Question

Sucrose in water is dextrorotatoiy, $[\alpha]_D$ =+ 66.4$^{\circ}$ when boiled with dil. HCl, the solution becomes leavo rotatory, $[\alpha]_D$ = - 39.9$^{\circ}$. In this process the sucrose breaks into

• A. L-glucose + D-fructose
• B. L-glucose + L-fructose
• C. D-glucose + D-fructose
• D. D-glucose + L-fructose

Answer 1

Answer: (C)

D-glucose + D-fructose

Answer 2

The aqueous solution of sucrose is dextrorotatory having $[\alpha]_D$ = + 66.4$^{\circ}$. On hydrolysis with dilute acids or enzyme invertase, cane sugar (sucrose) gives equimolar mixture of D-(+)-glucose and D-(-)-fructose .
So, sucrose is dextrorotatory but after hydrolysis gives dextrorotatory glucose and laevorotatory se. D-(-)-fructose has a greater specific i than D-(+)-glucose. Therefore, the resultant solution is laevorotatory in nature with specific rotation of -39.9$^{\circ}$.