The adenine ring influences the adenosine 5′-triphosphate hydrolysis

DFT calculations (ωB97X-D) of the adenosine 5′-triphosphate (ATP) hydrolysis were carried out. Four reactions (A), (B), (C), and (D) were investigated. Reaction (A) is of the acid catalysis and (B) is of the Mg²⁺ one with (H₂O) _n, n = 5, 11, and 17. (C) is of the myosin-model catalysis, and (D) is of the F₁-ATPase one. Transition states were determined precisely. For reaction (A), the experimental activation energy was reproduced well by the n = 11 and 17 models. For the Mg²⁺-containing hydrolysis, (B), 2 reactions (a) [without the Mg²⁺-adenine linkage] and (b) [with the connection] were examined and were compared. The reaction (b) was found to be more likely than (a) in both total and activation energies. The adenine ring works to enhance the polarity of transition states. For the myosin catalyzed (C) and in F₁-ATPase (D) hydrolyses, again, the reaction (b) is much more likely than (a). The proton transfer from the lytic water molecule leads to the protonation of the carboxylate of Glu459 in (C). The adenine ring was suggested to influence and promote the ATP hydrolysis.     

Hydrogen for fluorine exchange in C6F6 and C6F5H by monomeric [1,3,4-(Me3C)3C5H2]2CeH: experimental and computational studies

The net reaction of monomeric Cp'(2)CeH [Cp' = 1,3,4-(Me(3)C)(3)(C(5)H(2))] in C(6)D(6) with C(6)F(6) is Cp'(2)CeF, H(2), and tetrafluorobenzyne. The pentafluorophenylmetallocene, Cp'(2)Ce(C(6)F(5)), is formed as an intermediate that decomposes slowly to Cp'(2)CeF and C(6)F(4) (tetrafluorobenzyne), and the latter is trapped by the solvent C(6)D(6) as a [2+4] cycloadduct. In C(6)F(5)H, the final products are also Cp'(2)CeF and H(2), which are formed from the intermediates Cp'(2)Ce(C(6)F(5)) and Cp'(2)Ce(2,3,5,6-C(6)F(4)H) and from an unidentified metallocene of cerium and the [2+4] cycloadducts of tetra- and trifluorobenzyne with C(6)D(6). The hydride, fluoride, and pentafluorophenylmetallocenes are isolated and characterized by X-ray crystallography. DFT(B3PW91) calculations have been used to explore the pathways leading to the observed products of the exergonic reactions. A key step is a H/F exchange reaction which transforms C(6)F(6) and the cerium hydride into C(6)F(5)H and Cp'(2)CeF. This reaction starts by an eta(1)-F-C(6)F(5) interaction, which serves as a hook. The reaction proceeds via a sigma bond metathesis where the fluorine ortho to the hook migrates toward H with a relatively low activation energy. All products observed experimentally are accommodated by pathways that involve C-F and C-H bond cleavages.     

氟代苯阳离子的理论研究

用B3LYP方法及6-311G(d,p)和6-311 G(d,p)基组,对十二种氟代苯阳离子做了理论研究,优化了它们的电子基态的结构,计算了对应分子的垂直电离势(VIP)和绝热电离势(AIP)．依据Jahn．Teller理论,计算确定了1,3,5-C6H3F^ 3和C6F^ 6离子分别具有C2v(2↑B)和D2h(2↑B2g)结构(对应分子分别为D3h和D6h结构)．其余十个离子的构型的对称点群与对应分子相同,但构型参数值有明显差别．自然布居分析计算表明这些离子的正电荷主要分布在与F原子相连的C原子和各H原子上．B3LYP／6-311 G(d,p)级别上计算的各氟代苯分子的VIP和AIP值和实验值符合得很好．     

Optimizing the structures of minimum and transition state on the free energy surface

