The decomposition of C4H8 complexes at controlled internal energies

A coincidence technique is used to study the influence of the internal energy of the reactant ion on the cross section of the ion-molecule reactions in the C₂H₄⁺ + C₂H₄ system. The experiment is performed at thermal collision energies. In the ion-molecule reactions of C₂H₄⁺ + C₂H₄ our measurements indicate a barrier between the initially formed collision complex (C₂H₄)₂⁺* and a tight complex (C₄H₈⁺)*. Using an extension of our earlier developed statistical model, now including a potential barrier between the initially formed loose complex (C₂H₄)₂⁺* and the tight complex (C₄H₈⁺)*, our experimental data can be reproduced. For comparison also the internal energy dependence of the unimolecular decomposition of photoionised 1-C₄H₈⁺ is measured. Assuming that the photoionised 1-C₄H₈⁺ is identical with the tight (C₄H₈⁺)* complex, the model applied to the ion-molecule reactions describes also the unimolecular decay of 1-C₄H₈⁺ correctly, using the same set of parameters.     

An FTIR study of mechanisms for the HO radical initiated oxidation of C2H4 in the presence of NO: detection of glycolaldehyde

Using the long-path FTIR method, glycolaldehyde, CH₂(OH)CHO, was detected among the products in photolysis of mixtures containing C₂H₄, NO and RONO (R = alkyl group) at ppm concentrations in air. The results suggest the occurrence of both unimolecular dissociation and O₂ reaction of an oxy-radical, CH₂(OH)CH₂O, formed in the HO-initiated oxidation of C₂H₄ in the presence of NO.     

A theoretical study of the reaction of SiH2 with C2H2 and C2D2

Potential energy surfaces of the reaction of SiH₂ and C₂H₂ (and C₂D₂) have been calculated by means of ab initio molecular orbital theory at the QCISD/6-311G++(2df, 2p)//MP2/6-31G(d, p) level with corrections for the triple excitations to the QCISD energies. The barrier heights for the two reaction channels of the adduct, thus calculated, were further utilized for the dynamical calculation of the rate constants in the framework of quantum statistical Rice-Ramsperger-Kassel theory. Contributions of the rate constants of the various pathways to the total rate constant (K_T) for the disappearance of the reactants are critically examined and compared with experiment. The pressure dependence of K_T(C₂H₂) is primarily due to the formation of silirene. K_T(C₂D₂) is consistently higher than K_T(C₂H₂). The standard heat of formation of silirene is predicted to be 72.1 ± 3 kcal/mol. Rearrangement of silirene to vinylsilylene requires an activation energy smaller than that to silylacetylene.     

Darstellung und Molekülstruktur des (μ-Alkylidenamido)titanocenkomplexes [(C5H5)2TiCl]2[μ-{N=C(CH2C6H5)C(CH2C6H5)=N}]

Reduction of (C₅H₅)₂TiCl₂ with Zn in presence of benzyl cyanide gives the (μ-alkyl-ideneamido)titanocene complex [(C₅H₅)₂TiCl]₂[μ-{N=C(CH₂C₆H₅)---C(CH₂C₆H₅)=N}] with C---C bond formation between two benzyl cyanide molecules.

X-ray structure investigation indicates a symmetrical structure. The C=N distances are smaller than usual, the Ti---N distances are very short, and the Ti---N---C angle differs only a little from 180°, which infers a heteroallene structure of the complex.     

