Quantification of CH?π interactions: Implications on how substituent effects influence aromatic interactions

摘要

Attractive interactions between a substituted benzene ring and an α-substituted acetate group were determined experimentally by using the triptycene model system. The attractive interaction correlates well with the Hammett constants σ_m (R~2=0.90), but correlates much better with the acidity of the α-protons (R~2=0.98). A predominant CH?π interaction was found to control the conformational preference of model compounds 1a-g. Despite the predominance of the CH?π interaction in compounds 1a-g, a Hammett plot displays a fairly straight line for the substituent effect. These results show that when using Hammett plots in a simplified model system, a system designed to study the effect of X?π interactions could capture the X-H?π interaction instead.