General Index
D-Ketoses: Configuration
When the carbonyl function is a ketone group, the monosaccharides are called Ketoses.
Glycerone (Dihydroxyacetone), with three carbon atoms (ketotriose) is the simplest ketose:
Glycerone has no asymmetric carbons. Carbons 1 and 3 are equivalent. In Fischer projection:
Next in the ketose series is D-Erythrulose. This and its enantiomer L-Erythrulose, are the Ketotetroses:
This ketotetrose has only one asymmetric carbon, 3, with the same configuration of D-Glyceraldehyde.
There are four possible ketopetoses: D- and L-Ribulose, D- and L-Xilulose. We present the structure of D-Ribulose:
D-Ribulose has two asymmetric carbons, 3 and 4. Both have the same configuration as D-Glyceraldehyde. In the Fischer projection,
D-Fructose is a ketohexose:
In D-Fructose, carbons 4 and 5 have the same configuration as D-glyceraldehyde, while carbon 3 has that of L-Glyceraldehyde. So, carbons 3, 4 and 5 have the same configuration as carbons 3, 4 and 5 in D-Glucose.
In the Fischer projection, we represent D-Fructose as follows: