A Molecular Seesaw Balance: Evaluation of Solvent and Counteranion Effects on Pyridinium-π Interactions.

A molecular seesaw balance 1·MeI has been developed to measure pyridinium-π interactions. This balance adopts two distinct conformers, A and B, which are stabilized by a cation-π interaction and a π-π interaction, respectively. The conformer ratio was determined on the basis of the averaged (3)J coupling constants for H1-C-C-H2 and the corresponding boundary J values for conformers A and B. The effects of the solvent and the counteranion on the ΔG values were investigated using this molecular balance. Thermodynamic parameters obtained from a van't Hoff plot helped us to better understand the solvent and counteranion effects.