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

The Correct Option is C

Sucrose is a disaccharide composed of one molecule of glucose and one molecule of fructose. It is naturally dextrorotatory, meaning it rotates plane-polarized light to the right, with a specific optical rotation of [\alpha]_D = +66.4^\circ.

When sucrose is hydrolyzed by boiling with dilute hydrochloric acid (HCl), it undergoes inversion, where it breaks down into its constituent monosaccharides:

• D-glucose: a dextrorotatory monosaccharide.
• D-fructose: a levorotatory monosaccharide with a much stronger levorotatory effect than glucose's dextrorotatory effect.

Although D-glucose itself is dextrorotatory, the combined solution becomes levorotatory because [\alpha]_D of D-fructose (-92^\circ) is significantly more negative than that of D-glucose (+52.7^\circ), causing the net rotation to be to the left, with [\alpha]_D = -39.9^\circ.

This process is called inversion due to the change from dextrorotation to levorotation upon hydrolysis.

The correct answer is both D-glucose and D-fructose as both are involved in the reaction. Therefore, the correct answer is: D-glucose + D-fructose.