Definition of Optically Active
Optically active compounds are those compounds which have the ability to rotate the plane-polarized light. It was first recognized when the three-dimensional structure of the molecules was ought to be determined. Only those compounds rotate in plane-polarized light which constitutes chiral centers. Being optical active is a macroscopic property of the molecules that is depicted when they interact with light.
The optical activity of the compounds is determined by an instrument known as a polarimeter. The optically active compounds are of two types i.e. dextrorotatory and levorotatory. The plane rotates clockwise in the case of dextrorotatory and anti-clockwise in the case of levorotatory.