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.

The Influence of Boryl Substituents on the Formation and Reactivity of Adjacent and Vicinal Free Radical Centers

Abstract: Radicals containing α-boronate substituents were generated by bromine abstraction from 1-bromoalkyldioxaborolanes (boronic esters), by addition to vinyl boronate, and by hydrogen abstraction from alkyldioxaborolanes and observed by EPR spectroscopy. Unsymmetrically substituted α-boronate radicals displayed selective line broadening in their low-temperature spectra from which barriers to internal rotation about •CH2−B(OR‘)OR bonds were found to be 3 ± 1 kcal mol-1. Use of an empirical relationship between barrier height and bond dissociation energy led to BDE[(RO)2BCH2−H] = 98.6 kcal mol-1. Rate constants for hydrogen abstraction from 2,4,4,5,5-pentamethyl-1,3,2-dioxaborolane by tert-butoxyl radicals were determined from competitive EPR and product studies and found to be relatively small, comparable to those of unactivated methyl groups. Hydrogen abstraction from bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methane was found to be extremely difficult. The structures and energetics of α-boronate radical...

DFT+U Investigation of Propene Oxidation over Bismuth Molybdate: Active Sites, Reaction Intermediates, and the Role of Bismuth

Abstract: The mechanism by which propene is selectively oxidized to acrolein over bismuth molybdate has been investigated using the DFT+U variant of density functional theory. In agreement with experiment, the kinetically relevant step is found to be the initial abstraction of hydrogen by lattice oxygen. Several candidate lattice oxygen sites have been examined, the most active of which is found to be a bismuth-perturbed molybdenyl Mo═O oxygen. Hydrogen abstraction generates an allyl radical intermediate, which can diffuse freely across the catalyst surface and ultimately binds to a second molybdenyl oxygen to form an allyl alkoxy intermediate. A second hydrogen is abstracted from this intermediate to produce acrolein. Calculations suggest that only molybdenum centers are reduced during the reaction. However, presence of bismuth in the catalyst is essential for providing the requisite structural and electronic environment at the active site.

Rate coefficients for the reactions of OH radicals with Methylglyoxal and Acetaldehyde

Abstract: Rate coefficients have been measured for the reaction of OH radicals with methylglyoxal from 260 to 333 K using the discharge flow technique and laser-induced fluorescence detection of OH. The rate coefficient was found to be (1.32±0.30) × 10−11 cm3 molecule−1 s−1 at room temperature, with a distinct negative temperature dependence (E/R of −830 ± 300 K). These are the first measurements of the temperature dependence of this reaction. The reaction of OH with acetaldehyde was also investigated, and a rate coefficient of (1.45 ± 0.25) × 10−11 cm3 molecule−1 s−1 was found at room temperature, in accord with recent studies. Experiments in which O2 was added to the flow showed regeneration of OH following the reaction of CH3CO radicals with O2. However, chamber experiments at atmospheric pressure using FTIR detection showed no evidence for OH production. FTIR experiments have also been used to investigate the chemistry of the CH3COCO radical formed by hydrogen abstraction from methylglyoxal. © 1995 John Wiley & Sons, Inc.

Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

Abstract: Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.