H原子和(CH3)2SiH2抽提反应的理论研究

采用UMP2/6-31G(d)理论水平优化了H原子和(CH3)2SiH2抽提反应势能面上的所有驻点,并在此水平基础上进行了内禀反应坐标(IRC)的计算,得到该反应的反应途径(MEP)。应用变分过渡态理论及最小能量途径半经典绝热基态隧道效应校正(MEPSAG)、小曲率半经典绝热基态隧道效应校正(SCSAG)等方法对上述反应进行了动力学研究,期望从理论上提供一套温度范围较宽、精度较高的动力学数据,为阐明反应机理和解释实验结果提供理论依据。     

HNCS与CX(X=H,F,Cl)自由基反应的理论研究

用量子化学密度泛函理论的UB3LYP方法，在6-31 G^*水平上按BERNY能量梯度解析法全参数优化了HNCS与CX(X=H，F，Cl)反应势能面上各驻点的几何构型，通过同一水平的振动频率分析确认了中问体和过渡态，并得到各驻点的零点能校正(Ezpc)．通过内禀反应坐标(IRC)计算确认了反应物、中间体、过渡态和产物的相关性并得到最小能量途径(MEP)．为了得到体系势能面的更准确信息，在各驻点的UB3LYP／6-31 G^*构型基础上，又进行了UQCISD(T)／6-311 G^**水平上的单点能计算，得到体系的势能面信息和可能的反应机理．应用变分过渡态理论及最小能量途径半经典绝热基态(MEPSAG)、小曲率半经典绝热基态(SCSAG)隧道效应校正的方法计算了标题反应在250～1500K温度范围内的速率常数．研究结果表明，HNCS与CX自由基反应是通过分子间H原子迁移及N—C键的断裂，生成产物CS NCXH．反应均为放热反应．     

CH(^4∑^-)+H2O→CH2(^3B1)+OH的直接动态学研究

用从头算方法计算了反应CH(^4∑^-)+H2O→CH2(^3B1)+OH的反应途径。在此基础上, 计算沿反应途径的动态学性质和正则变分过渡态理论的速率常数, 并进行隧道效应校正。结果表明, 电子相关能对反应活化位垒影响较大; 反应存在返回效应和隧道效应, 用正则变分过渡态方法和小曲率近似的隧道校正是有效的。     

氢抽提反应CHBr2+HBr→CH2Br2+Br的直接动力学研究

采用直接动力学方法,对CHBr2+HBr→CH2Br2+Br反应通道进行了理论研究,在B3LYP/6-311+G(d,p)水平下获得了优化几何构型、频率以及最小能量路径,更精确的单点能在B3LYP/6-311++G(3df,2pd)水平下完成.利用正则变分过渡态理论,结合小曲率隧道效应校正方法计算了反应通道在220 K～2 000 K温度范围内的速率常数.在整个反应区间,隧道效应对反应的影响比较大;变分效应在低温时有一定的影响,在高温区间的影响很小可以忽略.计算得到的速率常数和已有实验值很好地吻合.     

HNCO+OH->H2O+NCO的反应机理

采用从头算分子轨道法 (UHF/6 31G 水平 ,并用MP4加以相关能校正 )研究了HNCO OHH2 O NCO反应机理 .同时用Morokuma数值法获得了反应途径即内禀反应坐标 (IRC) .沿着IRC ,运用反应途径哈密顿理论 ,获得反应途径动态学信息 .在此基础上 ,根据过渡态理论和相应隧道效应校正 ,计算了在不同温度下的反应速率常数 ,得到了和实验相一致的结果 .计算结果表明 ,此反应是一步直接型的抽提H反应 .     

CH_3CN+CH_3→CH_2CN+CH_4氢消除反应的直接动力学研究

采用直接动力学方法,对乙腈与甲基的反应进行了理论研究.在BHandHLYP/6-311G(d,p)和MP2/6-311G(d,p)水平下获得,稳定点的几何结构、振动频率及最小能量路径(MEP),在G3(MP2)和MC-QCISD水平下对能量信息进一步确认.利用正则变分过渡态理论,结合小曲率隧道效应校正(CVT/SCT)方法计算了该反应在220K～2000K的速率常数,与实验值符合得很好.     