多环芳烃与不饱和自由基氢提取反应类的动力学研究

对2~6个环的多环芳烃的氢提取反应类进行了系统研究, 提取氢原子的不饱和自由基包括丙炔基自由基（C₃H₃）、 烯丙基自由基（C₃H₅）、 丁二烯基自由基（nC₄H₅, iC₄H₅）、 环戊二烯基自由基（C₅H₅）以及苯基自由基（C₆H₅）. 采用M06-2X/cc-pVTZ方法得到了多环芳烃的电子结构信息, 利用过渡态理论并结合Eckart隧道校正, 计算了所有反应在500~2500 K范围内的反应速率常数.考察了多环芳烃的大小、 结构对反应速率常数的影响, 对比了不同氢提取自由基及不同氢提取反应类型的速率常数. 结果表明, 多环芳烃的大小对反应速率常数影响不大, 但是多环芳烃的环结构对反应速率常数影响较大. 将不同的氢提取反应类简化为发生在五元环上的C₅类和发生在六元环上的C₆类两类, 结果表明, C₆类的反应活性高于C₅类. 研究了nC₄H₅, iC₄H₅以及C₆H₅自由基与多环芳烃的氢提取反应, 它们的氢提取反应活性大小顺序为C₆H₅>nC₄H₅>iC₄H₅. 通过对每类典型反应的速率常数取平均值, 总结出相应类型的速率规则, 可用于构建多环芳烃和碳烟机理.     

Self-termination rate of para-substituted benzyl radicals in aqueous solutions: a time-resolved study

The self-termination rates of the benzyl radical (C₆H₅---CH₂^√) and para-substituted benzyl radicals (X---C₆H₄---CH₂^√) were studied in aqueous solutions. The Arrhenius parameters and activation energies were determined in the temperature range 275.5–328 K. The kinetic activation energies of these radicals were close to the dynamic activation energy of the solvent, indicating that the termination rate is controlled by diffusion. The values for the rate constants (2k_t (10⁹ dm³ mol⁻¹ s⁻¹)) and the activation energies (E (kJ mol⁻¹)) were 5.94±0.52 and 14.69±0.61 for CH₃O---C₆H₄---CH₂^√, 4.52±0.2 and 17.65±1.16 for CH₃7z.sbnd;C₆H₄---CH₂^√, 3.07±0.45 and 17.58±0.97 for H---C₆H₄---CH₂^√, 4.13±0.81 and 19.10±1.20 for Cl---C₆H₄---CH₂^√ and 4.17±0.44 and 14.62±0.52 for NO₂---C₆H₄---CH₂^√.     

Rate coefficients for the reactions of cyclohexadienyl (c-C6H7) radicals with O2 and NO at room temperature

Rate coefficients for the reactions of cyclohexadienyl (c-C₆H₇) radicals with O₂ and NO were measured at 296 ± 2 K. The c-C₆H₇ radicals were detected selectively by laser-induced fluorescence. The rate coefficient for the reaction of c-C₆H₇ with O₂, (4.4 ± 0.5) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, was independent of the bath-gas (He) pressure (13–80 Torr). In the reaction of c-C₆H₇ with NO, thermal equilibrium among c-C₆H₇, NO, and C₆H₇NO was observed. The forward and reverse reactions were in the falloff region, and the equilibrium constant was (1.5 ± 0.6) × 10⁻¹⁵ cm³ molecule⁻¹.     

Pathways for the thermally induced dehydrogenation of C60H2

The thermolysis of C₆₀H₂ to yield C₆₀ and H₂ was studied by hybrid density functional theory (B3LYP/6-311G**//B3LYP/3-21G). The concerted loss of dihydrogen requires an activation energy of 92 kcalmol⁻¹ atT=452 K. An alternative radical mechanism, which is first order in the C₆₀H₂ concentration, has an activation energy at 452 K of only 61 kcalmol⁻¹. Monitoring of the C₆₀H₂ decomposition in 1,2-dichloro-[D₄]-benzene solution by NMR spectroscopy indicates a pseudo first-order reaction with an activation energy of 61.38±2.35 kcalmol⁻¹.     

Ab initio computation of the potential energy surfaces of the water·hydrocarbon complexes H2O·C2H2, H2O·C2H4 and H2O·CH4: minimum energy structures, vibrational frequencies and hydrogen bond energies

