Editing Hexose (section)

==Classification==
===Aldohexoses===
The aldohexoses are a subclass of the hexoses which, in the linear form, have the carbonyl at carbon 1, forming an [[aldehyde]] derivative with structure {{chem2|H\sC(\dO)\s(CHOH)5\sH}}.<ref name=lind2007>{{cite book |title=Essentials of Carbohydrate Chemistry and Biochemistry |author=Thisbe K. Lindhorst |authorlink=Thisbe Lindhorst |publisher=Wiley-VCH |edition=1 |year=2007 |isbn=3-527-31528-4}}</ref><ref name=robyt1997>{{cite book |title=Essentials of Carbohydrate Chemistry |publisher=Springer |author=John F. Robyt |edition=1 |year=1997 |isbn=0-387-94951-8}}</ref>  The most important example is [[glucose]].

In linear form, an aldohexose has four [[chiral centre]]s, which give 16 possible aldohexose [[stereoisomer]]s (2<sup>4</sup>), comprising 8 pairs of [[enantiomer]]s.  The linear forms of the eight {{sc|D}}-aldohexoses, in the [[Fischer projection]], are

<gallery>
File:DAllose Fischer.svg | <div align="center">{{sc|D}}-[[Allose]]<br />000</div>
File:DAltrose Fischer.svg | <div align="center">{{sc|D}}-[[Altrose]]<br />001</div>
File:DGlucose Fischer.svg | <div align="center">{{sc|D}}-[[Glucose]]<br />010</div>
File:Mannose.svg | <div align="center">{{sc|D}}-[[Mannose]]<br />011</div>
File:DGulose Fischer.svg | <div align="center">{{sc|D}}-[[Gulose]]<br />100</div>
File:DIdose Fischer.svg | <div align="center">{{sc|D}}-[[Idose]]<br />101</div>
File:DGalactose Fischer.svg | <div align="center">{{sc|D}}-[[Galactose]]<br />110</div>
File:DTalose Fischer.svg | <div align="center">{{sc|D}}-[[Talose]]<br />111</div>
</gallery>

Of these {{sc|D}}-isomers, all except {{sc|D}}-altrose occur in living organisms, but only three are common: {{sc|D}}-glucose, {{sc|D}}-galactose, and {{sc|D}}-mannose. The {{sc|L}}-isomers are generally absent in living organisms; however, {{sc|L}}-altrose has been isolated from strains of the bacterium ''[[Butyrivibrio fibrisolvens]]''.<ref>{{Ref patent
 |country=US |number=4966845 |title=Microbial production of {{sc|L}}-altrose |invent1=Stack; Robert J. |status= patent |gdate=1990-10-30
|assign1=Government of the United States of America, Secretary of Agriculture
 |class=}}</ref>

When drawn in this order, the Fischer projections of the {{sc|D}}-aldohexoses can be identified with the 3-digit [[binary number]]s from 0 to 7, namely 000, 001, 010, 011, 100, 101, 110, 111.  The three [[bit]]s, from left to right, indicate the position of the hydroxyls on carbons 4, 3, and 2, respectively: to the right if the bit value is 0, and to the left if the value is 1.

The chemist [[Hermann Emil Fischer|Emil Fischer]] is said{{citation needed|date=July 2020}} to have devised the following [[mnemonic]] device for remembering the order given above, which corresponds to the configurations about the chiral centers when ordered as 3-bit binary strings:
:'''All''' '''altr'''uists '''gl'''adly '''ma'''ke '''gu'''m '''i'''n '''gal'''lon '''ta'''nks.
referring to '''all'''ose, '''altr'''ose, '''gl'''ucose, '''ma'''nnose, '''gu'''lose, '''i'''dose, '''gal'''actose, '''ta'''lose.

The Fischer diagrams of the eight {{sc|L}}-aldohexoses are the mirror images of the corresponding {{sc|D}}-isomers; with all hydroxyls reversed, including the one on carbon 5.

===Ketohexoses===
A ketohexose is a [[ketone]]-containing hexose.<ref name=lind2007/><ref name=robyt1997/><ref name=orch1980>{{cite book | title = The vocabulary of organic chemistry | editor = Milton Orchin | publisher = Wiley | year = 1980 | isbn = 978-0-471-04491-8 | url-access = registration | url = https://archive.org/details/vocabularyoforga0000unse }}</ref> 
The important ketohexoses are the 2-ketohexoses, and the most important 2-ketose is [[fructose]].

Besides the 2-ketoses, there are only the 3-Ketoses, and they do not exist in nature, although at least one 3-ketohexose has been synthesized, with great difficulty.

In the linear form, the 2-ketohexoses have three chiral centers and therefore  eight possible stereoisomers (2<sup>3</sup>), comprising four pairs of enantiomers.  The four {{sc|D}}-isomers are:

<gallery>
File:DPsicose Fischer.svg | <div align="center">{{sc|D}}-[[Psicose]]<ref name=pub-D-psicose>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/D-Psicose#section=Names-and-Identifiers|title={{sc|D}}-Psicose|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2018-04-26}}</ref></div>
File:D-Fructose.svg | <div align="center">{{sc|D}}-[[Fructose]]<ref name=pub-fructose>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/5984#section=Top|title=Fructose|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2018-04-26}}</ref></div>
File:DSorbose Fischer.svg | <div align="center">{{sc|D}}-[[Sorbose]]<ref name=pub-sorbose>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/107428#section=Top|title=Sorbose, {{sc|D}}-|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2018-04-26}}</ref></div>
File:DTagatose Fischer.svg | <div align="center">{{sc|D}}-[[Tagatose]]<ref name=pub-tagatose>{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/92092#section=Top|title=Tagatose|last=Pubchem|website=pubchem.ncbi.nlm.nih.gov|language=en|access-date=2018-04-26}}</ref></div>
</gallery>

The corresponding {{sc|L}} forms have the hydroxyls on carbons 3, 4,and 5 reversed.  Below are
depiction of the eight isomers in an alternative style:

<gallery>
File:Psicose.png | <div align="center">{{sc|D}}-[[Psicose]]</div>
File:D-fructose CASCC.png | <div align="center">{{sc|D}}-[[Fructose]]</div>
File:D-sorbose.png | <div align="center">{{sc|D}}-[[Sorbose]]</div>
File:Tagatose.png | <div align="center">{{sc|D}}-[[Tagatose]]</div>
</gallery>
<gallery>
File:L-psicose.png | <div align="center">{{sc|L}}-[[Psicose]]</div>
File:L-fructose.png | <div align="center">{{sc|L}}-[[Fructose]]</div>
File:Sorbose.png | <div align="center">{{sc|L}}-[[Sorbose]]</div>
File:L-tagatose.png | <div align="center">{{sc|L}}-[[Tagatose]]</div>
</gallery>