Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following statements about sucrose. 1\. hydrolysis of sucrose with dilute acid yields an equimolar mixture of D-glucose and D-fructose 2\. acid hydrolysis of sucrose is accompanied by a change in optical rotation 3\. in sucrose, the glycosidic linkage is between C-1 of glucose and \(\mathrm{C}-2\) of fructose 4\. aqueous solution of sucrose exhibits mutarotation Which of the statements are correct? (a) 1 and 2 only (b) 2 and 3 only (c) 1,2 and 3 (d) 1,3 and 4

Step-by-Step Solution

Answer

(c) 1, 2, and 3 are correct.

Step 1: Understanding Sucrose Hydrolysis

Sucrose, when hydrolyzed with a dilute acid, breaks down into its constituent sugars - D-glucose and D-fructose. Both these products are formed in equal amounts, making statement 1 true.

Step 2: Optical Rotation Change

During acid hydrolysis of sucrose, the optical rotation changes because sucrose breaks down into glucose and fructose, which have different optical activities. Thus, statement 2 is also true.

Step 3: Analyzing Glycosidic Linkage

In sucrose, the glycosidic linkage is indeed between the C-1 atom of glucose and the C-2 atom of fructose, confirming statement 3 as true.

Step 4: Evaluating Mutarotation in Sucrose

Sucrose does not undergo mutarotation in aqueous solution because it doesn't have a free anomeric carbon that can equilibrate between alpha and beta forms, unlike glucose and fructose individually or other simple sugars. Therefore, statement 4 is false.

Step 5: Consolidation and Selection

With statements 1, 2, and 3 being true and 4 false, the combination of correct statements corresponds to option (c) 1, 2, and 3.

Key Concepts

Optical Rotation

Optical rotation refers to the ability of chiral molecules to rotate the plane of polarized light. When a substance like sucrose is dissolved in a solution, it interacts with light in a unique way. This ability is measured using a device called a polarimeter.

• Chiral molecules are those that cannot be superimposed on their mirror image. Examples include glucose and fructose, which are the products of sucrose hydrolysis.
• Sucrose itself has an optical rotation, the value of which changes during hydrolysis because its breakdown products, glucose and fructose, have different optical properties.

The measurement of this change in optical rotation helps in understanding the chemical reactions involving solutions, such as verifying the breakdown of sucrose.

Glycosidic Linkage

A glycosidic linkage is a type of covalent bond that joins carbohydrate molecules together. It connects one sugar molecule to another, or to another type of molecule. This bond is essential for forming disaccharides like sucrose.

• In sucrose, the glycosidic linkage occurs specifically between the C-1 atom of glucose and the C-2 atom of fructose.
• This linkage is complex and requires an enzymatic reaction for formation and cleavage, highlighting its strength and biological importance.

Understanding glycosidic linkages can provide insights into the stability and reactivity of different sugar molecules, their role in energy storage, and their breakdown during digestion.

Mutarotation

Mutarotation is a phenomenon observed in carbohydrates where there is a change in the optical rotation as the solution equilibrates between different anomeric forms. This is common in carbohydrates that have a free anomeric carbon.

• Glucose and fructose exhibit mutarotation because they can cyclize and form different anomeric forms with varying optical rotations.
• Sucrose, however, does not show mutarotation as it is a non-reducing sugar. Its glycosidic linkage connects the anomeric carbons of glucose and fructose, preventing the necessary equilibrium.

Understanding mutarotation is key for evaluating the behavior of sugar solutions and their interactions in biological and chemical processes.