 The experimentally determined relationship between the rotational strength (R) of a sample and the Δε is given by
The rotational strength has also been determined theoretically,
We see from these two equations that in order to have non-zero formula_3, the electric and magnetic dipole moment operators (formula_4 and formula_5) must transform as the same irreducible representation.formula_6 and formula_7 are the only point groups where this can occur, making only chiral molecules CD active.Simply put, since circularly polarized light itself is "chiral", it interacts differently with chiral molecules.