DFT法研究离子液中EMIM＋催化丁烯双键异构反应机理

利用密度泛函方法(DFT)分别在B3LYP/6-31G**和B3LYP/6-311＋＋G**的计算水平上优化了离子液体中1-乙基-3-甲基咪唑阳离子(EMIM＋)催化丁烯双键异构反应过程中的反应物、产物以及过渡态的几何构型,分析了反应过程中键参数的变化.通过振动分析对平衡态和过渡态进行了验证,并得到了零点能.通过计算内禀反应坐标(IRC),确认了对应于过渡态的反应物和产物. 计算结果表明,EMIM＋催化丁烯双键异构可以基元反应的方式一步完成,1-丁烯异构化为2-丁烯的活化能约为192 kJ•mol－1, 逆反应活化能约为208 kJ•mol－1, 可在室温或高于室温条件下进行.     

2-(氟代己酰胺基)-苯甲醛与NH3反应生成3-(1-亚胺基氟烷基)- 1H-喹啉-2-酮的反应机理理论研究

采用密度泛函方法(DFT)研究了2-(氟代己酰胺基)-苯甲醛与NH3的微观反应机理. 在B3LYP/6-31G*水平上优化了反应物、过渡态、中间体及产物的几何构型, 通过振动分析确认了过渡态的结构, 并用内禀反应坐标方法(IRC)确认反应途径. 应用分子中的原子理论(AIM)分析了这些物质的成键特征. 报道了可能的反应通道, 其中Re→TS1→ IM1→TS2→IM2→TS3→IM3→TS4→IM7→TS11→IM9→TS12→IM10→TS13→IM11→TS14→P1具有相对较低的活化能, 是反应的主要通道, 理论预测的主要产物与实验吻合. 采用连续介质模型(PCM)方法研究了反应体系的溶剂化效应, 结果表明反应过程中各物质的能量比气相要低. 溶剂化效应使转化能垒有一定程度的升高.     

4-氟苯甲醛、β-萘胺和Meldrum酸-锅反应生成1-(4-氟苯基)-1,2-二氢苯并[f]喹啉-3(4H)-酮的反应机理理论研究

采用密度泛函理论(DFT)研究了4-氟苯甲醛、β-萘胺和Meldrum酸一锅反应生成1-(4-氟苯基)-1,2-二氢苯并[f]喹啉-3(4H)-酮的微观反应机理.在B3LYP/6-311G*基组水平上优化了反应物、过渡态、中间体及产物的几何构型,通过振动分析确认了过渡态的结构,并用内禀反应坐标(IRC)确认反应途径.应用分子中的原子理论(AIM)分析了这些物质的成键特征.采用SCRF(PCM)方法研究了反应体系的溶剂化效应.报道了可能的反应路径,其中Re→TS1→IM1→TS2→IM2→TS3→IM3→TS4→IM5→TS7→IM9→TS13→IM10→TS14→P3具有相对较低的活化能,是反应的主要通道,理论预测的主要产物与实验吻合.     

4-氟苯甲醛、β-萘胺和Meldrum酸一锅反应生成1-(4-氟苯基)-1,2-二氢苯并[f]喹啉-3(4H)-酮的反应机理理论研究

采用密度泛函理论(DFT)研究了4-氟苯甲醛、β-萘胺和Meldrum酸一锅反应生成1-(4-氟苯基)-1,2-二氢苯并[f]喹啉-3(4H)-酮的微观反应机理.在B3LYP/6-311G*基组水平上优化了反应物、过渡态、中间体及产物的几何构型,通过振动分析确认了过渡态的结构,并用内禀反应坐标(IRC)确认反应途径.应用分子中的原子理论(AIM)分析了这些物质的成键特征.采用SCRF(PCM)方法研究了反应体系的溶剂化效应.报道了可能的反应路径,其中Re→TS1→IM1→TS2→IM2→TS3→IM3→TS4→IM5→TS7→IM9→TS13→IM10→TS14→P3具有相对较低的活化能,是反应的主要通道,理论预测的主要产物与实验吻合.     

