Aromaticity and Through-Space Interaction between Aromatic Rings in [2.2]Paracyclophanes

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Computational Chemistry

Background:

• [2.2]Paracyclophanes are unique molecules featuring two benzene rings bridged by ethylene units.
• Understanding the electronic properties and intermolecular interactions within these structures is key to their application.
• Previous studies have explored their synthesis and basic structural features.

Purpose of the Study:

• To investigate the aromaticity and nonbonded interactions in [2.2]paracyclophanes using computational methods.
• To determine the extent of aromaticity in the solid state via the HOMA index.
• To elucidate the nature of interactions between the aromatic rings in various [2.2]paracyclophane derivatives.

Main Methods:

• Calculation of the HOMA index for solid-state [2.2]paracyclophanes.
• Application of Atoms in Molecules (AIM) analysis to identify bonding and non-bonding interactions.
• Utilization of Non-Covalent Interactions (NCI) analysis to visualize inter-ring interactions.
• Investigation of both crystal structures and computationally optimized geometries.

Main Results:

• The HOMA index revealed a slight decrease in aromaticity for the studied [2.2]paracyclophanes in the solid state.
• AIM analysis confirmed the presence of a C···C bond path between the aromatic rings in only a limited number of derivatives.
• NCI analysis successfully visualized the significant role of dispersion and repulsive forces between the aromatic rings across all investigated [2.2]paracyclophanes.
• The study identified specific [2.2]paracyclophanes exhibiting distinct interaction patterns.

Conclusions:

• A combination of AIM and NCI analyses is essential for a comprehensive understanding of nonbonded interactions in [2.2]paracyclophanes.
• The interplay of attractive and repulsive forces significantly influences the electronic and structural properties of these molecules.
• The findings provide valuable insights for the rational design and synthesis of novel paracyclophane derivatives with tailored properties.