Textbook Question
In the monosaccharide hemiacetal shown below number all the carbon atoms, identify the anomeric carbon atom, and identify it as the α or ß anomer. <IMAGE>
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Ch.20 Carbohydrates
Chapter 20, Problem 20.2
Draw the structures of an aldopentose and a ketohexose.
Verified step by step guidance1
Identify the general structure of an aldopentose: An aldopentose is a monosaccharide with five carbon atoms and an aldehyde group at the first carbon. The general formula is C5H10O5.
Draw the linear structure of an aldopentose: Start with a chain of five carbon atoms. Place an aldehyde group (CHO) at the first carbon. The remaining carbons will have hydroxyl groups (OH) and hydrogen atoms (H) attached.
Identify the general structure of a ketohexose: A ketohexose is a monosaccharide with six carbon atoms and a ketone group at the second carbon. The general formula is C6H12O6.
Draw the linear structure of a ketohexose: Start with a chain of six carbon atoms. Place a ketone group (C=O) at the second carbon. The remaining carbons will have hydroxyl groups (OH) and hydrogen atoms (H) attached.
Ensure correct stereochemistry: For both structures, ensure that the hydroxyl groups are placed in a way that reflects the specific stereochemistry of the sugar, which can vary among different aldopentoses and ketohexoses.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldopentose
An aldopentose is a five-carbon sugar (pentose) that contains an aldehyde group (-CHO) at one end. This structure is characterized by the presence of four hydroxyl groups (-OH) attached to the carbon atoms, which can exist in both linear and cyclic forms. Common examples include ribose and arabinose, which play crucial roles in biological processes such as RNA structure.
Ketohexose
A ketohexose is a six-carbon sugar (hexose) that features a ketone group (C=O) typically located at the second carbon atom. This type of sugar has five hydroxyl groups and can also exist in linear and cyclic forms. Fructose is a well-known example of a ketohexose, and it is significant in metabolism and energy production in living organisms.
Structural Representation of Sugars
The structural representation of sugars involves depicting their molecular structure, which can be shown in linear or cyclic forms. In the linear form, the carbon skeleton is displayed with functional groups, while the cyclic form illustrates how the sugar molecules can form rings through intramolecular reactions. Understanding these representations is essential for studying carbohydrate chemistry and their biological functions.
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Related Practice
Textbook Question
l-Fucose is one of the naturally occurring l monosaccharides. It is present in the short chains of monosaccharides by which blood groups are classified (see the Chemistry in Action “Cell-Surface Carbohydrates and Blood Type” on p. 640). Compare the structure of l-fucose shown in the margin with the structures of α- and ß-d-galactose and answer the following questions.
d. Fucose” is a common name. Is 6-deoxy-l-galactose a correct name for fucose? Why or why not? <IMAGE>
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Textbook Question
Draw the structure of the α and ß anomers that result from the reaction of methanol and ribose. Are these compounds acetals or hemiacetals?
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Textbook Question
Draw the structures of a ketohexose.
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Textbook Question
Identify the following as diastereomers, enantiomers, and/or anomers. (a) ß-d-fructose and
ß-d-fructose (b) d-galactose and l-galactose (c) l-allose and d-glucose (both aldohexoses)
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Textbook Question
Hydrolysis of both glycosidic bonds in the following trisaccharide A, B, C yields three monosaccharides.
c. Draw the Fischer projections for the three monosaccharides.
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