Chapter 4.4, Problem 6P

Interpretation Introduction

Interpretation:

The specific rotation of enantiopure cholesterol and the fraction of synthetic cholesterol in the given mixture are to be determined.

Concept introduction:

The specific rotation, denoted by $\text{[α]}$, can be calculated from the observed rotation using the following expression:

$\text{[α]}\text{=}\frac{\text{100}\text{α}}{\text{cl}}$

Where

$\text{α}$ is the observed rotation

$c$ is the concentration of the sample in grams per $\text{100 mL}$ of solution

$l$ is the length of the polarimeter tube in decimeters.

The optical purity is equal to the percentage enantiomeric excess, which can be determined from the following expression:

$\text{Optical purity=}\frac{\text{specific rotation of sample}}{\text{specific rotation of pure enantiomer}}\text{×100}$

The percent enantiomeric excess is the difference between the percentages of major and minor enantiomers.

$\text{\%}\text{Enantiomeric excess}\text{=}\left(\text{\% Major enantiomer}\right)\text{-}\left(\text{\% Minor enantiomer}\right)$

A racemic mixture is the mixture of equal composition of enantiomers.