Theoretical Study for the [2+2] Cycloaddition Reaction Mechanism of Ketenes and their Derivatives

2019 ◽  
Vol 35 (5) ◽  
pp. 1550-1556 ◽  
Author(s):  
Haydar A ◽  
Mohammad- Salim ◽  
Hassan H Abdallah
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Theoretical Study ◽  
Cycloaddition Reaction ◽  
Stationary Points ◽  
Concerted Mechanism ◽  
Fukui Functions ◽  
Carbon Centers ◽  
Local Properties ◽  
Global And Local

This study presents the intramolecular [2+2] cycloaddition reaction of ketenes to form cyclobutanones using B3LYP-D3/6-311++G(d,p) level of approximation. The concerted mechanism path was studied in detail. The structures of all intermediates and transition states were located using same level of theory. The influences of the substituents (-H, -CH3, -NH2, -F, -OH and –CN) were also discussed. The analysis of stationary points and the energetic parameters indicates that the substituted ketene with –CN group has the highest activation energy; however, ketene with –NH2 group has the lowest one. Conversely, in-tramolecular [2+2] cycloaddition records the highest degree of asynchronicity with –NH2 group and lowest with –CN group. The calculated thermodynamic parameters at room temperature have been listed and analyzed. The global and local properties of reactants involved in the intramolecular [2+2] cycloaddition reactions and the Fukui functions for an electrophilicity and local electrophilicity were also elucidated for carbon centers of each reactant.

Theoretical study on the reaction of atomic oxygen with unsymmetrical dimethylhydrazine

2013 ◽  
Vol 91 (5) ◽  
pp. 315-319 ◽  
Author(s):  
Jinmiao Wen ◽  
Yafang Tian ◽  
Hongqing He ◽  
Li Wang
Keyword(s):  
Rate Constants ◽  
Room Temperature ◽  
Theoretical Study ◽  
Single Point ◽  
State Theory ◽  
Stationary Points ◽  
Energy Profiles ◽  
Unsymmetrical Dimethylhydrazine ◽  
Increasing Temperature ◽  
Dynamics Method

A dual-level direct dynamics method is employed to study the reaction mechanism of (CH3)2NNH2 (unsymmetrical dimethylhydrazine) with the oxygen (O) atom. The geometries and frequencies of all the stationary points are optimized at the MPW1K/6-311G (d, p) level, and the energy profiles are further refined by the interpolated single-point energies (ISPE) method at the BMC-CCSD level of theory. The rate constants of the O atom with (CH3)2NNH2 are evaluated over a wide temperature range of 200–2000 K by using the canonical variational transition-state theory (CVT) with the small curvature tunneling correction (SCT). The agreement between the theoretical and experimental rate constants is good around room temperature. The channels of H abstraction from the -NH2 position favor temperatures below 1200 K. With increasing temperature, contributions from other channels should be taken into account. The reactivity of N2H4, CH3NHNH2, and (CH3)2NNH2 toward atomic O is compared to explore the methylation effect.

scholarly journals Theoretical study on the mechanism of the cycloaddition reaction between ketenimine and hydrogen cyanide

2016 ◽  
Vol 81 (2) ◽  
pp. 187-195 ◽  
Author(s):  
Wenxing He ◽  
Xiaojun Tan ◽  
Nana Wang ◽  
Hong Zhang
Keyword(s):  
Potential Energy Surfaces ◽  
Theoretical Study ◽  
Cycloaddition Reaction ◽  
Stationary Points ◽  
Interstellar Space ◽  
Transfer Processes ◽  
Energy Surfaces ◽  
Pericyclic Reaction ◽  
Reaction Processes ◽  
Imidazole Compounds

The cycloaddition reaction mechanism between interstellar molecules ketenimine and HCN has been investigated employing the second-order M?ller-Plesset perturbation theory (MP2) method in order to better understand the reactivity of nitrogenous cumulene ketenimine with carbon-nitrogen triple bond compound HCN. Geometry optimizations and vibrational analyses have been performed for the stationary points on the potential energy surfaces of the system. The calculated results show that it can be produced the five-membered cyclic carbene intermediates through pericyclic reaction processes between ketenimine and HCN. Through the following H-transfer processes, carbene intermediates can isomerize to the pyrazole and imidazole compounds, respectively. The present study is helpful to understand the formation of prebiotic species in interstellar space.

