McConnell’s model for through-space magnetic interaction can be interpreted from the vantage point of molecular orbital interactions. Intermolecular magnetic interactions are analyzed in several stacking modes of allyl, diphenylmethyl, and nitroxide radical systems. The nodal properties which lead to the overlap (or lack of it) of the singly occupied molecular orbitals in these systems play an essential role in the ferromagnetic coupling of molecules in extended systems. These nodal characteristics and the overlaps governing orbital interaction are as important, we argue, as the spin-polarization effects from electron correlation.