A corrected benzene nitration three-step mechanism derived by DFT calculation and MO theory

Density-functional theory (DFT) calculations at the LC-wHPBE/6-311++G(d,p) level found that textbook three-step nitration mechanism of benzene in mixed acids was seriously wrong. Step 1 generating nitronium ion (NO2+) is not spontaneous, NO2+ generated by Lewis collision, and needs to overcome a barrier Ea = 18 or 22 kcal/mol acid nitric acid. Obtaining collision quantum chemical highlight study. The reaction system (NO2+ + H2O) HSO4⎺ NO3⎺ nH2O (n ≥ 1) can make spontaneously change HNO3 through poly(≥3)-molecular acidification. Sulfuric greatly reduce [H2O] increase [NO2+]. Therefore, rate much faster than 2, C6H6 NO2+, an electrophilic addition, follows transition state theory, low barrier, ΔE* 7 kcal/mol. product 2 σ-complex C6H6-NO2+. essence addition transfer HOMO-1 electrons LUMO NO2+. 3 spontaneous acid-base neutralization without any generates target nitrobenzene C6H5NO2. are two active intermediates nitration. control step σ-complex, but generate DFT calculation obtains barriers ΔE*, heats ΔHσ ΔHp each nitration, resulting total heat ΔH -35 It consistent with experimental -34 Based on results, corrected proposed.