H~2O+CN→HCN+OH的IRC解析及其反应动力学研究

本文用能量梯度法,在UHF/3-21G水平上,优化了反应H~2O+CN→HCN+OH的反应物,产物及其过渡态的几何构型,得到了该反应的活化能为32.6kJ/mol, 与实验所得的测量值相一致,同时用Morokuma的数值分析方法,得到了该反应的内禀反应坐标(IRC),沿着IRC,对反应过程中体系构型的变化进行了分析,并计算IRC 运动与垂直于IRC简正振动之间的偶合常数,讨论振动频率的变化,并结合偶合常数进行分子动态学分析,用传统过渡态理论,变分过渡态理论及相关的隧道校正等方法计算该反应的速率常数,结果与实验值基本吻合(如T=763K时,K~(计算值)^(CVT/SCSAG)=3.09×10^1^0,K~(实验值)=(5.1±0.6)×10^1^0,单位为cm^3·mol^-^1·s^-^1)     

亚烷基卡宾与丙烯环加成反应机理的理论研究

用二阶微扰理论研究了单重态亚烷基卡宾与丙烯环加成反应的机理，采用 MP2/6-31G~*方法计算了势能面上各驻点的构型参数、振动频率和能量。根据所得 势能面上的能量数据可以预言，反应（1）的a途径和反应（2）的b途径将是单重态 亚烷基卡宾与丙烯环加成反应的两条相互竞争的主反应通道，两反应途径均由两步 组成，(I)两反应物分别生成了富能中间体INT1a和INT2b，它们均是无势垒的放热 反应，放出的能量分别为60.28和26.33kJ·mol~(-1).(II)中间体INT1a和INT2b分 别通过过渡态TS1a和TS2b异构化为三元环产物P1和四元环产物P2，其势垒分别为 16.43和12.73kJ·mol~(-1)。     

H_20 CN→HCN OH的IRC解析及其反应动力学研究

本文用能量梯度法,在UHF/3-21G水平上,优化了反应H_2O CN→HCN OH的反应物、产物及其过渡态的几何构型,得到了该反应的活化能为32.6kJ/mol,与实验所得的测量值相一致;同时用Morokuma的数值分析方法,得到了该反应的内禀反应坐标(IRC);沿着IRC,对反应过程中体系构型的变化进行了分析,并计算IRC运动与垂直于IRC简正振动之间的偶合常数,讨论振动频率的变化,并结合偶合常数进行分子动态学分析;用传统过渡态理论、变分过渡态理论及相关的隧道校正等方法计算该反应的速率常数,结果与实验值基本吻合(如T=763K时,K_(计算值)~(CVT/SCSAG)=309×10~(10),K_(实验值)=(5.1±0.6)×10~(10),单位cm~3·mol~(-1)·s~(-1)).     

乙炔与氢原子反应的IRC和反应速度常数的从头算研究

乙炔与氢原子反应:H+H—C≡C—H→ H—C≡C:+H_2在碳氢化合物的氧化、光解和热解中都具有重要意义。Dagaut等人做过动力学研究,但从理论角度研究其反应动力学尚未见报道。本文用量化方法在反应途径哈密顿基础上,求得了反应途径(IRC)上各点的IRC曲率(B_F)、IRC与其它各振动模式之间的耦合常数(B_(F,t))等,并计算出反应速度常数。 本文用HF/6-31G优化出了过渡态的几何构型(图1),并给出了过渡态的虚振动模式。     

金属Ir4簇催化乙烯加氢反应势能面的理论研究

应用密度泛函理论(DFT)对金属Ir4簇催化乙烯加氢反应的反应机理进行了详尽的理论研究．在B3LYP／ECP[C,H:6-311G(d)和6-31G(d);Ir:LANL2DZ]理论水平下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,并且用组态相互作用CCSD／ECP[C,H:6-311G(d,p);Ir:LANL2DZ]计算了各驻点的单点能,构建了该反应的基态势能面．为了验证过渡态的真实性,在B3LYP／ECP理论水平下做了内禀反应坐标(IRC)计算和频率分析．计算结果表明:金属Ir4簇催化乙烯加氢反应为双通道(a和b)反应,经过多个反应步骤完成;通道a:R→TSR-1→I1→TS1-2→I2→TS2-3→I3→TS3-P→P为较为可行的反应通道．     

甲苯热裂解机理的AM1研究(Ⅱ)动力学分析

在（Ⅰ）报热力学的基础上,本文用Gaussian98程序包中AM1法UHF计算,对碳材料用碳前驱体甲苯热裂解机理进行了动力学研究,通过用QST2方法寻找过渡态并经过内禀反应坐标IRC验证。计算得到了甲苯5种热裂解路径的活化能;用过渡态理论,计算了得到了这些路径在298－1073K温度范围内的速率常数。动力学计算结果表明：甲苯在热解温度低于963K时的主反应路径为甲苯热裂解生成苄基自由基的反应;该主反应路径又是经过由反应物→中间体→产物而完成,速控步为反应物→中间体,速控步的活化能△E^O=E(TS1′）-E（R）=227.20kJ.mol^-1;当温度高于963K或1073K左右时,主反应路径转为苯环上脱甲基生成苯基和甲基自由基的路径。以上研究结果与实验结果相一致。     

