共查询到20条相似文献,搜索用时 15 毫秒
1.
Sakai S 《The journal of physical chemistry. A》2006,110(30):9443-9450
The reaction mechanisms of the electrocyclic ring closure of bis(allene) and vinylallene were studied by ab initio MO methods. The conrotatory and disrotatory pathways of the electrocyclic reactions from bis(allene) to bis(methylene)cyclobutene were determined by a CASSCF method. The transition state on the conrotatory pathway is 26.8 kcal/mol above bis(allene) and about 23 kcal/mol lower than that on the disrotatory pathway at a MRMP calculation level. The activation energy on the conrotatory pathway is lower by 23 kcal/mol than that of the electrocyclic reaction of butadiene. This lower energy barrier comes from the interactions of the "side pi orbitals" of the allene group. The interaction of the "vertical pi orbitals" of the allene group is predominant at the early stage of the reaction. The activation energy of the electrocyclic reaction of vinylallene is about 8.5 kcal/mol higher than that on the conrotatory pathway of bis(allene). 相似文献
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C. -H. Tung X. -H. Wang Y. -M. Ying Z. -Q. Yang 《Research on Chemical Intermediates》1995,21(6):613-620
Photolysis of phenyl phenylacetate and its derivatives in homogeneous solutions results in photo-Fries rearrangement products,
phenols and diphenylethane as well as phenyl benzyl ethers. Photolysis of these esters adsorbed on silica surface leads only
to the formation of or/tho-hydroxyphenones and phenyl benzyl ethers. This observation demonstrates that silica surfaces suppress diffusion and rotation
of the photogenerated radicals. Application of a weak external magnetic field upon photolysis of these esters adsorbed on
silica surface results in no change in the product distribution, suggesting that the photochemical reaction of these esters
originates from the excited singlet state. The rate of the formation of the ortho rearrangement product from the geminate radical pairs adsorbed on silica surfaces is estimated to be 2.0 x 108 s-1. 相似文献
3.
The chemistry of the atmosphere encompasses a vast number of reactions acting on a plethora of intermediates. These reactions, occurring sequentially and in parallel, give rise to intertwined and irreducible mechanisms describing the complex chemical transformations of organic and inorganic compounds in the atmosphere. The complexity of this system is that it requires combined experimental, theoretical, and modeling approaches to elucidate the characteristics of the individual reactions, and their mutual interaction. In this review, we describe recent results from quantum chemical and theoretical kinetic studies of relevance to atmospheric chemistry. The review first summarizes the most commonly used theoretical methodologies. It then examines the VOC oxidation initiation channels by OH, O(3), NO(3) and Cl, followed by the reactions of the alkyl, alkoxy, alkylperoxy and Criegee intermediates active in the subsequent oxidation steps. Specific systems such as the oxidation of aromatics and the current state of knowledge on OH-regeneration in VOC oxidation are also discussed, as well as some inorganic reactions. 相似文献
4.
Maria del Carmen Michelini Nino Russo Stefano Alcaro Lucyna A. Wozniak 《Tetrahedron》2012,68(27-28):5554-5563
The mechanism of the Stec reaction between phosphoroselenanilidate or phosphonoanilidate and CS2, activated by strong bases, has been studied computationally, using DFT methods, and experimentally, by low temperature 31P NMR spectroscopy. From molecular calculations, the reaction pathway of the reaction has been revealed with several transition states and intermediates, including a low energy spirocyclic pentacoordinate transition state and acyclic tetracoordinate intermediates, which eventually were correlated with short living molecules detected by NMR spectroscopy. 相似文献
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After defining reaction mechanism, reaction path, reaction coordinate, reaction profile, and classical trajectories, dynamic and static approaches suitable (or promising) for analysis of reaction mechanism are critically discussed. 相似文献
7.
Yi-Zhen Tang Jing-Yu Sun Hao Sun Ya-Ru Pan Rong-Shun Wang 《Theoretical chemistry accounts》2008,119(4):297-303
The mechanisms of the reaction of NCCO with molecular oxygen are investigated at the G3MP2//B3LYP/6-311G(d,p) levels for the
first time. The calculation results show that two mechanisms are involved, namely, O attack on α atom mechanism and O attack on β atom mechanism, with six products yielded. The most feasible channel is the addition of O2 to β atom in NCCO radical leading to the energy-rich intermediate IM1, NCC(O)OO, which can isomerize to a four-center-structure
IM3, and then undergoes C–C and O–C bond fission to form P1(NCO + CO2) finally. The barriers are 27.3 and 25.4 kcal/mol, respectively. For other channels involved in the two mechanisms, with
less stable initial adducts and higher barrier, they are less conceivable dynamically and thermochemically. 相似文献
8.
Howard E. Zimmerman 《Tetrahedron》1974,30(12):1617-1628
In this publication we have reviewed examples derived from our photochemical investigations where stereochemistry provides information allowing elucidation of the mechanistic details of electronically excited state transformations. The reactions discussed include unimolecular rearrangements of both singlet and triplet excited state species. 相似文献
9.
