Abstract
The geometric parameters of stationary points on the potential surface energy of the chlorination reaction of nitrobenzene in the presence of Aluminium chloride as catalyst were investigated theoretically by hybrid DFT (Density Functional Theory) calculations in order to determine his general reaction mechanism in gas phase and in solution. The results obtained by DFT have been compared with CCSD(T) method which is the most powerful post-Hartree Fock method in terms of inclusion of dynamic correlation. Although the electrophilic substitution reaction is widely taught in most courses in organic chemistry, the mechanism has been very few studied theoretically. The results obtained in gas phase are consistent with the traditional description of these reactions: the orientation of this substitution in meta position depends on the stability of a reaction intermediate (Wheland said). Without taking in consideration the reactants and products, six stationary points are found on the potential surface energy of this reaction. The reaction has also been studied in the presence of solvent and we’ve noted that the influence of solvent decreases the electrostatic attraction on the Wheland complex, but the general reaction mechanism remains unchanged in solution.
Highlights
Many researchers are very interested to study theoretically the reactivity or the geometry of molecules with quantum chemical methods
In the molecular orbital calculation, the chemical species participating in the chlorination reaction are assumed to be nitrobenzene (C6H5-NO2), molecular chlorine (Cl2) and Lewis acid, so that the reacting system is considered to be neutral at the starting point and to be more realistic in describing the overall reaction pathway
The relative energies obtained for the chlorination of nitrobenzene in the presence of Aluminium Chloride as catalyst in gas phase are in Table 1 below: Table[1] Relative energies (ΔE) for chlorination reaction of nitrobenzene in gas phase; the reactants are taken as reference
Summary
Many researchers are very interested to study theoretically the reactivity or the geometry of molecules with quantum chemical methods. A relative recent paper has confirmed the presence of many intermediates in the case of chlorination reaction of non substituted benzene catalysed by AlCl3: Two complexes Π and one σ have been characterized in this study [12]. In the electrophilic substitution with benzene derivatives, the orientation of the second substitution depends on the nature of the first substituent and the stability of the intermediate σ called Wheland complex [17]. We’ve propose to explore the potential surface energy of the chlorination reaction of nitrobenzene (which have an acceptor substituent of electron) in the presence of Aluminium chloride as catalyst in order to determine the geometry of all stationary points and his general reaction mechanism in gas phase and in solution before validate or invalidate the Wheland interpretation which said that the orientation of this reaction depends on the stability of a reaction intermediate
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