Theoretical study of the reaction of Cu with OCS

The reactivity of Cu⁺ with OCS on both singlet and triplet potential energy surfaces (PES) has been investigated at the UB3LYP/6-311+G(d) level. The object of this investigation was the elucidation of the reaction mechanism. The calculated results indicated that both the C–S and C–O bond activations proceed via an insertion–elimination mechanism. Intersystem crossing between the singlet and triplet surfaces may occur along both the C–S and C–O bond activation branches. The ground states of CuS⁺ and CuO⁺ were found to be triplets, whereas CuCO⁺ and CuCS⁺ have singlet ground states. The C–S bond activation is energetically much more favorable than the C–O bond activation. All theoretical results are in line with early experiments.     

气相中Cu＋和Zn＋与SCO反应的理论研究

为更清晰地揭示M^＋与SCO基元反应的机理, 采用密度泛函B3LYP方法, 在6-311＋＋G**基组水平上研究了Cu^＋＋SCO和Zn^＋＋SCO反应体系. 对反应势能面上各驻点的几何构型进行了全优化, 用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证. 在Cu^＋与SCO的反应中, 对影响反应机理和反应速率的势能面交叉现象进行了讨论, 运用Hammond假设和Yoshizawa等的内禀反应坐标垂直激发的计算方法找到了势能面交叉点. 计算结果表明, C—S和C—O键的活化都是通过插入消去机理, 但C—S键的活化在能量上更占优势. 计算确认了标题反应的主通道, 所有的计算结果与实验吻合.     

A density functional theory study on the reactions of Y atom and Y+ cation with carbonyl sulfide

The mechanism of the title reactions have been studied by using the DFT (B3LYP/ECP/6‐311+G*) level of theory. Both ground and excited state potential energy surfaces are discussed. It is found the reaction mechanism is insertion mechanism both along the C? S and C? O bond activation branches, but the C? S bond activation is much more favorable in energy than the C? O bond activation. The reaction of Y atom with SCO was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, have been explained according to the mechanism revealed in this work. Different from that of Y + SCO system, the reaction between Y⁺ cation and SCO involves potential energy curve‐crossing which dramatically affects reaction mechanism. Due to the intersystem crossing existing in the reaction process of Y⁺ with SCO, the intermediates SY⁺(η²CO) and OY⁺(η²CS) may not form. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical study of the reaction of Cr+ with SCO in gas phase

To elucidate the mechanism of reaction M⁺ + SCO, the reaction of Cr⁺ + SCO has been investigated using density functional theory (DFT) with the popular hybrid functional, B3LYP, in conjunction with 6‐311+G* basis set on both the sextet and quartet potential energy surfaces (PESs). To obtain an accurate evaluation of the activation barrier and reaction energy, the coupled cluster single‐point calculations using the B3LYP structures is performed. The crossing points (CPs) of the different PESs have been localized with the approach suggested by Yoshizawa and colleagues. The involving potential energy curve‐crossing dramatically affects reaction mechanism. The present results show that the reaction mechanism is insertion‐elimination mechanism both along the C? S and C? O bond activation branches, but the C? S bond activation is much more favorable than the C? O bond activation in energy. All theoretical results not only support the existing conclusions inferred from early experiment study, but also complement the pathway and mechanism for this reaction. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Density functional studies of the reactivity in the C–F bond activation of fluoromethane by bare lanthanum monocation

The potential energy surface and reaction mechanism corresponding to the reaction of lanthanum monocation with fluoromethane, which represents a prototype of the activation of C–F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, namely after coordination of CH₃F to La⁺, electron transfer from La⁺ to the fluorine takes place, which favours the homolytic cleavage of the C–F bond to form LaF⁺ species and methyl radical. The related thermochemistry data involved in reaction of La⁺+CH₃F were determined, which can act as a guide for further experimental researches. The electron-transfer reactivity of the reaction was analyzed by using a state correlation diagram, in which a strongly avoided crossing behaviour on the transition state region was shown. The calculated state split energy between the ground and excited state on the transition state is 18.01 kcal mol⁻¹. The reaction of La⁺ with CH₃F was concluded to process in the adiabatic potential surface. The present results support the reaction mechanism inferred early from experimental data.     