The mechanism of the chlorination reaction of trichlorogermyl acrylic acid has been studied systematically using quantum chemistry methods. Geometries of reactants, transition states and products have been optimized at the B3LYP/6-311G(d,p) level. Vibrational frequencies, IR intensities and relative energies for various stationary points have been determined. The reaction pathways have been identified by intrinsic reaction coordinate (IRC) calculations. Theoretical analysis provides conclusive evidence that the process proceeds through two and three pathways for the first and second reaction steps, respectively. 相似文献
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Fernández I Sierra MA Gómez-Gallego M Mancheño MJ Cossío FP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(20):5988-5996
The photocarbonylation reaction of Group 6 Fischer carbene complexes has been studied by DFT and experimental procedures. The process occurs by intersystem crossing (ISC) from the lowest excited singlet state (S1) to the lowest triplet state (T1), the latter structure being decisive for the outcome of the reaction. Methylenepentacarbonylchromium(0) complexes, alkoxypentacarbonylchromium(0)carbene complexes, and alkoxyphosphinetetracarbonylchromium(0) carbene complexes have coordinatively unsaturated chromacyclopropanone T1 structures with a biradical character. The evolution of the metallacyclopropanone species occurs by a jump (spin inversion) to the S(0) hypersurface by coordination of a molecule of the solvent, leading to ketene-derived products in the presence of ketenophiles or reverting to the starting carbene complex in their absence. The T1 excited states obtained from methylenephosphinetetracarbonylchromium(0) complexes and pentacarbonyltungsten(0)carbene complexes are unable to produce the carbonylation. The reaction with ketenophiles is favored in coordinating solvents, which has been tested experimentally in the reaction of alkoxypentacarbonylchromium(0) complexes and imines. 相似文献
12.
Lai‐Cai Li Yan Zheng Dong Zha An‐Min Tian Ming‐Hou Xu 《International journal of quantum chemistry》2006,106(7):1672-1682
The reaction mechanism of CH2CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH2CH + HNCO → IMA1 → TSA1 → CH2CH2 + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
13.
A sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO2, O3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies. 相似文献
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Xiu Hui Lu Yue Hua Xu Ping Ping Xiang Xin Che 《International journal of quantum chemistry》2008,108(1):75-83
Mechanism of the cycloadditional reaction between singlet germylidene (R1) and formaldehyde (R2) has been investigated with MP2/6‐31G* method, including geometry optimization, and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet germylidene and formaldehyde is reaction (4) , which consists of three steps: the two reactants (R1, R2) first form an intermediate INT1b through a barrier‐free exothermic reaction of 28.1 kJ/mol; this intermediate reacts further with formaldehyde (R2) to give an intermediate INT4, which is also a barrier‐free exothermic reaction of 37.2 kJ/mol; subsequently, the intermediate INT4 isomerizes to a heteropolycyclic germanic compound P4 via a transition state TS4, for which the barrier is 18.6 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in thermodynamic property and reaction rate. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
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Xiu Hui Lu Hai Bin Yu Wei Rong Wu Yue Hua Xu 《International journal of quantum chemistry》2007,107(2):451-457
Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second‐order Møller–Plesset (MP2)/6‐31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero‐point energy (ZPE) and CCSD(T)/6‐31G* single‐point calculations. From the PES obtained with the CCSD(T)//MP2/6‐31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four‐membered ring intermediate, INT2, which is a barrier‐free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four‐membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier‐free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier‐free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
19.
The reaction mechanisms of allyl-lithium and allyl-sodium with ethylene were studied by ab initio molecular orbital (MO) methods. The reaction mechanisms were analyzed by a CiLC-IRC method on the basis of ab initio CASSCF MOs. The ene reaction pathways of allyl-Li and allyl-Na with ethylene were located. The complex between allyl-metal and ethylene for both systems is found in the first step of the reaction, and then the metal migration and new C-C bond formation occur synchronously through the transition state. The complexation energies are -13.2 and -9.6 kcal/mol for Li and Na systems, respectively. The activation energy barriers from the reactants are 3.5 kcal/mol for the Li system and 2.0 kcal/mol for the Na system at the MRMP2 calculation level. These barriers are significantly lower than that of the ene reaction of propene with ethylene as the parent reaction. The CiLC-IRC analysis shows that the reaction of allyl-metal with ethylene is a concerted ene reaction mechanism, not a metal catalysis and/or a stepwise reaction. 相似文献
20.
The kinetics for the gas-phase reaction of phenyl radical with propyne has been measured by cavity ring-down spectrometry (CRDS), and the mechanism and initial product branching have been elucidated with the help of quantum chemical calculations. Absolute rate constants measured by the CRDS technique can be expressed by the following Arrhenius equation: (k/cm(3) mol(-1) s(-1)): k(propyne)(T=301-428 K)=(3.68+/-0.92) x 10(11)exp[-(1685+/-80)/T]. The experiment is unable to distinguish between the possible reactive channels, but theory indicates that phenyl radicals preferably add to the unsaturated terminal carbon atom in propyne under our experimental conditions. Theoretical kinetic calculations, employing high-level G2M(RCC, RMP2) and G3 energetic and IRCMax(RCCSD(T)//B3LYP-DFT) molecular parameters, reproduce the total experimental rate constants within a factor of three. Calculated total and branching rate constants are provided for high-T kinetic modeling. Addition reactions of phenyl to C3H4 are estimated to be less important molecular-growth pathways in high-T conditions (T>1000 K) in comparison to the C6H5 + C2H2 reaction. 相似文献