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Chapter 28: Problem 55

The term "epimer" is used to describe diastereomers that differ in the configuration about a single carbon atom. Which pairs of the eight possible aldopentoses are epimers?

Short Answer

Expert verified
The pairs of epimers among the eight possible aldopentoses are (D-arabinose, D-ribose), (D-xylose, D-lyxose), (D-allose, D-glucose), and (D-altrose, D-mannose).

Step by step solution

01

Determine the Structure of Aldopentoses

Each of the eight aldopentoses can exist in D- and L- forms but here you only need to consider D-forms. \ - D-arabinose: HOCH2(CHOH)3CHO \ - D-xylose: HOCH2(CHOH)2CHOHCHO \ - D-lyxose: HOCH2CHOH(CHOH)2CHO \ - D-ribose: HOCH2CHOH(CHOH)CHOHCHO \ - D-allose: HOCH2CHOHCHOH(CHOH)2CHO \ - D-altrose: HOCH2CHOHCHOHCHOHCHO \ - D-glucose: HOCH2CHOHCHOH(CHOH)CHOHCHO \ - D-mannose: HOCH2CHOHCHOHCHOH(CHOH)2CHO
02

Identify Epimers

Now check the configurations of each aldopentose to see which pairs differ in the configuration of only one carbon atom. After analyzing each pair, the pairs of epimers are (D-arabinose, D-ribose), (D-xylose, D-lyxose), (D-allose, D-glucose), and (D-altrose, D-mannose)
03

Checking Understanding

Check your understanding by making sure that each pair of identified aldopentoses indeed differ only in the configuration of a single stereogenic carbon.

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