单线态卡宾衍生物与臭氧反应机理的密度泛函数理论研究

用密度泛函理论中B3LYP方法,在6-31G(d)水平上优化了单线态卡宾衍生物(CX~2,X=F,Cl,Br)与臭氧反应过程中驻点的几何构型,通过振动分析对反应过渡态和中间体构型进行确认,对单点进行了CCSD(T)/6-31G(d)计算,并进行了零点能(ZPE)校正,同时对反应绝对速率常数进行了理论计算,研究结果表明：相对CF~2和CCl~2而言CBr~2对臭氧的损耗较大,卡宾衍生物与臭氧反应过程均为强放热反应。     

过氧烷基自由基分子内氢迁移反应类速率常数的计算

过氧烷基自由基分子内氢迁移是低温燃烧反应中的一类重要基元反应. 本文用等键反应方法计算了该类反应的动力学参数. 所有反应物、过渡态、产物的几何结构均在B3LYP/6-311+G(d,p)水平下优化得到. 本文提出了用过渡态反应中心几何结构守恒作为反应类判据, 并将该分子内氢迁移反应分为四类, 包括(1,3)、(1,4)、(1,5)、(1,n) (n=6, 7, 8)氢迁移类. 分别将这4 类反应类中最小反应体系作为类反应的主反应, 并分别在B3LYP/6-311+G(d,p)低水平和CBS-QB3 高水平下得到其近似能垒和精确能垒. 其余氢迁移反应作为目标反应, 在B3LYP/6-311+G(d,p)低水下计算得到其近似能垒, 再采用等键反应方法校正得到目标反应的精确反应势垒和精确速率常数. 研究表明, 采用等键反应方法只需在低水平用从头算计算就可以得到大分子反应体系的高精度能垒和速率常数值, 且本文按等键反应本质的分类方法更能揭示反应类的本质, 并对反应类的定义给出了客观标准. 本文的研究为碳氢化合物低温燃烧模拟中重要的过氧烷基分子内氢迁移反应提供了准确的动力学参数.     

CH3(2A′)自由基与臭氧反应机理的量子化学研究

用量子化学UMP2方法，在6-311++G**基组水平上研究了CH3(2A′)自由基与臭氧反应机理，全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型，在UQCISD(T)/6-311++G**水平上计算了它们的能量；并对它们进行了振动分析，以确定中间体和过渡态的真实性；同时应用经典过渡态理论计算了反应的速率常数，并与实验值进行了比较, CH3自由基与臭氧反应速率常数的理论计算结果为: 4.73×10－14 cm3•molecule－1•s－1，与实验报导的结果(k=2.52×10－14 cm3•molecule－1•s－1)很接近，同时发现CH3(2A′)自由基与O3的反应是强放热反应.     

卤代硅烯异构化为卤代甲硅烷基硅烯的热力学与动力学分析

利用密度泛函理论(DFT) 中的B3LYP方法,全参数优化了卤代硅烯HXSi=SiXH（X=F、Cl、Br、I）异构化反应的反应物、产物及过渡态的几何构型,计算出了它们的振动频率、零点振动能(ZPVE)和总能量,并对它们进行了振动分析,以确定过渡态的真实性。又计算了反应的热力学函数变化,平衡常数及速率常数,比较了不同卤素对反应的影响。热力学与动力学计算结果表明,该异构化反应过程是一个放热的、且在低温下可自发进行的反应,但对于溴代硅烯和碘代硅烯而言,当温度达到1000 K时,反应开始转化为非自发反应。     

乙炔基自由基C2H与氧气反应的密度泛函理论研究

应用量子化学从头算和密度泛函理论(DFT)对C₂H自由基和O₂的反应进行了研究.在B3LYP/6-311G^**水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,并计算出它们的振动频率和零点振动能(ZPVE).各物种的总能量由CCSD(T)/6-311G^**//B3LYP/6-311G^**给出,并对能量进行了零点能校正.计算结果表明,反应物中自由基C₂H中的边端C进攻O₂形成了中间体1 (HCCOO),中间体1是一个加合产物.由中间体1经过不同的反应通道可以生成不同的产物P₁ (HCO+CO), P₂ (HCCO+O), P₃(CO₂+CH), P₄ (C₂O+OH)和P₅ (2CO+H).反应通道之间存在着竞争机制.其中P₁, P₂是主要产物,其次还有一定比例的P5生成,而产物P₃, P₄的生成几率较低.各条反应通道化学反应热的计算与实验吻合较好.     

