Theoretical studies on the structures, thermodynamic properties, detonation properties, and pyrolysis mechanisms of spiro nitramines

Density function theory (DFT) has been employed to study the geometric and electronic structures of a series of spiro nitramines at the B3LYP/6-31G level. The calculated results agree reasonably with available experimental data. Thermodynamic properties derived from the infrared spectra on the basis of statistical thermodynamic principles are linearly correlated with the number of nitramine groups as well as the temperature. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that some compounds with the predicted densities of ca. 1.9 g/cm3, detonation velocities over 9 km/s, and detonation pressures of about 39 GPa (some even over 40 GPa) may be novel potential candidates of high energy density materials (HEDMs). Thermal stability and the pyrolysis mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6-31G level and the activation energies (E(a)) with the selected PM3 semiempirical molecular orbital (MO) based on the unrestricted Hartree-Fock model. The relationships between BDE, E(a), and the electronic structures of the spiro nitramines were discussed in detail. Thermal stabilities and decomposition mechanisms of the title compounds derived from the B3LYP/6-31G BDE and the UHF-PM3 E(a) are basically consistent. Considering the thermal stability, TNSHe (tetranitrotetraazaspirohexane), TNSH (tetranitrotetraazaspiroheptane), and TNSO (tetranitrotetraazaspirooctane) are recommended as the preferred candidates of HEDMs. These results may provide basic information for the molecular design of HEDMs.     

Theoretical studies on the structures, thermodynamic properties, detonation properties, and pyrolysis mechanisms of four trinitrate esters

Density function theory (DFT) has been employed to study the geometric and electronic structures of four trinitrate ester including nitroglycerin (NG), butanetriol trinitrate (BTTN), trimethanolethane trinitrate (TMETN) and trimethylolpropane trinitrate (TMPTN) at the B3LYP/6-31G^* level. Their IR spectra were obtained and assigned by vibrational analysis. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties were evaluated, which were linearly related with the number of methylene groups as well as the temperature, obviously showing good group additivity. Detonation performances were evaluated by the Kamlet–Jacobs equations based on the calculated densities and heats of formation. It is found that density, detonation velocity, detonation pressure are decrease with the increase of the number methylene groups. Thermal stability and the pyrolysis mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6-31G^* level. For the nitrate esters, the ONO₂ bond is a trigger bond during thermolysis initiation process.     

Theoretical studies on the heats of formation, detonation properties, and pyrolysis mechanisms of energetic cyclic nitramines

Density functional theory calculations were performed to find comprehensive relationships between the structures and performance of a series of highly energetic cyclic nitramines. The isodesmic reaction method was employed to estimate the heat of formation. The detonation properties were evaluated by using the Kamlet-Jacobs equations based on the theoretical densities and HOFs. Results indicate the N-NO(2) group and aza N atom are effective substituents for enhancing the detonation performance. All cyclic nitramines except C11 and C21 exhibit better detonation performance than HMX. The decomposition mechanism and thermal stability of these cyclic nitramines were analyzed via the bond dissociation energies. For most of these nitramines, the homolysis of N-NO(2) is the initial step in the thermolysis, and the species with the bridged N-N bond are more sensitive than others. Considering the detonation performance and thermal stability, twelve derivatives may be the promising candidates of high energy density materials (HEDMs). The results of this study may provide basic information for the further study of this kind of compounds and molecular design of novel HEDMs.     

Theoretical studies on the structures, densities, detonation properties and pyrolysis mechanism of energetic compounds containing pyridine ring

Density function theory has been employed to study a series of compounds containing pyridine ring at the B3LYP/6-31G* level. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and heats of formation. Some compounds have high densities (ca. 1.9 g cm⁻³) and good performance (detonation velocities over 9 km s⁻¹, detonation pressures about 39 GPa) and may be the potential candidates of high energy density materials. The thermal stability and the pyrolysis mechanism of the title compounds were investigated by the bond dissociation energies and the impact sensitivity predicted. Solvent effect has been investigated and it makes the title compounds more stable in solutions.     

