acidic hydrogens

[spoog74]

i always thought that acidic protons came off of alpha carbons? There was a question in a practice exam that i took and it asked for the most acidic hydrogen and the answer was a hydrogen that came off an oxygen of a carboxyllic acid.


Can someone confirm this?

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[hcualex]

Its an acid.... acids give off hydrogens. Alpha hyrdogens get taken off carbonyl groups. Acids are more acidic than carbonyls

 

[invictusx]

i always thought that acidic protons came off of alpha carbons? There was a question in a practice exam that i took and it asked for the most acidic hydrogen and the answer was a hydrogen that came off an oxygen of a carboxyllic acid.


Can someone confirm this?

The protons off the alpha carbons are indeed acidic but carboxylic acids are more acidic. They are acidic by nature. Carboxylic acid hydrogens has a pKa ~ 5, which is much less than alpha hydrogens

 

[vicsin]

Protons attached directly to oxygens are the most acidic.

 

[LaughingGas]

i always thought that acidic protons came off of alpha carbons? There was a question in a practice exam that i took and it asked for the most acidic hydrogen and the answer was a hydrogen that came off an oxygen of a carboxyllic acid.


Can someone confirm this?

alpha Hydrogens are acidic compared to other C-H bonds, ranging from pka of 35 (least acidic being alpha hydrogen of amide) hydrogen on alpha carbon between di-carbonyl groups (one of the dicarbonyl derivatives having lowest pka of 10).
Yet carboxylic acid has usually pka of 5.
Lower pka = more acidic.

 

[rav4182]

CORRECTION:

let me give you all a tip that i wish i knew before my test

benzene aldehyde hydrogens are not acidic at all

 

[bharat008]

let me give you all a tip that i wish i knew before my test

aldehyde hydrogens are not acidic at all

not true.. If you remove the H of aldehyde then you will form ENOLATE which is really stable since it doesn't have any donating alkyl groups to the anion. No EDG to anion means the base is really stable.. Therefore, it's more acidic when compared to ketone..

Depends on how you do it..
Below is the general trend from most acidic to least acidic.

Aromatic with EWG > Carboxylic Acid>Alcohol>Ketone/Aldehyde>Alkynes>Alkenes>Alkanes

Hope that helps..