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

Abstract

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.

Regioselectivity and Mechanism of Synthesizing N-Substituted 2-Pyridones and 2-Substituted Pyridines via Metal-Free C-O and C-N Bond-Cleaving of Oxazoline[3,2-a]pyridiniums

“…We postulated that the reason may involve pyridinium−π interaction (cation−π interaction) between the benzene ring and the pyridinium moiety. The proposed cation−π interaction is an intermolecular interaction which is different from the reported intramolecular cation−π interaction15.…”

“…In contrast, the energy of attacking C8 of 4a by 6I and 6J are much higher (31.1 and 27.0 kcal/mol). As shown in Figs 10 and 11, the benzene ring and the pyridinium are almost parallel to each other, indicating the effect of pyridinium−π interaction (cation−π interaction)15 between them, which may contribute to reduce the free energy barrier of transition state.…”

Some Recent Advances in the Design and Use of Molecular Balances for the Experimental Quantification of Intramolecular Noncovalent Interactions of π Systems

“…In addition to the molecular balances considered above, there have been reports describing other balances, although they have not been used as widely as those considered in previous sections. Based on the aforementioned bicyclo[4.2.2] skeleton, Yamada et al . developed a molecular seesaw balance to study aryl⋅⋅⋅pyridinium interactions.…”

“… A seesaw balance of Yamada et al . Vicinal 3 J (H,H) couplings of protons H 1 ,H 2 and H 1 ,H 3 were used for estimating populations of conformer A and B.…”

“…In addition to the molecular balances considered above, there have been reports describing other balances, although they have not been used as widely as those considered in previous sections. Based on the aforementioned bicyclo[4.2.2] skeleton, [34] Yamada et al [39] developed am olecular seesaw balance to study aryl···pyridinium interactions. Similar to balanceso f Motherwell,[26] at wo-site fast exchange (in the NMR timescale) between conformers Aa nd B ( Figure 20) was analysed using NMR J couplings and the preference of conformer Awas established.…”