Solvent Modulation of Aromatic Substituent Effects in Molecular Balances Controlled by CH-π Interactions

Area of Science:

• Chemical Physics
• Supramolecular Chemistry
• Physical Organic Chemistry

Background:

• CH-π interactions are vital in biological and chemical systems.
• Solvation and substituent effects influence CH-π interactions, but their interplay is not well understood.

Purpose of the Study:

• To quantitatively correlate substituent effects in CH-π interactions with solvent properties.
• To explore the influence of solvation on the interplay between aromatic substituents and CH-π interactions.

Main Methods:

• Conformational analysis of aryl-substituted molecular balances to measure CH-π interaction energies.
• Utilizing Hunter's solvation model to interpret conformational free energy changes.
• Applying Hammett plots to quantify substituent sensitivity (ρ values).

Main Results:

• A direct quantitative correlation was found between substituent effects in CH-π interactions and the hydrogen-bond acceptor constants of the solvent.
• The sensitivity of aromatic substituent effects (ρ) linearly correlates with the solvent's hydrogen-bond acceptor propensity (βs): ρ = 0.06βs - 0.04.
• Solvation/desolvation of the aryl proton was identified as the key factor controlling substituent effects.

Conclusions:

• The study establishes a predictive model for CH-π interactions based on solvent properties.
• This finding deepens the understanding of non-covalent interactions in chemical and biological contexts.
• The quantitative relationship provides a valuable tool for designing molecules and predicting their behavior in different solvents.