The relation of molecular structure to the six perturbation parameters h(D), s(D), l(D), h, s, and l of the theory of MCD (magnetic circular dichroism) spectra of pi systems derived from 4N-electron perimeters (parts 1-3) is developed explicitly. The MCD spectra of acenaphthylene and pleiadiene are interpreted in the way of illustration. Simple PMO arguments are used to derive general rules for the response of the MCD spectra of nonaromatic cyclic pi chromophores to inductive and mesomeric effects of substituents.