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

Short answer

Option (a) is correct; sucrose is non-reducing due to acetal linkage between anomeric carbons.

Step-by-step solution

Understand the Definition of Non-Reducing Sugar

Non-reducing sugars do not have a free anomeric carbon that can act as a reducing agent. This typically occurs when the anomeric carbons of the sugar molecules are involved in a glycosidic bond.

Analyze the Structure of Sucrose

Sucrose is a disaccharide composed of glucose and fructose. The anomeric carbon of glucose is linked to the anomeric carbon of fructose through a glycosidic bond (1-2 linkage), rendering both anomeric carbons involved in the acetal linkage.

Determine Which Choice Matches the Definition

Option (a) states that both anomeric carbon atoms in sucrose form an acetal linkage. This means neither anomeric carbon is free to react as a reducing agent, classifying sucrose as a non-reducing sugar.

Analyze the Incorrect Options

Option (b) references an \( \alpha \)-hydroxy keto group, which is not relevant to the reducing properties. Option (c) mentions equal amounts of \( \mathrm{D}(+) \) glucose and \( \mathrm{D}(-) \) fructose, which refers to its composition not reducing capabilities. Option (d) refers to hydrolysis, not the inherent nature of the bond in sucrose.

Key concepts

Anomeric Carbon

In carbohydrate chemistry, an anomeric carbon is a pivotal point. It is the carbon atom in a sugar molecule that is connected to two oxygen atoms. This specific carbon is involved in forming the ring structure of the sugar. When the carbohydrate forms a ring, the anomeric carbon becomes a fresh center where the structural designation of alpha (\(\alpha\)) or beta (\(\beta\)) takes place.
In the context of sugars, this carbon can either be free to participate in reactions or locked in a bond. An anomeric carbon becomes free when it is not bound in a glycosidic linkage and can participate in oxidation reactions. However, when it forms a glycosidic bond, it is not available for such reactions, making the sugar non-reducing.

The role of anomeric carbons is crucial in determining the reducing capabilities of sugars. In sucrose, both the anomeric carbons from glucose and fructose are involved in a glycosidic bond, meaning neither is free, rendering sucrose a non-reducing sugar.

Sucrose Structure

Sucrose is one of the most well-known sugars, commonly referred to as table sugar. It is a disaccharide, meaning it is composed of two monosaccharides: glucose and fructose.
Sucrose’s structure involves these two sugars linked together. Specifically, the link is between the anomeric carbon of glucose and the anomeric carbon of fructose. This linkage is a result of a glycosidic bond.
Due to this connection, both the glucose and fructose components have their anomeric carbons involved in the bonding. This characteristic of the structure ensures that the sugar is non-reducing. Its inability to open and present a free anomeric carbon makes it stable and less reactive than reducing sugars.
By analyzing this structure, one can understand why sucrose doesn’t participate in typical redox reactions that involve the reducing end of sugar molecules.

Glycosidic Bond

The glycosidic bond is a type of covalent bond that fundamentally connects two sugar molecules, forming disaccharides or even larger carbohydrates through polymerization.
In sucrose, this bond specifically links the anomeric carbon of glucose, which is \(\alpha\)-D-glucopyranose, to the anomeric carbon of \(\beta\)-D-fructofuranose. This particular bond is referred to as an \(\alpha\)1-\(\beta\)2-glycosidic linkage, highlighting both the configuration positions of the carbons involved.

Forming a glycosidic bond alters the chemical properties of the sugars significantly. Once formed, the bond locks the sugar, preventing the opening of their rings and making their anomeric carbons unavailable for further chemical reactions, except for hydrolysis.

• Glycosidic bonds can be hydrolyzed through acidic environments or specific enzymes. In sucrose, breaking this bond results in equal parts glucose and fructose.

Understanding glycosidic bonds is crucial, as they are key to the structure and function of carbohydrates in biological systems.