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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: 9780137566471당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Mullins 1st EditionCh. 27 - Carbohydrates, Nucleic Acids, and Lipids문제 69
26장, 문제 69

Upon dissolving α-D-glucose or β-D-glucose in water, the specific rotation gradually changes, eventually reaching +52.6° for both solutions. Explain what is happening here.

검증된 단계별 안내
1
Understand the concept of mutarotation: Mutarotation is the change in the optical rotation of a solution due to the interconversion between different anomers of a sugar (α and β forms) in aqueous solution. This occurs because the sugar exists in equilibrium between its cyclic and open-chain forms.
Recognize the structure of α-d-glucose and β-d-glucose: Both are cyclic forms of glucose, differing in the orientation of the hydroxyl group (-OH) on the anomeric carbon (C1). In α-d-glucose, the -OH group is on the opposite side of the ring relative to the CH2OH group, while in β-d-glucose, the -OH group is on the same side as the CH2OH group.
Describe the equilibrium process: When α-d-glucose or β-d-glucose is dissolved in water, the cyclic forms open up to form the linear chain structure. The linear chain then closes back into cyclic forms, allowing interconversion between the α and β anomers. This process establishes an equilibrium mixture of α-d-glucose, β-d-glucose, and a small amount of the open-chain form.
Explain the change in specific rotation: The specific rotation of a solution depends on the proportions of the α and β anomers present. Initially, the specific rotation reflects the predominant form (α or β) in the solution. As equilibrium is reached, the specific rotation stabilizes at +52.6°, which corresponds to the equilibrium mixture of α-d-glucose and β-d-glucose in water.
Conclude with the significance of the equilibrium: The final specific rotation of +52.6° is a characteristic property of the equilibrium mixture of α-d-glucose and β-d-glucose in water. This demonstrates the dynamic nature of mutarotation and the ability of glucose to interconvert between its anomeric forms in aqueous solution.

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주요 개념

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Anomeric Effect

The anomeric effect refers to the preference of certain anomers (α and β forms of sugars) to adopt specific conformations in solution. In the case of glucose, the α and β anomers can interconvert in water, leading to a mixture of both forms. This phenomenon affects the optical rotation of the solution as the equilibrium shifts between the two anomers.
추천 영상:
가이드 코스
2:02
Directing Effects in Substituted Pyrroles, Furans, and Thiophenes Concept 1

Optical Activity

Optical activity is the ability of a substance to rotate the plane of polarized light. This property is significant in carbohydrates like glucose, where the specific rotation is a measure of how much the light is rotated by a solution of the sugar. The specific rotation can change as the concentration of different anomers in solution varies, reflecting the dynamic equilibrium between them.
추천 영상:
08:17
Mutorotation and Optical Activity

Mutarotation

Mutarotation is the process by which the optical rotation of a sugar solution changes over time as the anomers interconvert. For glucose, this involves the conversion between α-d-glucose and β-d-glucose in water, leading to a gradual change in specific rotation until it stabilizes at a constant value. This process is crucial for understanding the behavior of sugars in solution.
추천 영상:
03:06
Mechanism
관련 실천
교과서 질문

Starting with a Fischer projection of d-glucose (and other sugars), switch only the stereocenter that gave it the designation of d. What new sugar have you made? [Hint: The answer is not l-glucose.]

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교과서 질문

Suggest a mechanism by which TXB2 might be formed from TXA2 in an acid-catalyzed hydrolysis reaction. [The structure has been simplified.]

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교과서 질문

(a) Suggest an arrow-pushing mechanism for the mutarotation of α-d-glucose to β-d-glucose in the presence of acid. Acid isn’t necessary, but it does increase the rate of the process.

(b) What is the role of acid in your mechanism?

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교과서 질문

The α- and β-anomers of glucose are shown here.

In solution, these two epimers can interconvert through a process called mutarotation. What is the ratio of anomers (α:β) when the specific rotation is +52.6°

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교과서 질문

The α- and β-anomers of glucose are shown here. In solution, these two epimers can interconvert through a process called mutarotation.

Given that α-D-glucose has a specific rotation of + 112.2° , why is the specific rotation of β-D-glucose not -112.2°? What molecule would have a specific rotation of -112.2°?

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교과서 질문

Is the compound d or l?

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