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Question #44966

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The Question

L-Phenylalanine (Compound $\mathbf{P}$ ) is reacted with excess $\ce{CH3OH}$ in the presence of dry $\ce{HCl(g)}$ to form intermediate $\mathbf{Q}$ . Subsequent treatment of $\mathbf{Q}$ with excess acetic anhydride in the presence of pyridine at 298 K yields Compound $\mathbf{R}$ . Let $K_D$ represent the partition coefficient defined as $[\text{Solute}]_{\text{ether}} / [\text{Solute}]_{\text{water}}$ at pH 7.0. Let $T_m$ represent the melting point, and $\mu$ represent the molecular dipole moment. Which of the following correctly compares the physical properties of $\mathbf{P}$ and $\mathbf{R}$ ?

Options

A.
$K_D(\mathbf{P}) < K_D(\mathbf{R})$ , $T_m(\mathbf{P}) > T_m(\mathbf{R})$ , $\mu(\mathbf{P}) > \mu(\mathbf{R})$
B.
$K_D(\mathbf{P}) > K_D(\mathbf{R})$ , $T_m(\mathbf{P}) < T_m(\mathbf{R})$ , $\mu(\mathbf{P}) < \mu(\mathbf{R})$
C.
$K_D(\mathbf{P}) < K_D(\mathbf{R})$ , $T_m(\mathbf{P}) > T_m(\mathbf{R})$ , $\mu(\mathbf{P}) < \mu(\mathbf{R})$
D.
$K_D(\mathbf{P}) < K_D(\mathbf{R})$ , $T_m(\mathbf{P}) < T_m(\mathbf{R})$ , $\mu(\mathbf{P}) > \mu(\mathbf{R})$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Amino Acid Zwitterion pH Sensitivity|Basicity-Solvation Competition

Why This Question Is Tricky

Common Mistakes

This question tests the 'Physical-Organic' interface by evaluating the consequences of masking a zwitterion.

Students often memorize that amino acids are water-soluble and have high melting points, but fail to recognize that these properties stem entirely from their zwitterionic electrostatic lattice and ion-dipole solvation.

By converting the amino acid to an N-acetyl methyl ester, the strong ion-ion interactions are destroyed.

The trap lies in visualizing the drastic shift in intermolecular forces: the partition coefficient shifts heavily towards the non-polar solvent, and both the melting point and dipole moment plummet.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Biomolecules - Class 12
Concept	Amino Acid Zwitterion pH Sensitivity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free