Measurement of Optical Activity.
d = density of liquid
A glass tube pT containing optically active liquid or solution is placed in the polarimeter.
A beam of monochromatic light passes through it after being polarized by polarizer P.
The sample rotates the plane of polarized light through a certain angle.
The analyzer A is rotated through the same angle to get a dark field of view again.
This angle and its direction are noted with the help of a graduated disc.
The substance is laevorotatory if the analyzer is rotated in the anticlockwise direction. It is Dextrorotatory if the analyzer is rotated in the clockwise direction.
Importance In Chemistry.
- Optical activity depends upon the arrangement of atoms in the molecule. Thus it is a constitutive property. It is employed in ascertaining the structure of compounds.
- Only those organic compounds containing asymmetric carbon atom are optically active. A carbon atom with four different groups of atoms is called asymmetric carbon, e.g., lactic acid and maleic acid are optically active and have been assigned the formulas: