The Strength of Parallel-Displaced Arene−Arene Interactions in Chloroform
摘要:
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.
A Threshold for Charge Transfer in Aromatic Interactions? A Quantitative Study of π-Stacking Interactions
作者:Benjamin W. Gung、Mehul Patel、Xiaowen Xue
DOI:10.1021/jo051808a
日期:2005.12.1
Attractive interactionsbetween substituted arenes in the parallel displaced configuration have been quantitatively studied using triptycene-derived molecular conformational reporters. Charge-transfer bands are observed for models where the interactions are between strong donor and acceptors. Substituent effects on the strength of the aromaticinteraction follow opposite trends for strongly electron-deficient
The Strength of Parallel-Displaced Arene−Arene Interactions in Chloroform
作者:Benjamin W. Gung、Xiaowen Xue、Hans J. Reich
DOI:10.1021/jo050049t
日期:2005.4.1
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.