Theoretical Study on the Structures and Isomerization of Germylenoid GeH_2LiCl

Using geometrical optimization and DFT method at the B3LYP/6-311++G (3df,3pd) level, four equilibrium geometries and one transition state of GeH2LiCl were identified, and the structures at the MP2/6-311++G(3df,3pd) level were calculated simultaneously. We also studied the solvent effects on the structures of Germylenoid GeH2LiCl at the B3LYP/6-311++G (3df,3pd) level. The two more stable forms are suggested to be the p-complex and three-membered ring. The vibrational frequencies and infrared intensities were computed at the B3LYP/6-311++G (3df,3pd) level.     

A Density Functional Study on the Hydrolysis Process of Non-classical Transplatin（Ⅱ） with Two Same Planar Heterocycle Amines

In the present work, the hydrolysis process of non-classical transplatin（Ⅱ） with two same planar heterocycle amines has been studied using hybrid density functional theory （B3LYP） and IEF-PCM solvation models. Optimizations were performed at the B3LYP level using a combined basis set of （LanL2DZ＋6-31 ＋G（d,p）） with single-point energy evaluations using the B3LYP/6-31 ＋ ＋G（3df,2pd） approach in vacuo and in aqueous solution. For the obtained structures of reactants, intermediates, transition states, and products, both thermodynamic （reaction energies and Gibbs energies） and kinetic （reaction barriers） characteristics were estimated. In comparison with cisplatin, decreased activation energies were obtained. The result implies that the non-classical transplatin with two same planar heterocycle amines increases the equatorial steric effect and lowers reaction barriers, which may assist in designing novel Pt-based anticancer drugs.     

The molecular structure of fluoromalononitrile as determined by gas-phase electron diffraction and ab initio calculations

The molecular structure of fluoromalononitrile was studied by means of gas-phase electron diffraction and quantum mechanical methods using HF/6-31G(d), MP2/6-311++G(2df,2pd) and DFT/B3LYP/6-31G(d), B3PW91/6-31G(d), B3LYP/6-311++G(2df,2pd) and B3PW91/6-311++G(2df,2pd). The r(g) and angle(alpha) structural parameters we obtained from the present analysis are: CC=1.487(5) A, CN=1.157(3) A, CF=1.386(5) A, CH=1.096 A (ass.), angleCCC=106.7(1.0) degrees , angleCCF=108.0(0.7) degrees , angleCCN=177.6(2.0) degrees . Uncertainties in parenthesis are 3sigma.     

Basis set and method dependence in quantum theory of atoms in molecules calculations for covalent bonds

The influence of various small- and medium-size basis sets used in Hartree-Fock (HF) and density functional theory (DFT)/B3LYP calculations on results of quantum theory of atoms in molecules based (QTAIM-based) analysis of bond parameters is investigated for several single, double, and triple covalent bonds. It is shown that, in general, HF and DFT/B3LYP methods give very similar QTAIM results with respect to the basis set. The smallest 6-31G basis set and DZ-quality basis sets of Dunning type lead to poor results in comparison to those obtained by the most reliable aug-cc-pVTZ. On the contrary, 6-311++G(2df,2pd) and in a somewhat lesser extent 6-311++G(3df,3pd) basis sets give satisfactory values of QTAIM parameters. It is also demonstrated that QTAIM calculations may be sensitive for the method and basis set in the case of multiple and more polarized bonds.     

Theoretical study and rate constant computation on the reaction HFCO + OH --> CFO + H2O

The potential energy surface, including the geometries and frequencies of the stationary points, of the reaction HFCO + OH is calculated using the MP2 method with 6-31+G(d,p) basis set, which shows that the direct hydrogen abstraction route is the most dominating channel with respect to addition and substitution channels. For the hydrogen abstraction reaction, the single-point energies are refined at the QCISD(T) method with 6-311++G(2df,2pd) basis set. The calculated standard reaction enthalpy and barrier height are -17.1 and 4.9 kcal mol(-1), respectively, at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The reaction rate constants within 250-2500 K are calculated by the improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) correction at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The fitted three-parameter formula is k = 2.875 x 10(-13) (T/1000)1.85 exp(-325.0/T) cm(3) molecule(-1) s(-1). The results indicate that the calculated ICVT/SCT rate constant is in agreement with the experimental data, and the tunneling effect in the lower temperature range plays an important role in computing the reaction rate constants.     

FC(O)O自由基与NO2反应的量子化学研究

用量子化学DFT, MP2, G3和G3MP2方法对FC(O)O自由基与NO₂的反应机理进行了理论研究. 优化了反应势能面上各驻点的几何结构, 通过内禀反应坐标(IRC)计算和振动分析, 确认了反应中的过渡态, 并用过渡态理论(TST)计算了相关反应的速率常数.     

