Topic
Transition state
About: Transition state is a research topic. Over the lifetime, 4978 publications have been published within this topic receiving 117965 citations. The topic is also known as: transition state of elementary reaction.
Papers published on a yearly basis
Papers
More filters
••
TL;DR: The mechanism of the oxygen insertion by dioxiranes into alkane C−H bonds has been investigated theoretically in this paper, where Substituent effects, stereoselectivity, and the possibility of the formation of radical pairs are discussed.
Abstract: The mechanism of the oxygen insertion by dioxiranes into alkane C−H bonds has been investigated theoretically. Becke3LYP hybrid DFT calculations with the 6-31G* basis set on the reactions of dioxirane and cyanodioxirane with methane and on the reactions of cyanodioxirane with ethane, propane, and isobutane predict that the reactions are concerted with highly asynchronous transition states. The transition states have considerable diradical character, but are polarized as well. Substituent effects, stereoselectivity, and the possibility of the formation of radical pairs are discussed.
45 citations
••
TL;DR: In this article, the authors used the density functional theory code DMol3 to investigate important pathways in the methanol-to-gasoline conversion process over zeolite catalysts.
Abstract: First-principles calculations using the density functional theory code DMol3 were performed to investigate important pathways in the methanol-to-gasoline conversion process over zeolite catalysts. Reaction paths and energy barriers involving the CO bond cleavage and the first CC bond formation were explored using all-electron periodic supercell calculations and newly implemented algorithms for the optimization of intermediates and transition states. The simulations indicate that the formation of surface ylide involves prohibitively high barriers, whereas surface methoxyl species can easily react with methanol to form ethanol. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
45 citations
••
TL;DR: High-pressure limit rate constants have been calculated for all the reaction channels by conventional transition state theory with asymmetric Eckart tunneling corrections and 1-D hindered rotor approximations in the temperature range 500-2000 K.
Abstract: This work presents an abinitio and chemical kinetic study of the reaction mechanisms of hydrogen atom abstraction by the HȮ2 radical on five ketones: dimethyl, ethyl methyl, n-propyl methyl, iso-propyl methyl, and iso-butyl methyl ketones. The Moller–Plesset method using the 6-311G(d,p) basis set has been used in the geometry optimization and the frequency calculation for all the species involved in the reactions, as well as the hindrance potential description for reactants and transition states. Intrinsic reaction coordinate calculations were carried out to validate all the connections between transition states and local minima. Energies are reported at the CCSD(T)/cc-pVTZ//MP2/6-311G(d,p) level of theory. The CCSD(T)/cc-pVXZ method (X = D, T, Q) was used for the reaction mechanism of dimethyl ketone + HȮ2 radical in order to benchmark the computationally less expensive method of CCSD(T)/cc-pVTZ//MP2/6-311G(d,p). High-pressure limit rate constants have been calculated for all the reaction channels by con...
45 citations
••
TL;DR: In this paper, Quadratic hypersurfaces were fitted in the neighborhood of the most important points of the potential energy hypersurface and vibrational analysis were performed thereupon, to obtain an idea of the importance of tunneling of H atoms through the reaction barrier, and this effect was shown to be non-negligible.
Abstract: Five hydrogen abstraction reactions, CH4 + R → CH3 + HR have been studied usingab initio SCF and CI methods. R was successively chosen as H, CH3, NH2, OH and F. Geometries were fully optimized at SCF level and energies were computed at CI level for products, reactants and transition states. Quadratic hypersurfaces were fitted in the neighborhood of the most important points of the potential energy hypersurfaces and vibrational analysis were performed thereupon. Wigner's and Christov's approximations were used to obtain an idea of the importance of tunneling of H atoms through the reaction barrier, and this effect was shown to be non-negligible. Finally, rate constant calculation were carried out at different temperatures.
45 citations
••
TL;DR: The substituent effect of different p-substituted triphenylsilyl chlorides on silylation-based kinetic resolutions was explored, and linear free-energy relationships were found correlating both selectivity factors and initial rates to the σ(para) Hammett parameters.
Abstract: The substituent effect of different p-substituted triphenylsilyl chlorides on silylation-based kinetic resolutions was explored. Electron-donating groups slow down the reaction rate and improve the selectivity, while electron-withdrawing groups increase the reaction rate and decrease the selectivity. Linear free-energy relationships were found correlating both selectivity factors and initial rates to the σpara Hammett parameters. A weak correlation of selectivity factors to Charton values was also observed when just alkyl substituents were employed but was nonexistent when substituents with more electronic effects were incorporated. The rate data suggest that a significant redistribution of charge occurs in the transition state, with an overall decrease in positive charge. The linear free-energy relationship derived from selectivity factors is best understood by the Hammond postulate. Early and late transition states describe the amount of substrate participation in the transition state and therefore the ...
45 citations