气相中环丁烯负离子与N2O反应机理的理论研究

采用MP2和B3LYP两种计算方法,在6-31 G(d,p)的基组下,对气相中环丁烯负离子与N2O反应的微观机理进行了较为系统的计算研究,并在相同基组下进一步用QCISD方法在MP2优化构型的基础上进行了单点能校正.结果表明,该反应存在两条反应通道,每条反应通道又包含着三条反应路径,产物分别为乙烯基重氮甲基负离子与甲醛,同时也应能检测到少量的环丁烯酮负离子及N2等产物.其中,通道1是主反应通道,路径1为主反应路径,路径3是路径1和2的竞争反应.理论计算结果与实验预测基本一致.     

气相中环丁烯负离子与N2O反应机理的理论研究

采用B3LYP 和MP2两种计算方法,在6-31++G(d, p)的基组下,对气相中环丁烯负离子与N2O反应的微观机理进行了较为系统的计算研究。结果表明,该反应存在两条反应通道,每条反应通道又包含着三条反应路径,产物分别为乙烯基重氮甲基负离子与甲醛,同时也应能检测到少量的环丁烯酮负离子及N2等产物。其中,通道1是主反应通道,路径1为主反应路径,路径3是路径1、2的竞争反应。理论计算结果与实验预测基本一致。     

气相中呋喃负离子与N2O反应机理的理论研究

采用QCISD和MP2两种计算方法,在6-31＋＋G(d,p)的基组下,对气相中呋喃负离子与N2O反应的微观机理进行了较为系统的计算研究。结果表明,通道1中的路径1和2为此反应体系的主反应路径,其各反应驻点的能量均低于反应物的,并且互为竞争路径。主要产物为C4H3NO- 和NO,同时也应能检测到少量的C4H3O2- 和N2。理论计算结果与实验预测基本一致。此外,对于次要路径也做了简要说明,并且此反应体系的所有反应路径均为强放热过程。     

气相中烯丙基负离子与N2O反应机理

采用二阶微扰理论的MP2/6-31G(d,p)方法对气相中烯丙基负离子与N2O的反应机理进行了理论计算研究, 并在相同基组下进一步用CCSD(T)方法进行了单点能的校正. 计算结果表明, 该反应存在三条反应通道, 产物分别为cis-CH2CHCNN-+H2O, trans-CH2CHCNN-+H2O和CH2CCH-+N2+H2O, 其中生成cis-CH2CHCNN-和trans-CH2CHCNN-的两条通道为相互竞争的主反应通道, 计算结果与实验相吻合. 同时利用传统的过渡态理论, 计算了各反应通道在298 K时, 速控步骤的反应速率常数k(T).     

α-氰基-P-X苯基乙酸乙酯的[Cu^2+(OH^-)TMEDA]2Cl2-催化氧化偶联反应机理

在[Cu^2+(OH^-)TMEDA]2Cl2^-催化下(TMEDA为N, N, N', N;-四甲基乙二胺),α-氰基-P-X苯基乙酸乙酯(X=OCH3, CH3, Cl, H和NO2)经氧化偶联反应, 获得高产率的二聚体。产物中meso异构体的含量均大于dl异构体的含量。IR, 1H NMR和EPR对反应过程进行研究, 结果表明, 反应机理为底物以CN取代催化剂中的OH^-, 生成反应中间体配合物, OH-夺取底物的α-H, 产生相应的碳负离子, 碳负离子向Cu^2+单电子转移生成自由基, 自由基偶合而生成产物。氧将Cu^+氧化为Cu^2+, 使反应继续进行。     

