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Spatial Separation of Molecular Conformers and Clusters
Published on: January 9, 2014
The strength of parallel-displaced arene-arene interactions in chloroform
Benjamin W Gung1, Xiaowen Xue, Hans J Reich
1Department of Chemistry & Biochemistry, Miami University, Oxford, Ohio 45056, USA. gungbw@muohio.edu
Abstract:
[reaction: see text] Triptycene-derived compounds have been prepared to serve as conformational equilibrium reporters for direct measurements of arene-arene interactions in the parallel-displaced orientation. A series of such compounds bearing arenes with different substituents were synthesized, and the ratios of the syn and anti conformers were determined by variable-temperature NMR spectroscopy. The syn conformer allows attached arenes to interact with each other while the anti conformer does not. The free energies derived from the syn/anti ratios in chloroform range from slightly positive (0.2 kcal/mol) to considerably negative (-0.98 kcal mol) values. The interactions between the arenes bearing electron-donating groups (EDG) are either negligible or slightly repulsive, while the interactions between arenes bearing electron-withdrawing groups (EWG) are attractive. Intermediate free energy values are obtained for those compounds bearing arenes with one EDG and one EWG.
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