Theoretical studies on the structures and vibrational spectra of Ni, Pd, and Pt phthalocyanines

Electronic structure calculations and spectroscopic assignments for metallophthalocyanines NiPc, PdPc and PtPc are performed on optimized geometries at B3LYP/LANL2DZ level. The order of the sizes of the central hole is computed to be PdPc > PtPc > NiPc, with the hole size of PdPc close to that of PtPc. The Mulliken charges of the central M vary in the order of PtPc > NiPc > PdPc, and the HOMO-LUMO gaps are in the order of NiPc < PdPc < PtPc, in agreement with the experimental result. The simulated IR spectra for the three derivatives are compared with the experimental absorption spectra, and very good consistency has been obtained. The simulated medium intensity bands associated with the metal-ligand vibrations which appear as singlet bands at 880, 877 and 883 cm⁻¹, respectively, exhibit the order of PtPc > NiPc > PdPc, which is the same order as experiment. Furthermore, the metal-ligand vibrational bands for Raman spectra shift in the order NiPc > PtPc > PdPc. The strongest Raman lines predicted at 1562, 1532 and 1534 cm⁻¹ for NiPc, PdPc and PtPc are very sensitive to the metal ion.     

A theoretical study on the vibrational spectra and thermodynamic properties for the nitro derivatives of phenols

The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Their IR spectra are obtained and assigned by vibrational analysis and are reliable compared with the experimental results. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties are evaluated, which are linearly related with the number of nitro and hydroxy groups as well as the temperature, obviously showing good group additivity.     

多溴代芴热力学性质的理论预测研究

为了预测环境污染物多溴代芴的热力学性质,计算了60种多溴代芴的分子连接性指数、电性距离矢量指数、电性拓扑状态指数以及分子形状指数.采用多元线性回归的方法建立了多溴代芴化合物的标准生成焓(Δ_fH~0)、标准熵(S~0)、标准生成吉布斯自由能(Δ_fG~0)及等容热容等热力学性质的QSPR相关性模型,方程的相关系数值均在0.99以上.与相关文献的相关系数R和标准误差S进行比较,该模型具有良好的预测能力和稳定性.     

Theoretical investigation on density,detonation properties,and pyrolysis mechanism of nitro derivatives of benzene and aminobenzenes

Nitro derivatives of benzene and aminobenzenes are optimized at the DFT‐B3LYP/6‐31G* level. The heat of formation (ΔH_f) and crystal theoretical density (ρ) are estimated to evaluate the detonation properties using the modified Kamlet–Jacobs equations. Thermal stability and the pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDE) at the unrestricted B3LYP/6‐31G* level. The kinetic parameter and the static electronic structural parameters can be used to predict the stability and the relative magnitude of the impact sensitivity of homologues. According to the quantitative standard of the energy and the stability as an HEDC, the title compounds having more than four nitro groups satisfy this requirement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical studies on molecular structure and vibrational spectra of 8-hydroxyquinolinium picrate

Quantum chemical calculations of geometrical structure and vibrational wavenumbers of 8-hydroxyquinolinium picrate (8-HQP) were carried out by ab initio HF and density functional (DFT/B3LYP) method with 6-31++G(dp) basis set. The calculated geometric parameters of 8-HQP are presented. A detailed interpretation of the infrared spectra of 8-hydroxyquinolinium picrate (8-HQP) are also reported. Theoretical molecular frontier orbital energies of the title compound have been calculated using the method mentioned above in order to understand this phenomenon in the context of molecular orbital picture. The molecular HOMOs and LUMOs generated via HF and B3LYP method have been outlined.     

FC(O)NCS分子振动光谱的理论研究

采用DFT(B3LYP)方法,以6-3G*为基组对FC(O)NCS的顺式和反式两种构型的几何结构,振动谐性力场和红外光谱进行了研究。B3LYP/6-31G*计算水平和大多数有机分子的一套固定标度因子进行标度。根据标度后的理论力场进行简正坐标分析得到的势能分布(PED)和红外光谱强度值对FC(O)NCS分子的顺式和反式两种构型的振动基频进行了理论归属。     

Theoretical studies of molecular structure and vibrational spectra of O-ethyl benzoylthiocarbamate

O-Ethyl benzoylthiocarbamate has been synthesized and characterized by elemental analysis and FT-IR. The crystal structure was determined by X-ray diffraction analysis. Title compound crystallizes in the orthorhombic space group Pna2(1), with Z=4. Unit cell parameters a=9.941(3)A, b=9.352(3)A, c=10.962(3)A and V=1019.1(5)A(3). The molecular geometry and vibrational frequencies of O-ethyl benzoylthiocarbamate in the ground state has been calculated using the Hartree-Fock and density functional using Becke's three-parameter hybrid method with the Lee, Yang, and Parr correlation functional (B3LYP) methods with 3-21G and 6-31G(d) basis sets. The computational frequencies are in good agreement with the observed results. Comparison of the observed fundamental vibrational frequencies of O-ethyl benzoylthiocarbamate and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.     

Theoretical studies of molecular structure and vibrational spectra of melaminium citrate

The molecular geometry and vibrational frequencies of melaminium citrate in the ground state have been calculated using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and density functional theory (DFT, B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of melaminium citrate and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.     

