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.     

烷基过氧化氢中氢提取反应类大分子体系的反应能垒与速率常数的精确计算

自由基与分子反应是一类具有负活化能的非基元反应,通常认为是通过反应复合物的两步过程,在大气化学和碳氢燃料燃烧机理中广泛存在,且在理论计算和实验上广泛研究.以碳氢燃料燃烧机理中重要反应类羟基自由基提取烷基过氧化氢α位氢的反应为研究对象,通过量化计算揭示其反应规律,计算得到其精确动力学参数.在所研究反应类中,定义第一步反应复合物的生成反应的标准摩尔吉布斯自由能变化等于零时所对应的温度为其转折温度T_c,并表明了当T >> T_c时可采用稳态近似法处理该类反应体系,得到总包反应速率常数.所有反应涉及的物种几何结构优化和频率分析均在BHandHLYP/6-311G（d,p）水平下得到,并在所研究反应类中选取了5个代表反应,通过CCSD（T）/CBS单点能计算,得到其最高转折温度为195.17 K,远远低于碳氢燃料燃烧模拟通常关注温度范围的最低温度650 K,表明用稳态近似法处理该类负活化能反应体系是合理的.计算还表明,该类反应的过渡态反应中心几何结构守恒,因此可将等键反应方法引入类反应,通过对低水平从头算得到的反应能垒进行校正,以得到高精度的结果.为了验证等键反应方法的可靠性,选取5个反应作为研究对象,将低水平BHandHLYP/6-311G（d,p）的校正结果和高水平CCSD（T）/CBS直接计算的结果进行比较,反应能垒最大绝对偏差由校正前的19.99 kJ·mol^－1降到校正后的1.47 kJ·mol^－1,表明用等键反应方法,只需在低水平从头算水平下就可以得到高水平的计算结果,从而可解决大分子体系精确动力学参数缺乏的问题.利用等键反应方法计算了20个反应的反应能垒,并结合过渡态理论计算得到了总包反应的速率常数,并揭示了该类反应只在低温段呈现负活化能关系.     

HNCO+HCO→NCO+CH2O氢转移反应的从头算及动力学研究

在UMP2(Full)/6-311G(d,p)计算水平上,优化了标题反应的反应物、过渡态、产物的几何结构,沿最小能量途径讨论了异氰酸(HNCO)和甲酰自由基(HCO)发生氢转移反应位能面上驻点的结构以及相互作用分子结构变化.指出该反应是一个N-H键断裂和C-H键生成的协同反应.进一步采用UQCISD(T,Full)方法对反应途径上的驻点进行了单点能量校正,得出该反应的计算位垒是91.47 kJ/mol,与实验值108.92 kJ/mol接近在500～2500K实验温度范围内,运用变分过渡态理论(CVT)计算得到的速率常数与实验观测值进行了比较     

CH2O＋O[^3P]→CHO＋OH反应途径和变分速率常数

采用QCISD/6-311G犤d,p犦从头算方法,优化了吸氢反应CH2O+O犤3P犦→CHO+OH的反应物、过渡态和产物的几何结构,并用QCISD(t,full)/6-311G//QCISD/6-311G方法对各驻点进行了单点校正,得出正逆反应的活化位垒分别为38.86kJ·mol-1和67.23kJ·mol-1.IRC(内禀反应坐标)分析指出,该反应是一个C-H键断裂和H-O键生成协同进行的反应,而且在反应途径上存在一个引导反应进行的振动模式,其引导反应进行s区间为-0.4～0.75(amu)1/2.在1300～2270K温度范围内运用改进的变分过渡态理论(ICVT),计算了反应速率常数,与实验结果相当一致.     

Waddington反应机理中β-断键反应类动力学研究

β-羟基烷基过氧自由基(β-HOROO·)是烯烃低温燃烧的主要中间体,其主要消耗通道为Waddington反应通道,即首先分子内发生1,5-H迁移生成β-氢过氧烷氧自由基(β-HOORO·),随后β-HOORO·发生β-断键生成醛(或酮)和OH自由基。本文针对该反应通道的第二步反应,对不同烷基R的β-HOORO·的β-断键反应类的动力学开展了系统研究。对该反应类,根据β-HOORO中连接-OOH的C原子(C_(-OOH))和连接-O·的C原子(C_(-O·))类型不同,划分为不同子类,并对每一子类选取不同取代基大小作为代表反应,开展了能垒和速率常数的规律研究。物种几何结构优化和反应能垒的计算均在M06-2X/6-311++G(d,p)水平进行,反应的高压极限速率常数则采用过渡态理论计算。本文构建了该类反应的速率规则和Evan-Polanyi线性自由能关系,考察了C_(-OOH)和C_(-O·)不同类型以及取代基大小对反应动力学参数的影响。本文的研究为烯烃低温燃烧中重要的β-HOORO·发生β-断键反应类提供了准确的动力学参数,有助于烯烃燃烧详细机理的构建以及机理自动生成。     

