Monosaccharide
From Freepedia
Monosaccharides, sometimes misspelled monosacharides, are carbohydrates in the form of simple sugars. Monosaccharides are usually colorless, water soluble crystalline solids. Some monosaccharides have a sweet taste.
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 different chemical and physical properties.
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Structure
With few exceptions (e.g. deoxyribose), monosaccharides have the empirical chemical formula:
- (CH2O)n
Monosaccharides contain either a ketone or aldehyde functional group, and hydroxyl groups on most or all of the non-carbonyl carbon atoms.
Cyclic structure
Most monosaccharides form cyclic structures, which predominate in aqueous solution, by forming hemiacetals or hemiketals (depending on whether they are aldoses or ketoses) with themselves. Glucose, for example, forms a hemiacetal linkage between its Carbon 1 and the hydroxyl group of its Carbon 5. Since such a reaction introduces an additional chiral center, two anomers are formed from earesenting the cyclic structure of monosaccharides is the Haworth projection.
Isomerism
The total number of possible stereoisomers of one compound (n) is dependent on the number of chiral centers (c) in the molecule: n = 2c.
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Monosaccharides are classified by the number of carbon atoms they contain:
- Triose, 3 carbon atoms
- Tetrose, 4 carbon atoms
- Pentose, 5 carbon atoms
- Hexose, 6 carbon atoms
- Heptose, 7 carbon atoms
Monosaccharides are classified the type of keto group they contain:
All these classifications can be combined, resulting in names like D-aldohexose or ketotriose.
Monosaccharides are classified according to their configuration at carbon 2:
- D or d, configuration like in D-glyceraldehyde
- L or l, configuration like in L-glyceraldehyde
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List of polysaccharides
This is a list of some common monosaccharides, not all are found in nature - some have been synthesised:
- Trioses: glyceraldehyde and dihydroxyacetone
- Tetroses: erythrose threose
- Pentoses:
- Hexoses:
- Heptoses:
- Keto-heptoses: mannoheptulose, sedoheptulose
Reactions
- Formation of acetals.
- Formation of hemiacetals and hemiketals.
- Formation of ketals.