Theoretical investigation of the reactions of La atom and La<Superscript>+</Superscript> cation with carbonyl sulfide

The potential energy surfaces for the La+SCO and La⁺+ SCO reactions have been theoretically investigated by using the DFT (B3LYP/ECP/6-311+G(2d)) level of theory. Both ground and excited state potential energy surfaces (PES) are discussed. The present results show that the reaction mechanism is insertion mechanism both along the C-S and C-O bond activation branches, but the C-S bond activation is much more favorable in energy than the C-O bond activation. The reaction of La atom with SCO was shown to occur preferentially on the ground state (doublet) PES throughout the reaction process, and the experimentally observed species, have been explained according to the mechanisms revealed in this work. While for the reaction between La⁺ cation with SCO, it involves potential energy curve-crossing which dramatically affects reaction mechanism, and the crossing points (CPs) have been localized by the approach suggested by Yoshizawa et al. Due to the intersystem crossing existing in the reaction process of La⁺ with SCO, the products SLa⁺(η²CO) and OLa⁺(η²CS) may not form. This mechanism is different from that of La + SCO system. All our theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.     

Theoretical Study on the Mechanism of the Gas-phase Reaction of Sc＋ with Propargyl Alcohol

In order to elucidate the reaction mechanisms of reaction Sc^＋ with propargyl alcohol (PPA), the triplet potential energy surface for the reactions has been theoretically investigated using a DFT method. The geometries for the reactants, intermediates, transition states and products were completely optimized at B3LYP/DZVP level. The single point energy of each stationary point was calculated at MP4/(6-311＋G** for C, H, O and Lanl2dz for Sc^＋) level. All the transition states were verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The present results show that the reaction takes an insertion-elimination mechanism both along the O—H and C—O bond activation branches, but the C—O bond activation is much more favorable in energy than the O—H bond activation. All theoretical results not only support the existing conclusions inferred from early experiment, but also complement the pathway and mechanism for this reaction.     

Theoretical studies of the NTO unimolecular decomposition

This work studies 39 decomposition paths among 18 intermediates and 14 transition states. Three types of intra-molecular proton migration and the direct scission of C–NO₂ were regarded as the initial steps of the unimolecular decomposition of NTO. The activation energies of the radicalization C–NO₂ homolysis step are 79.158, 79.781 and 80.652 kcal mol⁻¹. The activation energies of the ionization C–NO⁻¹₂ scission step are 262.488, 263.138 and 272.278 kcal mol⁻¹. The bottle neck activation energies of the C–NO₂H cleavage are 54.936, 63.257 and 71.247 kcal mol⁻¹. Two paths have the smallest bottle neck activation energy. Both of them have two proton migration steps and one internal rotation step prior to C–NO₂H cleavage. At lower temperatures, energy accumulated slowly. When the energy is high enough and reaction time is long enough for structure transformation, these two mechanisms should be the most probable decomposition paths. At high temperatures, the shortest (four steps) mechanism which goes through radicalization C–NO₂ scission should be the dominant path. There are five tautomers found in this study. Four of them are intra-molecular proton migration tautomers. The other one is an internal rotational tautomer. Their energy barriers for structure transfer are lower than any of the activation energies of the decomposition reactions. It may be regarded as one explanation of the insensitive property of NTO.     

Velocity map imaging of the photolysis of n-C4H9Br in UV region

Using velocity map ion imaging technique, the photodissociation of n-C₄H₉Br in the wavelength range 231–267 nm was studied. The results and our ab initio calculations indicated that the absorption of n-C₄H₉Br in the investigated region originated from the excitations to the lowest three repulsive states, as assigned as 1A″, 2A′ and 3A′ in C_s symmetry. Dissociations occurred on the PES surfaces of the three states, terminating in C₄H₉+Br (²P_3/2) or C₄H₉ + Br^* (²P_1/2) as two channels, and being impacted by an avoided crossing between the PES surfaces of the 2A′ and 3A′ states. The transition dipole to the 1A″ state was perpendicular to the symmetry plane, so perpendicular to the C–Br bond. The transitions to the 3A′ state was polarized parallel to the symmetry plane, and also parallel to the C–Br bond. While the transition dipole to the 2A′ state was in the symmetry plane, but formed an angle of about 53.1° with the C–Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways, for the photolysis of n-C₄H₉Br near 234 nm and 267 nm.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)₂ (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn–syn and 24(12)% syn–anti conformer (ΔH⁰=H⁰(syn–anti)−H⁰(syn–syn)=1.11(32) kcal mol⁻¹) which is in agreement with the interpretation of the IR spectra (68(5)% syn–syn and 32(5)% syn–anti, ΔH⁰=0.87(11) kcal mol⁻¹). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F₂ groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn–anti structure (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol⁻¹) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)₂ skeleton were derived (r_a values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.     