Transition Structures for the Aromatic Claisen Rearrangements by the Molecular Orbital Method

Ab initio calculations were performed for eight Claisen rearrangements, eqs 1-8. Transition-state (TS) structures of [3,3] sigmatropic rearrangements of reactions 1-4 are similar, but their activation energies (E(a)'s) are different, E(a)(1) < E(a)(2) and E(a)(3) < E(a)(4). From the intermediate of reaction 3, a hydrogen is moved intermolecularly to form the product, o-allyl phenol. The lower reactivities of reactions 2 and 4 relative to reactions 1 and 3 are ascribed to large endothermicities in the sigmatropic rearrangements, respectively. Chair-type transition states are more favorable than boat-type transition states in reactions 1-4. The allyl group is released from the in-plane C-X (X = O or N) sigma bond and is captured by the pi-type lone-pair electrons. The sulfur- and phosphorus-containing rearrangements, reactions 5-8, are computed to have smaller activation energies but are to be less exothermic than those of oxgyen- and nitrogen-containing rearrangements.     

Reactivity of alkanes on zeolites: a computational study of propane conversion reactions

In this work, quantum chemical methods were used to study propane conversion reactions on zeolites; these reactions included protolytic cracking, primary hydrogen exchange, secondary hydrogen exchange, and dehydrogenation reactions. The reactants, products, and transition-state structures were optimized at the B3LYP/6-31G level and the energies were calculated with CBS-QB3, a complete basis set composite energy method. The computed activation barriers were 62.1 and 62.6 kcal/mol for protolytic cracking through two different transition states, 30.4 kcal/mol for primary hydrogen exchange, 29.8 kcal/mol for secondary hydrogen exchange, and 76.7 kcal/mol for dehydrogenation reactions. The effects of basis set for the geometry optimization and zeolite acidity on the reaction barriers were also investigated. Adding extra polarization and diffuse functions for the geometry optimization did not affect the activation barriers obtained with the composite energy method. The largest difference in calculated activation barriers is within 1 kcal/mol. Reaction activation barriers do change as zeolite acidity changes, however. Linear relationships were found between activation barriers and zeolite deprotonation energies. Analytical expressions for each reaction were proposed so that accurate activation barriers can be obtained when using different zeolites as catalysts, as long as the deprotonation energies are first acquired.     

Activation barriers for DNA alkylation by carcinogenic methane diazonium ions

Methylation reactions of the DNA bases with the methane diazonium ion, which is the reactive intermediate formed from several carcinogenic methylating agents, were examined. The SN2 transition states of the methylation reactions at N7, N3, and O6 of guanine; N7, N3, and N1 of adenine; N3 and O2 of cytosine; and O2 and O4 of thymine were calculated using the B3LYP density functional method. Solvation effects were examined using the conductor-like polarizable continuum method and the combined discrete/SCRF method. The transition states for reactions at guanine N3, adenine N7, and adenine N1 are influenced by steric interactions between the methane diazonium ion and exocyclic amino groups. Both in the gas phase and in aqueous solution, the methylation reactions at N atoms have transition states that are looser, and generally occur earlier along the reaction pathways than reactions at O atoms. The forming bonds in the transition states in water are 0.03 to 0.13 A shorter than those observed in the gas phase, and the activation energies are 13 to 35 kcal/mol higher. The combined discrete/SCRF solvation energy calculations using base-water complexes with three water molecules yield base solvation energies that are larger than those obtained from the CPCM continuum method, especially for cytosine. Reactivities calculated using barriers obtained with the discrete/SCRF method are consistent with the experimentally observed high reactivity at N7 of guanine.     

