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 3J 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.