enter image description here

On the 3rd diagram (from left), the one with net charge = -1 ,

Why did it lose the H to OH- from the CH2CO2H from the neutral form ?

I was told that while moving to the right , the OH- will take H+ electrons meaning it should take H+ from NH3 .. ?

Is there any reason why they took the H from CH2CO2H ?

Any help would be appreciated!


1 Answer 1


The -CO₂H groups are carboxylic acid groups, better represented as -COOH. These, being acidic, have a lower pKₐ than the -NH₃⁺ group and so as the pH increases these -COOH groups lose their protons first.

The pKₐ values for the three are shown below the arrows: as you can see the α carboxylic acid is more acidic than that in the side chain, but they are both much more acidic than the protonated amino group.


Not the answer you're looking for? Browse other questions tagged .