Answer
The structures of the major forms of glutamic acid at pH values
of 1, 3.2, 7, and 11 are shown in the picture below.
The side-chain carboxylic acid is a weaker acid than the acid group next to the α-carbon atom because the NH3+ group is a strong electron-withdrawing group that strengthens the nearby COOH by 2-3 pK units as compared to the side chain COOH, which is not affected by induction in this molecule.
Work Step by Step
The general rule when determining if a group will be protonated is: at solution pH below the group's pKa value, the group will be protonated; at pH higher than the group's pKa value, it will not be protonated.
