Question

Choose the correct option for structures of A and B, respectively:

• A.
• B.
• C.
• D.

Hint:

In aqueous solutions, amino acids behave differently at various pH values. At low pH, the amino group is protonated and the carboxyl group remains neutral, while at high pH, the amino group is deprotonated and the carboxyl group becomes negatively charged.

Answer 1

The Correct Option is B

At pH 2, the amino group (-NH\(_2\)) is protonated to form an ammonium ion (-NH\(_3^+\), and the carboxyl group (-COOH) remains in its protonated form, as carboxyl acids are not deprotonated at this pH.
So, compound A will have the structure: \[ \text{H}_3\text{N} - \text{CH} - \text{COOH} \] At pH 10, the amino group remains in its deprotonated form (-NH\(_2\)) and the carboxyl group is deprotonated to form a carboxylate ion (-COO\(^-\)).
Therefore, compound B will have the structure: \[ \text{H}_2\text{N} - \text{CH} - \text{COO}^- \] Thus, the correct option is option (2).