Chapter 22, Problem 23P

Interpretation Introduction

Interpretation:

The reason for the fact that d-mannose can exist as dextrorotatory as well as levorotatory is to be explained.

Concept introduction:

By convention, the terms dextrorotation and levorotation (or laevorotation) represent the movement of plane polarized light clockwise or anticlockwise, respectively, for a compound as seen by the observer whom the light is approaching. The compound exhibiting dextrorotation is said to be dextrorotatory and that exhibiting levorotation is said to be levorotatory.

The dextrorotation and levorotation can be quantized by measuring the degree of specific rotation of the compound, $\alpha$, which can be given as;

$\begin{array}{l}\text{[}\alpha \text{]}=\frac{\alpha }{c\times l},\text{ where α is the observed rotation (in degrees)}\\ \text{ c is the concentration of the solution of an enatiomer (in g/mL)}\\ \text{ and l is the length of the polarimeter tube (in decimeters) }\end{array}$

The value of dextrorotation is positive (+) and that of levorotation is negative (-).