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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.


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TL;DR: This work uses microkinetic modeling and periodic DFT calculations to predict a quantitative relation between the ammonia heat of adsorption and the rate of propene methylation from first principles, and proposes that this is the first step toward descriptor-based design of solid acid catalysts.
Abstract: Recent work has reported the discovery of metal surface catalysts by employing a descriptor-based approach, establishing a correlation between a few well-defined properties of a material and its catalytic activity. This theoretical work aims for a similar approach in solid acid catalysis, focusing on the reaction between propene and methanol catalyzed by Bronsted acidic zeotype catalysts. Experimentally, the ammonia heat of adsorption is often used as a measure of the strength of acid sites. Using periodic DFT calculations, we show that this measure can be used to establish scaling relations for the energy of intermediates and transition states, effectively describing the reactivity of the acid site. This allows us to use microkinetic modeling to predict a quantitative relation between the ammonia heat of adsorption and the rate of propene methylation from first principles. We propose that this is the first step toward descriptor-based design of solid acid catalysts.

88 citations

Journal ArticleDOI
TL;DR: In this article, a cross molecular beam technique was used to study the reaction between ground state carbon atoms, C(3Pj), and acetylene, C2H2(X 1Σg+), at three collision energies between 8.8 and 45.0 kJ/mol−1 using the crossed molecular beams technique.
Abstract: The reaction between ground state carbon atoms, C(3Pj), and acetylene, C2H2(X 1Σg+), is studied at three collision energies between 8.8 and 45.0 kJ mol−1 using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of C3H at m/e=37 are recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions decreasingly forward scattered with respect to the carbon beam as the collision energy rises from 8.8 to 28.0 kJ mol−1, and isotropic at 45.0 kJ mol−1. Reaction dynamics inferred from the experimental data and ab initio calculations on the triplet C3H2 and doublet C3H potential energy surface suggest two microchannels initiated by addition of C(3Pj) either to one acetylenic carbon to form s-trans propenediylidene or to two carbon atoms to yield triplet cyclopropenylidene via loose transition states located at their centrifugal barriers. Propenediylidene rotates around its B/C axis and undergoes [2,3]-H-migration to prop...

87 citations

Journal ArticleDOI
TL;DR: The dependence of the rate constant on solvent polarity is an important mechanistic criterion which should always be used in conjunction with other diagnostics tool as discussed by the authors. But the violation of stereo-specificity becomes greater with increasing solvent specificity.
Abstract: The dependence of the rate constant on solvent polarity is an important mechanistic criterion which should always be used in conjunction with other diagnostics tool. The slow step of 2 + 2 cycloadditions of tetracyanoethylene (TCNE) with enol ethers [1], thioenol ethers [2] and trans-fixed 1,3-dienes [3] is the formation of a zwitterionic intermediate. The log k2 values are linear functions of the Dimroth-Reichardt parameter ET. The rate accelerations of TCNE cycloadditions in going from cyclohexane to acetonitrile amount to 29,000 for anethole, 10,800 for 1-ethoxyisobutene, 2,600 for butyl vinyl ether, 17,000 for ethyl 1-propenyl sulfide and 54,000 for verbenene. The violation of stereo-specificity becomes greater with increasing solvent polarity. In contrast, the additions of TCNE to anthracene [4] and related Diels-Alder reactions show only a minute solvent dependence. The same is true for 1,3-dipolar cycloadditions of diazoalkanes [5], phenyl azide [6], C-phenyl-n-methylnitrone and azomethine imines to various dipolarophiles. These concerted cycloadditions are characterized by early transition states, i.e., there is hardly any change of solvation energy during the activation process. A dichotomy of reaction paths was found for diazocarbonyl compounds and enamines. Whereas dialkylaminocyclohexenes produce cycloadducts, the corresponding enamines containing the cyclopentene ring undergo azo coupling furnishes enamino-hydrazones via a zwitterionic intermediate. The contrasting dependence of rate on solvent polarity supports different mechanism [7]. Dimethylketene combines with N-isobutenylprrolidine to give a 3-pyrrolidinocyclobutanone as 1:1 adduct and a δ-methylene-δ-lactone as 2:1 adduct. The dependence of the product ratio on the concentration of dimethylketene allows to disent angle a concerted pathway and a reaction via a zwitterionic intermediate which can be intercepted by a second molecule of dimethylketene (see formula Scheme) [8]. The different solvent dependencies of the two reaction branches confirm the mechanistic divergence.

87 citations

Journal ArticleDOI
TL;DR: In this paper, the reaction mechanism for Cu[9]aneN3Cl2-catalyzed hydrolysis of ethyl 4-nitrophenyl phosphate was probed using kinetic isotope effects and isotope exchange experiments.
Abstract: The reaction mechanism for Cu[9]aneN3Cl2-catalyzed hydrolysis of ethyl 4-nitrophenyl phosphate was probed using kinetic isotope effects and isotope exchange experiments. The solvent deuterium isotope effect (Dk = 1.14), combined with the absence of 18O incorporation into 4-nitrophenol, suggests that hydrolysis proceeds through intramolecular attack of the metal-coordinated hydroxide at the phosphorus center. The secondary 15N isotope effect (15k = 1.0013 ± 0.0002) implies that loss of the leaving group occurs at the rate-limiting step with approximately 50% bond cleavage in the transition state. This study is one of the first applications of the secondary 15N isotope effect to simple metal-promoted hydrolysis reactions, and the result is consistent with concerted bond formation and cleavage. A mechanism consistent with the isotope studies is presented.

87 citations

Journal ArticleDOI
TL;DR: In this article, a series of Car-Parrinello simulations were performed to investigate the dissociation of H 2 O in water and an intramolecular O-H bond length was chosen as the reaction coordinate and its value was increased in increments of 0.1 A.

87 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202364
2022136
2021148
2020155
2019145
2018147