title: Electron Transfer in Electrophilic Aromatic Nitration and Nitrosation: Computational Evidence for the Marcus Inverted Region.
abstract: Electrophilic aromatic nitrosation and nitration are among the most important electron transfer (ET) reactions. According to the electron transfer theory, an ET process can be described with two electron-localized diabatic states, and the electronic coupling between these two states, together with the organization energy and reaction energy, determine the ET efficiency. A proper definition of the strictly electron-localized states thus is the key. Here we used the valence bond theory to derive the diabatic states and probe the interactions of NO(+) and NO2(+) with benzene and identify the origin of their significant difference in reactivity. Results show that the high deformation cost for NO2(+) overshadows the fact that it has much high charge transfer interaction in [C6H6,NO2](+). While NO(+) uses π orbitals to bind benzene and the orbital switch results in a high barrier from π- to σ-complex, NO2(+) uses a vacant σ(Nsp(2)) orbital, making the transition nearly barrierless. Significantly, we found that the post-ET state [C6H6(+)-NO] is more stable than the prior-ET state [C6H6,NO(+)]. Energy profiles with respect to the distance between the electrophile and the benzene confirm that the ET reaction of benzene and NO(+) falls in the Marcus inverted region, and the outer-sphere ET occurs at ∼2.6 Å with the electronic coupling energy of 1.06 eV, compared with the experimental estimate 1.4 ± 0.5 eV.
authors.affiliation: Department of Chemistry, Western Michigan University , Kalamazoo, Michigan 49008, United States.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Western Michigan University , Kalamazoo, Michigan 49008, United States.
authors.forename: Yirong
authors.initials: Y
authors.lastname: Mo