In previous post, we mentioned that enantiomers (also known as optical isomers) rotate plane-polarised light in opposite directions and are said to exhibit optical activity. So how do we know if an organic molecule rotate plane-polarised light? We use an instrument known as a polarimeter.
A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarised light through an optically active compound.
Some chemical substances are optically active, and polarized (uni-directional) light will rotate either to the left (counter-clockwise) or right (clockwise) when passed through these compounds. The amount by which the light is rotated is known as the angle of rotation.
Today, we shall take a closer look at:
- Meaning of Optical Activity
- Plane-Polarised Light
- How a Polarimeter Works
Meaning of Optical Activity
All molecules, whether chiral or achiral, are able to rotate plane-polarised light due to interaction with the electron cloud of the molecule. For a particular molecule, the extent and direction of rotation depends on the orientation of the molecule in relation to the plane-polarised light.
For achiral molecules (compounds not exhibiting enantiomerism), each of these rotations are cancelled out due to the symmetry of the molecules… Continue reading ...