scholarly journals QUANTUM CHEMITRY STUDY ON STRUCTURES, ACTIVITIES AND REACTIONS OF ONIUM-BORONIUM DICATIONS

2010 ◽  
Vol 13 (2) ◽  
pp. 45-52
Author(s):  
Thanh Tho Bui ◽  
Tran Thi Bao Vo
Keyword(s):  
Activation Energy ◽  
Intrinsic Reaction Coordinate ◽  
Kinetic Control ◽  
Ab Initio Methods ◽  
Thermodynamic Control ◽  
Imaginary Frequency ◽  
Theoretical Investigations ◽  
Transition Structures ◽  
Frequency Calculation ◽  
Energy Activation

This paper provides information about theoretical investigations of structures of onium-boronium dications X+BH3+, X+BH5+; (X= NH3, PH3, H2O, H2S) and some reactions of them in thermodynamic control and kinetic control. Two kinds of reactions studied are complexation of onium-boronium dications X+BH3+ with H2 leading to X+BH5+ and deprotonation of X+BH5+ to give X+BH4. The similar studies with boronium ion analog BH4+ and BH6+ is carried out and results obtained pointed out that the eletrophility of onium-boronium dications is more stronger than that of boronium ion: onium-boronium dications X+BH3+, X+BH5+ are superelectrophiles. The structures of onium-boronium dications and boronium ions are optimized by using ab initio methods at the MP2/6-311+G** level of Gaussian 03W, revision B.04 and represented with Gaussview 3.0. Frequency calculation is performed to assure the obtained structures corresponding to minimun energies and have no any imaginary frequency. The transition structures are calculated and verified due to Intrinsic Reaction Coordinate Calculations. The properties of structures, as MP2 energy, Gibbs free energy, activation energy are also examined.

scholarly journals Computational mechanistic study of the unimolecular dissociation of ethyl hydroperoxide and its bimolecular reactions with atmospheric species

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Mansour H. Almatarneh ◽  
Asmaa Alnajajrah ◽  
Mohammednoor Altarawneh ◽  
Yuming Zhao ◽  
Mohammad A. Halim
Keyword(s):  
Activation Energy ◽  
Density Functional ◽  
Computational Study ◽  
Basis Sets ◽  
Mechanistic Study ◽  
Intrinsic Reaction Coordinate ◽  
Unimolecular Dissociation ◽  
Phase Reaction ◽  
Atmospheric Species ◽  
Solvation Models

Abstract A detailed computational study of the atmospheric reaction of the simplest Criegee intermediate CH2OO with methane has been performed using the density functional theory (DFT) method and high-level calculations. Solvation models were utilized to address the effect of water molecules on prominent reaction steps and their associated energies. The structures of all proposed mechanisms were optimized using B3LYP functional with several basis sets: 6-31G(d), 6-31G (2df,p), 6-311++G(3df,3pd) and at M06-2X/6-31G(d) and APFD/6-31G(d) levels of theory. Furthermore, all structures were optimized at the B3LYP/6-311++G(3df,3pd) level of theory. The intrinsic reaction coordinate (IRC) analysis was performed for characterizing the transition states on the potential energy surfaces. Fifteen different mechanistic pathways were studied for the reaction of Criegee intermediate with methane. Both thermodynamic functions (ΔH and ΔG), and activation parameters (activation energies Ea, enthalpies of activation ΔHǂ, and Gibbs energies of activation ΔGǂ) were calculated for all pathways investigated. The individual mechanisms for pathways A1, A2, B1, and B2, comprise two key steps: (i) the formation of ethyl hydroperoxide (EHP) accompanying with the hydrogen transfer from the alkanes to the terminal oxygen atom of CIs, and (ii) a following unimolecular dissociation of EHP. Pathways from C1 → H1 involve the bimolecular reaction of EHP with different atmospheric species. The photochemical reaction of methane with EHP (pathway E1) was found to be the most plausible reaction mechanism, exhibiting an overall activation energy of 7 kJ mol−1, which was estimated in vacuum at the B3LYP/6-311++G(3df,3pd) level of theory. All of the reactions were found to be strongly exothermic, expect the case of the sulfur dioxide-involved pathway that is predicted to be endothermic. The solvent effect plays an important role in the reaction of EHP with ammonia (pathway F1). Compared with the gas phase reaction, the overall activation energy for the solution phase reaction is decreased by 162 and 140 kJ mol−1 according to calculations done with the SMD and PCM solvation models, respectively.

