The distonic ion ·CH2CH2CH+OH,keto ion CH3CH2CH=O +·, enol ion CH3CH=CHOH+·, and related C3H6O+· radical cations. Stabilities and isomerization proclivities studied by dissociation and neutralization-reionization

Metastable ion decompositions, collision-activated dissociation (CAD), and neutralization-reionization mass spectrometry are utilized to study the unimolecular chemistry of distonic ion ^·CH₂CH₂CH^?OH (2^+·) and its enol-keto tautomers CH₃CH=CHOH^?· (1 ^+·) and CH₃CH₂CH=O ^+· (3^+·). The major fragmentation of metastable 1^+·–3^+· is H^· loss to yield the propanoyl cation, CH₃CH₂C≡O⁺. This reaction remains dominant upon collisional activation, although now some isomeric CH₂=CH-CH⁺ OH is coproduced from all three precursors. The CAD and neutralization-reionization (⁺NR⁺) spectra of keto ion 3 ^+· are substantially different from those of tautomers 2^+· and 1^+·. Hence, 3^+· without sufficient energy for decomposition (i. e. , “stable” 3^+·) does not isomerize to the ther-modynamically more stable ions 2^+· or 1^+·, and the 1,4-H rearrangement H-CH₂CH₂CH=O^+·(3 ^+·) → CH₂CH₂CH⁺ O-H (2 ^+·) must require an appreciable critical energy. Although the fragment ion abundances in the ⁺ NR ⁺ (and CAD) spectra of 1 ^+· and 2 ^+· are similar, the relative and absolute intensities of the survivor ions (recovered C₃H₆O^+· ions in the ⁺NR⁺ spectra) are markedly distinct and independent of the internal energy of 1 ^+· and 2 ^+·. Furthermore, 1 ^+· and 2 ^+· show different MI spectra. Based on these data, distonic ion 2 ^+· does not spontaneously rearrange to enol ion 1 ^+· (which is the most stable C₃H₆O^+· of CCCO connectivity) and, therefore, is separated from it by an appreciable barrier. In contrast, the molecular ions of cyclopropanol (4 ^+·) and allyl alcohol (5 ^+·) isomerize readily to 2 ^+·, via ring opening and 1,2-H^? shift, respectively. The sample found to generate the purest 2 ^+· is α-hydroxy-γ-butyrolactone. Several other precursors that would yield 2 ^+· by a least-motion reaction cogenerate detectable quantities of enol ion 1 ^+·, or the enol ion of acetone (CH₂=C(CH₃)OH^+·, 6 ^+·), or methyl vinyl ether ion (CH₃OCH=CH ₂ ^+· , 7 ^+·). Ion 6 ^+· is coproduced from samples that contain the —CH₂—CH(OH)—CH₂— substructure, whereas 7 ^+· is coproduced from compounds with methoxy substituents. Compared to CAD, metastable ion characteristics combined with neutralization-reionization allow for a superior differentiation of the ions studied.     

A photoionization study of the ion-neutral complexes CH3CH +CH 3 · CH2CH3] and CH3CH2CH+CH 3 · CH3 in the gas phase: Formation,H-transfer and C—C bond formation between partners,and channeling of energy into dissociation

Photoionization mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the n-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex CH₃CH⁺CH ₃ ^· CH₂CH₃ (3), but not through CH₃CH⁺CH₂CH ₃ ^· CH₃ (4). The appearance energy for C₃Hin ₇ ⁺ formation from 1 is 66 kJ mol^?1 below that expected for the formation of n-C₃H ₇ ⁺ and just above that expected for formation of i-C₃H ₇ ⁺ . This demonstrates that the H shift that isomerizes C₃H ₇ ⁺ is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 → CH₃CH⁺CH₂CH₃ + CH₃ by direct cleavage of the C1–C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 → 2 → 4 → C4H ₈ ⁺ + CH₄ occurs in this same energy range. Thus some of the potential energy made available by the isomerization of n-C₄H₉ in 1 is specifically channeled into the coordinate for dissociation. In contrast, analogous formation of 3 by 1 → 3 is predominantly followed by reaction between the electrostatically bound partners.     

