We demonstrate that a Kramers-Kronig transform, which is equivalent to a Hilbert transform, is also equivalent to a double Fourier transform, through application to the infrared spectrum of liquid benzene and the corresponding range of refractive index.  We present a mathematical proof of the equivalence of these transforms.  Both based on molecular properties associated with the electric dipolar moment, the optical spectra in absorption and optical dispersion thus become equivalent, although experimental aspects might make one method easier to apply in a particular spectral region.  These dipolar effects are distinct from the effects of electric dipolar polarizability, which governs the Raman scattering phenomenon; its transform yields another property so far unexplored.