Question

What is essentially the difference between $\alpha$ - glucose and $\beta$ - glucose? What is meant by pyranose structure of glucose?

Answer 1

$\alpha$- glucose and $\beta$- glucose are two cyclic hemiacetal forms of glucose which differ only in the configuration of hydroxyl group (-OH) at anomeric carbon. Such isomers are called anomers. The six-membered cyclic structure of glucose is called pyranose structure.

Pyranose structure of glucose: The six memebred ring contains oxygen atom because of its resemblance with pyran is called pyranose form.

$\alpha$-D-glucose and $\beta$-D-glucose are stereoisomers, they differ in 3-dimensional configuration of atoms/groups at one or more positions.

Note: that the structures are almost identical, except that in the $\alpha$ form, the OHOH group on the far right is down and in the $\beta$ form, the OHOH group on the far right is up.