Semiempirical calculation of the CH4 + CH3 · → CH3 · + CH4 radical-reaction potential surfaces in a basis of frontier orbitals

A semiempirical approach is suggested to describe potential-energy surfaces (PESs) of some radical reactions in the zero-differential overlap (ZDO) approximation. An incomplete basis set is used including only frontier (single-filled) radical molecular orbitals (MOs) depending on geometrical parameters. All possible configurations are taken into account. The parameter selection techniques are analyzed. The approach is applied to PES calculation of the CH₄ + CH₃ · CH₃ · + CH₄ reaction. Some points of the PES are verified by a nonempirical method using the perturbation theory and taking into account the correlation energy. The relaxation energies are calculated. The one-center parameters are determined nonempirically from the CH₃ + CH₃ ·, and CH₃ ^– energetics. The two-center parameters are found by modeling the CH₄ CH₃ · + H and C₂H₆ 2CH₃ reactions in the same single-orbital approximation. The energy parameters of the reactions considered are overestimated by 10%, whereas the geometrical parameters are under-estimated by 15%. Further, a comparative analysis of the Hartree-Fock solutions and those including correlation interactions (CIs) is given. The variations in the spin and charge densities on the reaction centers are considered.Institute of Chemical Kinetics and Combustion, Academy of Sciences of the USSR, Siberian Branch, Novosibirsk. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 499–506, July–August, 1991. Original article submitted February 10, 1989.     

How do dimethyl oxalate ions CH3O-C(=O)-C(=O)-OCH 3 ·+ break in half? Loss of CH 3 · + CO2 versus CH3O-C-O·

The interesting unimolecular dissociation chemistry of dimethyl oxalate (DMO) ions, CH₃O-C(=O)-C(=O)-OCH ₃ ^·+ , has been studied by vacuum ultraviolet photoionization and tandem mass spectrometry based experiments. The measured appearance energy (AE) for the generation of CH₃O-C=O⁺ (10. 5 eV) is not compatible with a simple bond cleavage involving the cogeneration of the radical CH₃O-C=O^· whose calculated AE is 11 kcal/mol higher. However, because the CH₃O-C=O^· radical is thermodynamically less stable than its dissociation products CH₃ ^· and CO₂, by 19 kcal/mol, a two-step dissociation of ionized DMO into CH₃O-C=O⁺ + CH ₃ ^· + CO₂ is energetically feasible. Collision induced dissociative ionization experiments clearly show that low energy DMO ions dissociate into CH₃ ^· + CO₂ without the intermediacy of CH₃O-C=O^·. Experiments using a charged collision chamber further indicate that CO₂ is released first, followed by loss of CH₃ ^· and not vice versa and a mechanism is proposed. The measured AE, which we assign to the two-step process, is 8 kcal/mol higher than the calculated value. This could be due to a competitive shift caused by a prominent low energy decarbonylation reaction yielding the hydrogen bridged radical cation CH₂=O … H … O=C-OCH₃ ^·+. However, from metastable ion observations and AE measurements on deuterium labeled DMO ions, it follows that there is no competitive shift and that the elevated AE for the two-step process corresponds to the barrier for the first step, loss of CO₂. Finally, neutralization-reionization experiments on ionized DMO and CH₃O-C=O⁺ provide evidence for the existence of CH₃O-C=O^· as a kinetically stable radical.     

Intramolecular Rearrangements of >Si(O–C·=O)(CH2–CH3) and >Si(CH2–CH·–CH3)(CH2–CH3) Radicals

Using ESR and IR spectroscopy, the structures of >Si(O–C^·=O)(CH₂–CH₃) (1) and >Si(CH₂–CH^·–CH₃)(CH₂–CH₃) (2) radicals were deciphered. The directions and kinetic parameters of reactions of intramolecular rearrangements in these radicals were determined. The reactions of hydrogen atom abstraction in radical (1) from the CH₂ and CH₃ groups were studied. It was found that the endothermic reaction of hydrogen atom abstraction from the methyl group occurs at a higher rate than the exothermic reaction with the methylene group. The differences are determined by changes in the size of a cyclic transition state. Based on the experimental data, the strengths of separate C–H bonds in surface fragments are compared. The rearrangement >Si(CH₂–CH^·–CH₃)(CH₂–CH₃) >Si(C^·(CH₃)₂)(CH₂–CH₃) was discovered and its mechanism was determined. One of its steps is the skeletal isomerization Si- (2)- _. (1)Si- (1)- _. (2). Experimental data are analyzed using the results of quantum-chemical calculations of model systems.     

CH3O2·+ClO气相反应的密度泛函理论研究

用密度泛函方法在CCSD(T)/ 6-311++G// B3LYP/ 6-311G**水平上研究了气相反应CH3O2*+ClO的反应机理.得到了不同能量产物的可能的反应通道,获得反应势能面.整个反应过程为多通道反应,经过多个步骤完成,共找到7个中间体和10个过渡态,产物1CH3OCl+3O2(P1)和1 CH2O+1HOOCl(P4)为能量较低产物,通道1a:R→IM1→TS1/ 3→IM3→P1,4a:R→IM1→TS1/ P4→P4和4b:R→IM2→TS2/ P4→P4为较为可行的反应通道.     

