The molecular geometries and electronic structures of 30 nitrobenzenes have been calculated by using semi-empirical MO AM1 and PM3 methods. EHOMO, ELUMO, ENHOMO, ENLUMO, AE, QNO2, Qc and V were selected as the structural descriptors. The acute toxicity （-log/C50） of nitrobenzenes to tetrahymena pyriformis along with the above eight structural parameters was used to establish the quantitative structure-activity relationships （QSARs）. The results indicate that the established model based on AM I method is superior to that on PM3 method not only for the stability but also for the predictive powers of the model. Based on AM1 parameters, a further classifying discussion was presented for the study of nitrobenzene toxic mechanism. The results show that the substituents, nitro group and halogen substituents on the aromatic ring are crucial to the chemicals＇ toxicity. For nitrobenzenes without halogen or other substituent, the reduction of nitro group is the main route. However, for those with halogen substituents, their next lowest unoccupied molecular orbital may take part in the toxic action betweeen the chemicals and macromolecules, and ENLUMO has the most important effect on these chemicals＇ toxicity.
In this paper, the fully optimized molecular geometries and electronic structures of six 1,2,3- and 1,2,4-triazoles were calculated using density functional theory B3LYP/6-311G^＊＊ method. The salvation energies were obtained by SCRF in THF. The results show that the total energies of F are the lowest both in gas and liquid phases, and the order of thermodynamic stabilities of the title compounds is F〉D〉C〉B〉E〉A. Their frontier orbital energy gaps and electron delocalization also support that F is the most stable. All the computed conclusions are in good agreement with the experiments. Vibrational frequencies of the title compounds were computed. The thermodynamic properties and their temperature curves of six compounds were obtained by using the statistical thermodynamic method with the temperature ranging from 200 to 1000 K.
LU Ya-Lin GONG Xue-Dong JU Xue-Hai JI Guang-Fu XIAO He-Ming
Seven optimized configurations and their electronic structures of 4-amino-5-nitro- 1,2,3-triazole dimers on their potential energy surface have been obtained by using density functional theory （DPT） method at the B3LYP/6-311＋＋G＊＊ level. The maximum intermolecular interaction energy is -35.42 kJ/mol via the basis set superposition error-correction （BSSE） and zero point energy-correction （ZPE）. Charge transfers between the two subsystems are small. The vibration analysis of optimized configurations was performed, and the thermodynamic property changes from monomer to dimer have been obtained with the temperature ranging from 200 to 800 K on the basis of statistical thermodynamics. It is found that the hydrogen bonds contribute to the dimers dominantly, and the extent of intermolecular interaction is mainly determined by the hydrogen bonds＇ strength rather than their number. The dimerization processes of Ⅳ, Ⅴand Ⅵ can occur spontaneously at 200 K.
LU Ya-Lin GONG Xue-Dong JU Xue-Hai MA Xiu-Fang XIAO He-Ming
A series of adamantyl nitrates have been theoretically studied from gas to solid to search for new po-tential high energy density compounds (HEDCs). The heats of formation (HOFs) for the 26 title com-pounds were calculated by designing isodesmic reactions at the B3LYP/6-31G level. It was found that the HOFs of the 26 isomers with the same number of —ONO2 groups (n) are not correlated well with the corresponding substituted positions. According to the obtained heats of detonation (Q),detonation velocities (D),and detonation pressures (P) using the Kamlet-Jacobs equations,it was found that when n=7～8,the adamantyl nitrates meet the criterion as an HEDC. The calculations on bond dissociation energies of O—N (EO—N) showed that the adamantyl nitrates with gemi —ONO2 always have the worst stability among the isomers,and all the adamantyl nitrates with gemi —ONO2 have similar stability. Due to the complexity of their structures,values of EO—N do not decrease with the increase of the substituent number n obviously,and the stability of adamantyl nitrates is not determined by only one structural parameter. Considering the stability requirement,only 1,2,4,6,8,9,10-adamantyl heptanitrate is recom-mended as a feasible HEDC. Molecular packing searching for 1,2,4,6,8,9,10-adamantyl heptanitrate among 7 most possible space groups (P21/c,P-1,P212121,P21,Pbca,C2/c,and Pna21) using Compass and Dreiding force fields showed that this compound tends to crystallize in P21/c. Ab initio periodic calculations on the electronic structure of the predicted packing showed that the O—NO2 bond is the trigger bond during thermolysis,which agrees with the result derived from the study of dissociation energies of O—N bonds.
