Rebek Imide Platforms as Model Systems for the Investigation of Weak Intermolecular Interactions |
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Authors: | Dr Michael Harder Marjorie A Carnero?Corrales Dr Nils Trapp Dr Bernd Kuhn Prof?Dr François Diederich |
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Institution: | 1. Laboratorium für Organische Chemie, ETH Zürich, H?nggerberg, HCI, 8093 Zürich (Switzerland), Fax: (+41)?44‐632‐1109;2. Small Molecule Research, Roche Innovation Center Basel, F. Hoffmann‐La Roche Ltd, Grenzacherstrasse 124, 4070 Basel (Switzerland) |
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Abstract: | A Rebek imide receptor with an acetylene‐linked phenyl ring complexes 2,6‐di(isobutyramido)pyridine in (CDCl2)2 via triple H‐bonding and π–π‐stacking interactions, and the influence of para‐substituents on both rings was investigated by 1H NMR binding titrations. When the phenyl ring was extended to biphenyl and the C(4)‐pyridine substituent varied, interaction energies increased in the order CH3CH2???phenyl<CH3S???phenyl<phenyl???phenyl?N‐methylcarboxamide???phenyl, highlighting the energetic gain from π stacking on amide fragments. The predicted preference of amide–π stacking for an antiparallel alignment of the local dipoles could not be confirmed with the studied system. Different substituents were introduced in the para position of the phenyl ring and their interaction with bound 2,6‐di(isobutyramido)pyridine was investigated. Theoretical predictions that the mere introduction of a substituent has a stabilizing effect on π–π stacking, regardless of its electronic nature, were experimentally confirmed. |
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Keywords: | amide– aromatic stacking host– guest model systems noncovalent interactions Rebek imide platforms substituent effects |
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