Monosaccharide

Monosaccharides are carbohydrates in the form of simple sugars.

Monosaccharides, crystalline, water soluble and sweet tasting. In solution they rotate plane polarised light.

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 chiral, giving rise to a number of isomeric forms all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but they have differing properties.

The monosaccharides are classified according to the D or L form of their isomerism. This is a list of some of the monosaccharides, not all are found in nature - some have been synthesised.

• trioses: glyceraldehyde and dihydroxyacetone
• tetroses: erythrose threose
• pentoses:
  • as aldo-pentoses:arabinose, lyxose , ribose(and the derived deoxyribose), xylose
  • as keto-pentoses:ribulose, xylulose
• hexoses:
  • as aldo-ketoses: allose , altose , galactose, glucose, gulose , idose , mannose, tagatose
  • as keto-hexoses: fructose
• keto-heptoses: mannoheptulose , sedoheptulose

Contents

1 Physical properties 2 Structure 2.1 Cyclic structure 2.2 Isomerism 3 Nomenclature 4 Reactions 5 See also 6 External links

Physical properties

Colourless, crystalline solids.(sweet)

Structure

With few exceptions (e.g. deoxyribose), they have the empirical chemical 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 number of possible stereo-isomers (n) is dependent on the number of chiral centers (c) in the molecule:- n = 2^c.

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