CH3O·2+NO气相反应的密度泛函理论研究

用密度泛函方法分别研究了单态和三态 CH3 O·2 NO CH3 O· NO2 气相反应 .结果表明 ,反应中 NO进攻 CH3 O·2 经过了一个顺反异构化的过程 ,摘取 CH3 O·2 的端基氧 .整个反应是吸热反应 ,理论计算吸热值为 5 0 .93k J/ mol,单态为多通道多步骤反应 ,决定速度步骤的能垒为 1 90 .6 1 k J/ mol.而三态为单通道反应 ,其决定速度步骤的能垒为 1 6 3.31 k J/ mol.三态反应为最佳反应通道 .该反应的研究将为保护臭氧层及大气环境提供重要的理论依据 .     

CH3CH2+O(3P)反应机理的理论研究

The reaction for CH3CH2+O(3P) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single-point calculations for all the stationary points were carried out at the QCISD(T)/6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major products are the CH2O＋CH3, CH3CHO+H and CH2CH2+OH in the reaction. For the products CH2O＋CH3 and CH3CHO+H, the major production channels are A1: (R)→IM1→TS3→(A) and B1: (R)→IM1→TS4→(B), respectively. The majority of the products CH2CH2+OH are formed via the direct abstraction channels C1 and C2: (R)→TS1(TS2)→(C). In addition, the results suggest that the barrier heights to form the CO reaction channels are very high, so the CO is not a major product in the reaction.     

CH3CH2O+HCHO反应机理及主通道速率常数

采用CCSD(T)/cc-pVDZ//B3LYP/6-311++G(d,p)双水平计算方法研究了CH₃CH₂O+HCHO反应的微观反应机理. 结果表明, 标题反应主要存在5个抽氢和3个氢迁移异构化反应通道, 其中抽氢通道R→ IMa(CH₃CH₂O…CH₂O)→TS1→ IM1b→P1(CH₃CH₂OH+CHO)为优势通道, 其表观活化能为14.65 kJ/mol. 利用变分过渡态理论(CVT)并结合小曲率隧道效应模型计算了主通道R1在275~1000 K温度范围内的速率常数k^TST, k^CVT和k^CVT/SCT, 在此温度区间内表观反应速率常数三参数表达式为k^CVT/SCT=2.26×10^-17 T^0.57 exp(-1004/T), 显示具有正温度系数效应.     

用变分过渡态理论研究CH3SiH3+H→CH3SiH2+H2反应动力学

用变分过渡态理论对CH3SiH3与H的抽提反应进行了理论研究;利用从头算计算了反应体系的构型、振动频率和能量等信息;计算了温度在298 ～1700K内反应的速率常数和穿透系数。结果表明,在室温下,变分对于此反应影响较大,隧道效应特别明显,计算得到的速率常数和实验值符合得很好。     

CF3CH3 --> HF + CF2CH2: a non-RRKM reaction?

The experimental shock tube data recently reported by Kiefer et al. [J. Phys. Chem. A 2004, 108, 2443-2450] for the title reaction at temperatures between 1600 and 2400 K have been compared to master equation simulations using three models: (a) standard RRKM theory, (b) RRKM theory modified by local random matrix theory, which introduces dynamical corrections arising from slow intramolecular vibrational energy randomization, and (c) an ad hoc empirical non-RRKM model. Only the third model provides a good fit of the Kiefer et al. unimolecular reaction rate data. In separate simulations, all three models accurately reproduce the experimental 300 K chemical activation data of Marcoux and Setser [J. Phys. Chem. 1978, 82, 97-108] when the energy transfer parameters are freely varied to fit the data. When experimental energy transfer parameters for a geometrical isomer (1,1,2-trifluoroethane) are used, the standard RRKM model fits the chemical activation data better than the other models, but if energy transfer in the 1,1,1-trifluoroethane is significantly reduced in comparison to the 1,1,2 isomer, then the empirical ad hoc non-RRKM model also gives a good fit. While the ad hoc empirical non-RRKM model can be made to fit the data, it is not based on theory, and we argue that it is physically unrealistic. We also show that the master equation simulations can mimic the Kiefer et al. vibrational relaxation data, which was the first shock tube observation of double-exponential relaxation. We conclude that, until more data on the trifluoroethanes become available, the current evidence is insufficient to decide with confidence whether non-RRKM effects are important in this reaction, or whether the Kiefer et al. data can be explained in some other way.     

Ten-Dimensional Quantum Dynamics Study of H+CH3D→H2+CH2D Reaction

The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method.The reac-tion dynam...     

