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 solve this question, let's analyze the assertion and reason provided.

Assertion (A):
All naturally occurring \(\alpha\)-amino acids except glycine are optically active.

Reason (R):
Most naturally occurring amino acids have L-configuration.

1. Optically Active Amino Acids:
Optical activity in amino acids arises from the presence of a chiral center at the \(\alpha\)-carbon (the carbon attached to the amino group, carboxyl group, and side chain). For an amino acid to be optically active, the \(\alpha\)-carbon must not be superimposable on its mirror image (i.e., it must be a chiral center).

2. Glycine and Optical Activity:
Glycine (NH₂CH₂COOH) is the only naturally occurring \(\alpha\)-amino acid that is not optically active. This is because its \(\alpha\)-carbon is not chiral (it is attached to two hydrogen atoms, making it achiral). Therefore, the assertion that all naturally occurring \(\alpha\)-amino acids except glycine are optically active is correct.

3. The L-Configuration of Amino Acids:
Most naturally occurring amino acids have the L-configuration at the chiral \(\alpha\)-carbon. The L-configuration is the stereochemical form found in proteins. However, the L-configuration does not directly determine optical activity; it is the presence of the chiral center that does.

4. Evaluation of Reason (R):
The reason is true, as most naturally occurring amino acids indeed have the L-configuration. However, the reason does not explain why amino acids are optically active. The optical activity arises from the chiral nature of the amino acid, not just its configuration.

5. Conclusion:
The assertion is correct, but the reason, while true, does not explain the optical activity. Therefore, the assertion is true, but the reason is not fully explanatory.

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