The DFT-B3LYP method, with the basis set 6-311G**, was employed to calculate the molecular geometries and electronic structures of 30 nitroaromatics. E_HOMO, E_LUMO, E_NHOMO, E_NLUMO, ΔE, Q_-NO2, Q_C(-NO2), Q_C(-NH2), Q_-NH2, μ and V were selected as quantum chemical descriptors. According to the type of substituents, the acute toxicity (－lg EC₅₀) of these compounds to golden orfe fish along with the above descriptors was used to establish the quantitative structure-activity relationships (QSAR). The results indicate that the type and number of the substituents affect the toxicity of these compounds directly. A nitro group substitution increases the toxicity of the compounds, and on the contrary, an amido group substitution decreases their toxicity. For multi-nitrobenzenes, the toxicity of the o- or p-substituted nitrobenzene is bigger than that of the m-substituted one. In conclusion, the nitro group is the main toxic group for both nitrobenzenes and nitroanilines. Wrapping or reducing the nitro groups will decrease the toxicity of the subject chemicals. Finally, the reactions between the reactive nitroso intermediates of nitrobenzene, 1,3-dinitrobenzene, and 1,4-dinitrobenzene and a protein sulphydryl group were simulated, and the toxic action processes of nitroaromatics were pointed out concretely. The influence of different numbers and different positions of the substituents on the molecular activity was discussed. The results are consistent with QSAR analysis. This study will also be beneficial to the molecular design of high energetic explosives.

Key words: nitroaromatics, toxicity, density functional theory, quantitative structure-activity relationship, toxic mechanism