Theoretical study of the reaction of Ni with OCS

The reactivity of Ni⁺ with OCS on both doublet and quartet potential energy surfaces (PES) has been investigated at the B3LYP/6-311+G(d) level. The object of this investigation was the elucidation of the reaction mechanism. The calculated results indicated that both the CS and CO bond activations proceed via an insertion–elimination mechanism. Intersystem crossing between the doublet and quartet surfaces may occur along both the CS and CO bond activation branches. The ground states of NiS⁺ and NiO⁺ were found to be quartets, whereas NiCO⁺ and NiCS⁺ have doublet ground states. The CS bond activation is energetically much more favorable than the CO bond activation. All theoretical results are in line with early experiments.     

Theoretical study on reaction mechanism of the vinyl radical with nitrogen atom

The complex triplet potential energy surface of the C₂H₃N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C₂H₃ radical with N(⁴S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C₂H₃+N(⁴S), the first step is the attack of the N atom on the C atom having one H atom attached in C₂H₃ radical and form the intermediate C₂H₃N(1). The associated intermediate 1 can lead to product P₁ CH₂CN+H and P₂ ³CH₂+³HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C₂H₃+N(⁴S) reaction is the channel leading to P₁, which is preferred to that of P₂ due to the comparative lower energy barrier. The formation of P₃ ³C₂H₂+³NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively.     

气相中CrO2+和H2反应的理论研究

用密度泛函UB3LYP/6-311++G(3df, 3pdpd)//6-311G(2dd, p)方法计算研究了在二重态和四重态两个势能面上的气相反应：CrO₂⁺ + H₂→CrO⁺+ H₂O. 对影响反应机理和反应速率的势能面交叉进行了讨论, 并运用Hammond 假设和Yoshizawa 等的内禀反应坐标(IRC)单点垂直激发计算的方法找出了势能面交叉点(crossing point (CP)). 运用碎片分子轨道(fragment molecular orbital(FMO))理论, 对初始复合物2IM1和4IM1的轨道相关进行了分析, 解释了CrO₂⁺活化H—H σ键及H₂迁移的机理.     

Structure and stability of thiourea with water, DFT and MP2 calculations

The relative stabilities of thiourea in water are investigated computationally by considering thiourea–water complexes containing up to 1–6 water molecules (CS(NH₂)₂(H₂O)_n=1–6) using density functional theory and MP2 ab initio molecular orbital theory. The results show that the thiourea complex is stable and has an unusually high affinity for incoming water molecules. The clusters are progressively stabilized by the addition of water molecules, as indicated by the increasing of the binding energy. The binding energy of the cluster to each H₂O molecule is about 33 kJ mol⁻¹ for n=1–5.The C–S bond, N–C bond distance, Mulliken populations and binding energy keep approximately constant as the clusters increase in size with an increasing number of H₂O molecules. As the solvation progresses, the C–S distance increases monotonically while the Mulliken populations on the C–S bond reduces monotonically with the addition of each H₂O molecule, indicating that the C–S bond of the thiourea unit in the clusters is de-stabilized with an increasing number of H₂O molecules. Charge transfers for the clusters are mainly found at N, S atoms of the thiourea.     

Pyrolysis mechanism of carbon matrix precursor cyclohexane(III)—pyrolysis process of intermediate 1-hexene

The pyrolysis mechanism of important intermediate 1-hexene of carbon matrix precursor cyclohexane was studied theoretically. Possible reaction paths were designed based on the potential surface scan and electron structure of the initial C–C bond breaking reactions. Thermodynamic and kinetic parameters of the possible reaction paths were computed by UB3LYP/6-31+G* at different temperature ranges. The results show that 1-hexene pyrolyzes at 873 K. When below 1273 K, the major reaction paths are those that produce C₃H₄, and above 1273 K, the major reaction paths are those that produce C₃H₃ from the viewpoint of thermodynamics. From the viewpoint of kinetics, the major product is C₃H₃, it results from the pyrolysis reaction of 1-hexene cracking bond C₃–C₄ and generating C₃H₅ and C₃H₇ with the activation energy ΔE₀^≠θ=296.32 kJ/mol. Kinetic results also show that product C₃H₄ accompany simultaneously, which is the side reaction starting from the pyrolysis of 1-hexene forming C₄H₇ and C₂H₅ with the activation energy of 356.73 kJ/mol. When reaching 1473 K, the rate constant of the rate-determining steps of these two reaction paths do not show much difference, which means both the reaction paths exist in the pyrolysis process at the high temperature. The above results are basically in accordance with mass spectrum analysis and far more specific.     

