Parent monosaccharides are polyhydroxy aldehydes H[CH(OH)]nC(2O)H or polyhydroxy ketones H1[CHOH]n1C(2O)[CHOH]m1H with three or more carbon atoms. The generic term 'monosaccharide' (as opposed to oligosaccharide or polysaccharide) denotes a single unit, without glycosidic connection to other such units. It includes aldoses, dialdoses, aldoketoses, ketoses and diketoses, as well as deoxy sugars, provided that the parent compound has a (potential) carbonyl group.
Any member of the class of organooxygen compounds that is a polyhydroxy-aldehyde or -ketone or a lactol resulting from their intramolecular condensation (monosaccharides); substances derived from these by reduction of the carbonyl group (alditols), by oxidation of one or more hydroxy groups to afford the corresponding aldehydes, ketones, or carboxylic acids, or by replacement of one or more hydroxy group(s) by a hydrogen atom; and polymeric products arising by intermolecular acetal formation between two or more such molecules (disaccharides, polysaccharides and oligosaccharides). Carbohydrates contain only carbon, hydrogen and oxygen atoms; prior to any oxidation or reduction, most have the empirical formula Cm(H2O)n. Compounds obtained from carbohydrates by substitution, etc., are known as carbohydrate derivatives and may contain other elements. Cyclitols are generally not regarded as carbohydrates.