scholarly journals Theoretical Study of the [4+2] Cycloaddition Reaction of Trifluoroethylene with Five-membered Chalcogens Heterocyclic Compounds

2019 ◽  
Vol 7 (2) ◽  
pp. 69-77
Author(s):  
Haydar A. Mohammad-Salim ◽  
Hassan H. Abdallah
Keyword(s):  
Gas Phase ◽  
Density Functional ◽  
Theoretical Study ◽  
Cycloaddition Reaction ◽  
Branching Ratio ◽  
Basis Set ◽  
Stationary Points ◽  
Functional Theory ◽  
Highest Occupied Molecular Orbital ◽  
Synthesis Reactions

[4+2] cycloaddition reaction has enormous significant in organic chemistry synthesis reactions and yet remains unexplored for the synthesis of fluorine-containing compounds. A density functional theory study of the stereo- and regioselectivity of the [4+2] cycloaddition reaction of trifluoroethylene with furan, thiophene, and selenophene was carried out in the gas phase. The B3LYP functional is used throughout in combination with 6-31G(d) basis set. The analysis of stationary points and the energetic parameters indicates that the reaction mechanism is concerted and confirms that the exo-adducts are thermodynamically and kinetically more favored than endo-adducts. The calculated branching ratio indicates that the exo-adducts have the higher percent yield than endoadducts and the yield of endo-adducts is increased only slightly on proceeding from furan, through thiophene, and onto selenophene. The analysis of the frontier molecular highest occupied molecular orbital (MO) and lowest unoccupied MO orbitals indicates that the exo-adducts are more stable due to their higher energy gab. The reaction energies were compared to the MP2/6-31G(d) and CCSD(T)/6-31G(d) calculations.

Cope Rearrangement in Bicyclo[5.1.0]octa-2,5-diene and its Mono- and Di-Hetero Analogues: A DFT Study

2017 ◽  
Vol 70 (6) ◽  
pp. 683
Author(s):  
Priya Yadav ◽  
Shilpa Yadav ◽  
Asha Gurjar ◽  
Raj K. Bansal
Keyword(s):  
Activation Energy ◽  
Gas Phase ◽  
Density Functional ◽  
Room Temperature ◽  
Transition States ◽  
Cope Rearrangement ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Free Activation Energy ◽  
Cope Rearrangements

The Cope rearrangements of bicyclo[5.1.0]octa-2,5-diene and its 4-hetero-(aza/oxa/phospha) and 4,8-dihetero analogues were investigated using density functional theory at the B3LYP/6–31+G* level in gas phase. The rearrangements of bicyclo[5.1.0]octa-2,5-diene and its symmetrical 4,8-dihetero analogues followed a concerted mechanism involving synchronous transition states. In other cases, although a concerted mechanism was observed, asynchronous transition states were involved. In the case of bicyclo[5.1.0]octa-2,5-diene, a degenerate Cope rearrangement was expected to occur at room temperature (25°C) due to a low free activation energy (ΔG‡ = 14.46 kcal mol–1). However, under similar conditions, the rearrangement of 4,8-dioxabicyclo[5.1.0]octa-2,5-diene was much slower (ΔG‡ = 23.85 kcal mol–1) and the 4,8-diaza- and diphospha analogues did not undergo Cope rearrangement. The Cope rearrangements of 4-phospha-, 8-aza-, 8-aza-4-oxa-, 8-aza-4-phospha-, and 8-oxa-4-phospha-bicyclo[5.1.0]octa-2,5-dienes were exergonic and were expected to occur spontaneously to form the corresponding products. In contrast, rearrangement of 8-oxabicyclo[5.1.0]octa-2,5-diene, though exergonic, was accompanied by a decrease in entropy, due to which Cope rearrangement would occur much more slowly and a mixture of both valence isomers would be formed. The Cope rearrangements of 4-aza-, 4-oxa-, 4-aza-8-oxa-, 8-phospha-, 4-aza-8-phospha-, 4-oxa-8-phospha-, and 4,8-diphospha-bicyclo[5.1.0]octa-2,5-dienes were endergonic; consequently either no Cope rearrangement would take place or it would occur sluggishly.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

scholarly journals Synthesis and electrical characterization of Ca2Nd4Ti6O20 ceramics

