Question

Sucrose in water is dextro-rotatory, [α]_D = +66.4°. When boiled with dilute HCI, the solution becomes leavo-rotatory, [α] = −20°. In this process the sucrose molecule breaks into ______.

विकल्प

• L-glucose + D-fructose

• L-glucose + L-fructose

• D-glucose + D-fructose

• D-glucose + L-fructose

Answer 1

Sucrose in water is dextro-rotatory, [α]_D = +66.4°. When boiled with dilute HCI, the solution becomes leavo-rotatory, [α] = −20°. In this process the sucrose molecule breaks into D-glucose + D-fructose.

Explanation:

When sucrose is hydrolyzed (boiled with dilute HCl), it breaks down into equal parts of D-glucose and D-fructose. While sucrose is dextrorotatory (+66.4°), the resulting mixture contains D-glucose (+52.7°) and D-fructose (−92.4°). Because the levorotatory (left-turning) effect of fructose is stronger than the dextrorotatory (right-turning) effect of glucose, the overall net rotation of the solution changes from positive to negative. This phenomenon is why the process is famously called the inversion of sugar.

\[\ce{\underset{\underset{(α)_D = 66.4^\circ}{Cane sugar}}{C12H22O11} + H2O \overset{HCl}{->} \underset{\underset{(α)_D = +52.5}{D-glucose}}{C6H12O6} + \underset{\underset{(α)_D = -92.4^\circ}{D-fructose}}{C6H12O6}}\]