Oxidative Aromatic Substitutions: Hartree−Fock/Density Functional and ab Initio Molecular Orbital Studies of Benzene and Toluene Nitrosation

Abstract

Aromatic nitrosations are prototypes of a recently proposed reaction mechanismoxidative aromatic substitutionsincorporating ground-state electron transfer prior to the substitution step. Ab initio MO and B3LYP hybrid Hartree−Fock/density-functional (HF/DF) calculations confirm that nitrosation proceeds through initial formation of intermediate electron donor−acceptor (EDA) π-complexes. Calculated π-complex geometries and energies agree qualitatively with experimental data and indicate the applicability of HF/DF methods for modeling EDA complexes. Subsequent transformation of (benzene−NO)+ and (toluene−NO)+ π-complexes into N-protonated nitroso-derivatives in B3LYP and MP2 calculations suggest an alternative to the currently proposed mechanism involving π-complex transformation into Wheland type σ-complexes (supported by CISD calculations). Kinetic analysis suggests the alternative mechanism is plausible and indicates that proton transfer from the N-protonated nitroso-derivatives to the medium would not be...