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Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 27 - Carbohydrates, Nucleic Acids, and LipidsProblem 39b
Chapter 26, Problem 39b

In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.
(b) Structural representation of disaccharides showing sugar linkages and hydroxyl groups.

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Identify the reducing end of the sugar: Look for the anomeric carbon that is not involved in a glycosidic bond. In the given disaccharide, the reducing end is the one with a free anomeric carbon, which is typically the hemiacetal or hemiketal group.
Determine the monosaccharides: Examine the structure to identify the two monosaccharide units. In this disaccharide, the first monosaccharide is glucose, as indicated by the presence of the six-membered ring with hydroxyl groups in the equatorial positions. The second monosaccharide is fructose, which is a five-membered ring with a ketone group.
Identify the type of glycosidic linkage: Look at the oxygen bridge connecting the two monosaccharides. The linkage is between the anomeric carbon of the first sugar and the hydroxyl group of the second sugar. In this case, it is a β(1→2) glycosidic linkage, as the oxygen bridge is formed between the first carbon of glucose and the second carbon of fructose.
Verify the orientation of the glycosidic bond: The bond is β if the oxygen bridge is above the plane of the sugar ring, and α if it is below. In this structure, the glycosidic bond is β because the oxygen is above the plane of the glucose ring.
Summarize the findings: The disaccharide consists of glucose and fructose linked by a β(1→2) glycosidic bond, with the reducing end being the free anomeric carbon on the fructose unit.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reducing and Non-reducing Sugars

Reducing sugars are carbohydrates that can donate electrons to other molecules, typically due to the presence of a free aldehyde or ketone group. In disaccharides, the reducing end is the monosaccharide unit that retains this reactive group, allowing it to participate in redox reactions. Non-reducing sugars, on the other hand, have their reactive groups involved in glycosidic linkages, preventing them from acting as reducing agents.
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Monosaccharide Composition

Disaccharides are formed by the condensation of two monosaccharides, which are the simplest form of carbohydrates. Common examples include glucose, fructose, and galactose. Understanding the specific monosaccharides that combine to form a disaccharide is crucial for identifying its properties and biological functions, as well as for determining its reducing nature.
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Glycosidic Linkage

A glycosidic linkage is a covalent bond that connects two monosaccharides through a dehydration reaction, resulting in the formation of a disaccharide. The type of glycosidic linkage is defined by the specific carbon atoms involved in the bond and the orientation of the hydroxyl groups (α or β). This linkage influences the disaccharide's stability, digestibility, and overall chemical behavior.
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Related Practice
Textbook Question

Identify the product when each of the following reactions is performed on the triglyceride of linoleic acid (linoleate).

(b) H2 , Ni (partial hydrogenation)

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Textbook Question

In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.

(a)

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Textbook Question

Ketohexoses form from aldohexoses. Suggest a mechanism for the acid-catalyzed version of this reaction. What type of reaction is this? [You’ve seen it before.]

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Textbook Question

Maltose, like cellobiose, is composed of two glucose units. What is the difference between maltose and cellobiose?

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Textbook Question

Identify the product when each of the following reactions is performed on the triglyceride of linoleic acid (linoleate).

(a) H2 , Pd

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Textbook Question

Predict the product of each of the following reactions.

(d)

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