Computational studies on the crystal structure, thermodynamic properties, detonation performance, and pyrolysis mechanism of 2,4,6,8-tetranitro-1,3,5,7-tetraazacubane as a novel high energy density material

Studies have suggested that octanitrocubane (ONC) is one of the most powerful non-nuclear high energy density material (HEDM) currently known. 2,4,6,8-Tetranitro-1,3,5,7-tetraazacubane (TNTAC) studied in this work may also be a novel HEDM due to its high nitrogen content and crystal density. Density functional theory and molecular mechanics methods have been employed to study the crystal structure, IR spectrum, electronic structure, thermodynamic properties, gas-phase and condensed-phase heat of formation, detonation performance, and pyrolysis mechanism of TNTAC. The TNTAC has a predicted density of about 2.12 g/cm(3), and its detonation velocity (10.42 km/s) and detonation pressure (52.82 GPa) are higher than that of ONC. The crystalline packing is P2(1)2(1)2(1), and the corresponding cell parameters are Z = 4, a = 8.87 ?, b = 8.87 ?, and c = 11.47 ?. Both the density of states of the predicted crystal and the bond dissociation energy of the molecule in gas phase show that the cage C-N bond is the trigger bond during thermolysis. The activation energy of the pyrolysis initiation reaction obtained from the B3LYP/6-311++G(2df,2p) level is 125.98 kJ/mol, which indicates that TNTAC meets the thermal stability request as an exploitable HEDM.     

Theoretical studies on the structural,spectroscopic, thermodynamic,and electronic properties of zoledronic acid

The structure, spectroscopic, thermodynamic, and electronic properties of zoledronic acid (ZL, 1-hydroxy- 2-(1H-imidazol-1-yl)ethane-1,1-diyldiphosphonic acid), typical third-generation nitrogen-containing bisphosphonates (N-BPs), have been investigated systematically. Six conformations are taken into account, including three unprotonated and three protonated structures. They are optimized by four different density functional theory (DFT) methods combined with four different basis sets to evaluate their performance in predicting the structural and spectral features of ZL. Thermodynamic properties are calculated based on the harmonic vibrational analysis, including the standard heat capacity (C _p,m ⁰ ), entropy (S _m ⁰ ), and enthalpy (S _m ⁰ ). The ¹H and ¹³C NMR chemical shifts are calculated using the GIAO method and compared with the experimental data. Molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) analyses are also performed to study the electronic characteristics of the title compound.     

Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

Theoretical studies on vibrational spectra of some halides of group IVB elements

The vibrational spectra of group IVB elements halides MX4 (M=Ti(IV), Zr(IV), Hf(II); X=F, Cl, Br and I), have been investigated by ab initio RHF, MP2 and density functional theory B3LYP method with LanL2DZ basis sets. The optimized geometries, calculated vibrational frequencies and Far-IR intensities of MX4 are evaluated via comparison with experimental data. The vibrational frequencies, calculated by these methods, are compared to each other. The results indicate that B3LYP method is more reliable than RHF and MP2 methods for the frequencies calculations for these compounds. With this method, some vibrational frequencies of M2X6(2+)(M=Ti(IV), Zr(IV) and Hf(II); X=F, Cl, Br and I) are also predicted.     

Electronic and vibrational spectra and thermodynamic functions of di-halogentoluenes

The i.r. and Raman spectra of liquid 2-fluoro-5-iodotoluene and 4-fluoro-2-iodotoluene and the near u.v. spectra of their vapour are reported. An assignment of fundamentals is proposed. Calculated values of the thermodynamic functions are given.     

X-ray,vibrational spectra and density functional studies on cynacure

The solid-state X-ray diffraction, FT-IR and FT-Raman measurements of cynacure have been performed. Optimized molecular structures and normal vibrations of cynacure and 2-(methylthio)aniline have been calculated in the gas phase at the B3LYP/6-311++G** level. Scaling factors that bring computational gas-phase frequencies in closer agreement with the solid-state experimental data have been calculated for each vibration type. The observed IR and Raman bands of cynacure and 2-(methylthio)aniline have been assigned in the frameworks of the calculated mode frequencies as well as the calculated IR and Raman intensities. The assignments of the normal modes of cynacure have been compared with those of the benzene and 2-(methylthio)aniline modes. The effects of the substitution on the benzene vibrational frequencies have been investigated. 2-(Methylthio)aniline and cynacure both have four stable conformers. The calculated ground-state energetics and vibrational spectra of 2-(methylthio)aniline and cynacure suggest the coexistence of their stable conformers at the room temperature.