Phenol and Toluene Stacking Interactions, Including Interactions at Large Horizontal Displacements. Study of Crystal Structures and Calculation of Potential Energy Surfaces

The study of crystal structures from the Cambridge Structural Database (CSD) shows that most of p-phenol/p-phenol and toluene/toluene stacking interactions are at large horizontal displacements (offsets) as well as benzene/benzene interactions. The interactions at large horizontal displacements are stabilized by the addition of simultaneous interactions in supramolecular structures in crystals. The stacking p-phenol/p-phenol tends to be orientated in a parallel and antiparallel fashion, while stacking toluene/toluene is almost all in an antiparallel orientation. It is in accordance with calculated interaction energies. Namely, the strongest interaction energies for parallel and antiparallel phenol/phenol dimers are −5.12 and −4.40 kcal/mol, at offsets of 1.5 and 3.0 Å, respectively, while for parallel and antiparallel toluene/toluene dimers, energies are −3.98 and −5.39 kcal/mol, at offsets of 3.0 Å. These interactions are stronger than benzene/benzene stacking (−2.85 kcal/mol), as a consequence of the presence of the substituents. Similar to benzene/benzene stacking, interactions for phenol/phenol and toluene/toluene stacking at large offsets (4.0 Å) can be strong, stronger than −2.0 kcal/mol.