草酰溴一价正离子(BrCO)+2几何构型及反应活性的DFT研究

用密度泛函方法BHandHIYP以6-311 G(d)和6-311 G(2df）为基组对草酰溴的一价正离子(BrCO)2^ 和中性分子(BrCO)2做了构象分析,结果表明,(BrCO)^ 2和(BrCO)2都具有平面反式和交叉式两种构象。交叉式构象存在超共轭现象。此外,对草酰溴离子、中性分子各解离通道初级反应的Gibbs自由能的计算,发现草酰溴离子C-C键解离通道的反应活性总体上大于中性分子,对该反应通道进一步做了反应机理研究,证实了热力学结论。     

CH3CH2S自由基H迁移异构化及裂解反应的理论研究

采用密度泛函方法(B3LYP)在6-311+G(d,p)基组水平上研究了CH3CH2S自由基H迁移异构化以及裂解反应的微观动力学机理. 在QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)+ZPE水平上进行了单点能校正. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)分别计算了在200~2000 K温度区间内的速率常数kTST和kCVT, 同时获得了经小曲率隧道效应模型(SCT)校正后的速率常数kCVT/SCT. 研究结果表明, CH3CH2S自由基1,2-H迁移、1,3-H迁移、C—C键断裂和β-C—H键断裂反应的势垒ΔE≠分别为149.74, 144.34, 168.79和198.29 kJ/mol. 当温度低于800 K时, 主要发生1,2-H迁移反应, 高于1800 K时, 主要表现为C—C键断裂反应, 在1300—1800 K范围内, 1,3-H迁移反应是优势通道, 在计算的整个温度段内, β-C—H键断裂反应可以忽略.     

一氟二氯代甲烷热解离动力学的理论研究

利用从头算和ＲＲＫＭ理论研究了一氟二氯代甲烷热解离动力学，并得到了一套热力学和动力学参数。研究了三种不同的解离通道：（１）ＨＣｌ＋ＣＦＣｌ_２，（２）Ｃｌ＋ＣＨＦＣｌ，（３）ＨＦ＋ＣＣｌ_２，它们的活化能分别为：２４３．３、２５８．９、３０９．８ｋＪ／ｍｏｌ。研究结果表明，氯化氢消除反应和碳氯键简单断键反应是两个主要的并且是竞争的通道，三个反应通道的高压速率常数分别为ｋ_１＝８．７４×１０~（１４）ｅｘｐ（－２９１６３Ｔ）_ｓ~（－１），ｋ_２＝７．０９×１０~（１５）ｅｘｐ（－３１１２１／Ｔ）_ｓ~（－１），Ｒ_３＝３．８７×１０~（１１）ｅｘｐ（－３７０３９／Ｔ）_ｓ~（－１），它们都具有明显的温度和压力依赖关系。     

二氯卡宾与甲醇及甲硫醇插入与氢抽提反应的量子化学计算

利用密度泛函和自然键轨道理论及电子密度拓扑分析方法，对单、三重态CCl2与CH3MH（M=O，S）中C—H和M—H键的插入反应及抽提氢反应进行了研究．在B3LYP／6-311G（d，p）水平上优化了势能面上构型，并以频率分析和内禀反应坐标法进行了确认．计算了各物种的CCSD（T）／6-211G（d，p）能量．结果表明，主反应通道主要发生在单重态势能面中，单重态CCl2既可以与C-H及M—H键发生插入反应，存在四条主反应通道，分别生成P1[CH3OCHCl2，反应Ⅰ（1）]，P3[Cl2HCCH2OH，反应Ⅰ（2）]和PS[CH3SCHCl2，反应Ⅱ（1）]，P7[Cl2HCCH2SH，反应Ⅱ（2）]，也可以与CH3MH发生抽提氢反应，分别生成P4[CH2O＋CH2Cl2，反应Ⅰ（3）]和P8[CH2S＋CH2Cl2，反应Ⅱ（3）]．同时，存在三重态CCl2与CH3SH插入生成^3P4[CH3SCHCl＋Cl]的反应通道．进一步对反应通道上的关键点进行了自然键轨道和电子密度拓扑分析．     