On the basis of ab initio MP2/6–31 + + G(2d,2p) calculations, we examined the potential energy surfaces of the water·hydrocarbon complexes H₂O·CH₄, H₂O·C₂H₂ and H₂O·C₂H₂ to locate all the minimum energy structures and estimate the hydrogen bond energies and vibrational frequencies associated with the C(spⁿ)---H·O and the O---H·C(spⁿ) bonds (n = 1−3). Our calculations show that H₂O·C₂H₂, H₂O·C₂H₄ and H₂O·CH₄ have two minimum energy structures (i.e., the C---H·O and O---H·C hydrogen bond forms), but H₂O·C₂H₄ has only one when the vibrational motion is taken into account, the O---H·C hydrogen bond form. We have also computed the barrier for the interconversion from one minimum to the other. The fully optimized geometries of H₂O·CH₄, H₂O·C₂H₄ and H₂O·C₂H₂ as well as the vibrational shifts of the C---H stretching frequencies in their C---H·O hydrogen-bonded forms are in good agreement with the available experimental data. The calculated hydrogen bond energies show that the C(spⁿ---H·O bond strengths decrease in the order C(sp)---H·O>C(sp²)---H·O>C(sp³)---O>C(sp³---H·O, which is also consistent with the available experimental data.     

Synthesis and characterization of (C5H9C9H6)2Yb(THF)2(II) (1) and [(C5H9C5H4)2Yb(THF)]2O2 (2), and ring-opening polymerization of lactones with 1

Reaction of YbI₂ with two equivalents of cyclopentylindenyl lithium (C₅H₉C₉H₆Li) affords ytterbium(II) substituted indenyl complex (C₅H₉C₉H₆)₂Yb(THF)₂ (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI₂ and cyclopentylcyclopentadienyl sodium (C₅H₉C₅H₄Na) gives complex [(C₅H₉C₅H₄)₂Yb(THF)]₂O₂ (2) in the presence of a trace amount of O₂, the molecular structure of which comprises two (C₅H₉C₅H₄)₂Yb(THF) bridged by an asymmetric O₂ unit. The O₂ unit and ytterbium atoms define a plane that contains a C_i symmetry center.     

SYNTHESIS of(η~5-C_9H_7)Ln(η~8-C_8H_8)·2THF AND CRYSTAL STRUCTURE OF(η~5-C_9H_7)Pr(η~8-C_8H_8)·2THF

The reaction of LnCl_3 with K _9H_7(C_9H_7=indenyl)andK_2C_8H_8(C_8H_8=cyclooctatetraene)in tetrahydrofuran(THF)give thecorresponding complexes(η~5-C_9H_7)Ln(η~8-C_8H_8)·2THF.The synthesis of(η~5-C_9H_7)Ln(η~8-C_8H_8)·2THF(Ln=Pr,Nd)and crystal structure of(η~5-C_9H_7)Pr(η~8-C_8H_8)·2THF are described.     

Synthesis and crystal structures of (C8h8)Nd(C5H9C5H4) (THF)2 and [(C8H8)Gd(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)2]

LnCl₃ (Ln=Nd, Gd) reacts with C₅H₉C₅H₄Na (or K₂C₈H₈) in THF (C₅H₉C₅H₄ = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C₅H₉C₅H₄)LnCl₂(THF)_n (orC₈H₈)LnCl₂(THF)_n], which further reacts with K₂C₈H₈ (or C₅H₉C₅H₄Na) in THF to form the litle complexes. If Ln=Nd the complex (C₈H₈)Nd(C₅H₉C₅H₄)(THF)₂ (a) was obtained: when Ln=Gd the 1 : 1 complex [(C₈H₈)Gd(C_%H₉)(THF)][(C₈H₈)Gd(C₅H₉H₄)(THF)₂] (b) was obtained in crystalline form.

The crystal structure analysis shows that in (C₈H₈)Ln(C₅H₉C₅H₄)(THF)₂ (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η⁵), cyclooctatetraenyl (η⁸) and two oxygen atoms from THF are coordinated to Nd³⁺ (or Gd³⁺) with coordination number 10.

The centroid of the cyclopentadienyl ring (Cp′) in C₅H₉C₅H₄ group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd³⁺ (or Gd³⁺). In (C₈H₈)Gd(C₅H₉C₅H₄)(THF), the cyclopentyl-cyclopentadienyl (η⁵), cyclooctatetraenyl (η⁸) and one oxygen atom are coordinated to Gd³⁺ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd³⁺, which is almost in the plane (dev. -0.0144 Å).     