α-氰基-P-X苯基乙酸乙酯的[Cu^2+(OH^-)TMEDA]2Cl2-催化氧化偶联反应机理

在[Cu~(2+)(OH~-)TMEDA]_2Cl_@~-催化下(TMEDA为N,N,N′,N′-四甲基乙二胺),α-氰基-p-X苯基乙酸乙酯(X=OCH_3,CH_3,Gl,H和NO_2)经氧化偶联反应,获得高产率的二聚体。产物中meso异构体的含量均大于dl异构体的含量。IR,~1HNMR和EPR对反应过程研究结果表明,反应机理为底物以CN取代催化剂中的OH~-,生成反应中间体配合物,OH~-夺取底物的α-H,产生相应的碳负离子,碳负离子向Cu~(2+)单电子转移生成自由基,自由基偶合而生成产物。氧将Gu~+氧化为Cu~(2+),使反应继续进行。     

过氧仲丁基自由基内氢转移及解离机理的理论计算研究

采用量子化学从头算MP2方法在6-31G(d)基组水平上系统地研究了过氧仲丁基自由基内三个不同碳位上的氢原子向O—O基的端O转移的过渡态结构, 讨论了这些氢转移反应过程中相关化学键的变化, 并在此基础上进一步研究了氢转移产物解离的过渡态结构. 结果表明具有四元环、五元环、六元环结构的三个氢转移过渡态对应的氢转移反应位垒分别是195.86, 176.43, 122.49 kJ•mol－1; 相应的氢转移产物进一步解离的反应位垒分别是3.53, 126.23, 154.2 kJ•mol－1, 对应的最终产物分别为HO自由基和丁酮, HO2自由基和丁烯, HOOCHCH3和乙烯.     

硅烯与异硫氰酸反应机理的量子化学研究

采用密度泛函理论B3LYP方法在B3LYP/6-311＋＋G**水平上对反应物、中间体、过渡态进行了全几何参数优化, 通过频率分析和IRC方法确认了中间体和过渡态. 又用QCISD(T)/6-311＋＋G**//B3LYP/6-311＋＋G**方法计算了各个驻点的单点能, 计算结果表明单重态的硅烯与异硫氰酸的反应有抽提硫、插入、抽提亚氨基的路径. 而经由三元环中间体的抽提硫反应SiH2＋HNCS→IM1→TS2→IM3→TS3→IM4→SiH2S＋HNC(P1), 反应能垒最低, 为主反应通道, 硫代硅甲醛和异氰氢酸为主产物. 硅烯直接抽提硫、插入N—H键和经由三元环中间体的亚氨基抽提反应为竞争反应通道, 在室温下可以发生, 应为次反应通道.     

O(3P)+O2H→OH+O2反应机理的密度泛函理论研究

用密度泛函理论方法研究了O(3P)与O2H反应生成羟基和氧分子的反应机理. 在PW91/6-31+G水平上用梯度解析技术全自由度优化上述反应物、产物和反应路径上的中间体及过渡态几何构型, 并通过频率振动分析加以确认, 计算IRC反应路径及中间体异构化过程, 确定了此反应的可能反应通道. 结果表明: 该反应是多通道多步骤的强放热反应. 首先形成顺式或反式O3H富能中间体, 此过程无能垒; 然后跨过一个能垒分解成产物OH和O2. 通道IM1→TS1比IM2→TS2克服的能垒要大, 反应放热372.822 kJ*mol-1. IM1TS3IM2 可相互转化.     

氧负离子与乙烯自由基反应的理论研究

在G3MP2B3理论水平下研究了氧负离子与乙烯自由基的反应机理. 反应入口势能面的刚性扫描显示: 对于不同的初始反应取向, 体系存在3种不同的反应机理, 分别对应直接脱水、插入反应和直接键合成中间体通道. 其中, 通过插入反应形成的富能中间体[CH2＝C—OH]－及键合中间体[CH2＝CHO]－都可以进一步经异构化和解离生成其它各种可能产物, 如C2H－＋H2O, OH－＋CH2C和 ＋CO产物通道. 基于计算得到的反应势垒的相对高度, 直接脱水反应显然是该反应体系最主要的产物通道, 同时我们还结合Mulliken电荷布居分析研究了其中涉及的电子交换过程. 由此, 计算结果证实了以往OH－与C2H2反应的实验研究结果. 此外, 还对比了该反应体系、氧原子与乙烯自由基、氧负离子与乙烯分子三个反应的不同机理.     

