Chapter 18, Problem 18.44P

Interpretation Introduction

Interpretation:

The relative amounts of the two anomers at equilibrium is to be calculated using the given data.

Concept introduction:

The amount by which the plane-polarized light is rotated on passing through a sample of a chiral compound depends on both the concentration of the chiral compound and the length of the sample tube through which the light travels.

${\text{α=([α]}}_{\text{λ}}^{\text{T}}\text{)(l)(c)}$

where ($\text{α}$) is the measured angle of rotation, c is the concentration of the sample in units of grams per milliliter ($\text{g/mL}$) and l is the length of the sample tube in units of decimeters ($\text{dm}$), and term ${\text{[α]}}_{\text{λ}}^{\text{T}}$ indicates the specific rotation of the chiral compound. Most often, the light used for measurement is the sodium $\text{D}$ line ($\text{589}\text{.6 nm}$), abbreviated simply $\text{D}$, and the temperature is $\text{20 °C}$. Therefore, the specific rotation is usually reported as ${\text{[α]}}_{\text{D}}^{\text{20}}$. Anomers are epimers of two cyclic monosaccharides or glycoside and differenciate by if they are aldoses at the configuration of C-1 or if they are ketoses in the configuration C-2. When a mixture of the anomers is dissolved in the solution, the resulting specific rotation changes at equilibrium. The specific rotation at equilibrium depends on the anomer which is excess in solution and whose specific rotation is more than the other.