共查询到20条相似文献,搜索用时 15 毫秒
1.
HONG San-Guo WANG Sheng Department of Chemistry Jiangxi Normal University Nanchang Jiangxi China 《中国化学》1994,12(6):490-494
MINDO/3 MO method has been used to study the mechanism of the consecutive addition of HCN to propionitrile. The results obtained for the first five steps show that the reaction is exothermic, and step 1 is the rate determining step. 相似文献
2.
The primary step of acetylene ozonation was studied by the B1LYP, PBE0, CASSCF, MRMP2, and CCSD methods using the 6-31+G**, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets. The study confirmed the earlier B3LYP-based conclusions that the intermediate complex, as well as the transition states of the concerted addition (Criegee’s mechanism) and unconcerted addition (DeMore’s mechanism), are involved in this reaction event. The activation enthalpy and entropy and rate constants of the reaction were calculated. Criegee’s mechanism was shown to dominate in the reaction with acetylene, but the contribution from DeMore’s mechanism is also noticeable, being 1–8%. 相似文献
3.
Alan C. Hopkinson Min H. Lien Imre G. Csizmadia Keith Yates 《Theoretical chemistry accounts》1980,55(1):1-14
The geometries of the 2-aminoethyl cation and the isomeric protonated aziridine have been optimized using ab initio molecular orbital calculations employing the split-valence shell 4-31G basis set. The protonated aziridine is computed to be the more stable ion by 46.5 kcal/mole (4-31G level) and 44.9 kcal/mole (double-zeta basis set). The profile to interconversion is found to have a barrier of less than 15 kcal/mole (relative to the 2-aminoethyl cation) and this profile is compared with those computed for the similar ions XCH2CH
2
+
where X=OH, F, SH and Cl. 相似文献
4.
Alan C. Hopkinson Min H. Lien Keith Yates Imre G. Csizmadia 《Theoretical chemistry accounts》1977,44(4):385-398
The geometries of the 2-chloroethyl and ethylenechloronium cations, two possible intermediates in the electrophilic addition of chlorine to ethylene, have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set.These geometries were then used to compute more accurate wave functions using Dunning's double-zeta basis set. The bridged chloronium ion was found to be more stable by 9.35 kcal/mole, the opposite order of stability from the C2H4F+ ions. Interconversion of the two C2H4Cl+ cations was computed to have a barrier of 6.25 kcal/mole.The activation energy for this chlorination reaction, using the ethylenechloronium cation and a chlorine anion at infinite separation as the model for the activated complex, was computed to be 128.7 kcal/mole, showing that this is not a feasible gas phase reaction. 相似文献
5.
Alan C. Hopkinson Min H. Lien Imre G. Csizmadia Keith Yates 《Theoretical chemistry accounts》1978,47(2):97-109
The geometries of the 2-hydroxyethyl and isomeric oxiranium cations have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set. These species are possible intermediates in both the electrophilic addition of OH to ethylene and in the acid catalysed ring opening of oxirane. The optimized structures were then used to compute more accurate wave functions using Dunning's double-zeta basis set, and with this large basis set the bridged oxiranium ion was found to be the more stable by 7.2 kcal/mole. The barrier to interconversion of these two C2H4OH ions was computed to be 25.0 kcal/mole above the oxiranium ion. 相似文献
6.
In terms of the MINDO/3 method, the surface potential energy of ethylene addition to AlH3 and Al(CH3)3 has been calculated.
MINDO/3 AlH3 Al(CH3)3.相似文献
7.
8.
I. B. Abdrakhmanov N. G. Nigmatullin B. G. Zykov Z. N. Saraeva O. A. Ponomarev G. A. Tolstikov 《Russian Chemical Bulletin》1991,40(3):552-556
Using the LCAO MO method in the MNDO approximation, we have compared the concerted [3, 3]-sigmatropic and stepwise mechanisms for the acid-catalyzed Claisen amino rearrangement. The latter is preferred.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 634–639, March, 1991. 相似文献
9.
A. G. Starikov R. M. Minyaev A. A. Starikova V. I. Minkin 《Russian Journal of Coordination Chemistry》2010,36(8):597-604
The addition reaction of two pyridine molecules to Ni(II) β-diketonate bis-chelate was studied by quantum chemical density
functional theory calculations (B3LYP/6-311++G(d, p)). The addition of the first pyridine molecule to the trans-position was found to be the most favorable channel for this two-stage process; the reaction is accompanied by a change in
the spin state of the system. The transition between the potential energy surfaces of different multiplicity occurs at the
first stage without considerable energy expenditure; the addition of the second pyridine molecule is barrierless. 相似文献
10.
《Tetrahedron: Asymmetry》1999,10(8):1617-1622
The hydrocyanation of N-Boc-N,O-isopropylidene-l-serinal 1 (Garner's aldehyde) is described. The influence of various reaction conditions (solvent, temperature, addition of a Lewis acid, presence of a biocatalyst) on the stereochemical outcome of the addition of HCN was investigated. The use of 2-pentanol as the solvent at room temperature afforded complete stereoselectivity. X-Ray analysis of the product showed the anti configuration. The results can be readily explained on the basis of a Felkin–Anh type model. 相似文献
11.
Altarawneh M Dlugogorski BZ Kennedy EM Mackie JC 《The journal of physical chemistry. A》2006,110(50):13560-13567
A density functional theory (DFT) study of the reaction of dibenzofuranyl radical with oxygen molecule has been made. The geometries, energies, and vibrational frequencies of the reactant, transition states, intermediates, and products have been calculated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level of theory. The initial reaction of dibenzofuran (DBF) with molecular oxygen results in the formation of the 1-dibenzofuranylperoxy radical. The stability of this adduct toward decomposition at low to intermediate temperatures results in it undergoing several possible rearrangements. The lowest energy pathway with a barrier of 24.2 kcal/mol involves a rearrangement to the 1,1-dioxadibenzofuran radical. The next lowest energy pathway involves fission of the O-O linkage whose reaction energy was found to be 37.6 kcal/mol. Transition state theory (TST) calculations indicate that the lowest energy pathway should predominate at temperatures up to about 1200 K. Two other unimolecular reaction pathways with barriers of 45.5 and 91.1 kcal/mol have also been discovered. The latter pathway leads to the formation of a para-quinone (dibenzofuran quinone) which has been detected experimentally in the low-temperature oxidation of DBF [Marquaire, P. M.; Worner, R.; Rambaud, P.; Baronnet, F. Organohalogen Compd. 1999, 40, 519]. Our quantum calculations, however, do not support this latter pathway to quinone formation. Instead, the quinone is most probably formed as a consequence of recombination of the 1-dibenzofuranyloxy radical (produced by peroxy fission) with an O atom in the para position. Each of the unimolecular reaction pathways have been subjected to detailed quantum chemical investigation and transition states and intermediates leading to the final products (principally CO, CO2, and C2H2 with traces of benzofuran and benzene) have been identified. For certain stable intermediates, their possible reactions with molecular oxygen have been further investigated quantum chemically. The present work therefore presents a detailed quantum chemical investigation of the reaction pathways in the low-temperature oxidation mechanism of DBF. Since the dibenzofuran moiety is present in the polychlorinated DBFs, our conclusions should be generally applicable to this family of compounds. 相似文献
12.
Mahadevappa Naganathappa Ajay Chaudhari 《International journal of quantum chemistry》2011,111(9):2064-2071
We present theoretical vibrational and absorption spectra of aminoacetonitrile, its cation, anion, cyanoprotonated, and aminoprotonated aminoacetonitrile. We used second‐order Moller–Plesset perturbation method (MP2) with TZVP basis set to obtain ground state geometries and vibrational spectra. Time dependent density functional theory method was used to obtain absorption spectra. Shifts in vibrational modes for aminoacetonitrile upon ionization and protonation are determined. The C≡N stretching mode which is the most important mode in detection of nitriles in space is more intense in aminoacetonitrile ions and its two protonated form and is less IR active for neutral aminoacetonitrile. The nature of electronic transition for these molecules is identified. All the electronic transitions for neutral aminoacetonitrile and its cation are the σ → σ* electronic transitions, whereas its anion and protonated aminoacetonitrile display the σ → σ* as well as π → π* transitions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 相似文献
13.
The mechanism of the primary step of the interaction between ozone and the double bond of ethylene has been investigated by
various methods of quantum chemistry (MP2, QCISD, CCSD, MRMP2) and density functional theory (PBE0, OPTX, CPW91, B3PW91, OLYO,
B3LYP, BLYP). The kinetics of two reaction pathways, namely, concerted ozone addition via a symmetric transition state (Criegee
mechanism) and nonconcerted ozone addition via a biradical transition state (DeMore mechanism) has been calculated. Both mechanisms
are describable well in the single-determinant approximation by the QCISD, CCSD, B3LYP, and PBE0 methods and in the multideterminant
approximation by the MRMP2 method. The other methods are less suitable for solving this problem. The calculated data demonstrate
that the reaction proceeds via both competing pathways. Rate constant values consistent with experimental data and plausible
Criegee-to-DeMore rate constant ratios have been obtained. The concerted addition of ozone to ethylene is significantly more
rapid than the nonconcerted addition. 相似文献
14.
Quantum chemical study on the mechanism of enantioselective reduction of prochiral ketones catalyzed by oxazaborolidines 总被引:1,自引:0,他引:1
The ab initio molecular orbital study on the mechanism of enantioselective reduction of 3,3-dimethyl butanone-2 with borane catalyzed by chiral oxazaborolidine is performed. As illustrated, this enantioselective reduction is exothermic and goes mainly through the formations of the catalyst-borane adduct, the catalyst-borane-3,3-dimethyl butanone-2 adduct, and the cata-lyst-alkoxyborane adduct with a B-O-B-N 4-member ring and through the decomposition of the catalyst-alkoxyborane adduct with the regeneration of the catalyst. During the hydride transfer in the catalyst-borane-3,3-dimethyl butanone-2 adduct to form the catalyst-alkoxyborane adduct, the hydride transfer and the formation of the B-O-B-N 4-member ring in the catalyst-alkoxyborane adduct happen simultaneously. The controlling step for the reduction is the transfer of hydride from the borane moiety to the carbonyl carbon of 3,3-dimethyl butanone-2. The transition state for the hydride transfer is a twisted chair structure and the reduction leads to 相似文献
15.
D. F. Mukhamedzyanova D. A. Pichugina M. S. Askerka A. F. Shestakov N. E. Kuz��menko 《Russian Chemical Bulletin》2011,60(8):1545-1555
The DFT calculations of allylbenzene double bond migration were performed in the presence of gold ions Au? and Au+ and the cluster Au4, which are models of active sites of the gold-containing catalysts. The mechanism of isomerization is determined by the charge of the metal. For the allylbenzene + Au+ system, the most appropriate mechanism is the multistage metal-allylic process passing through either the formation of a gold-hydride complex, or no hydride complex is formed in the presence of Au?. The calculated rate constant of the rate-determining step of the catalytic reaction increases in the order Au0 < Au? < Au+. The Au??+ particles are active sites in allylbenzene isomerization. Additional routes of accumulation of the trans-isomer result in the selective formation of trans-??-methylstyrene observed in the catalytic conversion of allylbenzene in the presence of gold nanoparticles. The metal-allylic mechanism is the most preferential in the presence of Au4 cluster. The high energy of the bond of allylbenzene with the cluster is possibly due to the high reactivity of the latter. 相似文献
16.
17.
Russian Chemical Bulletin - Quantum chemical calculations performed using the M06-2X/6-311+G(D) method have revealed some features of the reaction of benzene with bromine in the presence of... 相似文献
18.
Alan C. Hopkinson Min H. Lien Keith Yates Imre G. Csizmadia 《Theoretical chemistry accounts》1975,38(1):21-35
Non-empirical SCF-MO calculations were carried out on two limiting structures of C2H4F+, corresponding to the cyclic and open valence tautomers, both of which are possible reaction intermediates of the electrophilic addition reaction of F2 to CH2 =CH2. It was found that both species had thermodynamic stability, corresponding to two distinct minima on the energy surface. However, the 2-fluoroethyl carbonium ion showed a greater stability than the fluoronium ion by about 10 kcal/mole. 相似文献
19.
LI Yong-Hong HONG San-GuoDepartment of Chemistry Jiangxi Normal University Nanchang Jiangxi China 《中国化学》1996,14(2):105-108
MINDO/3 molecular orbital theory has been used to study the thermal rearrangements of HNCRCR'CO.The results obtained show that the activation energy of this rearrangement depends on the migrating group R and the group R'. 相似文献
20.
MNDO method has been employed to study the reaction paths and to optimize the structures of the reactants, products and transition states of the addition reactions of carbene with carbon monoxide and formaldehyde available. Mechanisms have been obtained. 相似文献