Question about Acidic Proton

[potbelly]

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Hi all,

In Beta- Keto Acid, which proton is the most acidic?

Usually in Carboxylic Acid, hydroxyl H is the most acidic but in B-Keto acid, alpha-H is also acidic. So I just want to make sure which Proton is the most acidic in Beta Keto Acid - Hydroxylic H or alpha-H ?


Thanks in advance.

 

[Doc Smile]

alpha proton.

remember the more stabalized the conjugate base the stronger the acid is (moer likely to lose a proton). by removing the alpha proton you can form an enolate, which is stabalized by resonance.

 

[potbelly]

alpha proton.

remember the more stabalized the conjugate base the stronger the acid is (moer likely to lose a proton). by removing the alpha proton you can form an enolate, which is stabalized by resonance.

Thank you. So if you take off lpha proton, you can make more resonances, hence more acidic. Right?

 

[Doc Smile]

Yes

organic chemistry is all about resonance. . .

 

[Doc Smile]

Quick note about acidic protons in general. . . correct me anyone if i am wrong,

but the order of acidic protons is alpha protons, tertiary allylic (or benzylic) protons, secondary allylic (or benzylic), primary allyliz (or benzylic), tertiary, secondary, primary

Of course steric hindarance plays a role.
am I missing any?

And there is almost always a question asking what is the least stable carbo cation formed from deprotanation and that is a loss of a vinyl proton. so:
H2C=C+-CH2