Substituent Effect on Infrared Spectra and Thermodynamic Properties of Polynitroamino Substituted Cyclopentane and Cyclohexane

Density functional theory method was employed to study the effect of the nitroamino group as a substituent in cyclopentane and cyclohexane, which usually construct polycyclic or caged nitramines. Based on the optimized molecular structures of two groups of monocyclic nitramines at the B3LYP/6-31G** level, the infrared (IR) spectra were obtained and assigned by harmonic vibrational analysis. The calculated results agree reasonably with the available experimental data. According to the principles of statistic thermodynamics, thermodynamic properties were derived from the IR spectra, which were linearly correlated with the number of nitroamino groups as well as the temperature. The.     

六硝基芪衍生物的红外光谱和热力学性质的理论研究

用量子化学密度泛函理论方法,在B3LYP/6-31G*水平下,对六硝基芪衍生物进行了几何构型全优化和电子结构计算。通过振动分析,求得它们的红外光谱并作归属。将理论计算IR谱与已知实验结果进行比较,表明本文所提供的计算结果是可靠的。对谐振频率以0.96进行标度后基于统计热力学原理求得它们的热力学性质,探讨了热力学性质随硝基数、氨基数、羟基数和温度变化的规律,发现有很好的线性关系,体现了很好的基团加和性。     

苯和苯胺类硝基衍生物的红外光谱和热力学性质的理论研究

用量子化学密度泛函理论方法,在B3LYP/6-31G*水平下,对苯和苯胺类硝基衍生物进行了几何构型全优化和电子结构计算。通过振动分析,求得它们的红外光谱并作归属。将理论计算IR谱与已知实验结果进行比较,表明本文所提供的计算结果是可靠的。对谐振频率以0.96进行标度后基于统计热力学原理求得它们的热力学性质,探讨了热力学性质随硝基数、氨基数和温度变化的规律,发现有很好的线性关系,体现了很好的基团加和性。     

Substituent effects on structural stability of formyl ketene and analysis of vibrational spectra of formyl haloketenes and formyl methylketene.

The conformational behavior and the structural stability of formyl fluoroketene, formyl chloroketene and formyl methylketene were investigated by utilizing quantum mechanical DFT calculations at B3LYP/6-31I + + G** and ab initio calculations at MP2/6-311 + + G** levels. The three molecules were predicted to have a planar s-cis<-->s-trans conformational equilibrium. From the calculations, the direction of the conformational equilibrium was found to be dependent on the nature of the substituting group. In formyl haloketenes, the cis conformation, where the C=O group eclipses the ketenic group, was expected to be of lower energy than the trans conformer. In the case of formyl methylketene the conformational stability was reversed and the trans form (the aldehydic hydrogen eclipsing the ketenic group) was calculated to be about 2 kcal mol(-1) lower in energy than the cis form. The calculated cis-trans energy barrier was found to be in the order: fluoride (15.3 kcal mol(-1)) > chloride (13.1 kcal mol(-1)) > methyl (11.7 kcal mol(-1). Full optimization was performed at the ground and the transition states of the molecules. The vibrational frequencies for the stable conformers of the three ketenic systems were computed at the DFT-B3LYP level, and the zero-point corrections were included into the calculated rotational barriers. Complete vibrational assignments were made on the basis of both normal coordinate calculations and comparison with experimental results of similar molecules.     

Thermodynamic Modeling of KF-CrF3 Binary System

A comprehensive thermodynamic model of KF-CrF₃ system was established. The intermediate phases K₂Cr₅F₁₇, KCrF₄, K₂CrF₅ and K₃CrF₆ were described by the stoichiometric compound model and the liquid phase by associated solution model. All the model parameters were optimized by the experimental phase equilibria data assisted by the first-principles prediction within the framework of the calculation of phase diagram(CALPHAD) method. It is demonstrated that the calculated results are fairly consistent with the experimental data, thus we obtained a set of self-consistent and reliable thermodynamic parameters which could well describe the phase equilibria and thermodynamic properties of KF-CrF₃ system.     