Au(111)面上噻吩加氢脱硫反应机理的理论研究

采用密度泛函理论方法研究了噻吩在Au(111)面上的吸附模式, 并探讨了其在Au(111)面上可能的加氢脱硫反应机理, 对不同机理下各个基元反应的过渡态进行了筛选, 得到了各个步骤的能量变化及所需活化能.计算结果表明, 噻吩在Au(111)面上以S端倾斜吸附在Top位时最稳定.直接脱硫机理表明, 其所需活化能较低, 升高温度有利于提高脱硫反应产率, 但脱硫产物较难控制; 间接脱硫机理表明, 脱硫反应最可能按照加氢异构方式进行, 降低温度有利于脱硫反应产率的提高.随着反应的进行, 噻吩环中的C—S键键长逐渐增大, 键能逐渐减小, 有利于C—S键断裂, 具体步骤为:(1) C₄H₄S+H₂α,α-C₄H₆S; (2) α,α-C₄H₆S+H₂C₄H₈S; (3) C₄H₈S+H₂C₄H₁₀+S, 其中S原子的脱去步骤所需活化能最高, 为反应的限速步骤.     

A comparative study on the nature and strength of O–O, S–S, and Se–Se bond

A computational study on dichalcogenide molecules (R₂X₂; X = O, S, Se; R = H, CH₃, NH₂) has been carried out employing B3LYP and MP2 levels using 6-31+G*, 6-311+G*, 6-311++G**, and PVDZ basis sets. The relative energies have been evaluated at G2MP2 also. The rotational barriers and bond dissociation energies indicate that S–S bond is stronger than Se–Se and O–O bond. NBO analysis at MP2/6-31+G* suggest the presence of partial π character between X–X bond that decreases in the order S–S > Se–Se > O–O. Fuki functions for nucleophilic and electrophilic attack fail to distinguish the reactivity of S and Se. The proton affinities of the O₂H₂, S₂H₂, Se₂H₂ decrease in the order Se > S > O.     

DFT study on the reaction mechanisms of polyfluorosulfonate ester with F

Gas-phase reaction of C(1)F₃S(2)O₂O(3)C(4)H₂C(5)F₃ and F⁻(16) is investigated using DFT method. The geometries of various stationary points and their relative energies are obtained from 6-31+G*, 6-311G**, and 6-311++G** levels. In the S_N2(C) reaction leading to the cleavage of the C(4)–O(3) bond, the reaction complex results from attacking of F⁻ at a hydrogen atom H11 attached to carbon atom C(4). Afterward, F⁻ is attacking the atom C(4) from the backside of the atom O(3) with the help of the neighboring effect, and meanwhile a multi-membered ring, F(16)–H(11)–C(4)–C(5)–F(16), is being formed. The S_N2(C) reaction is irreversible. On the contrary, the S_N2(S) reaction leading to the cleavage of the S(2)–O(3) bond is reversible, and it is initiated by attacking of F⁻ at the atom S(2) from the backside of the atom O(3). The products of the reaction CF₃SO₃CH₂CF₃ +F⁻ should be, thermodynamically, controlled due to the reversibility of the S_N2(S) reaction, and those result, chemospecifically, from the cleavage of the C–O bond. At last, the SCRF calculations confirm that the solvent effect is preferable to the S_N2(C) reaction.     

过渡金属离子与烷烃反应机理的理论研究──镍离子(2D)与丙烷反应中氢分子的还原消除机理

以Ni⁺与C₃H₈反应作为过渡金属离子与烷烃反应的范例体系,用B₃LYP密度泛函方法计算了[Ni,C₃,H₈]⁺基态势能面上各驻点的构型、频率和能量,结果表明,该反应的H₂分子消除需经历两个基元步骤,即Ni⁺首先插入一级或二级C-H键,然后经H转移过渡态异构化为较稳定的中间体,继而解离产生H₂分子.计算的反应热为142.28kJ/mol,与相应的实验值(127.85kJ/mol)符合较好.