Investigation of the formation of acid rain based on the sulfur tetroxide (SO4 (C2v)) and OH radical reaction

Structural Chemistry - The reaction pathways of sulfur tetroxide (SO4 (C2v)) with OH radical have been investigated at the MP2/6-31++G(d,p) and G3MP2B3 levels. The mechanism I (Transfer of O-atom...     

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.     

Theoretical study on the hydrogen abstraction reaction of CH3CH2F (HFC-161) with Cl atom

A direct dynamics method is employed to study the hydrogen abstraction reaction of CH₃CH₂F+Cl. Three distinct transition states are located, one for -H abstraction and two for β-H abstraction. The potential energy surface (PES) information is obtained at the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p), CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) and G2//MP2/6-311G(d,p) level. Based on the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) results, the rate constants of the three reaction channels are evaluated by using the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the temperature range of 220–2800 K. The calculated results indicate that -H abstraction dominates the total reaction almost over the whole temperature range.     

N(4S)+CH3X(X=Cl、Br)反应机理的理论研究

The reaction of N(4S)+CH3X(X=Cl、Br) was studied by the ab initio method. The geometries of the reactants, transition states and products were optimized at the MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single-point calculations for all the stationary points were carried out at the MP2/6-311++G(3df,2p) and the QCISD(T)/6-311+G(d,p) levels using the MP2/6-311+G(d,p) optimized geometries. The energies of all the stationary points were calculated by the G2MP2 method. The results of this theoretical study indicate that the reaction has three reaction channels: H abstraction reaction channel a, Cl or Br abstraction reaction channel b and substitution reaction channel c. For the N(4S)+CH3Cl reaction, reaction channel a is the main reaction channel. Reaction channels b and c may have a slight contribution in the reaction. For the N(4S)+CH3Br reaction, reaction channel a is the main reaction channel. Reaction channels b and c may have some contribution in the reaction.     

锗烯与异硫氰酸反应机理的量子化学研究

采用密度泛函理论B3LYP方法研究了GeH2自由基与HNCS的反应机理,并在B3LYP/6-311++G**水平上对反应物,中间体,过渡态进行了全几何参数优化,通过频率分析和IRC确定中间体和过渡态。为了得到更精确的能量值,用QCISD(T)/6-311++G**方法计算了各个驻点的单点能,计算结果表明单重态的锗烯与异硫氰酸的反应有抽提硫、插入N-H键、抽提亚氨基的路径,而经由三元环中间体的抽提硫反应GeH2+HNCS→IM3→TS2→IM4→TS3→IM5→GeH2S+HNC(P1),反应能垒最低,为主反应通道,甲锗硫醛和异氰氢酸为主产物。锗烯经由四元环中间体抽提硫的反应为竞争反应通道。     

A new scheme for determining the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of glycine and alanine peptides

In this paper a new scheme was proposed to calculate the intramolecular hydrogen-bonding energies in peptides and was applied to calculate the intramolecular seven-membered ring N-H...O=C hydrogen-bonding energies of the glycine and alanine peptides. The density-functional theory B3LYP6-31G(d) and B3LYP6-311G(d,p) methods and the second-order Moller-Plesset perturbation theory MP26-31G(d) method were used to calculate the optimal geometries and frequencies of glycine and alanine peptides and related structures. MP26-311++G(d,p), MP26-311++G(3df,2p), and MP2/aug-cc-pVTZ methods were then used to evaluate the single-point energies. It was found that the B3LYP6-31G(d), MP26-31G(d), and B3LYP6-311G(d,p) methods yield almost similar structural parameters for the conformers of the glycine and alanine dipeptides. MP2/aug-cc-pVTZ predicts that the intramolecular seven-membered ring N-H...O=C hydrogen-bonding strength has a value of 5.54 kcal/mol in glycine dipeptide and 5.73 and 5.19 kcal/mol in alanine dipeptides, while the steric repulsive interactions of the seven-membered ring conformers are 4.13 kcal/mol in glycine dipeptide and 6.62 and 3.71 kcal/mol in alanine dipeptides. It was also found that MP26-311++G(3df,2p) gives as accurate intramolecular N-H...O=C hydrogen-bonding energies and steric repulsive interactions as the much more costly MP2/aug-cc-pVTZ does.     

