Theoretical study of substituents effect on C–NO2 bond strength in mono substituted nitrobenzenes

Enthalpies of the C−N bond dissociation of nitrobenzene and twenty-seven mono substituted nitrobenzenes along with their formation enthalpies were calculated using different multilevel (G2, G3, G3B3, CBS-QB3) and density functional theory-based B3LYP and wB97XD techniques. The gas phase enthalpies of formation of mono substituted phenyl radicals were also calculated using these methods. The calculated values of reaction enthalpies were compared with available experimental data. We have concluded based on results of present and recent article, that B3LYP level of theory with 6-31G(d′f,p′) basis sets should proposed as the accurate method for calculating formation enthalpies of mono substituted nitrobenzenes as well as enthalpies of C–NO2 bond scission. Based on satisfactory correlation between experimental and calculated data we proposed revision of experimental activation energy of C–NO2 bond rupture in o-chloronitrobenzene, o- and m-nitrotoluene as wells as p-nitroaniline. Enthalpies of formation of some substituted phenyl radicals were estimated using experimental enthalpies of C–NO2 bond cleavage together with formation enthalpies of mono substituted nitrobenzenes and NO2 moiety.