Question

Among the following identify Zwitterionic form of amino acid

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

A zwitterion always contains both positive and negative charges simultaneously. For amino acids, the amino group becomes \(NH_3^+\) and the carboxyl group becomes \(COO^-\).

Answer 1

The Correct Option is B

Concept: A zwitterion is a dipolar ion that contains both a positively charged group and a negatively charged group within the same molecule. Amino acids commonly exist as zwitterions in aqueous solution and at their isoelectric pH. Amino acids contain:
• Amino group (\(-NH_2\))
• Carboxyl group (\(-COOH\)) In aqueous medium, proton transfer occurs from the carboxyl group to the amino group.

Step 1: Understand formation of zwitterion. The carboxyl group loses a proton: \[ -COOH \rightarrow -COO^- \] The amino group gains a proton: \[ -NH_2 \rightarrow -NH_3^+ \] As a result, both positive and negative charges are present simultaneously.

Step 2: Examine Option (A). \[ H_3N^+-CH(R)-COOH \] This structure contains a positive charge but no negative charge. Hence it is not a zwitterion.

Step 3: Examine Option (B). \[ H_3N^+-CH(R)-COO^- \] This structure contains:
• Positive charge on amino group
• Negative charge on carboxylate group Therefore it is a zwitterion.

Step 4: Examine Option (C). \[ H_2N-CH(R)-COOH \] No ionic charges are present. Hence it is not a zwitterion.

Step 5: Examine Option (D). \[ H_2N-CH(R)-COO^- \] Only a negative charge is present. Hence it is not a zwitterion.

Step 6: Final conclusion. The zwitterionic form is: \[ \boxed{H_3N^+-CH(R)-COO^-} \] Hence option (B) is correct.