An ab initio and matrix isolation infrared study of the 1:1 C2H2–CHCl3 adduct

The details of weak C–Hπ interactions that control several inter and intramolecular structures have been studied experimentally and theoretically for the 1:1 C₂H₂–CHCl₃ adduct. The adduct was generated by depositing acetylene and chloroform in an argon matrix and a 1:1 complex of these species was identified using infrared spectroscopy. Formation of the adduct was evidenced by shifts in the vibrational frequencies compared to C₂H₂ and CHCl₃ species. The molecular structure, vibrational frequencies and stabilization energies of the complex were predicted at the MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) levels. Both the computational and experimental data indicate that the C₂H₂–CHCl₃ complex has a weak hydrogen bond involving a C–Hπ interaction, where the C₂H₂ acts as a proton acceptor and the CHCl₃ as the proton donor. In addition, there also appears to be a secondary interaction between one of the chlorine atoms of CHCl₃ and a hydrogen in C₂H₂. The combination of the C–Hπ interaction and the secondary ClH interaction determines the structure and the energetics of the C₂H₂–CHCl₃ complex. In addition to the vibrational assignments for the C₂H₂–CHCl₃ complex we have also observed and assigned features owing to the proton accepting C₂H₂ submolecule in the acetylene dimer.     

Homochiral cyclopentane-based C1-symmetric P,P ligands C5H8(PPh2)(PR2) from C2-symmetric C5H8(PCl2)2

Treatment of 1,2-trans-C₅H₈(PCl₂)₂ with 1,2-C₂H₄(NHPr-i)₂ gave the C₂-symmetric perhydro-1,6,2,5-diazaphosphocine C₅H₈{P(Cl)N(Pr-i)CH₂}₂-cyclo, which produced dissymmetric C₅H₈(PPh₂){P[N(Pr-i)CH₂]₂-cyclo} on further reaction with PhMgBr. Cleavage of the P---N bonds with gaseous HCl afforded C₅H₈(PPh₂)(PCl₂), which was converted to C₅H₈(PPh₂){P(OPh)₂}₂ by reaction with phenol. All chiral P,P derivatives were obtained as racemates as well as resolved (1R,2R)- and (1S,2S)-enantiomers.     

Theoretical Study on the Kinetics for the Reactions of Heptyl Radicals with Methanol

Ab initio study of the reactions of n-heptyl radicals(1-C₇H₁₅, 2-C₇H₁₅, 3-C₇H₁₅, and 4-C₇H₁₅) with methanol was conducted over the temperature range of 300-1500 K. Transition states for the reaction channels producing C₇H₁₅OH, CH₃, C₇H₁₅OCH₃, H, C₇H₁₆, CH₂OH and CH₃O were identified and the geometries of all stationary points were calculated at BB1K/MG3S level of theory. The potential barrier heights of the corresponding transition states were predicted by the CBS-QB3//BB1K and G4//BB1K methods, indicating that the eight H-abstraction channels are more kinetically favorable than the channels where OH transfers from CH₃OH to C₇H₁₅ and where the C₇H₁₅OCH₃+H products are given. The rate constants of H-abstraction channels were calculated with TST and TST/Eck. Both the forward and reverse rate constants have positive temperature dependence and the tunneling effect is only important at the temperature lower than 700 K. For the reactions of H-atom abstraction from methyl in CH₃OH by n-heptyl, a reverse and the corresponding forward rate constant are roughly equal. For the reactions of H-atom abstraction from OH in CH₃OH by n-heptyl, a reverse rate constant is larger by several orders of magnitude than the corresponding forward one.     