2016 ◽  
Vol 34 (1) ◽  
pp. 164-168
Author(s):  
Raz Muhammad ◽  
Muhammad Uzair ◽  
M. Javid Iqbal ◽  
M. Jawad Khan ◽  
Yaseen Iqbal ◽  
...  
Keyword(s):  
Activation Energy ◽  
Dielectric Constant ◽  
Room Temperature ◽  
Sol Gel ◽  
Electrical Characterization ◽  
Sintered Sample ◽  
First Time ◽  
Alkoxide Precursors ◽  
Room Temperature Dielectric Constant

AbstractCa2Nd4Ti6O20, a layered perov skite structured material was synthesized via a chemical (citrate sol-gel) route for the first time using nitrates and alkoxide precursors. Phase analysis of a sample sintered at 1625 °C revealed the formation of an orthorhombic (Pbn21) symmetry. The microstructure of the sample after sintering comprised rod-shaped grains of a size of 1.5 to 6.5µm. The room temperature dielectric constant of the sintered sample was 38 at 100 kHz. The remnant polarization (Pr) and the coercive field (Ec) were about 400 μC/cm2 and 8.4 kV/cm, respectively. Impedance spectroscopy revealed that the capacitance (13.7 pF) and activation energy (1.39 eV) of the grain boundary was greater than the capacitance (5.7 pF) and activation energy (1.13 eV) of the grain.

Texture Gradient in ECAP Silver Measured by Synchrotron Radiation

2005 ◽  
Vol 495-497 ◽  
pp. 821-826 ◽  
Author(s):  
Werner Skrotzki ◽  
N. Scheerbaum ◽  
C.G. Oertel ◽  
Heinz Günter Brokmeier ◽  
Satyam Suwas ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Extrusion Direction ◽  
High Energy ◽  
Texture Gradient ◽  
Fcc Metals ◽  
Local Texture ◽  
Angular Pressing ◽  
Global And Local

Silver of 3N purity was deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. The global and local texture were investigated by neutron diffraction and high-energy synchrotron radiation, respectively. The texture is characterized by typical simple shear components of fcc metals which differently deviate from their ideal positions. Local texture measurements reveal that the intensity and inclination of the texture components with respect to the extrusion direction depend on the distance from the top of the extruded bar and change from pass to pass. Reasons for the texture gradient are discussed. The texture of silver is compared with that of copper having a higher stacking fault energy.

About the Electrical Activation of 1×1020 cm-3 Ion Implanted Al in 4H-SiC at Annealing Temperatures in the Range 1500 - 1950°C

2018 ◽  
Vol 924 ◽  
pp. 333-338 ◽  
Author(s):  
Roberta Nipoti ◽  
Alberto Carnera ◽  
Giovanni Alfieri ◽  
Lukas Kranz
Keyword(s):  
Activation Energy ◽  
Sheet Resistance ◽  
Annealing Time ◽  
Thermal Activation ◽  
Room Temperature ◽  
Annealing Temperature ◽  
Thermal Activation Energy ◽  
Electrical Activation ◽  
Temperature Range ◽  
Annealing Temperatures

The electrical activation of 1×1020cm-3implanted Al in 4H-SiC has been studied in the temperature range 1500 - 1950 °C by the analysis of the sheet resistance of the Al implanted layers, as measured at room temperature. The minimum annealing time for reaching stationary electrical at fixed annealing temperature has been found. The samples with stationary electrical activation have been used to estimate the thermal activation energy for the electrical activation of the implanted Al.

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