C-甲基硝酮与丙烯腈1,3-偶极环加成反应从头算研究

用从头算方法在MP2 / 6 31G(d)水平上研究了C 甲基硝酮与丙烯腈 1,3 偶极环加成反应 ,该反应可生成endo 4,exo 4,endo 5 ,exo 5四种不同的产物 ,反应势垒分别为 8.35、17.2 3、-0 .18和 4.88kJ/mol。在C 甲基硝酮与丙烯腈接近的过程中 ,首先生成 3个不同的氢键复合物 ,相对能量为 -4 7.8、-4 6 .6和 -33 .7kJ/mol。由这 3个不同的氢键复合物导致了 4个不同的过渡态而形成 4个不同的产物     

丁烯自由基和O2反应机理的理论研究

应用量子化学密度泛函理论(DFT)对丁烯自由基C₄H₇和O₂的反应机理进行了研究. 在B3LYP/6-31G(d,p)水平上优化了反应通道上的反应物、中间体、过渡态和产物的几何构型, 并计算出它们的振动频率和零点能(ZPVE), 并对能量进行了零点能校正. 计算结果表明, C₄H₇和O₂形成三种氧环中间体, 再分别分解, 这是主要的反应形式. 生成物主要为羰基化合物, 其次还有一定比例的CO.     

An MO study of regioselective amine addition to ortho-quinones relevant to melanogenesis

Energy profiles for alternative intramolecular cyclisations of 4-(aminoalkyl)-ortho-quinones have been calculated using the AM1 method and ab initio energies of the transition states are determined. In all the cases cyclisation at position 5 occurs via a significantly lower energy transition state than cyclisation at position 3. This is consistent with experimental observations. Optimal trajectories for attack have been determined from a study of the reactions of methylamine with 4-methyl-ortho-quinone. For cyclisation of aminoalkyl derivatives deviation from the optimal direction is less for reaction at position 5 but constraint on angle of attack only partially accounts for the regioselectivity. Intrinsic differences in the electronic energies of the alternative transition states are the main contributor to regioselectivity. The relative energies of transition states can be modified by variation of the substituent at position 4. The calculations suggest that seven-membered ring formation may occur via a boat transition state and steric hindrance in the seven-membered transition states may account for the experimentally observed influence of N-substituents on the mode of reaction.     

三氟化氯和环氧丙烷反应的理论研究

应用密度泛函理论对三氟化氯和环氧丙烷反应产生C3H5O和C1F2自由基的机理进行了研究。在B3PW91/6-31+G(d,p)水平优化了12个不同反应通道上各驻点(反应物、中间体、过渡态和产物) 的几何构型,并计算了它们的振动频率和零点振动能。采用CCSD(T)/6-31+ G(d,p) // B3PW91/6-31+G(d,p)单点能计算方法求得各物种的能量,并作了零点能校正。计算结果表明,三氟化氯和环氧丙烷反应可经过不同的反应路径引发C3H5O自由基和C1F2自由基,其中,三氟化氯呈对称的F原子与环氧丙烷的C(1)上与CH3在同一侧的上的H原子结合的活化能最低,仅为16.81 kJ/mol。     

基态氧(3^O2)氧化硅烯的密度泛函计算研究

采用密度泛函[B3LYP(full)/6-311+G^*]方法研究了基态氧(3^O2)氧化硅烯(Si2H4)的机理。计算了三重态初始中间体(IM(T1)到单重态中间体IM2(S0)反应交叉势能面,报道了各反应中间体、产物和过渡态的构型和能量,用频率分析方法对各过渡态进行了验证,进一步用IRC方法对主要的基元反应进行了考察,确定了历经生成1,2-二氧环氧硅烷中间体的氧化过程的主要反应通道。     

Density functional theory study on isomerization reactions of pyridazine derivatives bearing N,N‐dialkylaminoethyl group

The isomerization reactions of four pyridazine derivatives, i.e., 6‐chloro‐3‐hydroxy‐pyridazine, 1,2‐dihydrogen‐1‐methyl‐3,6‐pyridazindione, 6‐chloro‐3‐diethylamino‐ethoxy‐pyridazine, and 1‐methyl‐2‐diethylaminoethyl‐3,6(2H)‐pyridazindione, have been studied using density functional theory (DFT) B3LYP method at the 6‐311+G** basis set. The geometric structures of reactants, transition states and products have been optimized. The transition states have been explored and proved by vibration analysis as well as intrinsic reaction coordination (IRC) analysis. The activation energies of four reactions were calculated, and the corresponding isomerization mechanisms were also elucidated in theory. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