HNCO+OH→H2O+NCO的反应机理

采用从头算分子轨道法(UHF/6-31G**水平,并用MP4加以相关能校正)研究了HNCO+OH→H2O+NCO反应机理.同时用Morokuma数值法获得了反应途径即内禀反应坐标(IRC).沿着IRC,运用反应途径哈密顿理论,获得反应途径动态学信息.在此基础上,根据过渡态理论和相应隧道效应校正,计算了在不同温度下的反应速率常数,得到了和实验相一致的结果.计算结果表明,此反应是一步直接型的抽提H反应.     

2-羟基-1-氧基乙烯自由基(C2H3O2)的分子内质子转移反应的理论研究

用量子化学从头计算方法研究了2-羟基-1-氧基乙烯自由基的质子转移反应。首先, 在UHF/3-21G的水平上, 采用能量梯度法优化了反应物和过渡态的几何构型, 然后利用这两个优化的构型做了振动分析, 找出相应的振动频率和模式, 从而得到质子转移反应的活化熵值。此外, 又做了内禀反应坐标途径(IRC)。为了求得比较准确的反应势能剖面, 以便进行隧道效应校正, 用多体微扰法(二级微扰)同时在参加转移的氢原子上附加了扩散函数p(UMP_2/3-21G~+)在IRC的各点上进行能量校正。根据从以上计算结果拟合的抛物线势, 求出质子转移的隧道效应校正系数为19.9, 然后由过渡状态理论计算了此反应的比速常数为7.4×10~(11)s~(-1)。此外, 还得到了该自由基的分子内氢键键能和键长分别为19.2 kJ mol~(-1)和0.2057 nm(UMP_2/3-21G~+结果)。     

H3PO→H2POH异构化反应的直接动力学研究

在QCISD(T)/6-311C++G(2df,2pd)//QCISD/6-311C++G(d,p)+ZPE水平上,对H3PO的异构化反应H3PO→(1)H2POH(trans)→(2)H2POH(cis)进行了计算研究.结果表明,H原子由P原子向O原子迁移反应(1)的能垒为250.0kJ/mol,是反应速率控制步骤,而O_H键绕P_O键旋转的构型转化反应(2)的能垒只为12.3kJ/mol.利用经典过渡态理论(TST)与变分过渡态理论(CVT)分别计算了反应(1)在200～2000K温度区间内的速率常数kTST和kCVT,获得了经小曲率隧道效应(SCT)及Eckart模型校正后的速率常数kTST/Eckart和kCVT/SCT.对只涉及H原子迁移的反应(1),量子力学隧道效应的影响在低温段非常明显,而变分效应对反应速率常数的影响很小.     

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.     

Sc2MgGa2 and Y2MgGa2

Scandium magnesium gallide, Sc₂MgGa₂, and yttrium magnesium gallide, Y₂MgGa₂, were synthesized from the corresponding elements by heating under an argon atmosphere in an induction furnace. These intermetallic compounds crystallize in the tetragonal Mo₂FeB₂‐type structure. All three crystallographically unique atoms occupy special positions and the site symmetries of (Sc/Y, Ga) and Mg are m2m and 4/m, respectively. The coordinations around Sc/Y, Mg and Ga are pentagonal (Sc/Y), tetragonal (Mg) and triangular (Ga) prisms, with four (Mg) or three (Ga) additional capping atoms leading to the coordination numbers [10], [8+4] and [6+3], respectively. The crystal structure of Sc₂MgGa₂ was determined from single‐crystal diffraction intensities and the isostructural Y₂MgGa₂ was identified from powder diffraction data.     

Zur Kenntnis der Dialkalimetalldichalkogenide β-Na2S2, K2S2, α-Rb2S2, β-Rb2S2, K2Se2, Rb2Se2, α-K2Te2, β-K2Te2 und Rb2Te2

On Dialkali Metal Dichalcogenides β-Na₂S₂, K₂S₂, α-Rb₂S₂, β-Rb₂S₂, K₂Se₂, Rb₂Se₂, α-K₂Te₂, β-K₂Te₂ and Rb₂Te₂ The first presentation of pure samples of α- and β-Rb₂S₂, α- and β-K₂Te₂, and Rb₂Te₂ is described. Using single crystals of K₂S₂ and K₂Se₂, received by ammonothermal synthesis, the structure of the Na₂O₂ type and by using single crystals of β-Na₂S₂ and β-K₂Te₂ the Li₂O₂ type structure will be refined. By combined investigations with temperature-dependent Guinier-, neutron diffraction-, thermal analysis, and Raman-spectroscopy the nature of the monotropic phase transition from the Na₂O₂ type to the Li₂O₂ type will be explained by means of the examples α-/β-Na₂S₂ and α-/β-K₂Te₂. A further case of dimorphic condition as well as the monotropic phase transition of α- and β-Rb₂S₂ is presented. The existing areas of the structure fields of the dialkali metal dichalcogenides are limited by the model of the polar covalence.     

