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

Applicability of Hammett parameters (σ m and σ p ) was tested in extended π-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 π-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 Møller-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 (Δ E B ) and the ∑|σ m | values of the substituted nitrobenzenes. It was proposed previously that |σ m | contains information about the substituents' polarizability and controls electrostatic and dispersion interactions. The combination of ∑|σ m | and molar refractivity (as ∑ M r ) or change in polarizability (Δα: with respect to benzene) of nitrobenzene derivatives generated statistically significant correlation with respect to Δ E B , thereby supporting the hypothesis related to the validity of |σ m | correlations. The |σ p | 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 |σ m | 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···substituted benzene systems, and the present results show that such an idea could be used to predict Δ E B values in OSFF orientations, if the scaffolds are designed in such a way that substituted benzene systems cannot escape their π-clouds.