Explain the term dextrorotatory and laevorotatory.

Explanation

If a substance rotates the plane polarised light to the left i.e., in the anticlockwise direction, it is called laevorotatory or l-form and a negative sign is placed before the degree of rotation. On the other hand, if a substance rotates the plane polarised light to the right i.e., in the clockwise direction, it is called dextrorotatory or d-form and a +ve sign is placed before degree of rotation. The sign of optical rotation is not necessarily related to the absolute configuration of the molecule.