Question

Which of the following does not exist as a Zwitter ion?

• A. Glycine
• B. Glutamic acid
• C. Sulphanilic acid
• D. p-aminobenzoic acid

Answer 1

Answer: (D)

p-aminobenzoic acid

Answer 2

$o$-and $p$-aminobenzoic acids do not exist as a Zwitter ion. The lone pair of electrons on the $- NH _{2}$ group is donated towards the benzene ring due to resonance effect. As a result, acidic character of - COOH group and basic character of $- NH _{2}$ group decrease. Therefore, the weakly acidic - $COOH$ group cannot transfer a $H ^{+}$ion to the weakly basic - $NH _{2}$ group. Thus o-or $p$-aminobenzoic acids do not exist as Zwitter ion.