Help with Chad's Video Problem =( !!!!!

[Strag]

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The problem asks rank in order of increasing acidity. I don't have a picture but I'll describe the compounds.

I. Ketone with two methyl groups
II. Anhydride
III. Ketone with one methyl group and hydrogen attached.
IV. Formaldehyde

Answer is IV<I<III<II. Chad said that it's based on resonance. Anhydride has 3 resonance leading to weakest conjugate base and strongest acid, followed by I and III (but III being stronger with less e- donating group in methyl groups), and IV is weakest acid because it doesn't have alpha hydrogens.


But my problem is in my notes I said that aldehydes are better electrophiles than ketones because they have less electron donating groups and thus have a more partially positive carbonyl. Therefore, aldehydes are more acidic than ketones. In that case, wouldn't the order be I<III<IV<II?

This is really annoying me someone please help me out!!!

 

[Juggernauts]

The formaldehyde is pretty unreactive as a acid. It won't donate a hydrogen, and it is pretty content because he has the majority of the both hydrogens electrons in his outer valence shell. so he really does not need electrons either from a nucleophile, or maybe it's better said that b/c of the bonds with the two hydrogens he is really not an electrophile.

Now your spot on about the donating effects of the methyl group in regard to the aldehyde and ketone.

 

[recyrb]

stick with the cardio method to determin the acidity! --resonance---you are correct i have in my notes that the aldehyde alpha carbon is more acidic, but that is all aldehydes besides formaldehyde lol formaldehyde doesnt have any resonance so it will be very unstable. then ketone which has two donating groups with 2 resonance structures compared with the aldehyde which also has 2 resonance structures, but only one donating group, donation groups will make this CB more reactive. so its a weaker acid then the aldehyde which is obviously weaker than the hydride wheeew hope that helps

 

[FLOSS UR TEETH]

stick with the cardio method to determin the acidity! --resonance---you are correct i have in my notes that the aldehyde alpha carbon is more acidic, but that is all aldehydes besides formaldehyde lol formaldehyde doesnt have any resonance so it will be very unstable. then ketone which has two donating groups with 2 resonance structures compared with the aldehyde which also has 2 resonance structures, but only one donating group, donation groups will make this CB more reactive. so its a weaker acid then the aldehyde which is obviously weaker than the hydride wheeew hope that helps

CARDIO all the way baby