CH-pi aromatic interactions are ubiquitous in nature and are capable of regulating important chemical and biochemical processes. Solvation and aromatic substituent effects are known to perturb the CH-pi aromatic interactions. However, the nature by which the two factors influence one another is relatively unexplored. Here we demonstrate experimentally that there is a quantitative correlation between substituent effects in CH-pi interactions and the hydrogen bond acceptor constants of the solvating molecule. The CH-pi interaction energies were measured by the conformational study of a series of aryl-substituted molecular balances in which the conformational preferences depended on the relative strengths of the methyl and aryl CH-pi interactions in the folded and unfolded states, respectively. Due to the favorable methyl-aromatic interactions, the balances were found to exist predominantly in the folded state. The observed substituent effect in the conformational preferences of the balances was controlled by the explicit solvation/desolvation of the aryl proton. The interpretation of the conformational free energy as a function of substituents and solvation using Hunter's solvation model revealed that a linear relationship exists between the sensitivity of aromatic substituent effects (i.e., the rho values derived from Hammett plots) and the hydrogen-bond acceptor propensity (beta(s)) of the solvent molecule: rho = 0.06 beta(s) - 0.04.