Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pyranose is a collective term for carbohydrates which have a chemical structure that includes a six-membered ring consisting of five carbon atoms and one oxygen atom. The name derives from its similarity to the oxygen heterocycle pyran. A pyranose in which the anomeric OH at C(l) has been converted into an OR group is called a pyranoside.(Unlike a pyranoside, furanosides are five-membered acetals). 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.