反应类等键反应方法及类反应热动力学参数计算

本文提出了反应类等键反应方法,将通常用于热力学性质计算的等键反应方法推广用于类反应中反应势垒和反应焓变的计算. 对碳氢燃料低温燃烧反应机理中的一类重要反应类：?烷基自由基过氧化氢裂解生成烯烃和HO2自由基的反应势垒和反应焓变进行了计算. 通过对该类16个反应中的5个代表反应分别在不同计算水平HF、DFT、MP2、CCSD(T)的比较计算发现,采用等键反应方法可在较低从头算级别计算得到类反应较高精度的反应势垒,提高了计算的效率和精度. 本文采用反应类等键反应方法在B3LYP/6-311G(d,p)计算水平对该类16个反应进行了反应势垒和反应焓变的计算,并建立了反应势垒和反应能的线性自由能关系：delta V=71.02+0.41?delta E.     

用量子力学研究膦化三氢化铝储氢材料在磷化氢催化作用下的释氢反应机理

利用量子力学第一原理研究了储氢材料膦化三氢化铝(AlH3PH3)在催化剂膦(PH3)作用下的释氢反应机理;首先在MP2/aug-cc-pVDZ水平上计算了反应物、过渡态和产物的几何构型和频率,进而利用内禀反应坐标理论确定了反应的最小能量路径,随后在CCSD(T)/aug-cc-pVDZ水平上对基于MP2优化的几何构型进行了能量校正.结果表明,AlH3PH3释氢的能垒高于Al―P键的离解能,而催化剂PH3不能降低AlH3PH3的释氢能垒.因此,需要寻找其他的催化剂以使AlH3PH3成为一种合用的储氢材料.     

十氢化萘低温燃烧反应的动力学机理

采用量子化学方法研究了十氢化萘低温燃烧的动力学机理,获得了脱氢反应、自由基加氧反应及1,5氢迁移反应等反应的动力学参数,并在CBS-QB3水平下获得了相关物种的热力学参数,通过过渡态理论计算获得了具有紧致过渡态反应的高压极限速率常数,而无能垒反应的速率常数则由变分过渡态理论得到.基于此机理分析了十氢化萘低温反应的动力学规律和热力学机制.相比于链烷烃和单环烷烃,十氢化萘自由基加氧反应的速率常数随温度变化较快,1,5-氢迁移反应的能垒较高,揭示了物质结构对反应动力学的影响.热力学平衡常数分析结果表明,在低温下十氢化萘自由基加氧反应起主导作用.通过拟合获得了所有反应Arrhenius形式的速率常数,这些参数可用于双环烷烃低温燃烧机理的构建和优化.     

5-硝基-1-氢-四唑分子热分解反应机理的密度泛函理论研究

利用密度泛函理论研究了5-硝基-1-氢-四唑分子热分解的反应机理。首先用 B3LYP/6-31G（d）方法优化反应中反应物、过渡态、中间体以及产物的几何构型， 通过振动分析得到零点能校正值并确认反应的过渡态。此外，对各个构型作了 CCSD（T）/6-31G（d,p）水平下的单点计算。报道了三条可能的反应途径，即直接 开环途径和质子转移途径；其中N（1）-N（2）键断裂直接开环的机理与文献报道 一致；而涉及质子转移的反应途径则是一个新的发现；另一条关于N（4）-C（5） 键断裂直接开环的途径由于能垒较高，因此发生的几率较小。     

三氟乙烷与氟原子氢提取反应的动力学研究

采用双水平直接动力学方法研究了氢提取反应CH3CF3+F→CH2CF3+HF的反应机理.首先用MPW1K/6-311+G(d,p)方法优化了驻点的几何构型,并在相同水平上进行了频率分析,利用内禀反应坐标理论获得了最小的反应能量途径;随后,为了得到更准确的能量信息,采用MCG3-MPWPW91//MPW1K方法进行了单点能量校正;最后,根据变分过渡态理论计算了该反应在200² 000K温度范围内的速率常数.结果表明,理论计算值与已有的实验值吻合.     