A Theoretical Study on the Vibrational Spectra and Thermodynamic Properties for the Derivatives of 2,5-Dipicryl-1,3,4-oxadiazole with N3, ONO2, and NNO2 Groups

The derivatives of 2,5‐dipicryl‐1,3,4‐oxadiazole (DPO) were optimized to obtain their molecular geometries and electronic structures at the DFT‐B3LYP/6‐31G^* level. Their IR spectra were obtained and assigned by vibrational analysis. Compared with the experimental results, all the calculated IR data were found to be reliable. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties were evaluated, which are respectively linearly related with the number of azido, nitrate and nitramine groups as well as the temperature, obviously showing good group additivity.     

Vibrational spectroscopic investigation of methyl(5-[2-thienylcarbonyl]-1H-benzimidazol-2-yl: A comparative density functional study

FT-IR and Raman spectra of methyl(5-[2-thienylcarbonyl]-1H-benzimidazol-2-yl (nocodazole) are experimentally examined in the region of 4000–400 cm^?1. The optimized geometric parameters, conformational equilibria, normal mode frequencies, and corresponding vibrational assignments of nocodazole (C₁₄H₁₁N₃O₃S) calculated by means of the B3LYP hybrid density functional theory (DFT) method using the 6-31++G(d,p) basis set. Vibrational assignments are made based on the total energy distribution (TED) and the thermodynamic functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of nocodazole are calculated. Calculations are employed for four energetically possible conformers of nocodazole (N1, N2, N3, and N4) in the gas phase. A comparison between the experimental and theoretical results indicates that the B3LYP method is able to provide satisfactory results for predicting vibrational wavenumbers if calculated values are scaled properly and the structural parameters.     

甲酰氯异构化和光解的理论研究——从头算水平上的反应热力学、动力学分析

由于对化学反应体系解核运动Schrdinger方程困难,化学界常常求解参加反应粒子的电子运动Schrdinger方程,得到其电荷密度分布、自由价和键级等静态物理量,作为反应性指标;这虽有简明的优点,但往往缺乏传递性和统一性。如用电荷密度分布分析亲电反应,仅在同系物中有定性比较其反应性相对大小的意义,无定量价值。此外,用反应的势垒大小判断反应的难易,忽略了鞍点处曲率的影响,就动力学的Arrhenius速度常数公式看,     

Experimental and theoretical studies on vibrational spectra of 4-(2-furanylmethyleneamino)antipyrine, 4-benzylideneaminoantipyrine and 4-cinnamilideneaminoantipyrine

This work deals with the IR and Raman spectroscopy of 4-(2-furanylmethyleneamino) antipyrine (FAP), 4-benzylideneaminoantipyrine (BAP) and 4-cinnamilideneaminoantipyrine (CAP) by means of experimental and quantum chemical calculations. The equilibrium geometries, harmonic frequencies, infrared intensities and Raman scattering activities were calculated by density functional B3LYP method with the 6-31G(d) basis set. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries have been compared with the experimental data obtained from XRD data, which indicates that the theoretical results agree well with the corresponding experimental values. For the three compounds, comparisons and assignments of the vibrational frequencies indicate that the calculated frequencies are close to the experimental data, and the IR spectra are comparable with some slight differences, whereas the Raman spectra are different clearly and the strongest Raman scattering actives are relative tightly to the molecular conjugative moieties linked through their Schiff base imines. The thermodynamic properties (heat capacities, entropies and enthalpy changes) and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized strucutres.     

Ab initio studies of solvent effect on molecular conformation and vibrational spectra of diacetamide

The conformational equilibria and vibrational spectra of diacetamide have been investigated by ab initio molecular orbital studies using the basis sets 6-31g(d,p) and 6-31++g(d,p) at Hartree-Fock and MP2 levels. The vibrational spectra of diacetamide have been satisfactorily interpreted taking into consideration the agreement between the calculated harmonic vibrational frequencies, infrared and Raman band intensities and shifts in deuterated molecules with those observed. The solvent effects were investigated by the self-consistent reaction field (SCRF) theory. The effect of solvent on the conformational equilibria and vibrational spectra is discussed. The calculated changes in the geometry and vibrational spectra on going from the gas phase to the solvent medium are in accord with the increasing weight of the dipolar resonance structure of the amide group in more polar solvents.     