气相中CrO2^＋主活化甲烷C—H键的理论研究

用密度泛函UB3LYP／6-311＋＋G＊＊方法计算研究了气相中CrO2^＋（2^A1/4^A＂）活化甲烷C—H键的微观机理，找到了四条反应通道．对其中涉及的两态反应（TSR）进行了分析，并对影响反应机理和反应速率的势能面交叉现象（potential energy surfaces crossing）进行了详细讨论，进而运用Hammond假设和Yoshizawa等的内禀坐标单点垂直激发计算的方法找出了一系列势能面交叉点[crossing points（CPs）]，并作了相应的讨论．进一步用碎片分子轨道理论[fragment molecular orbital（FMO）]对TS1中的轨道相互作用进行了分析，解释了CrO2^＋活化甲烷C—H键的机理．     

H+HCNO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应H＋HCNO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过H迁移、N—O键或C—N键断裂等多步反应, 得到4种产物, 其中最主要产物为P1(HCN+OH).     

替马西泮醇解反应机理研究

大量镇静催眠药的滥用给食品安全带来了严重负面影响,时刻威胁着人们的身体健康和生命安全。本文采用B3LYP/6-311+G**和MP2/6-311+G**方法,研究了苯二氮类药物替马西泮(TMZ)在中性和酸性甲醇溶液中的醇解反应机理。结果显示,无论从热力学还是动力学上分析,TMZ分子在中性和酸性甲醇溶液中N1—C2键断裂开环降解反应(Path 2和Path 3)都很难发生;而中性甲醇溶液中断裂C3—N4键醇解开环降解反应(Path 1)从动力学上分析是可行的,反应涉及1个或2个显性甲醇溶剂分子参与反应,通过质子的受体与给体的酸碱催化作用促进反应的进行,液相能垒(ΔG≠)分别为85.7k J/mol和81.6k J/mol,应该为TMZ分子在甲醇溶液中醇解的优势反应路径。研究结果与实验观察一致。     

1, 2-二硒方酸气相酸性和芳香性的理论研究

在RHF/6-311G^*^*水平优化得到1,2-二硒方酸(3,4-二羟基-3-环丁烯-1,2-二硒酮)三种平面构象异构体的平衡几何构型。进一步用MP2(full)/6-311G^*//RHF/6-311G^*^*方法计算三种异构体的单点能量,发现ZZ型异构体是能量最低构象,且ZZ和ZE型能量非常接近。用优化的最稳定构象ZZ型异构体在RHF/6-311G^*^*//RHF/6-311G^*^*,RHF/6-311+G^*^*//RHF/6-311+G^*^*,MP2(full)/6-311+G^*^*//RHF/6-311+G^*^*和B3LYP/6-311+G^*^*//B3LYP/6-311+G^*^*水平计算其气相酸性[ΔGⅲ~(~2~9~8~K~)]和同键反应芳香性稳定化能(HASE)。用基团加和法(groupincrementapproach)在RHF/6-311+G^*^*//RHF/6-311+G^*^*和B3LYP/6-311+G^*^*//B3LYP/6-311+G^*^*水平计算其磁化率增量(Λ)。计算结果指出标题化合物的键长发生了平均化,同键反应芳香性稳定化能和磁化率增量均为负值,表明它具有芳香性,实现了标题化合物芳香性的几何、能量和磁性的判定。     

C8H10+·侧链分解过程反应机理的理论研究

正乙苯正离子自由基C8H10+·的分解可以作为研究烷基苯正离子反应机理的原型。使用Gaussian98程序包、在B3LYP/6-311++G**基组水平上对C8H10+·的分解反应体系进行了充分研究。C8H10+·的分解的链反应是由C-H键断裂开始的。作者用振动模式分析对所有反应通道进行了充分研究，以确定过渡态并阐明了反应机理。研究表明，能量上最有利的通道为C8H10+·→ TS4 → P2 + H·，产生C6H6+·+C2H4的通道也为竞争性反应通道。     

NO+HCCCO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应NO＋HCCCO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过O迁移、C—C键或N—O键断裂等多步反应, 得到4种产物, 其中, 最主要产物为P1(HCCO+NCO).     

