title: Quantitative assessment of substituent effects on cation-π interactions using molecular electrostatic potential topography.
abstract: A molecular electrostatic potential (MESP) topography based approach has been proposed to quantify the substituent effects on cation-π interactions in complexes of mono-, di-, tri-, and hexasubstituted benzenes with Li(+), Na(+), K(+), and NH(4)(+). The MESP minimum (V(min)) on the π-region of C(6)H(5)X showed strong linear dependency to the cation-π interaction energy, E(M(+)). Further, cation-π distance correlated well with V(min)-π distance. The difference between V(min) of C(6)H(5)X and C(6)H(6) (ΔV(min)) is proposed as a good parameter to quantify the substituent effect on cation-π interaction. Compared to benzene, electron-donating groups stabilize the di-, tri-, and hexasubstituted cation-π complexes while electron-withdrawing groups destabilize them. In multiple substituted complexes, E(M(+)) is almost equal (∼95%) to the sum of the individual substituent contributions (E(M(+)) ≈ Σ(ΔE(M(+)))), suggesting that substituent effect on cation-π interactions is largely additive. The ΔV(min) of C(6)H(5)X systems and additivity feature have been used to make predictions on the interaction energies of 80 multiple substituted cation-π complexes with above 97% accuracy. The average mean absolute deviation of the V(min)-predicted interaction energy, E(M(+))(V) from the calculated E(M(+)) is -0.18 kcal/mol for Li(+), -0.09 kcal/mol for Na(+), -0.43 kcal/mol for K(+), and -0.67 kcal/mol for NH(4)(+), which emphasize the predictive power of V(min) as well as the additive feature of the substituent effect.
authors.affiliation: Computational Modeling and Simulation Section, National Institute for Interdisciplinary Science and Technology (CSIR), Trivandrum, India 695019.
authors.forename: Fareed Bhasha
authors.initials: FB
authors.lastname: Sayyed
authors.forename: Cherumuttathu H
authors.initials: CH
authors.lastname: Suresh
mesh_terms: D001554:Benzene / Q000737:chemistry* / Q000378:metabolism; D002412:Cations / Q000737:chemistry* / Q000378:metabolism; D002627:Chemistry, Physical / Q000379:methods*; D004583:Electrons; D006860:Hydrogen Bonding; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D002412:Cations; D001554:Benzene