Question

The beta and alpha glucose have different specific rotations. When either is dissolved in water, their rotation changes until the same fixed value results. This is called:
A. Epimerization
B. Racemization
C. Anomerization
D. Mutarotation

Answer 1

Hint: It is a process which is related with the specific rotation. When we dissolve alpha and beta glucose in water then at some certain value their specific rotation becomes fixed which is +52.7 degree.

Complete Step By Step Solution:
It is given to us that there are alpha and beta glucose which have different specific rotations. And the values of specific rotation of alpha and beta glucose are +112 degree and +18.7 degree respectively. But when we dissolve them in water then at some certain value their specific rotation becomes fixed which is +52.7 degree. So we have to find out what this process is called.
a. Epimerization is the process of forming an epimer by changing one asymmetric centre in a compound that has more than one. So according to the definition this is an incorrect option as in the process specific rotation is changed but in this there is nothing like that.
b. Racemization is a process wherein optically active compounds (which consist of only one enantiomer) are converted into an equal mixture of enantiomers with zero optical activity. Which is also incorrect as it also does not specify anything about specific rotation.
c. Anomerization is the process of conversion of one anomer to the other. As is typical for stereo isomeric compounds, different anomers have different physical properties, melting points and specific rotations. It is also not the correct option as anomers are those which have different atoms attached to the carbon 1 atom which is not the case of alpha and beta glucose. So it is also incorrect.
d. The term mutarotation originates from the observed change in the optical rotation of the alpha and beta anomers of glucose upon dissolution in water.
Due to ring-chain tautomerism, the alpha and beta forms slowly interconvert until equilibrium is established.

So the correct option is D. Mutarotation

Note:
It is to be noted that anomerization is the process of conversion of one anomer to the other. For reducing sugars, anomerization is referred to as mutarotation and occurs readily in solution and is catalyzed by acid and base. As the ratio changes, the optical rotation of the mixture changes; this phenomenon is called mutarotation.