Ring structures of glucose :
Glucose has two cyclic structures (II and III) which are in equilibrium with each other through the open chain structure (I) in aqueous solution.
The ring structure of glucose is formed by reaction between the formyl ( – CHO) group and the alcoholic (- OH) group at C – 5.
Thus,
The ring structure is called a hemiacetal. The two hemiacetal structures (II and III) differ only in the configuration of C – I (Fig.), the additional chiral centre resulting from ring closure.
The two ring structures are called αand β- anomers of glucose and C-l is called the anomeric carbon.
The ring of the cyclic structure of glucose contains five carbons and one oxygen.
Thus,
It is a six membered ring.
It is called pyranose structure, in analogy with the six membered heterαyclic compound pyran (IV).
Hence glucose is also called glucopyranose.
