Large Amplitude Torsions in Nitrotoluene Isomers Studied by Rotational Spectroscopy and Quantum Chemistry Calculations

Rotational spectra of ortho-nitrotoluene (2-NT) and para-nitrotoluene (4-NT) have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter-wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations, the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the ¹⁴N nucleus and the internal rotation splittings arising from the methyl group. For 2-NT, an anisotropic internal rotation of coupled −CH₃ and −NO₂ torsional motions was identified by quantum chemistry calculations and discussed from the results of the MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono-substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier.     

硝基甲苯类炸药C-NO2键中点的静电势

利用HONDO程序包,采用从头计算法对硝基甲苯类炸药的分子结构及其C-NO2键中点的静电势进行了计算,讨论了硝基甲苯类炸药C-NO2键中点的静电势最大值Vmidmax与其实验撞击感度之间的关系.研究表明:对于硝基甲苯类炸药,可用其分子C-NO2键中点的静电势最大值Vmidmax来确定其撞击感度的变化趋势.以静电势为判据,讨论了硝基和甲基数目以及硝基和甲基的相对位置对这类炸药撞击感度的影响.     

CH3COOH.TiO2: An excellent catalyst for the green nitration of toluene by N2O4

The solvent-free nitration of toluene with N₂O₄ gas over solid acid catalysts is a green reaction for preparing the mono-nitrotoluene (NT) isomers. The acid-modified catalysts are more efficient than common catalysts for this type of reaction. For this purpose, a titanium dioxide (TiO₂) catalyst is synthesized with a sol-gel method and modified by acetic acid to increase catalytic properties. The acid-modified TiO₂ (CH₃COOH·TiO₂) is characterized by different analyses. To optimization of toluene nitration conditions, reaction temperature (X₁) (30 < X₁ < 60 °C), N₂O₄/toluene molar ratio (X₂) (0.5 < X₂ < 2), and the amount of catalyst (X₃) (0.05 < X₃ < 0.3 g) factors were investigated by Minitab software with the CCD-RSM. Three responses including the selectivity of meta-NT isomer (S_m), the ratio of para-NT to ortho-NT selectivity (S_p/o), and the selectivity of by-products (S_bp) were considered for the optimization. Statistical parameters were applied to evaluate the goodness of fitting for the models. Optimum values for X₁, X₂, and X₃ parameters are 57.9 °C, 1.91, and 0.25 g, respectively. The conversion of toluene under these conditions is 93.2%. The comparison of S_m, S_p/o, and S_bp in CH₃COOH.TiO₂ (1.51%, 0.8, and 5.48%, respectively) with Fe₂O₃ (8.5%, 0.43, and 20.57%, respectively), SiO₂ (8.43%, 0.48, and 16.24%, respectively), TiO₂ (5.9%, 0.57, and 13.87%, respectively), TiO₂–Fe₂O₃ (4.72%, 0.64, and 9.18%, respectively), and TiO₂–SiO₂ (4.42%, 0.67, and 5.73%, respectively) catalysts show that this catalyst has a low S_m and S_bp as well as a higher S_p/o than other mentioned catalysts. The mechanism of the mentioned reaction is reviewed in the presence of CH₃COOH·TiO₂ catalyst. The high stability of the CH₃COOH·TiO₂ is proved by the reusability test, and it is found that its stability against inactivation is more than the TiO₂ catalyst.     

Photo-induced isomerization of three nitrotoluene isomers: A matrix-isolation infrared spectroscopic and quantum-chemical study

The photo-induced isomerization reactions of ortho-, meta- and para-nitrotoluene molecules were investigated by matrix isolation infrared spectroscopy and quantum chemical calculations. Under UV irradiation of ortho-nitrotoluene in solid argon, the hydrogen atom transfer isomer was formed, as reported previously. It was found that the hydrogen atom transfer isomer is unstable and rearranged to its nitro isomer upon annealing. In addition, the nitrite isomer as well as its dissociation product tolyloxy radical was also formed. Only the nitrite isomers and the tolyloxy radicals were formed upon UV excitation of the meta- and para-nitrotoluene molecules. Infrared spectra and vibrational frequency assignments of the newly observed nitrite isomers and tolyloxy radicals are reported, which are supported by quantum chemical calculations.