Question

Assertion (A) : D (+) – Glucose is dextrorotatory in nature. Reason (R) : (+) represents dextrorotatory nature and D represents the configuration.

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

Hint:

Never confuse D/L notation with (+)/(–) notation. D and L indicate configuration relative to glyceraldehyde. (+)/(–) indicate the direction of optical rotation. A D-compound may be either dextrorotatory or levorotatory depending on its actual optical behaviour.

Answer 1

The Correct Option is A

Concept: In stereochemistry, the symbols D and L are used to indicate the relative configuration of a molecule with respect to D-glyceraldehyde and L-glyceraldehyde. These symbols provide information about the arrangement of atoms in space and are not directly related to the direction in which a compound rotates plane-polarized light. On the other hand, the symbols (+) and (–) indicate the optical activity of a compound. A compound that rotates plane-polarized light towards the right (clockwise direction) is called dextrorotatory and is represented by the symbol (+). A compound that rotates plane-polarized light towards the left (anticlockwise direction) is called levorotatory and is represented by the symbol (–). Therefore, D and (+) represent two completely different properties of a compound.

Step 1: Examining the Assertion carefully. The assertion states that D(+)-Glucose is dextrorotatory in nature. The symbol (+) explicitly indicates that the compound rotates plane-polarized light in the clockwise direction. Since clockwise rotation corresponds to dextrorotation, D(+)-glucose is indeed dextrorotatory. Therefore, the Assertion is true.

Step 2: Examining the Reason carefully. The reason states that \[ (+) \] represents dextrorotatory nature and \[ D \] represents configuration. This statement is scientifically correct. The symbol (+) tells us about optical rotation, whereas D indicates the relative stereochemical configuration of the molecule. Hence, the Reason is also true.

Step 3: Determining whether the Reason explains the Assertion. The Assertion says that D(+)-glucose is dextrorotatory. The Reason explains that the dextrorotatory nature comes from the (+) sign and that D merely denotes configuration. Thus, the Reason correctly explains why D(+)-glucose is called dextrorotatory. Therefore, both statements are true and the Reason is the correct explanation of the Assertion.

Final Conclusion: Assertion (A) is true. Reason (R) is true. Reason (R) correctly explains Assertion (A). \[ \boxed{\text{Option (A)}} \]