How Different Are Aromatic π Interactions from Aliphatic π Interactions and Non-π Stacking Interactions?

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Molecular Interactions

Background:

• Understanding non-covalent interactions is crucial for molecular assembly.
• Aromatic π systems play a significant role in various chemical and biological processes.
• Distinguishing between aromatic and aliphatic interactions is key to predicting molecular behavior.

Purpose of the Study:

• To compare the strengths of aromatic π interactions versus aliphatic π interactions.
• To investigate non-π stacking interactions in single-bonded σ systems.
• To analyze the energetic contributions (dispersion, electrostatics) to these interactions.

Main Methods:

• Computational investigation of model dimer systems.
• Analysis of acetylene, ethylene, ethane, benzene, and cyclohexane dimers.
• Evaluation of dispersion and electrostatic energy components.

Main Results:

• Ethylene dimer exhibits large dispersion energy; acetylene dimer shows strong electrostatic energy.
• Aromatic π interactions in benzene dimers are significantly strong, with substantial dispersion and electrostatic contributions.
• Aliphatic interactions in cyclohexane dimers are weaker compared to aromatic interactions.

Conclusions:

• Aromatic π interactions are stronger than aliphatic π interactions, driven by combined dispersion and electrostatic forces.
• The findings support the frequent occurrence of aromatic compounds in crystal packing and molecular self-engineering.
• Current density functional methods may not accurately capture the binding energy differences between aromatic and aliphatic dimers.