Presented here is the application of a scheme for optimizing the structures of minima and transition states on the free energy surface (FES) for a path along a fixed reaction coordinate with the aid of ab initio molecular dynamics (AIMD) simulation. In the direction of the reaction coordinate, the values corresponding to the stationary points were optimized using the quasi-Newton method, in which the gradient of the free energy along the reaction coordinate was obtained by a constraint AIMD method, and the Bofill Hessian update scheme was used. The equilibrium values for the other directions were taken as the corresponding averages in the dynamic simulation. This scheme was applied to several elementary bimolecular addition reactions: (A) BH(3) + H(2)O --> H(2)O.BH(3); (B) BF(3) + NH(3) --> FB(3).NH(3); (C) SO(3) + NH(3) --> O(3)S.NH(3); (D) C(2)H(4) + CCl(2) --> H(4)C(2).CCl(2); (E) Ni(NH(2))(2) + PH(3) --> (NH(2))(2)Ni.PH(3); (F) W(CO)(5) + CO --> W(CO)(6). For reactions A, B, C, and F, no transition state (TS) exists on the potential energy surface (PES). However there is a TS on the FES. This stems from the curvature difference of the PES and -TDeltaS as a function of the reaction coordinate. For all reactions, it is found that the TS shifts toward the complexation product with increasing temperature because of the curvature increase of -TDeltaS. The equilibrium bond distances for the inactive coordinates perpendicular to the reaction coordinate always increase with temperature, which is due to the thermal excitation and anharmonicity of the PES.     

Full-dimensional quantum dynamics study of exchange processes for the D + H2O and D + HOD reactions

The exchange processes of D + H(2)O and D + HOD reactions are studied using initial state-selected time-dependent wave packet approach in full dimension. The total reaction probabilities for different partial waves, together with the integral cross sections, are obtained both by the centrifugal sudden (CS) approximation and exact coupled-channel (CC) calculations, for the H(2)O(HOD) reactant initially in the ground rovibrational state. In the CC calculations, small resonance peaks in the reaction probabilities and quick diminishing of the resonance peaks with the increase of total angular momenta J do not lead to clear step-like features just above the threshold in the cross sections for the title reactions, which are different in other isotopically substituted reactions where the hydrogen atom was included as the reactant instead of the deuterium atom [B. Fu, Y. Zhou, and D. H. Zhang, Chem. Sci. 3, 270 (2012); B. Fu and D. H. Zhang, J. Phys. Chem. A 116, 820 (2012)]. It is interesting that the shape resonance-induced features resulting from the reaction tunneling are significantly diminished accordingly in the reactions of the deuterium atom and H(2)O or HOD, owing to the weaker tunneling capability of the reagent deuterium atom in the title reactions than the reagent hydrogen atom in other reactions. In the CS calculations, the resonance peaks persist in many partial waves but cannot survive the partial-wave summations. The cross sections for the D(') + H(2)O → D(')OH + H and D(') + HOD → D(')OD + H reactions are substantially larger than those for the D(') + HOD → HOD(') + D reaction, indicating that the D(')/H exchange reactions are much more favored than the D(')/D exchange.     

Microwave Fourier transform spectrum of the water-carbonyl sulfide complex

The microwave spectrum of the water-carbonyl sulfide complex H(2)O-OCS was observed with a pulsed-beam, Fabry-Perot cavity Fourier-transform microwave spectrometer. In addition to the normal isotopic form, we also measured the spectra of H(2)O-S(13)CO, H(2)O-(34)SCO, H(2) (18)O-SCO, D(2)O-SCO, D(2)O-S(13)CO, D(2)O-(34)SCO, HDO-SCO, HDO-S(13)CO, and HDO-(34)SCO. The rotational constants are B = 1522.0115(2) MHz and C = 1514.3302(2) MHz for H(2)O-SCO; B = 1511.9153(5) MHz and C = 1504.3346(5) MHz for H(2)O-S(13)CO; B = 1522.0215(3) MHz and C = 1514.3409(3) MHz for H(2)O-(34)SCO; B = 1435.9571(3) MHz and C = 1429.1296(4) MHz for H(2) (18)O-SCO, B = 1409.6575(5) MHz and C = 1397.9555(5) MHz for D(2)O-SCO; B = 1399.8956(3) MHz and C = 1388.3543(3) MHz for D(2)O-S(13)CO; B = 1409.6741(24) MHz and C = 1397.9775(24) MHz for D(2)O-(34)SCO; (B+C)/2 = 1457.9101(2) MHz for HDO-SCO; (B + C)/2 = 1448.0564(4) MHz for HDO-S(13)CO; and (B+C)/2 = 1457.9418(15) MHz for HDO-(34)SCO, with uncertainties corresponding to one standard deviation. The observed rotational constants for the sulfur-34 complexes are generally higher than those for the corresponding sulfur-32 isotopomers. The heavier isotopomers have smaller effective moments of inertia due to the smaller vibrational amplitude of the (34)S-C vibration (zero point) as compared to the (32)S-C, making the effective O-(34)S bond slightly shorter. Stark effect measurements for H(2)O-SCO give a dipole moment of 8.875(9)x10(-30) C m [2.6679(28) D]. The most probable structure of H(2)O-SCO is near C(2v) planar with the oxygen of water bonded to the sulfur of carbonyl sulfide. The oxygen-sulfur van der Waals bond length is determined to be 3.138(17) A, which is very close to the ab initio value of 3.144 A. The structures of the isoelectronic complexes H(2)O-SCO, H(2)O-CS(2), H(2)O-CO(2), and H(2)O-N(2)O are compared. The first two are linear and the others are T shaped with an O-C/O-N van der Waals bond, i.e., the oxygen of water bonds to the carbon and nitrogen of CO(2) and N(2)O, respectively.     

