What does „Specific Rotation“ mean?

Some materials like quartz, sucrose solutions or organic compounds are able to rotate the direction of oscillation of polarized light around a determined angle. They are called optically active and can be dextrorotatory or levorotatory.

The specific rotation is a substance-specific physical parameter, which can be determined by a polarimeter. It depends on the temperature and the wavelength of the light. For some samples this value depends on the concentration as well.


Specific rotation is defined as the angle of rotation in degrees of the plane of polarization of monochromatic light passing through a 100 ml long tube containing an optical active substance in solution at a concentration of 1 g/ml.

The specific rotation is e.g. one important parameter to control the purity of optical active substances of incoming products for the production of pharmaceutical and cosmetic products.