Three canonical configurations of (C 6 H 6 ) 2 are depicted in Fig. . These three geometries lie within ≈ 1 kcal/mol of one another, 234 with the parallel-displaced π-stacked structure being slightly lower in energy than the cofacial "sandwich" structure, which is itself a saddle point between symmetry-equivalent paralleldisplaced geometries. The T-shaped geometry is essentially iso-energetic with the parallel-displaced π-stacked structure.