Differential-thermoanalytische Untersuchung von einigen Phosphororganischen Verbindungen

The thermal transitions of phosphines, phosphonium salts and esters of phosphorus acids, as well as some reactions of different phosphorus compounds, were studied by DTA.

1. DTA data have been considered for various types of reactions: 1. A→B; 2. A→B+C
2. DTA of reactive mixtures: 1. A+B→C; 2. A+B→C+D

Examples of the use of DTA were shown for studying the processes of isomerization, decomposition, and different regroup reactions of addition, combination, exchange and disintegration. The simple method of DTA allows one to find the optimum conditions of the reactions and to establish their reaction paths.     

A simple method relating specific rate constants k(E,J) and Thermally averaged rate constants k(infinity)(T) of unimolecular bond fission and the reverse barrierless association reactions

This work describes a simple method linking specific rate constants k(E,J) of bond fission reactions AB --> A + B with thermally averaged capture rate constants k(cap)(T) of the reverse barrierless combination reactions A + B --> AB (or the corresponding high-pressure dissociation or recombination rate constants k(infinity)(T)). Practical applications are given for ionic and neutral reaction systems. The method, in the first stage, requires a phase-space theoretical treatment with the most realistic minimum energy path potential available, either from reduced dimensionality ab initio or from model calculations of the potential, providing the centrifugal barriers E(0)(J). The effects of the anisotropy of the potential afterward are expressed in terms of specific and thermal rigidity factors f(rigid)(E,J) and f(rigid)(T), respectively. Simple relationships provide a link between f(rigid)(E,J) and f(rigid)(T) where J is an average value of J related to J(max)(E), i.e., the maximum J value compatible with E > or = E0(J), and f(rigid)(E,J) applies to the transitional modes. Methods for constructing f(rigid)(E,J) from f(rigid)(E,J) are also described. The derived relationships are adaptable and can be used on that level of information which is available either from more detailed theoretical calculations or from limited experimental information on specific or thermally averaged rate constants. The examples used for illustration are the systems C6H6+ <==> C6H5+ + H, C8H10+ --> C7H7+ + CH3, n-C9H12+ <==> C7H7+ + C2H5, n-C10H14+ <==> C7H7+ + C3H7, HO2 <==> H + O2, HO2 <==> HO + O, and H2O2 <==> 2HO.     

C_2H_3与C_2H_5OH和CH_3HCO间的脱氢反应对乙醇-碳氢混合燃料燃烧过程的影响

在QCISD(T)/6-311++G(d,p)//B3LYP/6-311G(d,p)的水平下计算了乙醇及乙醇燃烧裂解产物与C2H3之间的脱氢反应机理,利用正则变分过渡态理论(CVT)结合小曲率隧道效应模型(SCT)计算400~2000 K范围内的速率,对比OH,H及CH3等自由基相似脱氢反应速率,选择2条具有较快反应速率的通道(C2H3+C2H5OH→TS1→C2H4+C2H5O和C2H3+CH3HCO→TS4→C2H4+CH3CO).将这2个反应耦合到正庚烷/乙醇混合燃料及异辛烷/乙醇混合燃料的机理中,利用CHEMKIN程序中预混火焰模型模拟混合燃料的燃烧过程并进行路径分析.对比相应的实验数据发现,改进的动力学模型对燃烧过程中C2H3路径上相近组分的预测精度有较大改善,而对C2H3路径上较远的组分丙炔(C3H4)和乙烯基乙炔(C4H4)等影响不大.     

