Solvation in nitration of benzene and the valence electronic structure of the Wheland intermediate

• Published in: Physical chemistry chemical physics : PCCP Vol. 24; no. 27; pp. 16453 - 16461
• Main Authors: Nakatani, Kaho, Teshigawara, Sho, Tanahashi, Yuta, Kasahara, Kento, Higashi, Masahiro, Sato, Hirofumi
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 13.07.2022
• Subjects: Benzene; Density distribution; Electron density; Electronic structure; Free energy; Hydrocarbons; Molecular structure; Nitration; Pi-electrons; Quantum chemistry; Self consistent fields; Solvation; Solvents; Statistical mechanics; Substitution reactions; Sulfuric acid
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d2cp01699k

Nitration of benzene is a representative aromatic substitution reaction related to the -complex (arenium ion or Wheland intermediate) concept. This reaction is typically carried out in a mixed acid solution to generate nitronium ions, and how solvent molecules play roles in the reaction has been of great interest. Here we will shed new light on the reaction, namely the electronic structure and the microscopic insights of the solvation, which have been rarely discussed so far. We studied this process using the reference interaction site model-self consistent field with constrained spatial electron density distribution (RISM-SCF-cSED) method, considering sulfuric acid or water molecules as a solvent. In this method, the electronic structure of the solute and the solvation structure are self-consistently determined based on quantum chemistry and statistical mechanics of molecular liquids. The solvation free energy surfaces in solution and solvation structures were verified. In the bond formation process of benzene and nitronium ions, the solvation structure by sulfuric acid molecules drastically changes and the solvation effect on the free energy is quite large. We revealed largely contributing resonance structures in the -electron system of the -complex in gas and solution phases by analysing the valence electronic structures. Nitration of benezene was studied with the reference interaction site model-self consistent field method, considering the sulfuric acid solvent. In the bond formation process, the solvation structure drastically changes due to the charge transfer.