Microwave spectrum of 3-butyne-1-thiol: evidence for intramolecular S-H...pi hydrogen bonding

The microwave spectrum of 3-butyne-1-thiol has been studied by means of Stark-modulation microwave spectroscopy and quantum-chemical calculations employing the B3LYP/6-311++G(3df,2pd), MP2/aug-cc-pVTZ, MP2/6-311++G(3df,2pd), and G3 methods. Rotational transitions attributable to two conformers of this molecule were assigned. One of these conformers possesses an antiperiplanar arrangement of the atoms S-C1-C2-C3, while the other is synclinal and stabilized by the formation of an intramolecular hydrogen bond between the H-atom of the thiol group and the pi-electrons of the C[triple bond]C triple bond. The energy difference between these conformers was estimated to be 1.7(4) kJ mol(-1) by relative intensity measurements, with the hydrogen-bonded conformer being lower in energy. The spectra of five vibrationally excited states of the synclinal conformer were observed, and an assignment of these states to particular vibrational modes was made with the aid of a density functional theory (DFT) calculation of the vibrational frequencies at the B3LYP/6-311++G(3df,2pd) level of theory.     

甲醛光催化降解反应机理的量子化学研究

分别采用B3LYP,MP2方法在6-311++G(2df,pd)水平研究了甲醛光催化降解反应的微观机理,找到了可能的反应通道,预测反应产物为HCOOH与H2O.并得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率.成功地解释了实验结论.从键长和能量的变化角度,讨论了化学反应过程中化学键的变化规律,整个反应通道中各势能面均较低,从理论角度分析该反应室温下能够进行,为空气中的甲醛降解反应的实验研究提供理论依据.     

OH-与CH2ClF反应的阴离子产物通道

理论研究了羟基负离子(OH^-)与氟氯代甲烷(CH₂ClF)反应的阴离子产物通道. 分别在B3LYP/6-31+G(d,p)和B3LYP/6-311++G(2d,p)水平上得到反应势能面上各关键物种的优化构型, 进而计算得到谐振频率和零点能. 基于CCSD(T)/6-311+G(3df,3dp)水平的相对能量, 描述了由质子转移和双分子亲核取代(S_N2)过程生成各阴离子产物的途径. 各阴离子产物途径势垒的计算结果表明质子转移过程是实验中的主要产物通道, 与以往实验测量的结论相符. 此外, 计算还显示双分子亲核取代过程得到了非典型的阴离子产物, 其中动力学效应可能会导致F^-的生成.     

One-photon mass-analyzed threshold ionization spectroscopy of 2-chloropropene (2-C3H5Cl) and its vibrational assignment based on the density-functional theory calculations

A high-quality mass-analyzed threshold ionization (MATI) spectrum of 2-chloropropene, 2-C3H5Cl, is reported. Its ionization energy determined for the first time from the 0-0 band position was 9.5395+/-0.0006 eV. Almost all the peaks in the MATI spectrum could be vibrationally assigned utilizing the frequencies calculated at the B3LYP6-311++G(3df,3pd) level and the Franck-Condon factors calculated with the molecular parameters obtained at the same level. In particular, the observed methyl torsional progression could be reproduced very well through quantum-mechanical calculations using the molecular parameters obtained at this level. Dramatic lowering of the torsional barrier inferred from the experimental data was entirely compatible with the B3LYP6-311++G(3df,3pd) results. The torsional barrier and the internal rotational constant determined by fits to six torsional peaks were 53.6 and 5.20 cm(-1), respectively. A brief discussion at the level of molecular orbital is presented to account for the dramatic lowering of the torsional barrier upon ionization.     

Theoretical Studies on Structures and Stabilities of C4H2+ Isomers

The structures, energies, stabilities and spectroscopies of doublet C₄H₂⁺ cations were explored at the DFT/B3LYP/6-311G(d,p), CCSD(T)/6-311+G(2df,2pd)(single-point), and G3B3 levels. Ten minimum isomers including the chainlike, three-member-ring, and four-member-ring structures are interconverted by means of 15 interconversion transition states. The potential energy surface was investigated. At the CCSD(T)/6-311+G(2df,2pd) and G3B3 levels, the global minimum isomer was found to be a linear HCCCCH. The structures of the stable isomer and its relevant transition state are further optimized at the QCISD/6-311G(d,p) level. The bonding nature and structure of isomer HCCCCH were analyzed.     

Direct dynamic study on the hydrogen abstraction reaction CH3CN + OH-->CH2CN + H2O

The reaction of acetonitrile with hydroxyl has been studied using the direct ab initio dynamics methods. The geometries, vibrational frequencies of the stationary points, as well as the minimum energy paths were computed at the BHandHLYP and MP2 levels of theory with the 6-311G(d, p) basis set. The energies were further refined at the PMP4/6-311+G(2df, 2pd) and QCISD(T)/6-311+G(2df, 2pd) levels of theory based on the structures optimized at BHandHLYP/6-311G(d, p) and MP2/6-311G(d, p) levels of theory. The Polyrate 8.2 program was employed to predict the thermal rate constants using the canonical variational transition state theory incorporating a small-curvature tunneling correction. The computed rate constants are in good agreement with the available experimental data.     

