Optical Activity
The ability of a substance to rotate the plane of polarised light passing through it.
Formula / equation
[α] = α / (l × c)
Unit
degrees
In depth
Measured with a polarimeter, the specific rotation is a characteristic constant once path length, concentration, temperature and wavelength are specified. Rotation to the right is labelled dextrorotatory and to the left laevorotatory, and the direction cannot be predicted from the R/S configuration.
Examples in the real world
Sucrose rotating light by +66.5°; the inversion of that rotation as sucrose hydrolyses to invert sugar.