hexopyranose

Hexopyranose is a cyclic form of a hexose sugar. Hexoses are carbohydrates with six carbon atoms. The "pyranose" designation indicates that the sugar has cyclized to form a six-membered ring, similar in structure to pyran. This ring consists of five carbon atoms and one oxygen atom.

In aqueous solution, hexoses exist in equilibrium between their open-chain (aldehyde or ketone) form and various cyclic hemiacetal or hemiketal forms. The pyranose form is the most prevalent cyclic form for most hexoses, including glucose, galactose, and mannose. The formation of the pyranose ring involves the reaction of the aldehyde or ketone group with a hydroxyl group on the sugar chain.

When the ring closes, a new chiral center is created at the anomeric carbon, which is the carbon atom that was previously the carbonyl carbon. This leads to the existence of two stereoisomers, known as anomers, designated as alpha (α) and beta (β). These anomers differ in the spatial orientation of the hydroxyl group attached to the anomeric carbon. The alpha anomer typically has its anomeric hydroxyl group pointing down (axial in the common chair conformation), while the beta anomer has it pointing up (equatorial). The relative proportions of the alpha and beta anomers depend on the specific hexose and the solvent conditions.