N-取代乙基吡唑热消除反应的量子化学研究

用MINDO/3方法研究了N-取代乙基吡唑热消除反应H₃C₃N₂CH₂CH₂X→H₄C₃N₂+H₂C=CHX(反应Ⅰ～Ⅲ,对应X=H,CH₃,F)的机理,结果表明,甲基的超共轭效应以及F的强吸电子作用和邻基参与使得反应Ⅱ和反应Ⅲ的活化势垒降低,比反应Ⅰ更易进行。     

A computational investigation on the geometries,stabilities, antioxidant activity,and the substituent effects of the L‐ascorbic acid and their derivatives

The geometries, stabilities, and antioxidant activities of L‐Ascorbic acid (1a), D‐erythroascorbate (2a), and D‐erythroascorbate glucoside (3a) as well as their sulfur and selenium derivatives are systematically investigated by using density functional theory. Emphasis is placed on studies of the two main mechanisms, that is, hydrogen atom donation and single‐electron transfer, and the O—H bond dissociation enthalpy and the ionization potential are computed in the gas phase and water solution. The calculated results indicate that the 2‐OH group in the five‐membered ring acts as an important H atom donor to free radicals. The 2‐OH radical spin density distribution shows that the unpaired electron is mostly located at the C3 atom of the five‐membered ring and partially at the vicinal O atoms, proving that a certain delocalization of the odd electron is effective in the five‐membered ring. In water aqueous solution, the antioxidant capacity and the electron donating ability are increased as the O atom in the five‐membered ring of 1a, 2a, and 3a is replaced by S and Se, respectively, in good agreement with experimental measurements; Furthermore, their antioxidant capacities are enhanced as compared with the standard antioxidant (resveratrol). © 2013 Wiley Periodicals, Inc.     

The Cycloaddition Reactions of Angle Strained Cycloalkynes. A Theoretical Study

The potential energy surfaces for the cycloaddition reactions of angle strained cycloalkynes to ethylene have been studied using ab initio methods. All the stationary points were determined with the MP2/6–311G (d,p) method with some calculations performed at the CCSD(T)/6–311G++G(d,p)//MP2/6–311G (d,p) level. Three kinds of cycloalkyne species, including monocyclic alkynes, bridged bicyclic alkynes, and heterocyclic alkynes, have been chosen in this work as model reactants. Two different reaction pathways have been proposed: (A) 1,2‐carbon shift and (B) 1,2‐hydrogen shift. That is, reactants → [2+1]‐TS‐1 → spiro‐carbene intermediate → (A) TS‐A → Pro‐A or (B) TS‐B → Pro‐B. As a result, it is found that ground‐state cycloalkyne appears to react more like a monocarbene than like an alkyne or a vicinal dicarbene as conventionally proposed. Our theoretical investigations also suggest that a cycloalkyne with a small C‐C≡C bond angle should be a good candidate for cycloaddition to an olefin. Moreover, in the cycloaddition reaction of a small (≤ six‐membered ring six‐membered) ring cycloalkyne, both 1,2‐carbon and 1,2‐hydrogen migrations will compete with each other. On the other hand, reactions involving larger (≥ seven‐membered) ring cycloalkynes should proceed with a 1,2‐carbon shift, leading to the major [2+2] cycloadduct. Furthermore, a configuration mixing model has been used to rationalize the computational results and to develop an explanation for the barrier heights. The results obtained allow a number of predictions to be made.     

苯酚羟基化制备苯二酚反应机理的理论研究

采用密度泛函理论(DFT)在UB3LYP/6-311G^**//UB3LYP/6-31G^*水平上研究了水溶液中羟基自由基进攻苯酚的邻位和对位生成邻苯二酚和对苯二酚的反应机理.结果表明,2个反应都存在3个过渡态,3个中间体,并通过振动分析对过渡态进行了确认.电荷密度的拓扑分析发现,邻位反应中羟基自由基的氧原子和苯酚环上的2个氢原子之间形成了氢键,并相应地形成了六元环和五元环结构.经单点能校正后,2个反应的主反应活化能十分接近,说明邻位和对位产物会同时存在,这与实验观测的结果一致.     

Relative reactivity of three and four membered rings--the absence of charge effect

Radical (neutral) and electrophilic (cationic) ring opening reactions were studied computationally in order to probe the difference in reactivity between three and four membered rings. Using the Marcus equation we have shown that the activation energy for the four membered ring opening is close to the Marcus predicted barrier whereas three membered rings display much higher reactivity than that predicted by the Marcus equation. Thus, the reactivity of the three membered rings is enhanced, in addition to the strain release, by another factor which is not operative in the four membered rings. It is clear also that this factor is not charge dependent. The possible origin of this effect is discussed.     