1,3,5,7-四硝基金刚烷结构和性能的理论研究

在DFT-B3LYP/6-31G*水平下求得1,3,5,7-四硝基金刚烷的全优化分子几何和电子结构. 经简谐振动分析求得其IR谱并作归属. 由统计热力学求得其不同温度下的热力学性质. 以非限制性半经验MO方法探讨其热解机理, 求得各反应通道的过渡态和活化能, 发现热解始于侧链C—NO₂键的均裂. 还基于理论计算密度和生成热, 以Kamlet-Jacobs方程估算其爆速和爆压.     

氢化可的松的热力学函数和晶体结构——密度泛函理论分析

采用密度泛函理论B3LYP/6-31G和B3LYP/6-311G*方法优化了气相状态氢化可的松的几何结构,利用优化的结构得到了氢化可的松各原子净电荷及前沿轨道分布;基于简谐振动分析求得氢化可的松的红外光谱频率和热力学函数;并计算了环己烷、乙酸丁酯、二氯乙烷、异丙醇、甲醇、水六种不同极性的溶剂对氢化可的松几何构型、电荷分布及能量的影响.结果表明,由理论计算得到的氢化可的松的晶体结构与实测的晶体结构接近.     

Simulated vibrational spectra of aflatoxins and their demethylated products and the estimation of the energies of the demethylation reactions

The structure of four natural mycotoxins, the aflatoxin B1, B2, G1 and G2 and their demethylated products were optimized with quantum chemical method. The energies and the thermodynamic functions of the molecules were calculated and applied to calculation of the reaction energies of the demethylations. Further results of the calculations are the vibrational force constants, the infrared spectra of the molecules and the assignments of the spectral bands.     

Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties

Thermodynamic properties of selected small and medium size molecules were calculated using harmonic and anharmonic vibrational frequencies. Harmonic vibrational frequencies were obtained by normal mode analysis, whereas anharmonic ones were calculated using the vibrational self-consistent field (VSCF) method. The calculated and available experimental thermodynamic data for zero point energy, enthalpy, entropy, and heat capacity are compared. It is found that the anharmonicity and coupling of molecular vibrations can play a significant role in predicting accurate thermodynamic quantities. Limitations of the current VSCF method for low frequency modes have been partially removed by following normal mode displacements in internal, rather than Cartesian, coordinates.     

Density functional theory calculation and vibrational spectroscopy study of 2-amino-4,6-dimethyl pyrimidine (ADMP)

The solid phase FTIR and FT-Raman spectra of 2-amino-4,6-dimethyl pyrimidine (ADMP) have been recorded in the regions 4000-400 cm(-1) and 3500-50 cm(-1) respectively. The structure was investigated by utilizing density functional theory (DFT) calculations with the Becke 3-Lee-Yang-Parr (B3LYP) method employing the 6-31+G and 6-311++G basis sets. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data. Complete vibrational assignments were made on the basis of normal coordinate analysis (NCA) for the molecule. The infrared and Raman spectra were also predicted from the calculated intensities. The observed and the calculated spectra were found to be in good agreement. The thermodynamic properties like entropies and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized structures.     

Vibrational spectroscopy (FT-IR and FT-Raman) investigation, and hybrid computational (HF and DFT) analysis on the structure of 2,3-naphthalenediol

