Surfing π Clouds for Noncovalent Interactions: Arenes versus Alkenes^†

Abstract

A comparative study of molecular balances by NMR spectroscopy indicates that noncovalent functional‐group interactions with an arene dominate over those with an alkene, and that a π‐facial intramolecular hydrogen bond from a hydroxy group to an arene is favored by approximately 1.2 kJ mol⁻¹. The strongest interaction observed in this study was with the cyano group. Analysis of the series of groups CH₂CH₃, CHCH₂, CCH, and CN shows a correlation between conformational free‐energy differences and the calculated charge on the C^α atom of these substituents, which is indicative of the electrostatic nature of their π interactions. Changes in the free‐energy differences of conformers show a linear dependence on the solvent hydrogen bond acceptor parameter β.