Question

Assertion (A): All naturally occurring \(\alpha\)-amino acids except glycine are optically active.
Reason (R): Most naturally occurring amino acids have L-configuration.

• A. Assertion (A) is true, but Reason (R) is false.
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• D. Assertion (A) is false, but Reason (R) is true.

Hint:

The L-configuration of amino acids contributes to their optical activity, except for glycine, which is achiral.

Answer 1

The Correct Option is A

To address this question, we will examine the provided assertion and reason.

Assertion (A):
Excluding glycine, all other naturally occurring \(\alpha\)-amino acids exhibit optical activity.

Reason (R):
The majority of naturally occurring amino acids possess the L-configuration.

1. Optical Activity in Amino Acids:
Optical activity in amino acids stems from the presence of a chiral center at the \(\alpha\)-carbon. This carbon atom is bonded to the amino group, carboxyl group, and the side chain. For an amino acid to be optically active, its \(\alpha\)-carbon must be chiral, meaning it cannot be superimposed on its mirror image.

2. Glycine's Lack of Optical Activity:
Glycine (NH₂CH₂COOH) is unique among naturally occurring \(\alpha\)-amino acids for not being optically active. This is due to its \(\alpha\)-carbon not being chiral; it is attached to two hydrogen atoms, rendering it achiral. Consequently, the assertion that all naturally occurring \(\alpha\)-amino acids except glycine are optically active is accurate.

3. The L-Configuration of Amino Acids:
Most naturally occurring amino acids adopt the L-configuration at their chiral \(\alpha\)-carbon. This L-configuration is the stereochemical form prevalent in proteins. However, the L-configuration itself does not confer optical activity; rather, it is the existence of the chiral center that is the direct cause of optical activity.

4. Evaluating Reason (R):
The reason stated is factually correct, as most naturally occurring amino acids do indeed have the L-configuration. However, this fact does not explain the underlying mechanism of optical activity in amino acids. Optical activity is a consequence of the amino acid's chirality, not solely its configuration.

5. Conclusion:
The assertion is correct. The reason, while true, does not provide an explanation for the optical activity. Therefore, the assertion is true, but the reason is not a valid explanation for it.

Final Answer:
The correct choice is that the assertion is true, but the reason is false.