Why is the hydrolysis of dextrorotatory sucrose (+66.5°) into an equimolar mixture of D-(+)-glucose and D-(-)-fructose referred to as the 'inversion of cane sugar'?

Answer and explanation

Correct answer: D. Rotation changes from +66.5° to -39.7° as levorotation of D-fructose exceeds dextrorotation of D-glucose

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(levorotatory).
  1. Step 1: Sucrose is dextrorotatory with a specific optical rotation of .
  2. Step 2: Upon acid- or enzyme-catalyzed hydrolysis, sucrose splits into equimolar amounts of D-(+)-glucose and D-(-)-fructose:
  3. Step 3: Calculating the net optical rotation of the resulting equimolar mixture:
  4. Step 4: Because the sign of optical rotation inverts from dextro () to levo (), the process is termed the 'inversion of cane sugar', and the hydrolyzed product mixture is known as invert sugar.
Answer
The optical rotation of the solution changes from dextrorotatory (+66.5°) to levorotatory (-39.7°) because the levorotation of D-(-)-fructose (-92.4°) exceeds the dextrorotation of D-(+)-glucose (+52.7°)
Why not the others: 'The molecular structure inverts stereocenters from D into L' is false because absolute configurations remain D; 'Pyranose rings invert into furanose...' is incorrect; 'Density inverts...' is physically irrelevant.

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