Premium
Experimental Support for the Role of Dispersion Forces in Aromatic Interactions
Author(s) -
Lima Carlos F. R. A. C.,
Rocha Marisa A. A.,
Gomes Lígia R.,
Low John N.,
Silva Artur M. S.,
Santos Luís M. N. B. F.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201201056
Subject(s) - chemistry , london dispersion force , substituent , intramolecular force , enthalpy , aromaticity , dispersion (optics) , computational chemistry , interaction energy , non covalent interactions , aryl , knudsen number , van der waals force , thermodynamics , alkyl , organic chemistry , molecule , hydrogen bond , physics , optics
Herein a core scaffold of 1‐phenylnaphthalenes and 1,8‐diphenylnaphthalenes with different substituents on the phenyl rings was used to study substituent effects on parallel‐displaced aromatic π⋅⋅⋅π interactions. The energetics of the interaction was evaluated in gas phase based on the standard molar enthalpies of formation, at T =298.15 K, for the compounds studied; these values were derived from the combination of the results obtained by combustion calorimetry and Knudsen/Quartz crystal effusion. A homodesmotic gas‐phase reaction scheme was used to quantify and compare the intramolecular interaction enthalpies in various substituted 1,8‐diphenylnaphthalenes. The application of this methodology allowed a direct evaluation of aromatic interactions, and showed that substituent effects on the interaction enthalpy cannot be rationalized solely on classical electrostatic grounds, because no correlation with the σ meta or σ para Hammett constants was observed. Moreover, the results obtained indicate that aromatic π⋅⋅⋅π interactions are significantly enhanced by substitution, in a way that correlates with the ability of the interacting aryl rings to establish dispersive interactions. A combined experimental and computational approach for calculation of the true aromatic π⋅⋅⋅π interaction energies in these systems, free of secondary effects, was employed, and corroborates the rationale derived from the experimental results. These findings clearly emphasize the role of dispersion and dilute the importance of electrostatic forces on this type of interactions.