Synthesis and Characterization of （CH3CH2CH2CH2NH3）2SnBr6

1 INTRODUCTION Recently, the researches on inorganic-organic hy-brid compounds represent an advanced field in mate-rial science[1]. At the molecular level, the combina-tion of two extremely different components providesan avenue to design new hybrid materials as well asthe ability to modulate properties of one or more ofthe components[2～6]. Some attractive properties, suchas efficient luminescence[2～4], ideal thermal and me-chanical stability, interesting magnetic[5], non-linearoptical[…     

Capture and dissociation in the complex-forming CH + H2 → CH2 + H, CH + H2 reactions

The rate coefficients for the capture process CH + H(2)→ CH(3) and the reactions CH + H(2)→ CH(2) + H (abstraction), CH + H(2) (exchange) have been calculated in the 200-800 K temperature range, using the quasiclassical trajectory (QCT) method and the most recent global potential energy surface. The reactions, which are of interest in combustion and in astrochemistry, proceed via the formation of long-lived CH(3) collision complexes, and the three H atoms become equivalent. QCT rate coefficients for capture are in quite good agreement with experiments. However, an important zero point energy (ZPE) leakage problem occurs in the QCT calculations for the abstraction, exchange and inelastic exit channels. To account for this issue, a pragmatic but accurate approach has been applied, leading to a good agreement with experimental abstraction rate coefficients. Exchange rate coefficients have also been calculated using this approach. Finally, calculations employing QCT capture/phase space theory (PST) models have been carried out, leading to similar values for the abstraction rate coefficients as the QCT and previous quantum mechanical capture/PST methods. This suggests that QCT capture/PST models are a good alternative to the QCT method for this and similar systems.     

Theoretical Studies on CH3SiH3+H→CH3SiH2+H2 Reaction with the Variational Transitional State Theory

The abstract reaction of CH3SiH3 with H has been studied by using the“direct dynamics”method of variational transition-state theory,which is based on the information on geometries,frequencies and energies calculated by ab initio along the minimum energy path.The rate constants and transmission coefficients were calculated for the temperature range 298～1700K.The result indicates that the variational effect on this reaction is great and the tunneling effect is very obvious at room temperature.The rate constants calculated match well with the experimental value.     

H+CH3NO2H2+CH2NO2反应途径和变分速率常数计算研究

采用MP2(FULL)/6-311G**从头算方法, 优化了H+CH3NO2H2+ CH2NO2反应的过渡态结构, 得出该反应的正逆反应的活化位垒分别是82.73和57.14 kJ*mol-1. 沿IRC分析指出该反应是一个H-H键生成和C-H键断裂的协同反应, 而且在反应途径上存在一个引导反应进行的振动模式, 这一反应模式引导反应进行的区间在-0.7～0.2( amu)1/2*a0之间; 在1 000～1 400 K温度范围内, 运用变分过渡态理论(CVT), 计算了该反应的速率常数, 计算结果与实验相一致.     

CF3CH2CH3+OH的反应机理及动力学性质的理论研究

采用密度泛函理论BB1K/6-31+G(d,p)计算了反应CF₃CH₂CH₃+OH各反应通道上驻点的稳定结构和振动频率, 并分别在BMC-CCSD, MC-QCISD和G3(MP2)水平上进行了单点能校正. 运用变分过渡态理论, 在BMC-CCSD//BB1K, MC-QCISD//BB1K, G3(MP2)//BB1K以及BB1K水平上计算了各反应通道的速率常数, 讨论了-CH₂和-CH₃基团上H提取通道对总反应的贡献, 并与已有实验和理论结果进行了对比. 计算结果表明, BMC-CCSD水平上的速率常数与实验测量值符合得很好, 进而给出了该水平上反应在200~1000 K温度范围内速率常数k(cm³?molecule^-1?s^-1)的三参数表达式: k=1.90×10^-21T^3.21exp(-292.62/T).     

配合物[Ni(IDB)2]2·(SO4)2·3CH3CH2OH·CH3OH·5H2O的合成、晶体结构及其荧光光谱的研究

标题配合物是由三齿配体Ⅳ,Ⅳ-二(2-苯并咪唑甲基)亚胺(IDB)与NiSO4·6H2O在甲醇-乙醇溶液中反应得到的紫色 晶体.X射线衍射测定了其单晶结构.结构分析表明,镍(Ⅱ)分别与两个IDB配体中的苯并咪唑的四个氮和胺基的两个 氮配位形成畸变的八面体构型.研究了纳米金和小牛胸腺DNA对配合物荧光的影响,探讨了配合物的荧光猝灭与恢复 的可能机理.     

CH3 CH2 +N(4S)反应机理的理论研究

The reaction for CH3CH2+N(4S) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single point calculations for all the stationary points were carried out at the QCISD(T)/ 6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major products are the CH2CH2+3NH and H2CN＋CH3, and the minor products are the CH3CHN+H in the reaction. The majority of the products CH2CH2+3NH are formed via a direct hydrogen abstraction channel. The products H2CN＋CH3 are produced via an addition/dissociation channel. The products CH3CHN+H are produced via an addition/dissociation channel.