Multiple Choice
Which sugar is an enantiomer of sugar A? How many stereoisomers does sugar A have?
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9. Carbohydrates
Stereochemistry of Monosaccharides
Multiple Choice
Use the Fischer projections of the four monosaccharides below to answer the next two problems (A & B).
A) The term that best describes the relationship of all four sugars to each other is:
a) Diastereomers.
b) Enantiomers.
c) Epimers.
A
Diastereomers
B
Enantiomers
C
Epimers
Verified step by step guidance1
Identify the configuration of each chiral center in the Fischer projections of the four monosaccharides. This involves looking at the orientation of the hydroxyl (OH) groups on each carbon atom.
Compare the configurations of the chiral centers between each pair of sugars. Determine if they are mirror images (enantiomers) or if they differ at one or more chiral centers (diastereomers or epimers).
Recall that enantiomers are non-superimposable mirror images and have opposite configurations at all chiral centers. Diastereomers are not mirror images and differ at one or more chiral centers. Epimers differ at only one chiral center.
Examine the highlighted chiral centers in the image. Notice that the sugars differ at more than one chiral center, which suggests they are not enantiomers or epimers.
Conclude that the relationship between the four sugars is best described as diastereomers, as they differ at multiple chiral centers but are not mirror images of each other.
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