Structure of pi-pi interactions in aromatic liquids
Thomas F Headen1, Christopher A Howard, Neal T Skipper
1London Centre for Nanotechnology, Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
Journal of the American Chemical Society
|January 28, 2010
Summary
Researchers used neutron diffraction to reveal the complex pi-pi interactions in liquid benzene and toluene. They found specific molecular arrangements, differing from simple dimer models, shape these aromatic liquids.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Physics
Background:
- Understanding liquid-state molecular interactions is crucial for predicting material properties.
- Aromatic pi-pi interactions are fundamental but challenging to characterize in liquids.
- Previous models of benzene and toluene liquid structures were based on dimer approximations.
Purpose of the Study:
- To elucidate the detailed structure of liquid benzene and toluene.
- To characterize aromatic pi-pi interactions in the liquid state.
- To construct a comprehensive spatial and orientational picture of these archetypal aromatic liquids.
Main Methods:
- High-resolution neutron diffraction.
- Hydrogen/deuterium isotopic labeling.
- Six-dimensional spatial and orientational analysis.
Main Results:
- Determined the nearest neighbor coordination shell for benzene and toluene (approx. 12 molecules).
- Revealed complex local orientational order beyond superficial isotropy.
- Identified distinct molecular arrangements at different separations: offset parallel contacts (<5 A) and perpendicular contacts (>5 A).
Conclusions:
- Liquid benzene and toluene exhibit specific, non-isotropic structures driven by pi-pi interactions.
- Observed liquid structures significantly differ from those predicted by molecular dimer energy surfaces.
- The 'anti-hydrogen-bond' configuration is not a dominant feature in the liquid state.
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