Observation of dihalide elimination upon electron attachment to oxalyl chloride and oxalyl bromide, 300-550 K

Rate coefficients have been measured for electron attachment to oxalyl chloride [ClC(O)C(O)Cl] and oxalyl bromide [BrC(O)C(O)Br] in He gas at 133 Pa pressure over the temperature range of 300-550 K. With oxalyl chloride, the major ion product of attachment is Cl2(-) at all temperatures (66% at 300 K); its importance increases slightly as temperature increases. Two other product ions formed are Cl- (18% at 300 K) and the phosgene anion CCl2O- (16% at 300 K) and appear to arise from a common mechanism. With oxalyl bromide, the Br2(-) channel represents almost half of the ion product of attachment, independent of temperature. Br- accounts for the remainder. For oxalyl chloride, the attachment rate coefficient is small [(1.8 +/- 0.5) x 10(-8) cm3 s(-1) at 300 K], and increases with temperature. The attachment rate coefficient for oxalyl bromide [(1.3 +/- 0.4) x 10(-7) cm3 s(-1) at 300 K] is nearly collisional and increases only slightly with temperature. Stable parent anions C2Cl2O2(-) and C2Br2O2(-) and adduct anions Cl- (C2Cl2O2) and Br- (C2Br3O2) were observed but are not primary attachment products. G2 and G3 theories were applied to determine geometries of products and energetics of the electron attachment and ion-molecule reactions studied. Electron attachment to both oxalyl halide molecules leads to a shorter C-C bond and longer C-Cl bond in the anions formed. Trans and gauche conformers of the neutral and anionic oxalyl halide species have similar energies and are more stable than the cis conformer, which lies 100-200 meV higher in energy. For C2Cl2O2, C2Cl2O2(-), and C2Br2O2(-), the trans conformer is the most stable conformation. The calculations are ambiguous as to the oxalyl bromide geometry (trans or gauche), the result depending on the theoretical method and basis set. The cis conformers for C2Cl2O2 and C2Br2O2 are transition states. In contrast, the cis conformers of the anionic oxalyl halide molecules are stable, lying 131 meV above trans-C2Cl2O2(-) and 179 meV above trans-C2Br2O2(-). Chien et al. [J. Phys. Chem. A 103, 7918 (1999)] and Kim et al. [J. Chem. Phys. 122, 234313 (2005)] found that the potential energy surface for rotation about the C-C bond in C2Cl2O2 is "extremely flat." Our computational data indicate that the analogous torsional surfaces for C2Br2O2, C2Cl2O2(-), and C2Br2O2(-) are similarly flat. The electron affinity of oxalyl chloride, oxalyl bromide, and phosgene were calculated to be 1.91 eV (G3), and 2.00 eV (G2), and 1.17 eV (G3), respectively.     

Quantum chemical study of chlorine-dissociation of oxalyl chloride (ClCO)_2→2Cl+2CO

It is very difficult to study the phenomenon that molecules are decomposed into several pho-tofragments by UV light, as the energy of lamp-house is insufficient. But the bond energy in oxa-lyl chloride is relatively low, for example, D0(ClCOCO-Cl) = 313.92 kJ/mol[1], D0(ClCO-CO) = 35.53 kJ/mol, and D0(Cl-CO) = 27.17 kJ/mol[2], so, oxalyl chloride, as a typical system for the study of multi-channel dissociation, can be dissociated into the four fragments Cl+Cl+CO+CO by the proper UV …     

Structure and torsional properties of oxalyl chloride fluoride in the gas phase: an electron-diffraction investigation

