Intermolecular noncovalent interactions with carbon in solution

Area of Science:

• Supramolecular Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• Carbon-centered noncovalent interactions (NCIs), such as n → π* interactions and carbon bonds, are crucial for molecular structure and function.
• Experimental evidence for these weak interactions in the solution phase is scarce, hindering a full understanding of their role.

Purpose of the Study:

• To provide experimental evidence for intermolecular carbon-centered NCIs in solution.
• To investigate the stabilization mechanisms and energetics of these interactions in a solution environment.
• To establish a new strategy for studying weak intermolecular forces in solution.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to detect and characterize the interactions.
• Molecular Dynamics (MD) simulations were used to model the behavior of the interacting molecules in solution.
• High-level quantum mechanical calculations, including Natural Bond Orbital (NBO) analyses, were performed to elucidate the electronic nature of the interactions.

Main Results:

• The pyridine-N-oxide:dimethyltetracyanocyclopropane (PNO-DMTCCP) complex was identified as a suitable model system for studying intermolecular NCIs in solution.
• Experimental data confirmed the presence of intermolecular n → π* interactions and carbon bonds within the PNO-DMTCCP complex.
• NMR studies revealed that these NCIs are enthalpy-driven, with a significant enthalpy change and dimerization energy comparable to hydrogen-bonded dimers.

Conclusions:

• This study successfully demonstrates the experimental observation and characterization of intermolecular carbon-centered NCIs in solution.
• The findings highlight the importance of n → π* interactions and carbon bonds in stabilizing molecular complexes in solution.
• A novel methodological approach has been established for investigating weak intermolecular interactions in the solution phase.