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Figure 1: Relationship between the acyclic and the cyclic isomers of fructose d - and l-isomers of fructose (open-chain form) Fructose is a 6-carbon polyhydroxyketone. [16] Crystalline fructose adopts a cyclic six-membered structure, called β-d-fructopyranose, owing to the stability of its hemiketal and internal hydrogen-bonding.
In 1897, an unfermentable product obtained by treatment of fructose with bases, in particular lead(II) hydroxide, was given the name glutose, a portmanteau of glucose and fructose, and was claimed to be a 3-ketohexose. [12] [13] However, subsequent studies showed that the substance was a mixture of various other compounds. [13] [14]
A open-chain form of glucose makes up less than 0.02% of the glucose molecules in an aqueous solution at equilibrium. [57] The rest is one of two cyclic hemiacetal forms. In its open-chain form, the glucose molecule has an open (as opposed to cyclic) unbranched backbone of six carbon atoms, where C-1 is part of an aldehyde group H(C=O)−.
For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
English: Chemical structure of open-chain glucose. Українська: D-глюкоза (стереоструктура) Date: 11 October 2009: Source:
This is an accepted version of this page This is the latest accepted revision, reviewed on 4 January 2025. Sweet-tasting, water-soluble carbohydrates This article is about the class of sweet-flavored substances used as food. For common table sugar, see Sucrose. For other uses, see Sugar (disambiguation). Sugars (clockwise from top-left): white refined, unrefined, unprocessed cane, brown Sugar ...
Wavy single bonds represent unknown or unspecified stereochemistry or a mixture of isomers. For example, the adjacent diagram shows the fructose molecule with a wavy bond to the HOCH 2 - group at the left. In this case the two possible ring structures are in chemical equilibrium with each other and also with the open-chain structure.
The open-chain form has a carbonyl at the end of the chain. Four isomers are cyclic, two of them with a pyranose (six-membered) ring, two with a furanose (five-membered) ring. Galactofuranose occurs in bacteria, fungi and protozoa, [ 8 ] [ 9 ] and is recognized by a putative chordate immune lectin intelectin through its exocyclic 1,2-diol.