The structure and torsional properties of oxalyl chloride fluoride in the gas phase have been measured by electron diffraction at temperatures of 22, 81, 158, and 310 °C. The molecule may be regarded as a hybrid of oxalyl chloride and oxalyl fluoride. Since the former exists as a more stable periplanar anti form (? = 180°) in equilibrium with a less stable gauche form (? ? 60°) and the latter as an equilibrium between two periplanar forms, anti and syn, the second form of oxalyl chloride fluoride is an interesting question. It was found to be gauche. The system was modeled as two rotational conformers related by a potential of the form 2V = V(1)(1 + cos??) - V(2)(1 - cos?2?) + V(3)(1 + cos?3?). The anti/gauche bond distances and bond angles (r(g)/Angstroms, ∠(α)/degrees) with estimated 2σ uncertainties at 22 °C are = 1.183(2)/1.182(2), Δr(C═O) = 0.003(6)/0.002(6) (assumed from theory), r(C-F) = 1.329(3)/1.335(3), r(C-Cl) = 1.738(2)/1.753(2), ∠(C-C-Cl) = 112.0(3)/111.9(3), ∠(C-C═O3) = 123.0(4)/123.2(4), ∠(O═C-Cl) = 125.0(2)/1.249(2), ∠(O═C-F) = 123.0(3)/125.1(3), and ∠(Cl-C-C-F) = 180.0/59.8. The variation of composition with temperature afforded a determination of the standard enthalpy and entropy of the reaction anti → gauche. The results are ΔH° = 2.5(12) kcal/mol and ΔS° = -6.5(33) cal/(mol·K). The structures and equilibria are discussed.     

Quantum chemical study of chlorine-dissociation of oxalyl chloride (ClCO)<Subscript>2</Subscript>→2Cl + 2CO

The multi-bond dissociation dynamics of oxalyl chloride ((ClCO)₂) is investigated by ab initio calculation. Dissociation of C-Cl bond of oxalyl chloride in the ground state is of barrierless. After the absorption of a photon, (ClCO)₂ is excited to the first excited state and one of its C-Cl bonds is broken to yield Cl and ClCOCO* free radicals. In addition, ClCOCO* with high energy is prone to release energy (Q), and to turn into ClCOCO in the ground state. The energy (Q) is adequate for ClCOCO to break down into ClCOand CO, and even for ClCO into Cl and CO. The result is consistent with the experimental data that Kong reported.     

Density functional theory studies on the dissociation energies of metallic salts: relationship between lattice and dissociation energies

The formation and physicochemical properties of polymer electrolytes strongly depend on the lattice energy of metal salts. An indirect but efficient way to estimate the lattice energy through the relationship between the heterolytic bond dissociation and lattice energies is proposed in this work. The heterolytic bond dissociation energies for alkali metal compounds were calculated theoretically using the Density Functional Theory (DFT) of B3LYP level with 6‐311+G(d,p) and 6‐311+G(2df,p) basis sets. For transition metal compounds, the same method was employed except for using the effective core potential (ECP) of LANL2DZ and SDD on transition metals for 6‐311+G(d,p) and 6‐311+G(2df,p) calculations, respectively. The dissociation energies calculated by 6‐311+G(2df,p) basis set combined with SDD basis set were better correlated with the experimental values with average error of ca. ±1.0% than those by 6‐311+G* combined with the LANL2DZ basis set. The relationship between dissociation and lattice energies was found to be fairly linear (r>0.98). Thus, this method can be used to estimate the lattice energy of an unknown ionic compound with reasonably high accuracy. We also found that the dissociation energies of transition metal salts were relatively larger than those of alkaline metal salts for comparable ionic radii. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 827–834, 2001     

Direct dynamic study on the hydrogen abstraction reaction CH3CN + OH-->CH2CN + H2O

The reaction of acetonitrile with hydroxyl has been studied using the direct ab initio dynamics methods. The geometries, vibrational frequencies of the stationary points, as well as the minimum energy paths were computed at the BHandHLYP and MP2 levels of theory with the 6-311G(d, p) basis set. The energies were further refined at the PMP4/6-311+G(2df, 2pd) and QCISD(T)/6-311+G(2df, 2pd) levels of theory based on the structures optimized at BHandHLYP/6-311G(d, p) and MP2/6-311G(d, p) levels of theory. The Polyrate 8.2 program was employed to predict the thermal rate constants using the canonical variational transition state theory incorporating a small-curvature tunneling correction. The computed rate constants are in good agreement with the available experimental data.     

