3.2.2. Homomolecular dimers, (C 6 H 5 X) 2 . We next consider (C 6 H 5 X) 2 for X = CH 3 , OH, and CN. The toluene dimer has been suggested as a model of π-π interactions in proteins, 182 and might be expected to afford different energy profiles as compared to dimers with polar substituents. One-dimensional energy profiles are plotted in Fig. for all three systems, using a lateral displacement coordinate representing slipstacking. The face-to-face separation is set to that of the minimum-energy parallel-displaced geometry for each system, which ranges from 3.9-4.1 Å. Despite profound differences in the polarity of the substituents, and an intermolecular hydrogen bond in the phenol dimer, each of these three systems exhibits offset This should be compared to other energy components for the system system, which can be found in Fig. .