MUTAROTATION

• Change in the specific optical rotation with time is called mutarotation.
• When D-glucose is crystallized at room temperature, and the fresh solution is prepared, its specific rotation is +112˚, but after 12-18 hours, it changes to +52.5 ˚
• If initial crystallization occurs at 98 ˚c temperature and then solubilized, the specific rotation is found to be +19 ˚ but also changes to +52.5 ˚.
• This change in rotation occurs because of the presence of anomeric carbon.
• The two forms of glucose, i.e., α D glucose exhibits optical rotation of +112 ˚, and β D glucose exhibits an optical rotation of +19 ˚, and both undergo mutarotation and at equilibrium 1/3 molecules are 77α type, and 2/3 molecules are β type. The equilibrium mixture has an optical rotation of 52.5˚.