A comprehensive theoretical study on the reactions of Sc+ with CnH2n+2 (n=1-3): structure,mechanism, and potential-energy surface

The reactions of Sc(+)((3)D) with methane, ethane, and propane in the gas phase were studied theoretically by density functional theory. The potential energy surfaces corresponding to [Sc, C(n), H(2n+2)](+) (n=1-3) were examined in detail at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(d,p) level of theory. The performance of this theoretical method was calibrated with respect to the available thermochemical data. Calculations indicated that the reactions of Sc(+) with alkanes are multichannel processes which involve two general mechanisms: an addition-elimination mechanism, which is in good agreement with the general mechanism proposed from earlier experiments, and a concerted mechanism, which is presented for the first time in this work. The addition-elimination reactions are favorable at low energy, and the concerted reactions could be alternative pathways at high energy. In most cases, the energetic bottleneck in the addition-elimination mechanism is the initial C--C or C--H activation. The loss of CH(4) and/or C(2)H(6) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed along both the initial C--C activation branch and the Cbond;H activation branch. The loss of H(2) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed not only by 1,2-H(2) and/or 1,3-H(2) elimination, but also by 1,1-H(2) elimination. The reactivity of Sc(+) with alkanes is compared with those reported earlier for the reactions of the late first-row transition-metal ions with alkanes.     

Bimetallic effects in homopolymerization of styrene and copolymerization of ethylene and styrenic comonomers: scope, kinetics, and mechanism

This contribution describes the homopolymerization of styrene and the copolymerization of ethylene and styrenic comonomers mediated by the single-site bimetallic "constrained geometry catalysts" (CGCs), (mu-CH2CH2-3,3'){(eta(5)-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 [EBICGC(TiMe2)2; Ti2], (mu-CH2CH2-3,3'){(eta(5)-indenyl)[1-Me2Si(tBuN)](ZrMe2)}2 [EBICGC(ZrMe2)2; Zr2], (mu-CH2-3,3'){(eta(5)-indenyl)[1-Me2Si(tBuN)](TiMe2)}2 [MBICGC(TiMe2)2; C1-Ti2], and (mu-CH2-3,3'){(eta(5)-indenyl)[1-Me2Si(tBuN)](ZrMe2)}2 [MBICGC(ZrMe2)2; C1-Zr2], in combination with the borate activator/cocatalyst Ph3C+ B(C6F5)4- (B1). Under identical styrene homopolymerization conditions, C1-Ti2 + B1 and Ti2 + B1 exhibit approximately 65 and approximately 35 times greater polymerization activities, respectively, than does monometallic [1-Me2Si(3-ethylindenyl)(tBuN)]TiMe2 (Ti1) + B1. C1-Zr2 + B1 and Zr2 + B1 exhibit approximately 8 and approximately 4 times greater polymerization activities, respectively, than does the monometallic control [1-Me2Si(3-ethylindenyl)(tBuN)]ZrMe2 (Zr1) + B1. NMR analyses show that the bimetallic catalysts suppress the regiochemical insertion selectivity exhibited by the monometallic analogues. In ethylene copolymerization, Ti2 + B1 enchains 15.4% more styrene (B), 28.9% more 4-methylstyrene (C), 45.4% more 4-fluorostyrene (D), 41.2% more 4-chlorostyrene (E), and 31.0% more 4-bromostyrene (F) than does Ti1 + B1. This observed bimetallic chemoselectivity effect follows the same general trend as the pi-electron density on the styrenic ipso carbon (D > E > F > C > B). Kinetic studies reveal that both Ti2 + B1 and Ti1 + B1-mediated ethylene-styrene copolymerizations follow second-order Markovian statistics and tend to be alternating. Moreover, calculated reactivity ratios indicate that Ti2 + B1 favors styrene insertion more than does Ti1 + B1. All the organozirconium complexes (C1-Zr2, Zr2, and Zr1) are found to be incompetent for ethylene-styrene copolymerization, yielding only mixtures of polyethylene and polystyrene. Model compound (mu-CH2CH2-3,3'){(eta(5)-indenyl)[1-Me2Si(tBuN)][Ti(CH2Ph)2]}2 {EBICGC[Ti(CH2Ph)2]2; Ti2(CH2Ph)4} was designed, synthesized, and structurally characterized. In situ activation studies with cocatalyst B(C6F5)3 suggest an eta(1)-coordination mode for the benzyl groups, thus supporting the proposed polymerization mechanism. For ethylene-styrene copolymerization, polar solvents are found to increase copolymerization activities and coproduce atactic polystyrene impurities in addition to ethylene-co-styrene, without diminishing the comonomer incorporation selectivity. Both homopolymerization and copolymerization results argue that substantial cooperative effects between catalytic sites are operative.     