Molecular structure and conformational composition of 2-chloro-1-phenylethanone, ClH2C-C(=O)Ph, obtained using gas-phase electron-diffraction data and results from theoretical calculations

The structure and conformation of 2-chloro-1-phenylethanone, ClH(2)C-C(=O)Ph (phenacyl chloride), have been determined by gas-phase electron diffraction (GED), augmented by results from ab initio molecular orbital calculations, employing the second-order M?ller-Plesset (MP2) level of theory and the 6-311+G(d) basis set. The molecules may exist as a mixture of different conformers with the C-Cl bond either syn (torsion angle phi = 0 degrees ) or gauche to the carbonyl bond. At 179 degrees C, the majority of the molecules (90 +/- 11%) have the gauche conformation (phi = 112(3) degrees). Torsion is also possible about the C-Ph single bond. Both experimental and theoretical data indicated, however, that the phenyl ring is coplanar or nearly coplanar with the carbonyl group. The results for the principal distances (r(g)) and angles (angle(alpha)) for the gauche conformer from a combined GED/ab initio study (with estimated 2sigma uncertainties) are the following: r(C-C)(phenyl) = 1.394(2) (average value) A, r(C(phenyl)-C(carbonyl)) = 1.484(5) A, r(C(carbonyl)-C(alkyl)) = 1.513(5) A, r(C-Cl) = 1.790(5) A, r(C=O) = 1.218(6) A, r(C-H)(phenyl) = 1.087(9) (average value) A, r(C-H)(alkyl) = 1.090(9) A (average value), angle C(phenyl)-C=O = 119.5(9) degrees, angle C(phenyl)-C(carbonyl)-C(alkyl) = 119.2(10) degrees, angle C-C-Cl = 109.8(12) degrees, angle C(2)-C(1)-C(carbonyl) = 122.8(15) degrees, angle C-C(alkyl)-H = 111.2 degrees (ab initio value).     

Influence of the d orbital occupation on the nature and strength of copper cation-pi interactions: threshold collision-induced dissociation and theoretical studies

Threshold collision-induced dissociation techniques are employed to determine the bond dissociation energies of a wide variety of copper cation-pi complexes, Cu(+)(pi-ligand), where pi-ligand = benzene, flurobenzene, chlorobenzene, bromobenzene, iodobenzene, phenol, toluene, anisole, pyrrole, N-methylpyrrole, indole, naphthalene, aniline, N-methylaniline, and N,N-dimethylaniline. The primary and lowest energy dissociation pathway corresponds to the endothermic loss of the intact neutral pi-ligand for all complexes except those to N-methylpyrrole, indole, aniline, N-methylaniline, and N,N-dimethylaniline. In the latter complexes, the primary dissociation pathway corresponds to loss of the intact ligand accompanied by charge transfer, thereby producing a neutral copper atom and ionized pi-ligand. Fragmentation of the pi-ligands is also observed at elevated energies in several cases. Theoretical calculations at the B3LYP/6-311G(d,p) level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Multiple low-energy conformers are found for all of the copper cation-pi complexes. Theoretical bond dissociation energies are determined from single point energy calculations at the B3LYP/6-311+G(3df,2p) level of theory using the B3LYP/6-311G(d,p) optimized geometries. The agreement between theory and experiment is very good for most complexes. The nature and strength of the binding in these copper cation-pi complexes are studied and compared with the corresponding cation-pi complexes to Na(+). Natural bond orbital analyses are carried out to examine the influence of the d orbital occupation on copper cation-pi interactions.     

Microwave spectrum of 3-butyne-1-thiol: evidence for intramolecular S-H...pi hydrogen bonding

The microwave spectrum of 3-butyne-1-thiol has been studied by means of Stark-modulation microwave spectroscopy and quantum-chemical calculations employing the B3LYP/6-311++G(3df,2pd), MP2/aug-cc-pVTZ, MP2/6-311++G(3df,2pd), and G3 methods. Rotational transitions attributable to two conformers of this molecule were assigned. One of these conformers possesses an antiperiplanar arrangement of the atoms S-C1-C2-C3, while the other is synclinal and stabilized by the formation of an intramolecular hydrogen bond between the H-atom of the thiol group and the pi-electrons of the C[triple bond]C triple bond. The energy difference between these conformers was estimated to be 1.7(4) kJ mol(-1) by relative intensity measurements, with the hydrogen-bonded conformer being lower in energy. The spectra of five vibrationally excited states of the synclinal conformer were observed, and an assignment of these states to particular vibrational modes was made with the aid of a density functional theory (DFT) calculation of the vibrational frequencies at the B3LYP/6-311++G(3df,2pd) level of theory.