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Ch. 20 - The Organic Chemistry of Carbohydrates
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Non è quello che usi tu?Cambia libro di testo
Capitolo 20, Problema 5d

d. What sugar is the C-4 epimer of D-lyxose?

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1
Understand the concept of epimers: Epimers are stereoisomers that differ in the configuration of only one stereogenic center (chiral carbon) while the rest of the molecule remains the same. In this case, we are looking for the C-4 epimer of D-lyxose.
Draw the Fischer projection of D-lyxose: D-lyxose is an aldopentose (a five-carbon sugar with an aldehyde group). Its configuration is as follows: the hydroxyl (-OH) groups on carbons 2, 3, and 4 are arranged as right, left, and left, respectively, in the Fischer projection.
Identify the C-4 carbon: In the Fischer projection of D-lyxose, the C-4 carbon is the fourth carbon from the top (starting from the aldehyde group). The hydroxyl group on this carbon is on the left side.
Change the configuration at C-4: To find the C-4 epimer, invert the configuration of the hydroxyl group at C-4. This means the hydroxyl group on C-4 will now be on the right side instead of the left, while the configurations of all other chiral carbons remain unchanged.
Determine the name of the new sugar: After changing the configuration at C-4, the resulting sugar is D-xylulose. Verify the structure to ensure that only the C-4 configuration has been altered and that the sugar remains an aldopentose.

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Epimers

Epimers are a specific type of diastereomer that differ in configuration at only one stereogenic center. In the context of sugars, this means that two sugars can have the same molecular formula and differ only at one carbon atom's stereochemistry. Understanding epimers is crucial for identifying relationships between different sugars, such as d-lyxose and its epimer.
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Identifying Types of Stereoisomers

D-lyxose

D-lyxose is a five-carbon aldose sugar that is part of the pentose family. It has specific stereochemical configurations at each of its chiral centers, which are essential for its biological function and reactivity. Knowing the structure of d-lyxose helps in determining its epimer by analyzing the configuration at the C-4 position.
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Monosaccharides - D and L Isomerism

Sugar Structure and Configuration

The structure and configuration of sugars are defined by their carbon skeletons and the arrangement of hydroxyl groups around the chiral centers. For d-lyxose, the configuration at C-4 is critical for identifying its epimer. By changing the configuration at this specific carbon, one can derive the C-4 epimer, which is essential for answering the question.
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Reducing Sugars