Question

In a diabetic some glucose is converted to sorbitol, an alcohol that accumulates in the eye and can cause cataracts. Draw the open-chain structure of sorbitol, which is identical to that of D-glucose except that the aldehyde group has been reduced to an alcohol group. Can sorbitol form a five- or six-membered cyclic hemiacetal? Explain why or why not. (Hint: The open-chain structure of glucose is found in Section 20.1.)

Name: Problem 15, Chapter 22: Fundamentals of General, Organic, and Biological Chemistry
Uploaded: 2022-02-25T04:14:45-08:00
Duration: 2 min 35 s
Channel: Vivek Singh

   In a diabetic some glucose is converted to sorbitol, an alcohol that accumulates in the eye and can cause cataracts. Draw the open-chain structure of sorbitol, which is identical to that of D-glucose except that the aldehyde group has been reduced to an alcohol group. Can sorbitol form a five- or six-membered cyclic hemiacetal? Explain why or why not. (Hint: The open-chain structure of glucose is found in Section 20.1.)

Fundamentals of General, Organic, and Biological Chemistry

John McMurry, David… 1st Edition

Chapter 22, Problem 15

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Solved by Expert Vivek Singh

02/25/2022

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Sorbitol, also known as glucitol, is a type of carbohydrate that falls into the category of sugar alcohols. It is commercially used to preserve moisture, provide sweetness, and give texture to products. It also has potential benefits for digestive and oral health. Show more…

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In a diabetic some glucose is converted to sorbitol, an alcohol that accumulates in the eye and can cause cataracts. Draw the open-chain structure of sorbitol, which is identical to that of D-glucose except that the aldehyde group has been reduced to an alcohol group. Can sorbitol form a five- or six-membered cyclic hemiacetal? Explain why or why not. (Hint: The open-chain structure of glucose is found in Section 20.1.)

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Key Concepts

Cyclic Hemiacetal Formation

In sugars, cyclic hemiacetal formation occurs when a carbonyl group (either an aldehyde or a ketone) reacts with a hydroxyl group on the same molecule to form a ring—most commonly a five-membered (furanose) or six-membered (pyranose) ring. This intramolecular reaction requires the presence of a reactive carbonyl group, which acts as an electrophile, enabling the cyclization process that stabilizes the sugar structure.

Functional Group Reduction in Sugars

When a sugar, such as D-glucose, is reduced to form a sugar alcohol like sorbitol, the aldehyde group is converted into an additional hydroxyl group. This reduction removes the essential reactive carbonyl functionality that is necessary for the formation of a cyclic hemiacetal. Consequently, without a carbonyl group to participate in an intramolecular nucleophilic attack, sugars like sorbitol remain in their open-chain form and are unable to form five- or six-membered cyclic hemiacetals.

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