Quantitative model for rationalizing solvent effect in noncovalent CH–Aryl interactions† †Electronic supplementary information (ESI) available: Correlation plots; proton and carbon NMR spectra of the molecular balances, and the xyz coordinate of the optimized geometries. See DOI: 10.1039/c5sc03550c

Establishing a linear relationship between CH–aryl interaction energies and the properties of the solvating media. The strength of CH–aryl interactions (Δ G ) in 14 solvents was determined via the conformational analysis of a molecular torsion balance. The molecular balance adopted folded and unfolded conformers in which the ratio of the conformers in solution provided a quantitative measure of Δ G as a function of solvation. While a single empirical solvent parameter based on solvent polarity failed to explain solvent effect in the molecular balance, it is shown that these Δ G values can be correlated through a multiparameter linear solvation energy relationship (LSER) using the equation introduced by Kamlet and Taft. The resulting LSER equation [Δ G = –0.24 + 0.23 α – 0.68 β – 0.1 π * + 0.09 δ ]—expresses Δ G as a function of Kamlet–Taft solvent parameters—revealed that specific solvent effects ( α and β ) are mainly responsible for “tipping” the molecular balance in favour of one conformer over the other, where α represents a solvents' hydrogen-bond acidity and β represents a solvents' hydrogen-bond basicity. Furthermore, using extrapolated data ( α and β ) and the known π * value for the gas phase, the LSER equation predicted Δ G in the gas phase to be –0.31 kcal mol –1 , which agrees with –0.35 kcal mol –1 estimated from DFT-D calculations.