Question

Statement–I: Sucrose is dextrorotatory and upon hydrolysis it becomes laevorotatory. Statement–II: Sucrose on hydrolysis gives glucose and fructose such that the laevorotation of glucose is more than the dextrorotation of fructose. Choose the correct option.

• A. Both Statement–I and Statement–II are correct
• B. Both Statement–I and Statement–II are incorrect
• C. Statement–I is correct, Statement–II is incorrect
• D. Statement–II is correct, Statement–I is incorrect

Hint:

Sucrose hydrolysis produces \textbf{invert sugar} because the strong laevorotation of fructose dominates over the dextrorotation of glucose, reversing the direction of optical rotation.

Answer 1

The Correct Option is C

Concept: Optical rotation depends on the net effect of all optically active components present in a solution. On hydrolysis, sucrose breaks into two monosaccharides—glucose and fructose—each having its own specific rotation.
Step 1: Nature of sucrose. Sucrose is dextrorotatory, having a specific rotation of approximately: \[ [\alpha]_D \approx +66.5^\circ \] Hence, Statement–I (first part) is correct.
Step 2: Effect of hydrolysis of sucrose. On hydrolysis: \[ \text{Sucrose} \xrightarrow{\text{hydrolysis}} \text{Glucose} + \text{Fructose} \] Specific rotations: \[ \text{Glucose: } +52.5^\circ \quad (\text{dextrorotatory}) \] \[ \text{Fructose: } -92.4^\circ \quad (\text{laevorotatory}) \] The magnitude of laevorotation of fructose is greater than the dextrorotation of glucose. Therefore, the resulting mixture (called invert sugar) becomes laevorotatory. Thus, Statement–I (second part) is also correct.
Step 3: Evaluate Statement–II. Statement–II claims: \[ \text{Laevorotation of glucose}>\text{Dextrorotation of fructose} \] This is incorrect because:
Glucose is dextrorotatory, not laevorotatory
Fructose is laevorotatory, not dextrorotatory
Magnitude of rotation of fructose (\(\sim 92^\circ\)) is greater than that of glucose (\(\sim 52^\circ\)) Hence, Statement–II is incorrect.
Step 4: Final conclusion.
Statement–I is correct
Statement–II is incorrect Therefore, the correct option is (3).