Ketose

In organic chemistry, a ketose is a monosaccharide containing one ketone (>C=O) group per molecule.

[3] Ketoses that are bound into glycosides, for example in the case of the fructose moiety of sucrose, are nonreducing sugars.

[3] Ketoses and aldoses can be chemically differentiated through Seliwanoff's test, where the sample is heated with acid and resorcinol.

[4] The test relies on the dehydration reaction which occurs more quickly in ketoses, so that while aldoses react slowly, producing a light pink color, ketoses react more quickly and strongly to produce a dark red color.

All ketoses listed here are 2-ketoses, in other words, the carbonyl group is on the second carbon atom from the end:

Fructose , an example of a ketose. The ketone group is the double-
bonded oxygen.
Family tree of D -ketoses up to hexoses: dihydroxyacetone (1); D -erythrulose (2); D -ribulose (3a); D -xylulose (3b); D -psicose (4a); D -fructose (4b); D -sorbose (4c); D -tagatose (4d)