Ab initio Study of the Potential Energy Surface and Product Branching Ratios for Reaction of O（^1D） with C2H5CI

The potential energy surface of O（^1D）＋C2H5Cl reaction was studied using QCISD（T）/6- 311＋＋G（d,p）//MP2/6-31G（d,p） method. The calculations reveal an insertion-elimination mechanism. The insertion reaction of O（^1D） and C2H5Cl produces two energy-rich intermediates, IM1 and IM2, which subsequently decompose into various products. The calculations of the branching ratios of various products formed through the two intermediates were carried out using RRKM （Rice-Ramsperger-Kassel-Marcus） theory at the collision energies of 0, 20.9, 41.8, 62.7, 83.6, 104.5, and 125.4 kJ/mol. HCl is the main decomposition product for IM1; CH2OH is the main decomposition product for IM2. Since IM1 is more stable than IM2, HCl is probably the main product of the O（^1D）＋C2H5Cl reaction.     

Modern valence-bond description of chemical reaction mechanisms: the 1,3-dipolar addition of diazomethane to ethene

The electronic mechanism for the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane (CH2N2) to ethene (C2H4) is described through spin-coupled (SC) calculations at a sequence of geometries along the intrinsic reaction coordinate obtained at the MP2/6-31G(d) level of theory. It is shown that the bonding rearrangements occurring during the course of this reaction follow a heterolytic pattern, characterized by the movement of three well-identifiable orbital pairs, which are initially responsible for the pi bond in ethene and the C-N pi bond and one of the N-N pi bonds in diazomethane and are retained throughout the entire reaction path from reactants to product. Taken together with our previous SC study of the electronic mechanism of the 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne (C2H2) (Theor. Chim. Acc. 1998, 100, 222), the results of the present work suggest strongly that most gas-phase concerted 1,3-dipolar cycloaddition reactions can be expected to follow a heterolytic mechanism of this type, which does not involve an aromatic transition state. The more conventional aspects of the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane to ethene, including optimized transition structure geometry, electronic activation energy, activation barrier corrected for zero-point energies, standard enthalpy, entropy and Gibbs free energy of activation, have been calculated at the HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), MP2/6-31G(d,p), QCISD/6-31G(d) and CCD/6-31G(d) levels of theory. We also report the CCD/6-311++G(2d, 2p)//CCD/6-31G(d), MP4(SDTQ)/6-311++G(2d,2p)//CCD/6-31G(d) and CCSD(T)/6-311++G(2d, 2p)//CCD/6-31G(d) electronic activation energies.     

Interaction of anions with perfluoro aromatic compounds

The complexes formed by a variety of anions with perfluoro derivatives of benzene, naphthalene, pyridine, thiophene, and furan have been calculated using DFT (B3LYP/6-31++G**) and MP2 (MP2/6-31++G** and MP2/6-311++G**) ab initio methods. The minimum structures show the anion interacting with the pi-cloud of the aromatic compounds. The interaction energies obtained range between -8 and -19 kcal mol(-1). The results obtained at the MP2/6-31++G** and MP2/6-311++G** levels are similar. However, the B3LYP/6-31++G** results provide longer interaction distances and smaller interaction energies than do the MP2 results. The interaction energies have been partitioned using an electrostatic, polarization, and van der Waals scheme. The AIM analysis of the electron density shows a variety of topologies depending on the aromatic system considered.