Reliable predictions of the thermochemistry of boron-nitrogen hydrogen storage compounds: BxNxHy, x = 2, 3

Thermochemical data calculated using ab initio molecular orbital theory are reported for 16 BxNxHy compounds with x = 2, 3 and y > or = 2x. Accurate gas-phase heats of formation were obtained using coupled cluster with single and double excitations and perturbative triples (CCSD(T)) valence electron calculations extrapolated to the complete basis set (CBS) limit with additional corrections including core/valence, scalar relativistic, and spin-orbit corrections to predict the atomization energies and scaled harmonic frequencies to correct for zero point and thermal energies and estimate entropies. Computationally cheaper calculations were also performed using the G3MP2 and G3B3 variants of the Gaussian 03 method, as well as density functional theory (DFT) using the B3LYP functional. The G3MP2 heats of formation are too positive by up to approximately 6 kcal/mol as compared with CCSD(T)/CBS values. The more expensive G3B3 method predicts heats of formation that are too negative as compared with the CCSD(T)/CBS values by up to 3-4 kcal/mol. DFT using the B3LYP functional and 6-311+G** basis set predict isodesmic reaction energies to within a few kcal/mol compared with the CCSD(T)/CBS method so isodesmic reactions involving BN compounds and the analogous hydrocarbons can be used to estimate heats of formation. Heats of formation of c-B3N3H12 and c-B3N3H6 are -95.5 and -115.5 kcal/mol at 298 K, respectively, using our best calculated CCSD(T)/CBS approach. The experimental value for c-B3N3H6 appears to be approximately 7 kcal/mol too negative. Enthalpies, entropies, and free energies are calculated for many dehydrocoupling and dehydrogenation reactions that convert BNH6 to alicyclic and cyclic oligomers and H2(g). Generally, the reactions are highly exothermic and exergonic as well because of the release of 1 or more equivalents of H2(g). For c-B3N3H12 and c-B3N3H6, available experimental data for sublimation and vaporization lead to estimates of their condensed phase 298 K heats of formation: DeltaHf degrees [c-B3N3H12(s)] = -124 kcal/mol and DeltaHf degrees [c-B3N3H6(l)] = -123 kcal/mol. The reaction thermochemistries for the dehydrocoupling of BNH6(s) to c-B3N3H12(s) and the dehydrogenation of c-B3N3H12(s) to c-B3N3H6(l) are much less exothermic compared with the gas-phase reactions due to intermolecular forces which decrease in the order BNH6 > cyclo-B3N3H12 > cyclo-B3N3H6. The condensed phase reaction free energies are less negative compared with the gas-phase reactions but are still too favorable for BNH6 to be regenerated from either c-B3N3H12 or c-B3N3H6 by just an overpressure of H2.     

Theoretical study on the isomerization behavior between alpha,beta-unsaturated acyl radicals and alpha-ketenyl radicals

[reaction: see text] Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-zeta pseudopotential (DZP) basis set, with (QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (BHandHLYP, B3LYP) predict that alpha,beta-unsaturated acyl radicals and alpha-ketenyl radicals exist as isomers. At the CCSD(T)/cc-pVDZ//BHandHLY/cc-pVDZ level of theory, energy barriers of 15.1 and 17.7-21.7 kJ mol(-)(1) are calculated for the isomerization of s-trans-propenoyl and s-trans-crotonoyl radical to ketenylmethyl and 1-ketenylethyl radical, respectively. Similar results are obtained for the reactions of s-trans isomers involving silyl, germyl, and stannyl groups with energy barriers (DeltaE++) of 12.2-12.4, 13.1-13.9, and 12.9-18.2 kJ mol(-)(1) at the CCSD(T)/DZP//BHandHLYP/DZP calculation, respectively. These results suggest that alpha,beta-unsaturated acyl radicals and alpha-ketenyl radicals are not canonical forms but are isomeric species that can rapidly interconvert.     

An ab initio study of the Cl(P)+C2H6→C2H5+HCl abstraction reaction

Electronic energies, geometries, and harmonic vibration frequencies for the reactants, products, and transition state for the Cl(³P)+C₂H₆→C₂H₅+HCl abstraction reaction were evaluated at the HF and MP2 levels using several correlation consistent polarized-valence basis sets. Single-point calculations at PMP2, MP4, QCISD(T), and CCSD(T) levels were also carried out. The values of the forward activation energies obtained at the MP4/cc-pVTZ, QCISD(T)/cc-pVTZ, and CCSD(T)/cc-pVTZ levels using the MP2/cc-pVTZ structures are equal to −0.1, −0.4, and −0.3 kcal/mol, respectively. The experimental value is equal to 0.3±0.2 kcal/mol. We found that the MP2/aug-cc-pVTZ adiabatic vibration energy for the reaction (−2.4 kcal/mol) agrees well with the experimental value −(2.2–2.6) kcal/mol. Rate constants calculated with the zeroth-order interpolated variational transition state (IVTST-0) method are in good agreement with experiment. In general, the theoretical rate constants differ from experiment by, at most, a factor of 2.6.     

