New aspects of electrophylic aromatic substitution mechanism: Computational model of nitration reaction


Sandall [8] declared that the cause of NO+ reactivity was in its electronegativity, which is higher than that of NO2+. As to our results (Table V), it is softer electrophil, and the reason for its reactivity is that its reactive center is entirely open and the ion is smaller and more polar, thus creating a stronger electrostatic field. Additionally, although total enthalpy of nitrosation reaction and that of formation of σ-complex are smaller, the activation barrier is lower than in nitration reaction (see comparative values in Table VI). Therefore, there are all possibilities of catalysis of nitration reaction by nitrous acid:
NO2+ + HNO2 ⇒ NO+ + HNO3
NO+ + ArH ⇒ Ar–NO + H+
Ar–NO + H+ + HNO3 ⇒ Ar–NO2 + HNO2

Table VI. Thermochemical comparison of stages of nitration and nitrosation of benzene for AM1 and SM2.1.
ΔΔHf, gasΔΔHf, solvΔΔHf, solvΔΔHf, gas
C6H6, H+, HNO30000C6H6, H+, HNO2
C6H6, H2NO3+−1057374−98C6H6, H2NO2+
C6H6, NO2+, H2O−1164654−104C6H6, NO+, H2O
[O2N+ … C6H6], H2O−1128984−116[ON+ … C6H6], H2O
O2N-C6H6+, H2O−1256978−126ON-C6H6+, H2O
O2N-C6H5, H+, H2O−19−25−13−8ON-C6H5, H+, H2O