Topic
Hydrogen atom abstraction
About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.
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TL;DR: The kinetics of type I reactions with EDTA, dl-alpha-phenylglycine and diethanolamine are all consistent with a mechanism in which the rate-determining step, hydrogen abstraction by the FMN triplet, is followed by rapid reoxidation of reduced FMN by oxygen.
Abstract: 1. When a mixture of FMN and a reducing substrate (e.g. unprotonated amine) is illuminated oxygen is consumed. 2. The rate of oxygen uptake increases as oxygen concentration falls with some substrates (type I reaction), but with other substrates (typically aromatic compounds) the rate falls as the oxygen concentration falls (type II reaction). 3. The kinetics of type I reactions with EDTA, dl-alpha-phenylglycine and diethanolamine are all consistent with a mechanism in which the rate-determining step, hydrogen abstraction by the FMN triplet, is followed by rapid reoxidation of reduced FMN by oxygen. The reaction is faster at low oxygen concentrations because oxygen quenches the triplet. 4. The sensitivity of reaction rates to substituents in dl-alpha-phenylglycine can be described by a Hammett rho value of -0.6. 5. Individual rate constants for quenching and reaction of the FMN triplet with substrate were calculated (2.4x10(8) and 2.1x10(7)m(-1)s(-1) respectively for EDTA) on the assumption that oxygen quenches the triplet in a diffusion-controlled reaction. 6. The pH-dependences of oxygen uptake rates with six natural amino acids as substrates were measured. 7. Photoinactivations of l-glutamate dehydrogenase and d-amino acid oxidase by FMN were demonstrated.
52 citations
TL;DR: In this article, a solution-phase bimolecular reaction was observed directly for the first time using transient infrared absorption spectroscopy, and the observed reaction rate of HCl formation is (5.6 ± 1) × 10 9 M −1 s −1, which is approximately 14±6 times slower than previously reported gas-phase kinetic results.
52 citations
TL;DR: In this paper, the authors derived expressions for the recombination coefficient and the first-order rate constant, enabling these quantities to be calculated on the basis of postulated mechanisms and showed that the experimental activation energies are consistent with estimates using either Hirschfelder's rule or an expression utilizing the experimental desorption temperature.
Abstract: The data on the kinetics of the recombination of hydrogen atoms on various types of surfaces are analyzed in the light of the theory of absolute reaction rates. Expressions are derived for the recombination coefficient and the first‐order rate constant, enabling these quantities to be calculated on the basis of postulated mechanisms. It is shown that the experimental activation energies are consistent with estimates using either Hirschfelder's rule or an expression utilizing the experimental ``desorption temperature.'' For the reaction on dry oxides and dry glass good agreement is found assuming that reaction occurs between a gas‐phase hydrogen atom and an adsorbed hydrogen atom, the adsorption being of the van der Waals type at low temperatures and chemisorption at higher ones. The mechanism of surface poisoning by water vapor is shown to be not due to the necessity for desorbing the water molecule: in the high temperature region it is due to an increase in activation energy, the mechanism being S–OH+H→S–O+H2; in the low temperature region to a decrease in the number of active centers, the reaction being between a gaseous atom and a van der Waals adsorbed hydrogen atom above the water layer.
52 citations
TL;DR: In this article, the rate constants for the reaction of hydroxyl with isobutane with other aliphatic hydrocarbons and with other radical rates have been obtained.
52 citations
TL;DR: In this article, the authors performed ab initio and DFT calculations on model systems to understand the observed selectivity of zeolites and found that hydrogen abstraction from the methyl group (4position) of 2-methyl 2-butene is favored by a small margin.
52 citations