The FT-IR and FT-Raman vibrational spectra of 2,3-naphthalenediol (C(10)H(8)O(2)) have been recorded using Bruker IFS 66V spectrometer in the range of 4000-100 cm(-1) in solid phase. A detailed vibrational spectral analysis has been carried out and the assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The optimized molecular geometry and vibrational frequencies in the ground state are calculated by using the ab initio Hartree-Fock (HF) and DFT (LSDA and B3LYP) methods with 6-31+G(d,p) and 6-311+G(d,p) basis sets. There are three conformers, C1, C2 and C3 for this molecule. The computational results diagnose the most stable conformer of title molecule as the C1 form. The isotropic computational analysis showed good agreement with the experimental observations. Comparison of the fundamental vibrational frequencies with calculated results by HF and DFT methods. Comparison of the simulated spectra provides important information about the capability of computational method to describe the vibrational modes. A study on the electronic properties, such as absorption wavelengths, excitation energy, dipole moment and Frontier molecular orbital energies, are performed by time dependent DFT approach. The electronic structure and the assignment of the absorption bands in the electronic spectra of steady compounds are discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. On the basis of the thermodynamic properties of the title compound at different temperatures have been calculated. The statistical thermodynamic properties (standard heat capacities, standard entropies, and standard enthalpy changes) and their correlations with temperature have been obtained from the theoretical vibrations.     

FT-IR, FT-Raman spectra and quantum chemical calculations of some chloro substituted phenoxy acetic acids

In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of o-chlorophenoxy acetic acid (OCPAA) and p-chlorophenoxy acetic acids (PCPAA). The FT-IR and Fourier transform-Raman spectra of both the compounds was recorded in the solid phase. The optimized geometry was calculated by HF and B3LYP methods with 6-311++G(d,p) basis set and harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated by density functional B3LYP method with the 6-311++G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compounds were also performed at B3LYP/6-311++G(d,p) level of theory. A detailed interpretation of the infrared and Raman spectra of o-chloro and p-chlorophenoxy acetic acid is reported. The theoretical FT-IR spectrograms for the title molecules have been constructed.     

Acid-base equilibria in solutions of cephotaxime and cephtriaxone

The concentration constants of acid-base equilibria in aqueous solutions of cephotaxime and cephtriaxone were determined pH-metrically at 20°C against the background of 0.1, 0.4, 0.7, and 1.0 M solutions of KCl and KNO₃. The thermodynamic constants of these equilibria were calculated by the extrapolation of the concentration constants to zero ionic strength according to the Hückel equation. Cephotaxime and cephtriaxone ionic form sizes were calculated by the semiempirical PM3 method for energetically favorable conformations.     

白藜芦醇与DNA相互作用的研究

在pH=7.4的Tris-HCI缓冲溶液中,采用紫外光谱、荧光光谱及粘度法研究了白藜芦醇与小牛胸腺DNA(ctDNA)的相互作用。在生理条件下,白藜芦醇可以与ctDNA相互作用形成复合物,运用双倒数法求出了白藜芦醇与ctDNA相互作用的热力学参数。白藜芦醇能有效猝灭吖啶橙(AO)-DNA体系的荧光,猝灭方式为生成复合物的静态猝灭。粘度法实验证明ctDNA溶液的粘度随着白藜芦醇浓度的增加而增大。结果表明,白藜芦醇与DNA发生了较强的相互作用,其键合模式为经典的插入方式。     

Structures and energies of the tautomers of 1-nitroso-1,2,4-triazol-5-one-2-oxide: New triazol-5-one-n-oxides

Molecular orbital calculations at the DFT-B3LYP/aug-cc-pVDZ level are performed for the possible tautomers of 1-nitroso-1,2,4-triazol-5-one-2-oxide. We have examined the substitution effects of carbonyl, N-oxide, and nitroso groups by comparing the calculated geometries, relative energies, and electrostatic potentials of model molecules. The optimized structures, vibrational frequencies, and thermodynamic values for triazolone-N-oxides are obtained in the ground state. The results show that 1H, 4H tautomers are most stable. Detonation velocity and detonation pressure are evaluated by the Kamlet-Jacob equations based on the predicted density and the calculated heat of explosion. The explosive properties of the designed compounds seem to be promising compared with those of 1,3,5-trinitroperhydro-1,3,5-triazine (D 8.75 km/s, P 34.70 GPa), octahydro-1,3,5,7-tetrnitro-1,3,5,7-tetrazocine (D 9.10 km/s, P 39.3 GPa), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D 9.20 km/s, P 42.0 GPa).