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.