Theoretical Study of Reactivities in Electrophilic Aromatic Substitution Reactions:  Reactive Hybrid Orbital Analysis

Abstract

Orbital interactions in electrophilic aromatic substitution reactions of anisol, nitrobenzene, and some other analogues were studied. A single frontier orbital (FO), i.e., the HOMO of substituted benzenes, particularly of nitrobenzene, does not account for the regioselectivities of the reaction. We first applied configuration analysis to identify the relative importance of orbital interactions between an electrophile (H+ in this work) and the substituted benzenes. We herein define the reactive hybrid orbital (RHO) method for measuring the reactivity of each carbon atom of substituted benzene. An RHO is made by combining all occupied molecular orbitals properly so that the reactivity index for a reaction center, which is similar to superdelocalizability, is maximized. The RHO reactivity indices, λoc, ρoc, and , were shown to predict correctly the experimentally observed regioselectivity and reactivity in the electrophilic aromatic substitution reactions of anisol, nitrobenzene, and other monosubstituted benzenes. Moreover, it was shown that the RHO values for carbon atoms in a polycyclic aromatic hydrocarbon are in good agreement with experimentally determined partial rate factors.

The role of the Frontier orbitals in acid–base chemistry of organic amines probed by ab initio and chemometric techniques

“…Eighteen compounds, classified as aromatic (1-6), heterocyclic (7)(8)(9)(10)(11)(12)(13), and aliphatic (14)(15)(16)(17)(18) amines, were used in this study, and their experimental pK b values in water are depicted in Table I.…”

“…Thus, given the limitations of HOMO-LUMO argument and the new approaches proposed in the literature to understand the chemical reactivity, one must move forward the role of MOs in chemistry, giving rise to a new idea: the Frontier effective-for-reaction MO (FERMO) [9,[16][17][18][19][20][21][22][23][24][25].…”

Description of the Acid/Base Behavior of Organic Phosphines Using ab initio and Chemometric Approaches

“…Thus, given the limitations of HOMO-LUMO argument and the new approaches proposed in the literature to understand the chemical reactivity, one must move forward the role of molecular orbitals in chemistry, giving rise to a new idea: the Frontier Effective-for-Reaction Molecular Orbital (FERMO) [8][9][10][11][12][13][14][15][16][17][18] Actually, a careful study is still necessary to understand when the use of HOMO energy works or not. In addition, there is a lack of studies concerning a common and important base compounds in organic chemistry, the phosphines, and the relationship of their acid-base behavior with the corresponding MO energies.…”

A quantum chemical study on a set of non-imidazole H3 antihistamine molecules

“…This option was not discarded by Fukui [13] when commenting on the limitations of the HOMO-LUMO model for electron transfer. Using different methodologies, Fujimoto et al [14][15][16] and Hirao and Ohwada [17][18][19][20] maintained similar ideas to those of Da Silva et al [12].…”