Facile activation of H-H and Si-H bonds by boranes

The borane B(C(6)F(5))(3) is a precatalyst for H/Dexchange between H(2) and deuterium-labeled silanes (D(3)SiPh, D(2)SiMePh, DSiMe(2)Ph, DSiEt(3)). Experimental and DFT studies reveal that B(C(6)F(5))(3) itself cannot activate dihydrogen but converts to HB(C(6)F(5))(2) under the action of hydrosilane. The latter species easily activates H-H and Si-H bonds by a σ-bond metathesis mechanism, which was further confirmed by the reactions of BD(3)·THF with H(2).     

Neutral and cationic aluminium complexes of a sterically demanding N-imidoylamidine ligand

The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2 was prepared. Direct reactions with AlI3 or AlMe3 afforded [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3 and [i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4].AlMe3, 4 respectively. Thermolysis of 4 gave (i-Pr2C6H3NC(=CH2)(NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe2 6. Subsequent reaction with B(C6F5)3 gave the zwitterionic species [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe(mu-MeB(C6F5)3)] 7. In a related reactions of 2, [Ph3C][B(C6F5)4] and AlMe3, AlH3.NEtMe2 or AlD3.NMe3, the complexes [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4] (R = Me 5, H 8, D 9) and [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlH][B(C6F5)4] 10 are formed. Single-crystal X-ray data for 2, 3, 5 and 10 are reported.     

Optical absorption and EPR studies on some natural carbonate minerals

Limestone and dolomite minerals have been investigated by EPR and optical absorption studies. The optical absorption results indicate the presence of ferrous and ferric ion in both the minerals. The bands observed at 24,750, 22,780, 19,415 and 14,450cm(-1) are assigned to 6A1-->4T2 (4D), 6A1-->4E, 4A1 (4G), 6A1-->4T2 (4G) and 6A1-->4T1 (4G) d-d transitions of Fe3+ ions, respectively. A low energy band at 10,638cm(-1) is identified as being due to Fe2+ ion and can be attributed to 5T2g-->5E(g) transition. The weak band in the region 30,000-40,000cm(-1) corresponds to Fe-O charge transfer. Crystal field and Racah parameters evaluated for the Fe2+ ion are Dq=990cm(-1), B=885cm(-1) and C=3860cm(-1) and that for Fe3+ ions are Dq=1040cm(-1), B=703cm(-1) and C=3150cm(-1). The room temperature 9 and 35GHz EPR spectra of the minerals exhibit a sextet hyperfine pattern characteristic of Mn2+. The EPR parameters obtained for Mn2+ in limestone are g=2.00399, A= -9.411mT, D= -8.19mT and these values confirm that the Mn2+ ion are located in the calcite impurity. For Mn2+ in dolomite are g=2.0004, A= -9.45mT for Mn2+ substituted in the Ca lattice site and g=2.00984, A= -9.37mT, D= -9.94mT for substitution at the Mg site. The EPR spectra of heat-treated limestone and dolomite samples at 950 degrees C show a signal corresponding to CO2(-) ion.     

Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: intramolecular orbital alignment of the phenylthiyl radical

The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C(6)H(5)SH) or thiophenol-d(1) (C(6)H(5)SD) pumped at 243 nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C(6)H(5)S). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B(1)) and the first excited state (B(2)) species, respectively. The experimental energy separation between these two states is 2600+/-200 cm(-1) in excellent agreement with the authors' theoretical prediction of 2674 cm(-1) at the CASPT2 level. The experimental anisotropy parameter (beta) of -1.0+/-0.05 at the large translational energy of D from the C(6)H(5)SD dissociation indicates that the transition dipole moment associated with this optical transition at 243 nm is perpendicular to the dissociating S-D bond, which in turn suggests an ultrafast D+C(6)H(5)S(B(1)) dissociation channel on a repulsive potential energy surface. The reduced anisotropy parameter of -0.76+/-0.04 observed at the smaller translational energy of D suggests that the D+C(6)H(5)S(B(2)) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C(6)H(5)S(B(1)) channel may be directly accessed via a (1)(n(pi),sigma(*)) photoexcitation at 243 nm while the key feature of the photodissociation dynamics of the C(6)H(5)S(B(2)) channel is the involvement of the (3)(n(pi),pi(*))-->(3)(n(sigma),sigma(*)) profile as well as the spin-orbit induced avoided crossing between the ground and the (3)(n(pi),sigma(*)) state. The S-D bond dissociation energy of thiophenol-d(1) is accurately estimated to be D(0)=79.6+/-0.3 kcalmol. The S-H bond dissociation energy is also estimated to give D(0)=76.8+/-0.3 kcalmol, which is smaller than previously reported ones by at least 2 kcalmol. The C-H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the pi-pi(*)n(pi)-pi(*) transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.     

Formation and decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction

The formation and the decomposition of chemically activated cyclopentoxy radicals from the c-C5H9 + O reaction have been studied in the gas phase at room temperature. Two different experimental arrangements have been used. Arrangement A consisted of a laser-flash photolysis set up combined with quantitative Fourier transform infrared spectroscopy and allowed the determination of the stable products at 4 mbar. The c-C5H9 radicals were produced via the reaction c-C5H10 + Cl with chlorine atoms from the photolysis of CFCl3; the O atoms were generated by photolysis of SO2. Arrangement B, a conventional discharge flow-reactor with molecular beam sampling, was used to determine the rate coefficient. Here, the hydrocarbon radicals (c-C5H9, C2H5, CH2OCH3) were produced via the reaction of atomic fluorine with c-C5H10, C2H6, and CH3OCH3, respectively, and detected by mass spectrometry after laser photoionization. For the c-C5H9 + O reaction, the relative contributions of intermediate formation (c-C5H9O) and direct abstraction (c-C5H8 + OH) were found to be 68 +/- 5 and 32 +/- 4%, respectively. The decomposition products of the chemically activated intermediate could be identified, and the following relative branching fractions were obtained: c-C5H8O + H (31 +/- 2%), CH2CH(CH2)2CHO + H (40 +/- 5%), 2 C2H4 + H + CO (17 +/- 5%), and C3H4O + C2H4 + H (12 +/- 5%). Additionally, the product formation of the c-C5H8 + O reaction was studied, and the following relative yields were obtained (mol %): C2H4, 24%; C3H4O, 18%; c-C5H8O, 30%; c-C5H8O, 23%; 4-pentenal, 5%. The rate coefficient of the c-C5H9 + O reaction was determined relative to the reactions C2H5 + O and CH3OCH2 + O leading to k = (1.73 +/- 0.05) x 10(14) cm3 mol(-1) s(-1). The experimental branching fractions are analyzed in terms of statistical rate theory with molecular and transition-state data from quantum chemical calculations, and high-pressure limiting Arrhenius parameters for the unimolecular decomposition reactions of C5H9O species are derived.     

