Question

A 1.40 M mixture of alpha- and beta-D-glucose has an observed optical rotation (alpa)obs of 18.9° at 20 °C. What are the concentrations of the two anomers? Is the solution at equilibrium?

Answer 1

alfa D-glucose has a specific rotation of +112 degrees and beta D-glucose has a specific rotation of +18.7 degrees.

x (112) + (1-x) 18.7= 18.9 (let X be the mole fraction of alfa nad 1-x of beta D glucose)

x = 0.01 or 1 %

1-x = .99 = 99 %

% of alfa D-glucose 1 &

and % beta D-glucose is 99 %

The solution isnot in equilibrium, at equilibrium, specific rotation of α-D-glucose decreases from +112° to +52.5° and specific rotation of β-D-glucose increases from +18.7° to +52.5°.

This property is known as mutarotation