Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

Transition state theory

Abstract: The introduction of the activated complex permits a simple model of the crossing of potential barriers. With this model, the rate constant of any elementary reaction can be calculated, if the structure of the activated complex is known. The general results of transition state theory lead to an understanding of some important predictions of geochemical interest. For example, the effect of ionic strength on rates or the compensation law can be analyzed using transition state theory. The theory can also be applied to transport in condensed media as well as to heterogeneous reactions. Although the potential energy surfaces needed to calculate the rates of geochemical reactions can only be estimated in a rough way, transition state theory provides an important framework, which allows a molecular approach to kinetics. It is this unifying characteristic of the theory that makes it worthwhile for use in geochemical kinetics. (JMT)

Particle size, shape and activity for photocatalysis on titania anatase nanoparticles in aqueous surroundings.

Abstract: TiO2 nanoparticles have been widely utilized in photocatalysis, but the atomic level understanding on their working mechanism falls much short of expectations. In particular, the correlation between the particle structure and the photocatalytic activity is not established yet, although it was observed that the activity is sensitive to the particle size and shape. This work, by investigating a series of TiO2 anatase nanoparticles with different size and shape as the photocatalyst for water oxidation, correlates quantitatively the particle size and shape with the photocatalytic activity of the oxygen evolution reaction (OER). Extensive density functional theory (DFT) calculations combined with the periodic continuum solvation model have been utilized to compute the electronic structure of nanoparticles in aqueous solution and provide the reaction energetics for the key elementary reaction. We demonstrate that the equilibrium shape of nanoparticle is sensitive to its size from 1 to 30 nm, and the sharp cryst...

Reaction mechanisms in aromatic hydrocarbon formation involving the C5H5 cyclopentadienyl moiety

Abstract: The quantum chemical BAC-MP4 and BAC-MP2 methods have been used to investigate the reaction mechanisms leading to polycyclic aromatic hydrocarbon (PAH) ring formation. In particular we have determined the elementary reaction steps in the conversion of two cyclopentadienyl radicals to naphthalene. This reaction mechanism is shown to be an extension of the mechanism occurring in the H atomassisted conversion of fulvene to benzene. The net reaction involves the formation of dihydrofulvalene, which eliminates a hydrogen atom and then rearranges to form naphthalene through a series of ring closures and openings. The importance of forming the -CR(·)-CHR-CR′=CR″- moiety, which can undergo rearrangement to form three-carbon atom ring structures, is illustrated with the C4H7 system. The ability of hydrogen atoms to migrate around the cyclopentadienyl moiety is illustrated both for methyl-cyclopentadiene, C5H5CH3, and dihydrofulvalene, C5H5C5H5, as well as for their radical species, C6H7 and C5H5C5H4. The mobility of hydrogen in the cyclopentadienyl moiety plays an important role both in providing resonance-stabilized radical products and in creating the -CR(·) CHR-CR′=CR″- moiety for ring formation. The results illustrate the radical pathway for converting five-membered rings to aromatic six-membered rings. Furthermore, the results indicate the important catalytic role of H atoms in the aromatic ring formation process.

Gas-Phase Ionic Reactions: Dynamics and Mechanism of Nucleophilic Displacements

Abstract: Nucleophilic displacement reactions (the SN2 reaction) of ions in the gas phase are a prototypical reaction system that allows a study of dynamics, mechanisms, and structure-energy relations. This article reviews aspects of the kinetics (especially the applicability of statistical reaction rate theory), the relation of structure and reactivity, and the effects of small numbers of solvent molecules on the reaction and compares the behavior of the ionic reaction in the gas phase with that in solution.