Problem 93 - A Complete Resource Book in Chemistry for JEE Main

Question

Sucrose itself is a non reduction sugar. It is due to (a) the linkage of both the anomeric carbon atoms in an acetal form (b) the presence of \(\alpha\)-hydroxy keto group in its structure (c) the presence of equal amount of \(\mathrm{D}(+)\) glucose and \(\mathrm{D}(-)\) fructose (d) the easy conversion of sucrose into invert sugar on hydrolysis

Step-by-Step Solution

Answer

(a) the linkage of both the anomeric carbon atoms in an acetal form.

Step 1: Analyze the Question

The question asks us to determine why sucrose is classified as a non-reducing sugar. The options given focus on different chemical properties of sucrose.

Step 2: Understand Each Option

(a) Suggests that the linkage involves both anomeric carbons in an acetal form. (b) Mentions an b1-hydroxy keto group, which is not characteristic of sucrose. (c) Discusses the presence of glucose and fructose, but does not pertain to reduction. (d) Involves conversion into invert sugar, which is not directly linked to the non-reducing nature.

Step 3: Focus on Acetal Linkage

Sucrose combines glucose and fructose through their anomeric carbons, forming an acetal linkage. This prevents the compound from opening up into an aldehyde or ketone form, which is necessary for a reducing sugar.

Step 4: Confirm the Correct Option

Given that sucrose's non-reducing nature is due to the acetal linkage of its anomeric carbons, option (a) correctly explains why sucrose is a non-reducing sugar.

Key Concepts

Non-reducing sugars

Non-reducing sugars are carbohydrates that do not have the ability to act as a reducing agent for other compounds. This is due to the absence of free aldehyde or ketone groups when the sugar is in solution. In contrast, reducing sugars like glucose have these groups available, allowing them to participate in redox reactions.
Being a non-reducing sugar means that the sugar cannot revert to an open-chain form with an aldehyde or ketonic functional group. This characteristic is crucial in various biological and chemical applications, as it dictates the sugar's reactivity and stability.

• Sucrose is a primary example of a non-reducing sugar.
• This nature affects the sugar's chemical properties and potential reactions.

Understanding the concept of non-reducing sugars allows us to predict how sucrose will behave in different chemical environments, which is particularly important in fields like food chemistry and biochemistry.

Acetal linkage

An acetal linkage in carbohydrates refers to a bond formed between two sugar molecules via an oxygen atom. This linkage is crucial in determining the properties of the resultant sugar compound. In the case of sucrose, an acetal linkage is formed between the anomeric carbons of glucose and fructose.
This type of covalent bond locks the sugars in a cyclic configuration, prohibiting them from converting back into their aldehyde or ketonic forms. Without the free aldehyde or ketone group, the sugar cannot function as a reducing agent, rendering it non-reducing.

• Acetal linkages are essential in sugars like sucrose due to their stability.
• This linkage involves the C1 carbon of glucose and the C2 carbon of fructose.

By understanding the formation and stability of acetal linkages, we gain insight into why some sugars like sucrose cannot participate in certain reactions, thus affecting their use in various scientific and industrial processes.

Anomeric carbons

Anomeric carbons are critical in understanding the structure and function of carbohydrates. In a carbohydrate molecule, the anomeric carbon is the carbon atom that was the carbonyl carbon (C=O) in the sugar's linear form before it was cyclized. When the sugar forms a ring, this carbon becomes a new chiral center.
In the case of sucrose, anomeric carbons play a crucial role. Sucrose is formed through the linkage of the anomeric carbon of glucose (C1) with the anomeric carbon of fructose (C2). This unique bond formation is essential for its non-reducing nature.

• The presence of anomeric carbons affects the sugar's properties and reactivity.
• They determine whether the sugar is alpha or beta, which can influence its physical and chemical properties.

Understanding anomeric carbons helps explain why specific structural formations impact the chemical behavior of sugars like sucrose.

Hydrolysis of sucrose

The hydrolysis of sucrose is a process through which sucrose is broken down into its constituent sugars, glucose, and fructose. This reaction is typically catalyzed by the enzyme sucrase or by acid under laboratory conditions.
During hydrolysis, the acetal linkage between the glucose and fructose molecules is cleaved. This process converts sucrose into glucose and fructose, which are reducing sugars. The reaction can be represented as:\[\text{Sucrose} + \text{H}_2\text{O} \rightarrow \text{Glucose} + \text{Fructose}\]

• Hydrolysis is crucial for the digestion and metabolism of carbohydrates.
• It results in the conversion of non-reducing sugars into reducing sugars.

This reaction is essential not just biologically but also industrially in the production of invert sugar, often used to enhance sweetness and shelf life in food products.