Interactions of Substituted Nitroaromatics with Model Graphene Systems: Applicability of Hammett Substituent Constants To Predict Binding Energies

Applicability of Hammett parameters (sigma(m) and sigma(p)) was tested in extended pi-systems in gas phase. Three different model graphene systems, viz. 5,5-graphene (GR), 3-B-5,5-graphene (3BGR), and 3-N-5,5-graphene (3NGR), were designed as extended pi-systems, and interactions of various nitrobenzene derivatives (mainly m- and p-substituted together with some multiple substitutions) on such platforms were monitored using density functional theory (M06/cc-pVDZ, M06/cc-pVTZ, M06/sp-aug-cc-pVTZ) and Moller-Plesset second-order perturbation (MP2/cc-pV-DZ) theory. Offset face to face (OSFF) stackings were found to be the favored orientations, and reasonable correlations were found between binding energies (Delta E-B) and the Sigma vertical bar sigma(m)vertical bar values of the substituted nitrobenzenes. It was proposed previously that vertical bar sigma(m)vertical bar contains information about the substituents' polarizability and controls electrostatic and dispersion interactions. The combination of Sigma vertical bar sigma(m)vertical bar and molar refractivity (as Sigma M-r) or change in polarizability (Delta alpha: with respect to benzene) of nitrobenzene derivatives generated statistically significant correlation with respect to.EB, thereby supporting the hypothesis related to the validity of vertical bar sigma(m)vertical bar correlations. The vertical bar sigma(p)vertical bar parameters also maintain similar correlations for the various p-substituted nitrobenzene derivatives together with several multiply-substituted nitrobenzene derivatives. The correlation properties in such cases are similar to the vertical bar sigma(m)vertical bar cases, and the energy partition analysis for both the situations reveled importance of electrostatic and dispersion contributions in such interactions. The applicability of Hammett parameters was observed previously on the restricted parallel face to face orientation of benzene center dot center dot center dot substituted benzene systems, and the present results show that such an idea could be used to predict Delta E-B values in OSFF orientations, if the scaffolds are designed in such a way that substituted benzene systems cannot escape their pi-clouds.