scholarly journals The Application of Equivalent Age Concept to Sand Concrete Compared to Ordinary Concrete

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Nabil Bella ◽  
Ilham Aguida Bella ◽  
Aissa Asroun
Keyword(s):  
Activation Energy ◽  
Coarse Aggregate ◽  
Strength Development ◽  
Arrhenius Law ◽  
Ordinary Concrete ◽  
Equivalent Age ◽  
Heat Treated ◽  
Sand Filler ◽  
Energy Activation ◽  
Prestressed Beams

In this research the equivalent age concept was used, in order to simulate strength development of heat treated sand concrete compared with ordinary concrete at different temperature, 35, 55, and 70°C, and validate the simulation results with our experimental results. Sand concrete is a concrete with a lower or without coarse aggregate dosage; it is used to realize thin element as small precast prestressed beams, in injected concrete or in regions where sand is in extra quantity and the coarse aggregate in penury. This concrete is composed by principally sand, filler, superplasticizer, water, and cement. The results show that the simulation of ordinary concrete was acceptable with an error lower than 20%. But the error was considerable for the sand concrete. The error was due to large superplasticizer dosage, which modified the hardening of sand concrete; the most influent parameter in Arrhenius law is apparent energy activation, to search for the value of the activation energy which gives the best simulation; a superposition is used of two curves of different temperature and with superplasticizer dosage 4% and several values of activation energy, 15, 20, 25, and 30 × 10 kcal. The simulation becomes ameliorated with the adequate value of activation energy.

Experimental and Theoretical Investigation of the Reaction of Secondary Amines with Maleic Anhydride

2017 ◽  
Vol 70 (12) ◽  
pp. 1247 ◽  
Author(s):  
Manjinder Kour ◽  
Raakhi Gupta ◽  
Raj K. Bansal
Keyword(s):  
Maleic Anhydride ◽  
Carbonyl Group ◽  
Carbonyl Compounds ◽  
Secondary Amines ◽  
Kinetic Control ◽  
Thermodynamic Control ◽  
Carbonyl Carbon ◽  
Fukui Functions ◽  
Unsaturated Carbonyl Compound ◽  
Condensed Fukui Functions

The reaction of secondary amines, namely 1-methylpiperazine, pyrrolidine, morpholine, 2-methylpiperidine, and diethylamine, with maleic anhydride has been investigated experimentally and theoretically at the DFT level. Under kinetic control, i.e. at −78°C or −15°C, amines add across the C=O functionality exclusively and the initially formed addition products isomerize to the corresponding N-substituted maleimic acid derivatives. In contrast to the acyclic α,β-unsaturated carbonyl compounds, amine does not add across the C=C functionality in maleic anhydride even under thermodynamic control. This behaviour of maleic anhydride can be rationalized on the basis of the local condensed Fukui functions, which reveal that the carbonyl carbon atoms in maleic anhydride are much harder than in an acyclic α,β-unsaturated carbonyl compound, such as acrolein. This prompts the amines to attack the carbonyl group in maleic anhydride exclusively.

Activation Energy−Activation Volume Master Plots for Ion Transport Behavior in Polymer Electrolytes and Supercooled Molten Salts

2005 ◽  
Vol 109 (35) ◽  
pp. 16567-16570 ◽  
Author(s):  
Malcolm D. Ingram ◽  
Corrie T. Imrie ◽  
Zlatka Stoeva ◽  
Steven J. Pas ◽  
Klaus Funke ◽  
...  
Keyword(s):  
Activation Energy ◽  
Ion Transport ◽  
Polymer Electrolytes ◽  
Molten Salts ◽  
Activation Volume ◽  
Transport Behavior ◽  
Master Plots ◽  
Energy Activation

Helicity control in the synthesis of helicenes and related compounds

2006 ◽  
Vol 78 (2) ◽  
pp. 495-499 ◽  
Author(s):  
Ivo Starý ◽  
Irena G. Stará ◽  
Zuzana Alexandrová ◽  
Petr Sehnal ◽  
Filip Teplý ◽  
...  
Keyword(s):  
Asymmetric Synthesis ◽  
Kinetic Control ◽  
Thermodynamic Control ◽  
Further Development ◽  
Related Compounds

