What is optical rotation?

Light consists of electromagnetic waves, which’s vibrations are transverse to the direction of propagation. Polarized light is light, which’s vibration pattern exhibits preference. If natural light passes through a so called polarizing filter, most of its other vibrating directions will be filtered out, leaving only one specific direction. If this light is oscillating then in only one direction, it is called “linearly polarized”.

Optical rotation and polarized light

There is a great number of organic and inorganic substances being optically active in their crystalline, liquid or dissolved state. That means, these substances are able to rotate the direction of oscillation of polarized light around a determined angle. This is called optical rotation.

Optically active substances

Some well-known optical substances are tartaric acid, lactic acid, benzoic acid and derivatives, amino acids, proteins and of course sugars. If an optically active substance (e.g. sugar) is dissolved in an optically inactive liquid (as water for instance), the degrees of angle rotation, depend – amongst others – on the concentration of the solution. This angle of rotation is absolutely determined by a polarimeter with highest precision.