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. Ketoses can isomerize to aldoses through the Lobry-de Bruyn-van Ekenstein transformation.
Examples of ketoses
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)
All ketoses listed here are 2-ketoses, in other words, the carbonyl group is on the second carbon atom from the end: