A quantum chemical study on the mechanism of the consecutive addition of HCN to propionitrile

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.     

Quantum chemical study of the addition of ozone to acetylene

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%.     

Quantum chemical studies on electrophilic addition

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.     

Quantum chemical studies on electrophilic addition

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.     

Quantum chemical studies on electrophilic addition

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.     

Quantum chemical studies of ethylene addition to organoaluminium compounds

In terms of the MINDO/3 method, the surface potential energy of ethylene addition to AlH₃ and Al(CH₃)₃ has been calculated.

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MINDO/3 AlH₃ Al(CH₃)₃.

     

丙烯醛光致脱羰机理的量子化学研究

用量子化学方法研究了丙烯醛基态和激发态的反应途径, 通过比较不同反应途径的反应势垒和中间产物构型的稳定性, 从理论上得出该反应的反应机理。     

Quantum chemical study of the mechanism of the Claisen amino rearrangement

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.     

Quantum chemical study of pyridine addition to Ni(II) β-diketonate complexes

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.     

Diastereoselective addition of HCN to Garner's aldehyde

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.     

Quantum chemical study of low temperature oxidation mechanism of dibenzofuran

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.     

Spectroscopic characterization of aminoacetonitrile,its ions and protonated aminoacetonitrile using quantum chemical methods

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     

Quantum chemical study of the primary step of ozone addition at the double bond of ethylene

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.     

Quantum chemical study on the mechanism of enantioselective reduction of prochiral ketones catalyzed by oxazaborolidines

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     

Quantum chemical study of the charged gold atom influence on the mechanism of allylbenzene double bond migration

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.     

炼铝用碳阳极中碱金属氧化物作用机理的量子化学研究

本文应用CNDO/2法研究了炼铝用碳阳极中添加碱金属氧化物的吸附行为, 通过优化得到了吸附的最佳模型, 考察了吸附结合能随分子间距的变化, 进而给出了碱金属氧化物在碳阳极中作用的机理。量子化学计算结果表明: 碱金属氧化物添加到炼铝用碳阳极中起传输电子的电桥作用, 是碳阳极在空气中氧化反应以及铝电解时生成氧气的氧化反应的催化剂; 理论计算和实验结果二者吻合较好, 可以用来解释若干实验结果。     

Quantum chemical simulation for the mechanism of benzene bromination

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...     

A quantum chemical study on electrophilic addition

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.     

Quantum chemical study on the thermal rearrangements of HNCRCR''''CO

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'.     

Quantum chemical studies on addition reactions of carbene with carbon monoxide and formaldehyde

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.