Optical activity: Optical activity of an organic compound refers to the property of an organic compound by the virtue of which, it rotates the plane-polarized light (produced by passing ordinary light through Nicol prism) towards left or right when it is passed through their solutions and the compounds are known as optically active compounds.
The optical activity is of two types:
Dextrorotatory or d-form Dextrorotatory in Greek means right rotating, if the compound rotates the plane polarised light to the right, i.e., clockwise direction.
Laevorotatory or l-form Laevorotatory in Greek means left rotating if the compound rotates the plane polarised light to the left, i.e., anticlockwise direction.
Conditions for optical activity:
The compound should contain an asymmetrical carbon atom.
Molecules should not possess elements of symmetry.
The molecule should possess a chiral plane.
There is an asymmetric chiral carbon atom in lactic acid, along with four different groups that lead to two spatial configurations. These configurations are superimposable mirror images of each other.
So, d-lactic acid rotates the plane of polarized light towards right, whereas l-lactic acid rotates the plane of polarized light towards left.
