How Different Are Aromatic π Interactions from Aliphatic π Interactions and Non-π Stacking Interactions?
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Abstract
We compare aromatic π interactions with aliphatic π interactions of double- and triple-bonded π systems and non-π stacking interactions of single-bonded σ systems. The model dimer systems of acetylene (C<sub>2</sub>H<sub>2</sub>)<sub>2</sub>, ethylene (C<sub>2</sub>H<sub>4</sub>)<sub>2</sub>, ethane (C<sub>2</sub>H<sub>6</sub>)<sub>2</sub>, benzene (C<sub>6</sub>H<sub>6</sub>)<sub>2</sub>, and cyclohexane (C<sub>6</sub>H<sub>12</sub>)<sub>2</sub> are investigated. The ethylene dimer has large dispersion energy, while the acetylene dimer has strong electrostatic energy. The aromatic π interactions are strong with particularly large dispersion and electrostatic energies, which would explain why aromatic compounds are frequently found in crystal packing and molecular self-engineering. It should be noted that the difference in binding energy between the benzene dimer (aromatic–aromatic interactions) and the cyclohexane dimer (aliphatic–aliphatic interactions) is not properly described in most density functionals