Theoretical study of reactions between AlH(1Σ) and HF molecule

Reaction mechanisms between AlH (¹Σ) and HF molecule are theoretically investigated. Ab initio calculations demonstrate that there are two parallel reaction channels: one is an addition reaction to give H₂AlF via the three‐membered ring transition state (TS) and the other is a dehydrogenation reaction to give AlF+H₂ via the four‐membered ring TS. The addition reaction is thermodynamically favorable and the dehydrogenation reaction is kinetically favorable. Thermodynamics and Eyring transition state theory (TST) with the Wigner correction are also used to compute the thermodynamic functions, the equilibrium constants, A factors, and the rate constants of these reaction channels at 200–1000 K. From the thermodynamics and TST calculations, it is valuable to point out that consideration on the entropy and thermal enthalpy is quite important in the study of chemical reactions on the basis of ab initio method. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 417–424, 1999     

Chiral discrimination in hydrogen‐bonded complexes of hydrogen peroxide with methyl hydroperoxide: Theoretical study

For the first time, the discrimination of different chiral forms of 1:1 complexes with hydrogen peroxide and methyl hydroperoxide have been investigated using density functional theory (DFT) and Møller–Plesset type 2 (MP2) methods at varied basis set levels from 6‐31+G(d,p) to 6‐31++G(2d,2p). Three pairs of chiral enantiomers were considered. The optimized geometric parameters, interaction energies, and chirodiastatic energies for various isomers at different levels are estimated. To take into account the water solvation effect, the polarized continuum model (PCM) method has been used to evaluate the ΔG_solv. The gas phase results show that the heterochiral six‐membered ring complex (structure I) and homochiral five‐membered ring complexes (structures IV and V) are preferred configurations for the three pairs of chiral enantiomers. The solvation effect on six‐membered ring complexes (structures I and II) shows nonsignificant changes in the configurations preferred, but on five‐membered ring complexes, the homo‐/heterochiral preference is found to be inverse in the polar solvent. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Theoretical study of reactions between MH (M=B,Al) and the H2S molecule

Reaction mechanisms between MH (M=B, Al) and the H₂S molecule have been theoretically studied. The G3 ab initio and DFT calculations demonstrate that only one stable addition complex (HM:SH₂, M=B, Al) can be formed, and that, starting from the addition complex (HM:SH₂) two parallel reaction channels have been found: one is an addition reaction to give H₂MSH via the three‐membered ring transition state (TS), and the other is a dehydrogenation reaction to give MSH+H₂ via the four‐membered ring TS. Thermodynamics and Eyring transition state theory (TST) with the Wigner correction are also used to compute the thermodynamic functions, the equilibrium constants, A factors, and the rate constants of these reaction channels at 300–1500 K. The calculated results predict that the product H₂BSH in the system of BH+H₂S and the product AlSH+H₂ in the system of AlH+H₂S will be mainly observed. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Theoretical study of mechanism of forming a silapolycyclic compound between methylenesilylene and acetone

The mechanism of the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy profile, we predict that the cycloaddition reaction of forming a silapolycyclic compound between singlet methylenesilylene and acetone has two competitive dominant reaction pathways. First dominant reaction pathway consists of four steps: (I) the two reactants (R1, R2) first form an intermediate (INT1) through a barrier‐free exothermic reaction of 46.2 kJ/mol; (II) intermediate (INT1) then isomerizes to a planar four‐membered ring product (P3) via transition state (TS3) with an energy barrier of 47.1 kJ/mol; (III) planar four‐membered ring product (P3) further reacts with acetone (R2) to form an intermediate (INT4), which is also a barrier‐free exothermic reaction of 40.0 kJ/mol; (IV) intermediate (INT4) isomerizes to a silapolycyclic compound (P4) via transition state (TS4) with an energy barrier of 57.0 kJ/mol. Second dominant reaction pathway consists of three steps: (I) the two reactants (R1, R2) first form a four‐membered ring intermediate (INT2) through a barrier‐free exothermic reaction of 0.5 kJ/mol; (II) INT2 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier‐free exothermic reaction of 45.4 kJ/mol; (III) intermediate (INT5) isomerizes to a silapolycyclic compound (P5) via transition state (TS5) with an energy barrier of 49.3 kJ/mol. P4 and P5 are isomeric compounds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

N，N－二甲基甘氨酸乙酯分解反应机理的理论研究

利用量子化学计算方法MP2／6－31＋G^*研究了N，N－二甲基甘氨酸乙酯在气 相中热分解反应机理，并计算了反应的协同性，得出此反应是一个多步反应过程。 主要有两个阶段：第一个阶级是N，N－二甲基甘氨酸乙酯热分解产生N，－N二甲基 甘氨酸中间体和乙烯，第二个阶段是N，N－二甲基甘氨酸进一步分解生成三甲氨和 二氧化碳。第一个反应阶段为速率控制步骤。研究表明，该反应机理是一个非协同 的质子转移过程。计算结果与实验值吻合。