Esters and Ethers from Monosaccharides

Draw the most stable chair conformation of a-o-mannopyranose. 

Solution Recall from Example 16.3 that o-mannose differs from D-glucose only at C-2. Using the cyclic structure at the left of eq. 16.6 as a guide, we can write 

PROBLEM 16.8 o-Galactose differs from o-glucose only in the configuration at C-4. Draw the most stable chair conformation of -o-galactopyranose. 

Now that we have described the structures of monosaccharides, let us examine some of their common reactions. 

Monosaccharides contain hydroxyl groups. It is not surprising, then, that they undergo reactions typical of alcohols. For example, they can be converted to esters by reaction with acid halides or anhydrides. The conversion of)3-D-glucose to its pentaacetate by reaction with excess acetic anhydride is typical all five hydroxyl groups, including the hydroxyl at the anomeric C-1, are esterified. (To clarify the structure, the ring H s are omitted.) 

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