scispace - formally typeset
Search or ask a question
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
More filters
Journal ArticleDOI
TL;DR: The mechanism of 1,2-addition reactions of water, methanol, and trifluoromethanol to Si=Si, Si=C, and C=C bonds has been investigated by ab initio quantum chemical methods and reaction diagrams and proposed mechanisms explain the experimentally found regioselectivity and diastereoselectivities well.
Abstract: The mechanism of 1,2-addition reactions of water, methanol, and trifluoromethanol to Si=Si, Si=C, and C=C bonds has been investigated by ab initio quantum chemical methods. Geometries and relative energies of the stationary points and all the transition states were determined using the MP2/6-311++G(d,p), B3LYP/6-311++G(d,p), and CBS-Q levels of theory. The investigated reactions can be characterized by two main thermodynamical profiles. The type in which the reagent molecule attacks a carbon atom is moderately exothermic, with a high activation barrier. The second type, in which water or alcohol attacks a silicon, is strongly exothermic, with a small activation energy. At the early stage of all the reactions, a weakly bonded initial complex is found which determines the further mechanism of the reaction. On the basis of the HOMO, LUMO, and Laplacian of electron distribution of disilene and silene, several mechanisms have been assumed, depending on the substrate (disilene, substituted disilene, silene, or ethene) and the reagent (water, methanol, or trifluoromethanol). The reaction diagrams and proposed mechanisms explain the experimentally found regioselectivity and diastereoselectivity well.

45 citations

Journal ArticleDOI
TL;DR: An automated search method, the artificial force induced reaction (AFIR) method, is used and 91 syn- and 73 anti-TSs are found for the diastereoselective C-C bond formation step of the aqueous lanthanide-catalyzed Mukaiyama aldol reaction.
Abstract: To predict the stereoselectivity of large and flexible reaction systems, structural sampling of many transition states (TSs) is required. We used an automated search method, the artificial force induced reaction (AFIR) method, for TS sampling and found 91 syn- and 73 anti-TSs for the diastereoselective C–C bond formation step of the aqueous lanthanide-catalyzed Mukaiyama aldol reaction. Among them 11 syn- and six anti-TSs are found to contribute significantly to the diastereomeric ratio at room temperature.

45 citations

Journal ArticleDOI
TL;DR: The tautomerism of furoxan (1,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functionals as well as single-reference and multi-reference ab initio methods.
Abstract: The tautomerism of furoxan (1,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functionals as well as single-reference and multi-reference ab initio methods. The ring-opening process to 1,2-dinitrosoethylene is the most critical step of the reaction and cannot be treated reliably by low-level computations. The existence of cis-cis-trans-1,2-dinitrosoethylene as a stable intermediate is advocated by perturbational methods, but high-level coupled-cluster calculations identify this as an artifact. In contrast to the analogous reaction in benzofuroxans, cis-cis-cis-1,2-dinitrosoethylene was found to be a transition state rather than a local minimum. Model potentials were used to explain the occurrence and the disappearing of transition states and local minima relative to the reaction of benzofuroxan. Low-lying triplet states that can be accessed due to spin-orbit coupling were investigated as taking part in alternative routes to a proposed singlet pathway. Barriers for rotations of the nitroso groups on the S(0) and T(1) surfaces are reported.

45 citations

Journal ArticleDOI
TL;DR: A comparative density functional theory study of proline 1, beta-proline 5b, and 11 in the latter reaction revealed the origin of the improved enantioselectivity of 11 over 5b.
Abstract: 7-Azabicyclo[2.2.1]heptane-2-carboxylic acid 11 was prepared in enantiopure form, and its catalytic potential in the direct aldol reaction between acetone and 4-nitrobenzaldehyde was assessed. The bicyclic system was found to be more selective than its monocyclic analogue β-proline 5b. A comparative density functional theory study of proline 1, β-proline 5b, and 11 in the latter reaction revealed the origin of the improved enantioselectivity of 11 over 5b. The geometry of the carboxylic acid group in the transition states, which depended critically on pyrrolidine ring conformation, was found to play a key role.

45 citations

Journal ArticleDOI
TL;DR: The reaction rate enhancement in the reaction of allylboronate with benzaldehyde in the presence of AlCl3 has been studied theoretically and an analysis of electron populations and orbitals taking part in bond formation indicates that the AlCl2 molecule attached to the boronate oxygen atom strengthens the electrophilicity of theboron center, while it weakens the nucleophilicityof the C(gamma)-C(beta) bond.
Abstract: The reaction rate enhancement in the reaction of allylboronate with benzaldehyde in the presence of AlCl3 has been studied theoretically. B3LYP calculations find a relatively high activation barrier for the reaction of pinacol allylboronate with benzaldehyde in the absence of the Lewis acid. The reaction paths that go through the transition states coordinated by an AlCl3 molecule at one of the two oxygen atoms in the boronate give significantly lower values of activation energy. An analysis of electron populations and orbitals taking part in bond formation indicates that the AlCl3 molecule attached to the boronate oxygen atom strengthens the electrophilicity of the boron center, while it weakens the nucleophilicity of the Cγ−Cβ bond. The result supports the electrophilic boronate activation mechanism proposed by Rauniyar and Hall on the basis of experiments and kinetic studies. In contrast, the reaction path in which AlCl3 is coordinated to the carbonyl oxygen of benzaldehyde shows a higher activation bar...

45 citations


Network Information
Related Topics (5)
Ab initio
57.3K papers, 1.6M citations
93% related
Alkyl
223.5K papers, 2M citations
87% related
Catalysis
400.9K papers, 8.7M citations
86% related
Palladium
64.7K papers, 1.3M citations
86% related
Aryl
95.6K papers, 1.3M citations
86% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202364
2022136
2021148
2020155
2019145
2018147