Question

Which of the following gives the correct representation of zwitter ion of the given amino acid ?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

In a zwitter ion the -COOH proton moves to the -NH2, giving -COO(-) and -NH3(+) in one molecule.

Answer 1

The Correct Option is B

Step 1: Identify the amino acid.
The structure H2N-CH(CH3)-COOH is alanine. It has a basic -NH2 group and an acidic -COOH group.

Step 2: Recall how a zwitter ion forms.
The -COOH group gives its proton to the -NH2 group in the same molecule. The acid part becomes -COO(-) and the amine part becomes -NH3(+). The molecule is neutral overall but has two charges.

Step 3: Check option (1).
The right side is the same as the left side, with no charges. No proton moved, so this is not a zwitter ion. Wrong.

Step 4: Check option (2).
The right side shows H3N(+)-CH(CH3)-COO(-). The proton moved from COOH to NH2. This is the zwitter ion. Right.

Step 5: Check option (3).
The right side shows H2N-CH(CH3)-COO(-). Only a negative charge is present, so this is an anion and not a neutral zwitter ion. Wrong.

Step 6: Check option (4).
The right side shows H3N(+)-CH(CH3)-COOH. Only a positive charge is present, so this is a cation and not a zwitter ion. Wrong.

Final Answer:
The zwitter ion has NH3(+) and COO(-) in the same molecule, which is option (2). \[ \boxed{\text{Option (2)}} \]