In Experiment 2 we have seen how an electro magnetic wave interacts with an anisotropic medium. We have observed the phenomena called Optical Rotatory Dispersion where the optical rotation of a plane polarised light is studied as a function of wave length of the incident light. Now we will try to understand how the ORD spectra can be used to study the structure of an optically active substance. We will study different types of normal and abnormal ORD spectra and try to correlate them with structural properties of the chiral molecule.