烷基自由基β位裂解反应类反应势垒与速率常数的精确计算

提出反应类等键方法并用于高温燃烧机理中一类重要反应——烷基自由基β位裂解反应的反应势垒和速率常数的精确校正计算. 通过10种不同从头算水平对类反应中5个代表反应的反应势垒的计算发现, 用反应类等键反应方法和直接从头算方法获得的5 个代表反应的反应势垒最大绝对偏差的平均值分别为5.32 和16.16 kJ·mol^-1, 表明反应类等键反应方法计算的反应势垒对不同水平从头算方法的依赖性小, 可在较低从头算水平计算得到精确的反应势垒, 解决大分子体系反应势垒的精确计算问题. 此外应用反应类等键反应方法在BHandHLYP/cc-pVDZ 从头算水平计算了3 个代表反应的速率常数, 并与文献报道的实验值进行了比较, 其在500-2000 K温度区间内计算速率常数与实验速率常数中较大值与较小值的比值k_max/k_min的平均值为1.67, 最大值也仅有2.49. 表明应用反应类等键反应方法在较低从头算水平即可对同类反应的速率常数进行精确计算.最后在BHandHLYP/cc-pVDZ从头算水平用反应类等键反应方法计算了13个烷基自由基β位裂解反应的速率常数.     

Theoretical investigation on the kinetics and thermochemisty of H-atom abstraction reactions of 2-chloroethyl methyl ether (CH<Subscript>3</Subscript>OCH<Subscript>2</Subscript>CH<Subscript>2</Subscript>Cl) with OH radical at 298 K

Kinetics and thermochemistry of the H-atom abstraction reaction of CH₃OCH₂CH₂Cl with OH radical have been carried out using dual level of methods. Initially, geometry optimization and frequency calculations are performed at M06-2X/6-31+G(d, p) level of theory, and energetic calculations are further refined using CCSD(T)/6-311++G(d, p) level of theory in order to characterized all stationary points on potential energy surface (PES). The result shows that H-atom abstraction from –OCH₂ site of CH₃OCH₂CH₂Cl is dominant path. The rate constants are calculated using canonical transition state theory at 298 K, which are found to be in good agreement with the experimental data. We have presented the standard enthalpies of formation for CH₃OCH₂CH₂Cl and the radicals generated during the H-atom abstraction using group-balanced isodesmic reactions scheme. The atmospheric lifetime of title molecule is also calculated.     

Computational thermochemistry of glycolaldehyde

We use a variant of the focal point analysis to refine estimates of the relative energies of the four low‐energy torsional conformers of glycolaldehyde. The most stable form is the cis‐cis structure which enjoys a degree of H‐bonding from hydroxyl H to carbonyl O; here dihedral angles τ₁ (O?C? C? O) and τ₂ (C? C? O? H) both are zero. We optimized structures in both CCSD(T)/aug‐cc‐pVDZ and aug‐cc‐pVTZ; the structures agree within 0.01 Å for bond lengths and 1.0 degrees for valence angles, but the larger basis brings the rotational constants closer to experimental values. According to our extrapolation of CCSD(T) energies evaluated in basis sets ranging to aug‐cc‐pVQZ the trans‐trans form (180°, 180°) has a relative energy of 12.6 kJ/mol. The trans‐gauche conformer (160°, ±75°) is situated at 13.9 kJ/mol and the cis‐trans form (0°, 180°) at 18.9 kJ/mol. Values are corrected for zero point vibrational energy by MP2/aug‐cc‐pVTZ frequencies. Modeling the vibrational spectra is best accomplished by MP2/aug‐cc‐pVTZ with anharmonic corrections. We compute the Watsonian parameters that define the theoretical vibrational‐rotational spectra for the four stable conformers, to assist the search for these species in the interstellar medium. Six transition states are located by G4 and CBS‐QB3 methods as well as extrapolation using energies for structures optimized in CCSD(T)/aug‐cc‐pVDZ structures. We use two isodesmic reactions with two well‐established thermochemical computational schemes G4 and CBS‐QB3 to estimate energy enthalpy and Gibbs energy of formation as well as the entropy of the gas phase system. Our extrapolated electronic energies of species appearing in the isodesmic reactions produce independent values of thermodynamic quantities consistent with G4 and CBS‐QB3. © 2013 Wiley Periodicals, Inc.     

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。     

Gibbs energy of activation for thermal isomerization of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone by Gaussian‐4 theory and CCSD(T)/CBS computations

In this article, we examined the Gibbs energy of activation for the Z/E thermal isomerization reaction of (1Z)‐acetaldehyde hydrazone and (1Z)‐acetaldehyde N,N‐dimethylhydrazone, at 298.15 K in the solvent of cyclohexane. We carried out computations employing both the Gaussian‐4 (G4) theory and the coupled cluster method using both single and double substitutions and triple excitations noniteratively, CCSD(T). The CCSD(T) energy is extrapolated to the complete basis set (CBS). We compared the calculated results to the available experimental observation. It appeared that both G4 and CCSD(T)/CBS computations overestimated the experimental value by as much as about 6 and 12 kcal/mol in the present two cases. We discussed possible sources of error and proposed the experimental kinetic data could be questionable. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009