What is mutarotation ?

Explanation

Ordinary glucose is `alpha`-D-glucose (specific rotation = + `111^@`). On dissolving in water its specific rotation falls gradually to + `52^@`. The change in specific rotation of an optically active compounds in solution with time to an equilibrium value is called mutarotation. It is due to conversion of `alpha`-form into `beta`-form through an open chain structure. The equilibrium mixture contains 38% of `alpha`-D-glucose 62% of `beta`-D-glucose and a small amount of linear isomer.

The two cyclic hemiacetal forms of glucose differ in the configuration of the-OH group at C-1. Haworth structures of X and `beta`-D-glucose are given below.