Question

What is a Zwitterion? Explain with the example of Glycine.

Hint:

{Zwitterion = Internal salt} Example: Glycine → \( ^+NH_3-CH_2-COO^- \)

Answer 1

Concept: A zwitterion is a molecule that contains both a positive and a negative charge on different atoms but is overall electrically neutral. Such species are commonly observed in amino acids due to the presence of both acidic and basic functional groups. Definition: A zwitterion is a dipolar ion that has equal positive and negative charges within the same molecule, resulting in a net zero charge. Example: Glycine Glycine is the simplest amino acid with the structure: \[ NH_2-CH_2-COOH \] In aqueous solution, glycine undergoes an internal acid-base reaction:

• The amino group (\(NH_2\)) accepts a proton to become \(NH_3^+\).
• The carboxyl group (\(COOH\)) loses a proton to become \(COO^-\).

Thus, the zwitterionic form of glycine is: \[ ^+NH_3-CH_2-COO^- \]
Explanation:

• Contains both positive (\(NH_3^+\)) and negative (\(COO^-\)) charges.
• Overall charge remains zero.
• This form predominates at the isoelectric point (neutral pH).

Significance:

• Explains high melting points of amino acids
• Responsible for their amphoteric nature
• Affects solubility and conductivity in solution

Conclusion: Thus, a zwitterion is a dipolar ion with both positive and negative charges in the same molecule, as seen in glycine where \( ^+NH_3-CH_2-COO^- \) represents its zwitterionic form.