O（~1D）与CF_2HCl反应的理论研究

用量子化学密度泛函理论（DFT）和G3B3方法，对为（~1D）与CF_2HCl的反应 进行了研究，在B3LYP/6-311+G(d)，B3LYP/6-311+G(2df,2pd)和G3B3计算水平上， 优化了反应热能面上各驻点的几何结构，通过内禀反应坐标（IRC）计算和振动分 析，对反应过渡态进行了确认，并确定了反应机理。     

CH2=CHCl与O(3P)反应的理论研究

用量子化学密度泛函理论和QCISD(Quadratic configuration interaction calculation)方法,对0(^3P)与CH2CHCl的反应进行了理论研究．在UB3LYP／6—311 G(d,p),UB3LYP／6—31 (3df,3pd)计算水平上,优化了反应物、产物、中间体和过渡态的几何构型,并在UQCISD(T)／6—311 G(2df,2pO)水平上计算了单点能量．为了确证过渡态的真实性,在UB3LYP／6—311 G(3df,3pd)水平上进行了内禀坐标(IRC)计算和频率分析,并确定了反应机理．研究结果表明,反应主要产物为CH2CHO和Cl．     

Density functional study of the conformations and intramolecular proton transfer in thiohydroxamic acids

The conformational preferences of thiohydroxamic acids (N-hydroxythioamides) are investigated by the density functional B3LYP/6-311++G(3df,3pd)//B3LYP/6-31G(d) method in this work. Unlike hydroxamic acids, the thione and thiol forms are found to be equally stable in the gas phase, and the reaction pathways for the interconversion between the thione and thiol forms have been deduced to involve rotation about the C[double bond, length as m-dash]N bond of the thiol tautomer in the rate-determining step. The effect of aqueous solvation on the reactions has also been investigated. It is found that inclusion of a few explicit water molecules in an implicit solvent calculation is necessary in order to accurately account for hydrogen bonding effects. Thiohydroxamic acids, like their hydroxamic acid analogues, are found to be N-acids, both in the gas phase and in aqueous solution.     

Molecular structure and vibrational spectra of 3-amino-5-hydroxypyrazole by density functional method

In this work, we report a combined experimental and theoretical study on molecular and vibrational structure of 3-amino-5-hydroxypyrazole (3A5HP). The Fourier transform infrared and Fourier transform Raman spectra of 3A5HP were recorded in the solid phase. The molecular geometry and vibrational frequencies of 3A5HP in the ground state have been calculated by using the density functional method B3LYP with basis sets, 6-311++G(d,p), 6-311+G(3df,2p), 6-311+G(3df,2pd), CC-pVDZ, aug-CC-pVDZ and CC-pVTZ. The optimized geometrical parameters obtained by B3LYP show best agreement with the experimental values. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title molecule have been constructed.     

Theoretical study on the gas phase reaction mechanism of acetylene with nitrous oxide

The reaction mechanism of C₂H₂ and N₂O on the singlet potential energy surface is investigated in this study, at the B3LYP/6-311++G(3df,3pd), MP2/6-311++G(d,p), and CCSD(T) levels of theory. We have obtained three kinds of products in both methods, B3LYP and MP2, which have enough thermodynamic stability. The results reveal that the product P1, CH₂CO + N₂, is spontaneous and exothermic with ?86.176 and ?83.149 kcal/mol in Gibbs free energy and enthalpy of reaction at the MP2 level, respectively. Hence, the product P1 is thermodynamically the most favored adduct of the C₂H₂ + N₂O gas phase reaction at atmospheric pressure and 298.15 K temperature.     

CH2FCF3与O(1D)反应机理的理论研究

用量子化学密度泛函理论(DFT)和G3(MP2)B3方法,对O(1↑D)与CH2FCF3的反应进行了研究．在UB3LYP/6-31G(d)计算水平上,优化了反应势能面上各驻点的几何结构,在G3(MP2)B3水平上进行了单点计算,并利用UB3LYP/6-311 G(3df,3pd)计算的波函数进行了电荷密度分析．通过内禀坐标(IRC)计算和振动分析,对反应过渡态进行了确认,并确定了反应机理．     

OXO(X=Cl,Br)与H(2S)反应机理的量子化学研究

卤素二氧化物自由基(OXO)是重要的同温层物种，在极地的夜间含量尤其丰富，由于其光解产生的卤素原子会造成臭氧的严重损耗，因此愈来愈受到人们的广泛关注嘲．OXO自由基可以通过自由基之间的反应或微波放电等方式获得，有关它与其它大气物种的反应已经进行了许多研究，Bemand等在实验上研究了Cl，H，O与OClO的反应动力学，对于OBrO与H之间的反应目前尚未见实验研究的报道，只有Guhua等在理论上对部分XBrO2(X=H，Cl，Br)同分异构体进行了研究．     

2-溴丙酸气相热消除反应的机理

用密度泛函（DFT）方法,在B3LYP/6-31G**水平上对2-溴丙酸气相消除反应机理进行了研究.计算表明,反应主要是通过半极化五元环结构过渡态进行的,羧基上的氢原子协助溴原子离去,羧基氧原子帮助稳定过渡态.在B3LYP/6-311＋＋G(3df,3pd)水平上对B3LYP/6-31G**优化的几何构型进行了单点能计算,计算所得反应的速度控制步骤的活化能为189.461 kJ•mol－1,偏离实验值((180.3±3.4) kJ•mol－1)5.08％.