Assertion (A) : D (+) – Glucose is dextrorotatory in nature.
Reason (R) : (+) represents dextrorotatory nature and D represents the configuration.
Reason (R) : (+) represents dextrorotatory nature and D represents the configuration.
Show Hint
Optical rotation (+ or -) is an experimentally determined physical property.
All naturally occurring (+) glucose molecules belong to the D-series.
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Assertion (A) is false, but Reason (R) is true.
The Correct Option is B
Solution and Explanation
• Carbohydrate nomenclature uses specific prefixes to denote optical activity and relative configuration.
• D/L refers to the spatial arrangement (configuration) relative to glyceraldehyde.
• (+)/(-) refers to the direction in which the molecule rotates plane-polarized light (dextro or levo).
Step 1: Evaluate the Assertion
Naturally occurring Glucose rotates the plane of polarized light to the right.
It is indeed dextrorotatory, denoted as (+)-glucose.
Assertion is True.
Step 2: Evaluate the Reason
In nomenclature, the '+' symbol indicates dextrorotation.
The 'D' prefix signifies that the hydroxyl group on the lowest chiral carbon is on the right side in the Fischer projection.
Reason is True.
Step 3: Check for logical connection
The configuration (D) does not dictate or explain why the molecule is dextrorotatory (+).
There is no direct causal link between relative configuration and the direction of optical rotation.
Therefore, the reason is a true statement about nomenclature but not a physical explanation for the assertion.
The final answer is (B).
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