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 (1) H NMR binding titrations. When the phenyl ring was extended to biphenyl and the C(4)-pyridine substituent varied, interaction energies increased in the order CH3 CH2 ⋅⋅⋅phenyl<CH3 S⋅⋅⋅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.
Published Version
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