1, 3-丁二烯热裂解的动力学计算与模型研究

1, 3-丁二烯是碳氢燃料燃烧和裂解过程中生成的一种重要产物,也是形成多环芳烃(PAHs)的一种重要前驱体。目前,关于1, 3-丁二烯燃烧实验以及机理的研究较多,但是其热裂解机理的研究较少。本文在B3LYP/CBSB7水平下对1, 3-丁二烯裂解过程中相关反应的反应物、产物以及过渡态进行了几何结构优化和频率计算,并通过组合方法CBS-QB3计算得到了单点能和热力学参数。对于紧致过渡态的反应和无能垒反应,分别采用过渡态理论(TST)和可变反应坐标过渡态理论(VRC-TST)计算其高压极限条件下的反应速率常数。计算得到的反应速率常数与已有文献报导的结果吻合较好。通过量子化学计算,对Hidaka等人提出1, 3-丁二烯的热裂解机理模型进行了更新和改进:更新后的机理模型包含45个物种和224步反应,并对更新后的机理模型进行了模拟验证。结果表明,更新的机理模型能更好地预测1, 3-丁二烯激波管裂解实验过程中C₂H₂、1-丁烯-3-炔(C₄H₄)以及苯(C₆H₆)主要产物的浓度分布,为进一步完善核心机理(C₀-C₄)模型提供了可靠的热、动力学参数。     

硫代双烯酮与异氰酸环加成反应的理论研究

采用从头算ＲＨＦ／６－３１Ｇ方法研究了硫代双烯酮与异氰酸之间两种可能的环加成反应的机理,并对反应各驻点进行了电子密度拓扑分析研究．结果表明,这两个生成不同四元杂环产物的平行反应均为非同步的协同反应,但两个反应进行的难易程度不同,形成硫氮杂环的反应更容易一些,而形成氮杂环反应的产物在热力学上更稳定一些     

C2H与HO2双自由基反应的密度泛函理论研究

应用量子化学从头算和密度泛函理论(DFT)对C₂H与HO₂双自由基的单重态反应进行了研究.在UB3LYP/6-311G水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型.在CCSD(T)/6-311G^{**水平上计算了各物种的单点能,并对总能量进行了零点能校正.研究结果表明,反应物中自由基C₂H的边端C进攻自由基HO₂的边端O是主要的进攻方式.首先形成了中间体1(HCCOOH),由此经过不同的反应通道可以得到主要产物P1,次要产物P2,P3和P5.生成P1的反应热为-814.40kJ/mol.自由基C₂H的中间C进攻自由基HO₂的边端O是次要的进攻方式,可以得到产物P4和P6.根据势能面分析,所有反应均是放热反应.}     

SnCl4和DMF作用下1-三氯锡烷基-2,3-丁二烯与甲醛反应机理的理论研究

用密度泛函理论方法在B3LYP/6-31G^**水平上研究了SnCl4和DMF作用下1-三氯锡烷基-2,3．丁二烯与甲醛的反应机理．优化得到各驻点的几何构型,通过振动分析和内禀反应坐标对过渡态进行了确认．计算得到两条反应路径．研究表明,反应具有很强的选择性,主要得到DMF作用下1-三氯锡烷基-2,3-丁二烯与甲醛直接反应的产物．计算结果与实验事实一致．     

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。     

NCS自由基与NO反应动力学的理论研究

用量子化学密度泛函理论B3LYP/6-31+G^*和高级电子相关校正的偶合簇[CCSD(T)/6-311+G^*]方法,对NCS自由基与NO反应的机理和动力学进行了理论研究,得到了体系的势能面信息和可能的反应机理.计算了反应的热力学参数及反应能垒.采用传统过渡态理论计算了各反应通道的速率常数.研究结果表明,NCS自由基与NO反应中存在4个反应通道,产物分别为OCS+N₂,CS+N₂O,ONS+CN和ONCNS.从能量变化和反应速率两方面考虑,NCS+NOOCS+N₂应为主反应通道.