Monosaccharide

Monosaccharides are carbohydrates in the form of simple sugars.

Monosaccharides, like disaccharides, are sweet, water soluble and crystalline.

Monosaccharides are classified by the number of carbon atoms they contain (triose, tetrose, pentose, hexose and heptose) and by the active group, which is either an aldehyde or a ketone. These are then combined, e.g. aldohexoses, ketotrioses.

Further, each carbon atom that supports a hydroxyl group (except for the first and last) is optically active, allowing a number of different carbohydrates with the same basic structure. For instance, galactose is an aldohexose, but has different properties from glucose because the atoms are arranged differently.

Examples include:

• trioses: glyceraldehyde and dihydroxyacetone
• tetroses: erythrose
• pentoses: lyxose, ribose and deoxyribose
• hexoses : idose, glucose, fructose, and galactose
• heptoses:

Physical properties

Colourless, crystalline solids.

Structure

With a few notable exceptions (e.g. deoxyribose or amino sugars), they have the general structural formula:

(CH₂O)_n

Monosaccharides contain either a ketone or aldehyde functional group.

Cyclic structure

A common way of representing the cyclic structure of monosaccharides is the Haworth projection.

Isomerism

The D,L system is commonly used.

Nomenclature

Monosaccharides containing an aldehyde group are classified as aldoses. Those containing a ketone group are classified as ketoses.

Reactions

1. Formation of acetals.

See also

• Carbohydrate
• Disaccharide
• Oligosaccharide
• Polysaccharide

External links

Nomenclature of Carbohydrates

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