Hexose

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In organic chemistry, a hexose is a monosaccharide with six carbon atoms having the chemical formula C₆H₁₂O₆. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2.

Aldohexoses

The aldohexoses have four chiral centres for a total of 16 possible aldohexose stereoisomers (2⁴). The D/L configuration is based on the orientation of the hydroxyl at position 5, and does not refer to the direction of optical activity. The eight D-aldohexoses are:

   CH=O           CH=O          CH=O            CH=O
   |              |             |               |
  HC-OH        HO-CH           HC-OH         HO-CH
   |              |             |               |
  HC-OH          HC-OH       HO-CH           HO-CH
   |              |             |               |
  HC-OH          HC-OH         HC-OH           HC-OH
   |              |             |               |
  HC-OH          HC-OH         HC-OH           HC-OH
   |              |             |               |
   CH2OH          CH2OH         CH2OH           CH2OH 
 D-Allose       D-Altrose     D-Glucose       D-Mannose

   CH=O         CH=O            CH=O            CH=O
   |            |               |               |
  HC-OH      HO-CH             HC-OH         HO-CH
   |            |               |               |
  HC-OH        HC-OH         HO-CH           HO-CH
   |            |               |               |
HO-CH        HO-CH           HO-CH           HO-CH
   |            |               |               |
  HC-OH        HC-OH           HC-OH           HC-OH
   |            |               |               |
   CH2OH        CH2OH           CH2OH           CH2OH 
 D-Gulose     D-Idose         D-Galactose     D-Talose

Of these D isomers all, except altrose, are naturally occurring. L-altrose has been isolated from strains of the bacterium Butyrivibrio fibrisolvens.^[1]

A mnemonic (attributed to Louis Fieser) often employed to remember the eight aldohexoses is "all altruists gladly make gum in gallon tanks".

Ketohexoses

The ketohexoses have 3 chiral centres and therefore eight possible stereoisomers (2³). Of these, only the four D-isomers are known to occur naturally:

  CH2OH        CH2OH         CH2OH        CH2OH 
  |            |             |            |
  C=O          C=O           C=O          C=O
  |            |             |            |
 HC-OH      HO-CH           HC-OH      HO-CH
  |            |             |            |
 HC-OH        HC-OH       HO-CH        HO-CH
  |            |             |            |
 HC-OH        HC-OH         HC-OH        HC-OH
  |            |             |            |
  CH2OH        CH2OH         CH2OH        CH2OH 
D-psicose    D-fructose    D-sorbose    D-tagatose

Only the naturally occurring hexoses are capable of being fermented by yeasts.

Mutarotation

The aldehyde and ketone functional groups in these carbohydrates react with neighbouring hydroxyl functional groups to form intramolecular hemiacetals or hemiketals, respectively. The resulting ring structure is related to pyran, and is termed a pyranose. The ring spontaneously opens and closes, allowing rotation to occur about the bond between the carbonyl group and the neighbouring carbon atom, yielding two distinct configurations (α and β). This process is termed mutarotation. Hexose sugars can form dihexose sugars with a condensation reaction to form a 1,6-glycosidic bond.

Other Information

It is a weak acid and a weak electrolyte.^{[citation needed]}

References

See also

• Triose
• Tetrose
• Pentose
• Heptose
• Glucose

v • d • e Types of Carbohydrates
General:	Aldose | Ketose | Pyranose | Furanose
Geometry	Triose | Tetrose | Pentose | Hexose | Heptose | Cyclohexane conformation | Anomer | Mutarotation
Small/Large	Glyceraldehyde | Dihydroxyacetone | Erythrose | Threose | Erythrulose | Sedoheptulose
Trioses	Ketotriose (Dihydroxyacetone) | Aldotriose (Glyceraldehyde)
Tetroses	Erythrulose | Erythrose | Threose
Pentoses	Arabinose | Deoxyribose | Lyxose | Ribose | Ribulose | Xylose | Xylulose
Hexoses	Glucose | Galactose | Mannose | Gulose | Idose | Talose | Allose | Altrose | Fructose | Sorbose | Tagatose | Psicose | Fucose | Fuculose | Rhamnose
Disaccharides	Sucrose | Lactose | Trehalose | Maltose
Polymers	Glycogen | Starch (Amylose | Amylopectin) | Cellulose | Chitin | Stachyose | Inulin | Dextrin
Glycosaminoglycans	Heparin | Chondroitin sulfate | Hyaluronan | Heparan sulfate | Dermatan sulfate | Keratan sulfate
Aminoglycosides	Kanamycin | Streptomycin | Tobramycin | Neomycin | Paromomycin | Apramycin | Gentamicin | Netilmicin | Amikacin
Major families of biochemicals
Peptides | Amino acids | Nucleic acids | Carbohydrates | Nucleotide sugars | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides
Analogues of nucleic acids:		Analogues of nucleic acids:

be-x-old:Гексозы

da:Hexose de:Hexoseneo:Heksozo fr:Hexose it:Esoso nl:Hexosesv:Hexos uk:Гексози

Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .