Substituent effects on cation–π interactions: A quantitative study

A synthetic supramolecular complex has been adapted to quantify cation–π interactions in chloroform by using chemical double-mutant cycles. The interaction of a pyridinium cation with the π-face of an aromatic ring is found to be very sensitive to the π-electron density. Electron-donating substituents lead to a strong attractive interaction (−8 kJ/mol(−1)), but electron-withdrawing groups lead to a repulsive interaction (+2 kJ/mol(−1)).