states that the H on the methyl carbon on the ketone is more acidic than the H on the aldehyde. Doesn't proton acidity increase as the 's' character of the bond increases? This leads me to believe that the H on the aldehyde is more acidic- am I missing something here? I know that resonance plays a role in proton acidity, but don't they both have equal roles in this scenario? Any clarification would be great

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[themuffinman11]

When looking for the most acidic proton, always think how stable the conjugate base would be (so the molecule with the proton removed). Carbons that are Alpha (next to a carbonyl group) will have acidic protons because of resonance with the carbonyl. This is why the H on the methyl carbon on the ketone is more acidic. Removing the H from the aldehyde carbon would be very bad as a negative sp2 carbon is very unstable. Let me know if you need any clarification!

 

[dentalwhiz]

I just did another problem where you have to decide which proton would be most acidic. An aldehyde H is compared to a H on a methyl carbon (CH3-CH-C=OH) adjacent to it. It states that the aldehyde H would be more acidic. I'm so confused... I thought I had a solid grasp on these types of questions but I guess not... Doesn't the logic you just stated not apply in this situation?

 

[themuffinman11]

I just did another problem where you have to decide which proton would be most acidic. An aldehyde H is compared to a H on a methyl carbon (CH3-CH-C=OH) adjacent to it. It states that the aldehyde H would be more acidic. I'm so confused... I thought I had a solid grasp on these types of questions but I guess not... Doesn't the logic you just stated not apply in this situation?

Can you draw the structures out in both questions (or take a picture of each question) so I can just double check it