Aldose

Aldoses can be distinguished from ketoses, which have the carbonyl group away from the end of the molecule, and are therefore ketones.

[1] Examples of aldoses include glyceraldehyde, erythrose, ribose, glucose and galactose.

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

[3] 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.

Aldoses can tautomerize to ketoses in a dynamic process with an enol intermediate (more specifically, an enediol).

Fischer projection of D - glyceraldehyde
Family tree of aldoses: (1) D -(+)-glyceraldehyde; (2a) D -(−)-erythrose; (2b) D -(−)-threose; (3a) D -(−)-ribose; (3b) D -(−)-arabinose; (3c) D -(+)-xylose; (3d) D -(−)-lyxose; (4a) D -(+)-allose; (4b) D -(+)-altrose; (4c) D -(+)-glucose; (4d) D -(+)-mannose; (4e) D -(−)-gulose; (4f) D -(−)-idose; (4g) D -(+)-galactose; (4h) D -(+)-talose