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Quantitative determination of intermolecular interactions with fluorinated aromatic rings
H Adams1, J L Blanco, G Chessari
1Centre for Chemical Biology, Krebs Institute for Biomolecular Science, Department of Chemistry, University of Sheffield, UK.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|September 19, 2001
Summary
Substituent effects on aromatic ring interactions with pentafluorophenyl pi-systems were studied. Electron-withdrawing groups increased repulsion, while electron-donating groups induced attractive stacking interactions, explained by an electrostatic model.
Area of Science:
- Supramolecular Chemistry
- Organic Chemistry
- Physical Chemistry
Background:
- Understanding intermolecular forces is crucial in chemistry.
- Aromatic ring interactions and pi-systems are fundamental in molecular recognition.
Purpose of the Study:
- Investigate substituent effects on interactions between aromatic rings and pentafluorophenyl pi-systems.
- Elucidate the electrostatic and geometric factors governing these interactions.
Main Methods:
- Chemical double mutant cycle approach.
- Nuclear Magnetic Resonance (NMR) titrations (1H and 19F).
- X-ray crystallography and molecular mechanics calculations.
Main Results:
- Repulsive interactions dominate between aromatic rings and pentafluorophenyl pi-systems, increasing with electron-withdrawing substituents.
- Complex distortion occurs to minimize repulsion beyond a certain substituent limit.
- Electron-donating groups induce attractive stacking interactions, favoring a specific geometry.
Conclusions:
- Electrostatic interactions, particularly ring polarization and charge distribution, govern the observed attractive and repulsive forces.
- The findings support a model where pi-electron density and partial charges dictate the preferred orientation and strength of intermolecular interactions.