pyranose

In organic chemistry, pyranose is a collective term for saccharides that have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom (a heterocycle). There may be other carbons external to the ring. The name derives from its similarity to the oxygen heterocycle pyran, but the pyranose ring does not have double bonds. A pyranose in which the anomeric (hydroxyl group) at C(l) has been converted into an OR group is called a pyranoside. {| class="wikitable float-right" style="text-align:center; font-size:90;" |- | class="hintergrundfarbe6" colspan="4" | Tetrahydropyran |- | class="hintergrundfarbe5" align="left" | Name | Tetrahydropyran || α-D-(+)-Glucopyranose |- | class="hintergrundfarbe5" align="left" | structural formula | 70px|Tetrahydropyran || 150px|α-Glucopyranose |- | class="hintergrundfarbe5" align="left" | | Tetrahydropyrane ring highlighted blue | Tetrahydropyrane ring highlighted blue |- |}

==Formation == The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1. This forms an intramolecular hemiacetal. If reaction is between the C-4 hydroxyl and the aldehyde, a furanose is formed instead. The pyranose form is thermodynamically more stable than the furanose form, which can be seen by the distribution of these two cyclic forms in solution.