Thermal decomposition of Me3SnO2PCl2, Me2Sn(O2PCl2)2 and Ph3SnO2PCl2

TG and DTA studies on Me₃SnO₂PCl₂, Me₂Sn(O₂PCl₂)₂ and Ph₃SnO₂PCl₂ were carried out under dynamic argon atmosphere. The results show that the decomposition proceeds in different stages leading to the formation of Sn₃(PO₄)₂ as a stable product. This compound was characterized by IR spectroscopy. Decomposition schemes involving reductive elimination reactions were proposed.     

The alkali hypophosphites KH2PO2, RbH2PO2 and CsH2PO2

The structures of the hypophosphites KH₂PO₂ (potassium hypophosphite), RbH₂PO₂ (rubidium hypophosphite) and CsH₂PO₂ (caesium hypophosphite) have been determined by single‐crystal X‐ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.     

Crystal Structures of [Bu2Sn(O2PPh2)2], [Ph2Sn(O2PPh2)2], and [PhClSn(O2PPh2)OMe]2. Raman Spectra of [Ph2Sn(O2PPh2)2] and [PhClSn(O2PPh2)OMe]2

[(n‐Bu)₂Sn(O₂PPh₂)₂] ( 1 ), and [Ph₂Sn(O₂PPh₂)₂] ( 2 ) have been synthesized by the reactions of R₂SnCl₂ (R=n‐Bu, Ph) with HO₂PPh₂ in Methanol. From the reaction of Ph₂SnCl₂ with diphenylphosphinic acid a third product [PhClSn(O₂PPh₂)OMe]₂ ( 3 ) could be isolated. X‐ray diffraction studies show 1 to crystallize in the monoclinic space group P2₁/c with a = 1303.7(1) pm, b = 2286.9(2) pm, c = 1063.1(1) pm, β = 94.383(6)°, and Z = 4. 2 crystallizes triclinic in the space group , the cell parameters being a = 1293.2(2) pm, b = 1478.5(4) pm, c = 1507.2(3) pm, α = 98.86(3)°, β = 109.63(2)°, γ = 114.88(2)°, and Z = 2. Both compounds form arrays of eight‐membered rings (SnOPO)₂ linked at the tin atoms to form chains of infinite length. The dimer 3 consists of a like ring, in which the tin atoms are bridged by methoxo groups. It crystallizes triclinic in space group with a = 946.4(1) pm, b = 963.7(1) pm, c = 1174.2(1) pm, α = 82.495(6)°, β = 66.451(6)°, γ = 74.922(6)°, and Z = 1 for the dimer. The Raman spectra of 2 and 3 are given and discussed.     

Electrochemical study of (NEt4)2Cl2FeS2MoS2 and (NEt4)2Cl2FeS2MoS2FeCl2

Summary The ability of [MoS₄]^2–, anions to be used as ligands for transition metal ions has been widely demonstrated, especially with Fe²⁺. The present study has been restricted to linear complexes such as (NEt₄)₂ [Cl₂FeS₂MoS₂] and (NEt₄)₂[Cl₂FeS₂MoS₂FeCl₂]. Their electrochemical properties are described: upon electrochemical reduction, these compounds yield MoS₂, as a black precipitate, and an iron complex in solution, assumed to be [SFeCl₂]^2–. The electrochemical reduction goes through two electron transfers, coupled with the breakdown of the molecular skeleton: a DISPl and an ECE mechanism. Depending on the solvent, the following equilibrium may be observed: [Cl₄Fe₂MoS₄]^2–[Cl₂FeMoS₄]^2–+FeCl₂. The equilibrium constant, K_D, was evaluated by differential pulse polarography. K_D is tightly related to the donor number of the solvent.     

Formal [(2+2)+2] and [(2+2)+(2+2)] nonconjugated dienediyne cascade cycloadditions

[reaction: see text] Fluoranthene 2 and heptacycle 3 are easily accessible from the reaction of diyne 1 and norbornadiene (NBD) in the presence of the rhodium catalyst. The unusual [(2+2)+(2+2)] adduct 3 was confirmed by the X-ray crystal structure analysis.