Question

$D-$Fructose is the sweetest monosaccharide. How does the Fischer projection of $\mathrm{D}$-fructose differ from that of D-glucose?

Short answer

$D-$glucose is an aldohexose, whereas$D-$fructose is a ketohexose.

Step-by-step solution

Introduction

In this task, we must describe the structural difference between$D-$fructose and $D-$glucose (in Fischer projections).

Explanation

• Aldohexose and ketohexose, for example, are monosaccharides with six carbons.
• The aldehyde group is present in aldohexoses, whereas the ketone group is present in ketohexoses.
• $D-$fructose, a ketohexose, and$D-$glucose, an aldohexose, are the sugars in this example.

Draw the of  D-fructose from D-glucose. 

• This indicates that the distinction is between the first two carbons, which contain carbonyl groups (marked in blue in the Figure below).
• D-glucose has four stereogenic centres and an aldehyde group, whereas D-fructose has three stereogenic centres and a ketone group.
• The rest of the molecule is identical except for the first two carbons.