Dissociation reactions of the vinyl radical in the AA″ state

In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A²A″ state (C₂H₃ (A²A″)) and examined possible pathways for nonadiabatic dissociation of C₂H₃ (A²A″) into C₂H₂ (X¹Σ_g⁺). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C₂H₃ in the A²A″ state were explored: (1) C₂H₃ (A²A″) → C₂H₂ (trans, ³A_u) + H, (2) C₂H₃ (A²A″) → C₂H₂ (cis, ³A₂) + H, and (3) C₂H₃ (A²A″) → H₂CC (³A₂) + H. The CASSCF and CASPT2 potential energy curve calculations for the C₂H₃ (A²A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C₂H₃ (A²A″) into C₂H₂ (X¹Σ_g⁺) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C₂H₃ (A²A^′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C_2v bridge structures in the ²B₂, ²A₂, ²B₁, and ²A₁ states along the pathways of the 1²A^′ (X²A^′), 1²A″ (A²A″), 2²A″, and 2²A^′ states of C₂H₃, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C_2v (²A₂) structure and then ²A₂/²A₁ surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C_2v (²A₂) structure could not be accessed.     

A theoretical study on decomposition of carbon tetrachloride, trichloroethylene and ethyl chloride in dry air under the influence of an electron beam

New experimental data were published in literature regarding CCl₄, C₂HCl₃ and C₂H₅Cl decomposition in dry air under electron beam influence. Taking into account experimental data theoretical models of those species decomposition were established and computer simulations were performed by the authors of this work to find the kinetics of such processes. The results of the calculations and experimental data show that CCl₄ decomposition depends on delivered dose and initial CCl₄ concentrations. The calculation revealed that recombination of CCl⁺₄ and Cl⁻ is the source of CCl₃ radicals and that reaction may have an important role in the process of CCl₄ decomposition. A theoretical model of C₂HCl₃ decomposition in dry air under electron beam influence describes the decay of C₂HCl₃ and the formation of several products such as Cl₂, CCl₂O, CO, CO₂, HCl and C₂HCl₃O. The detailed comparison of experimental and theoretical data shows relatively good agreement in efficiency of C₂HCl₃ decomposition process, but it can be achieved only with an assumption that the relation between rate constants of C₂HCl₄O intermediate product decomposition (C₂HCl₃O+Cl and COCl₂+CHCl₂) should be around 20 and C₂HCl₃O oxidation rate should be not lower than 7.5×10⁻¹¹ cm³/mols. All those rate constants are not yet established experimentally. The results of the calculation of C₂H₅Cl decomposition and the data obtained experimentally were compared. The temperature, gas pressure, initial C₂H₅Cl concentration and dose range were equal in both cases. An elaborated model allow us to obtain quantitatively similar results as the experiments, but the degree of C₂H₅Cl decomposition for certain dose levels is significantly higher in experimental data. It is quite probable that some important processes have not been included to the theoretical model.     

Crystal structure of the 1/ 1 molecular complex of 5,5′,12,12′-bis(triseleno)bis(naphthacene-6,11-quinone) with benzonitrile, (C18H8Se3O2)2(C6H5CN)

The structure of the (C₁₈H₈Se₃O₂)₂(C₆H₅CN) molecular complex isolated from the TSeT + HgI₂ reaction in benzonitrile has been determined. The -Se-Se-Se- fragment has been found to have Se---Se bond lengths equal to 2.348(3) and 2.350(4) Å.     

Stability of the silicon-ruthenium bond in the presence of a strong nucleophile. Phase sensitive H NMR COSY and crystal structure of Ru(CO)2(NH2CH2C6H5)2(Si(C6H5)(CH3)2)I

The ruthenium(II) complex Ru(CO)₂(NH₂(NH₂CH₂C₆H₅)₂(Si(C₆H₅)(CH₃)₂)I has been prepared by the reaction of Ru(CO)₄(Si(C₆H₅)(CH₃)₂)I with benzylamine. Two-dimensional homonuclear ¹H NMR experiments examine the scalar coupling of the enantiotopic amino and methylene protons of the benzylamine ligand. X-ray analysis of Ru(CO)₂(NH₂CH₂C₆H₅)₂(Si(C₆H₅)(CH₃)₂)I·1/3C₅H₁₂ (triclinic; P ; a = 14.266(4), b = 15.748(5), c = 20.082(6) Å; = 94.38(3), β = 96.30(2), γ = 101.52(2)°) indicates three crystallographically unique complexes form a clathrate with a pentane guest.     

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.