proton acidity

[gamecock1992]

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would an anhydride have a more acidic proton than a carboxylic acid because it has two resonance structures?

 

[hope_to_match]

would an anhydride have a more acidic proton than a carboxylic acid because it has two resonance structures?

i don't think anhydride's protons are acidic at all

edit: what i mean by at all is that the anhydrides protons on methyl groups are unlikely to get deprotonated because they are not stabilized by resonance as opposed to acetic acid's proton on the -OH group which is

 

[jHoon]

i think carboxylic acids are as acidic as it gets. pka of around 4-5 (resonance over 2 oxygens making the conjugate base hella stable) anhydrides don't really have any acidic protons directly attached to any electronegative atoms, but it does have somewhat acidic alpha protons which also show double resonance. I think their pka's are like ~10

But resonance over 2 Oxygens simultaneously > resonance over 1 oxygen anyday (even if it has 2 oxygens to choose from)

 

[gamecock1992]

Thank you for both responses! I was meaning the alpha hydrogen in between the two carbonyls of an anhydride, but I see how a carboxylic acid would have a better resonance because it is between two oxygens! I was thinking the alpha carbon Hydrogen would have two resonance structures because of the two carbonyl groups so it would be more acidic than the one resonance structure of a carboxylic acid. I understand my mistake thanks!

 

[hope_to_match]

Thank you for both responses! I was meaning the alpha hydrogen in between the two carbonyls of an anhydride, but I see how a carboxylic acid would have a better resonance because it is between two oxygens! I was thinking the alpha carbon Hydrogen would have two resonance structures because of the two carbonyl groups so it would be more acidic than the one resonance structure of a carboxylic acid. I understand my mistake thanks!

btw you are confusing an anhydride (which has OXYGEN in between two carbonyls) and a dicarbonyl...in any case carboxylic acid is more acidic due to resonance (delocalization of electrons) pka of alpha H's is around 9-10..just make sure you get your structures right