Asymmetric synthesis of helicenes and their congeners has been demonstrated to rely either on enantioselective Ni0/PR3*-catalyzed [2+2+2] cycloisomerization of triynes or on diastereoselective CoI-catalyzed [2+2+2] cycloisomerization of chiral triynes. The former approach providing tetrahydrohelicenes in a nonracemic form requires further development as moderate enantioselectivities (up to 54 % ee) have so far been achieved under kinetic control. The latter approach affording helicene-like structures in a diastereomerically enriched form allows for reaching good to excellent diastereoselectivities (up to 100:0) under thermodynamic control.

scholarly journals Влияние водорода на флуктуационное охрупчивание алюминия

2019 ◽  
Vol 45 (17) ◽  
pp. 31
Author(s):  
Д.А. Индейцев ◽  
Е.В. Осипова
Keyword(s):  
Activation Energy ◽  
Hydrogen Embrittlement ◽  
Ab Initio ◽  
Aluminum Atom ◽  
Interstitial Site ◽  
Ab Initio Methods ◽  
Hydrogen Atoms ◽  
Vacancy Generation ◽  
Tetrahedral Voids ◽  
Kinetic Concept

The main processes occurring during vacancy generation in aluminum in the presence of hydrogen are described on the base of ab initio methods using the meta-functional SCAN. It was shown that hydrogen reduces the vacancy generation energy from 2.8 eV to 0.8 eV. In this case, eight hydrogen atoms located in the tetrahedral voids of the lattice around one aluminum atom make it much easier for it to move to the interstitial site. In accordance with the kinetic concept of embrittlement the dependence of the activation energy of hydrogen embrittlement of aluminum is calculated on the concentration of hydrogen and temperature. It is shown that hydrogen reduces the time of aluminum embrittlement only if its concentration in aluminum is more than critical one (~3⋅〖10〗^(-4) at T=293 K).

scholarly journals Quantum chemical study of the mechanism of the palladium-catalysed C−H acetoxylation of benzene

2019 ◽  
Vol 44 (1) ◽  
pp. 55-66
Author(s):  
Nazanin Beyzaie ◽  
Sayyed Faramarz Tayyari ◽  
Mohammad Vakili ◽  
Safar Ali Beyramabadi
Keyword(s):  
Activation Energy ◽  
Quantum Chemical ◽  
Quantum Chemical Study ◽  
Experimental Studies ◽  
Chemical Study ◽  
Rate Determining Step ◽  
High Valent ◽  
Square Complex ◽  
Step Mechanism ◽  
Energy Activation

In this work, the mechanism of the palladium-catalysed acetoxylation of benzene C-H has been studied theoretically in detail. Based on experimental studies, a four-step mechanism for this reaction had been proposed, that is, C−H activation of benzene is the rate-determining step which forms an intermediate ( k1 pathway) which is subsequently oxidized to produce a high-valent Pd intermediate ( k2 pathway). Using quantum chemical calculations, all pathways were investigated, and the activation energy, activation enthalpy and activation Gibbs free energy for all steps were calculated and compared with each other. It was determined that the RDS proceeds through a square complex instead of a T-shaped complex. The activation energy related to the k2 pathway is higher than that of the RDS, and therefore, a new mechanism is proposed.

scholarly journals Metal control of selectivity in acetate-assisted C–H bond activation: an experimental and computational study of heterocyclic, vinylic and phenylic C(sp2)–H bonds at Ir and Rh

2014 ◽  
Vol 5 (6) ◽  
pp. 2340-2346 ◽  
Author(s):  
Kevin J. T. Carr ◽  
David L. Davies ◽  
Stuart A. Macgregor ◽  
Kuldip Singh ◽  
Barbara Villa-Marcos
Keyword(s):  
Bond Activation ◽  
Computational Study ◽  
Metal Catalyst ◽  
Kinetic Control ◽  
Dft Studies ◽  
Thermodynamic Control

Experimental and DFT studies show the selectivity of C–H bond activation at [MCl2Cp*]2 (M = Ir, Rh) species can be controlled by the choice of metal catalyst, reflecting kinetic control at M = Ir and thermodynamic control at M = Rh.

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