This paper describes the synthesis and characterization of novel low molecular weight displacers for protein purification in cation-exchange systems. A series of displacers based on the pentaerythritol geometry are examined to identify high-affinity, low molecular weight displacers. The steric mass action (SMA) model is employed to evaluate the relative affinities of these displacers. A linear gradient method is described for the measurement of SMA model parameters of molecules. This work demonstrates that, in addition to the number of charges on a displacer molecule, the presence of aromatic moieties can have a profound effect on affinity. In particular, the placement of aromatic groups near the surface of a molecule is shown to result in significant increases in displacer efficacy. Finally, the efficacy of these displacers is examined in displacement experiments using a model protein. These results indicate that nonspecific interactions can play a major role in determining the affinity of a molecule for ion-exchange systems.