Question

Which of the following compounds can form a zwitterion ?

• A. Aniline
• B. Benzoic acid
• C. Acetanilide
• D. Glycine

Answer 1

The Correct Option is D

Zwitterions are compounds that contain both a positive and a negative charge within the same molecule. Typically, zwitterions are found in amino acids where the amino group can be protonated to form a positively charged ammonium ion, while the carboxyl group can lose a proton to form a negatively charged carboxylate ion.

Let's examine the given options:

1. Aniline (C₆H₅NH₂): This compound contains an amino group, but it lacks a carboxylic group that can deprotonate to form a carboxylate ion. Therefore, it cannot form a zwitterion.
2. Benzoic Acid (C₆H₅COOH): While benzoic acid can donate a proton from its carboxyl group, it does not have a basic group like an amino group to accept a proton and form a positive charge. Hence, it cannot form a zwitterion.
3. Acetanilide (C₈H₉NO): This compound is a derivative of aniline but with an acyl group attached to the nitrogen. Like aniline, it lacks both parts necessary to form a zwitterion: a protonatable amino group and a deprotonatable carboxylic group.
4. Glycine (NH₂-CH₂-COOH): Glycine is an amino acid and can form a zwitterion. In an aqueous solution, the amino group of glycine (NH₂) gets protonated to form NH₃⁺, and the carboxylic group (COOH) loses a proton to become COO^-. As a result, glycine exists as a zwitterion:
   \mathrm{NH_3^+ - CH_2 - COO^-}.

Therefore, the correct answer is Glycine, as it can exist as a zwitterion.