X, A, B, C, and D states of the C6H5F+ ion studied using multiconfiguration wave functions

Electronic states of the C6H5F+ ion have been studied within C2v symmetry by using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with an atomic natural orbital basis. Vertical excitation energies (Tv) and relative energies (Tv') at the ground-state geometry of the C6H5F molecule were calculated for 12 states. For the five lowest-lying states, 1(2)B1, 1(2)A2, 2(2)B1, 1(2)B2, and 1(2)A1, geometries and vibrational frequencies were calculated at the CASSCF level, and adiabatic excitation energies (T0) and potential energy curves (PEC) for F-loss dissociations were calculated at the CASPT2//CASSCF level. On the basis of the CASPT2 T0 calculations, we assign the X, A, B, C, and D states of the ion to 1(2)B1, 1(2)A2, 2(2)B1, 1(2)B2, and 1(2)A1, respectively, which supports the suggested assignment of the B state to (2)(2)B1 by Anand et al. based on their experiments. Our CASPT2 Tv and Tv' calculations and our MRCI T0, Tv, and Tv' calculations all indicate that the 2(2)B1 state of C6H5F+ lies below 1(2)B2. By checking the relative energies of the asymptote products and checking the fragmental geometries and the charge and spin density populations in the asymptote products along the CASPT2//CASSCF PECs, we conclude that the 1(2)B1, 1(2)B2, and 1(2)A1 states of C6H5F+ correlate with C6H5+ (1(1)A1) + F (2P) (the first dissociation limit). The energy increases monotonically along the 1(2)B1 PEC, and there are barriers and minima along the 1(2)B2 and 1(2)A1 PECs. The predicted appearance potential value for C6H5+ (1(1)A1) is very close to the average of the experimental values. Our CASPT2//CASSCF PEC calculations have led to the conclusion that the 1(2)A2 state of C6H5F+ correlates with the third dissociation limit of C6H5+ (1(1)A2) + F (2P), and a preliminary discussion is presented.     

Theoretical study on the mechanism and kinetics for the self-reaction of C2H5O2 radicals

Oxygen-to-oxygen coupling, direct H-abstraction and oxygen-to-(α)carbon nucleophilic substitution processes have been investigated for both the singlet and triplet self-reaction of C(2)H(5)O(2) radicals at the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) level to evaluate the reaction mechanisms, possible products and rate constants. The calculated results show that the title reaction mainly occurs through the singlet oxygen-to-oxygen coupling mechanism with the formation of entrance tetroxide intermediates, and the most dominant product is C(2)H(5)O + HO(2) + CH(3)CHO (P5) generated in channel R5. Beginning from the radical products of P5 (C(2)H(5)O, HO(2)) and reactant (C(2)H(5)O(2)), five secondary reactions HO(2) + HO(2) (a), HO(2) + C(2)H(5)O (b), C(2)H(5)O + C(2)H(5)O (c), HO(2) + C(2)H(5)O(2) (d), and C(2)H(5)O + C(2)H(5)O(2) (e) mainly proceed on the triplet potential energy surface. Among these reactions, (a), (b), and (d) are kinetically favorable because of lower barrier heights. The calculated rate constants of channel R5 between 200 and 295 K are almost independent of the temperature, which is in agreement with the experimental report. With regard to the final products distribution, CH(3)CHO, C(2)H(5)OH, C(2)H(5)OOH, H(2)O(2), and (3)O(2) are predicted to be major, whereas C(2)H(5)OOC(2)H(5) should be in minor amount.     

Frustrated beta-chloride elimination. Selective arene alkylation by alpha-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.     

分子束技术研究Ba与CHCl~3, CCl~4的反应

本文分别在交叉分子束和分子束-气体条件下, 利用化学发光方法, 研究了Ba(^3D)+CH~2Cl~2, CHCl~3,CCl~4和Ca(^1S~O),Ca(^3P),Ba(^1S～O)Ba(^3D)+CCl~4的反应, 实验得出了Ba(^3D)与CH~2Cl~2, CHCL~3, CCl~4反应时, A^2II,B~2Σ^+态BACl产物的发光截面对反应物碰撞能的依赖关系和反应阈能, 以及Ba(^3D)与CCl~4反应时, 产生电子激发态BaCl产物的光子产率。发现当Ba,Ca被激发到亚稳态时, Ba+CCl~4的反应电子基态BaCl产物的振动激发增加; 而Ca+CCl~4的反应电子基态CaCl产物的转动激发增加. 并针对以上结果进行分析讨论。