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.

LOW-TEMPERATURE ION TRAP STUDIES OF N+(3 Pja ) + H2(j) → NH+ + H

Abstract: Using a low-temperature 22-pole ion trap apparatus, detailed measurements for the title reaction have been performed between 10 K and 100 K in order to get some state specific information about this fundamental hydrogen abstraction process. The relative population of the two lowest H2 rotational states, j = 0 and 1, has been varied systematically. NH+ formation is nearly thermo-neutral; however, to date, the energetics are not known with the accuracy required for low-temperature astrochemistry. Additional complications arise from the fact that, so far, there is no reliable theoretical or experimental information on how the reactivity of the N+ ion depends on its fine-structure (FS) state 3 Pja . Since in the present trapping experiment, thermalization of the initially hot FS population competes with hydrogen abstraction, the evaluation of the decay of N+ ions over long storage times and at various He and H2 gas densities provides information on these processes. First assuming strict adiabatic behavior, a set of state specific rate coefficients is derived from the measured thermal rate coefficients. In addition, by recording the disappearance of the N+ ions over several orders of magnitude, information on nonadiabatic transitions is extracted including FS-changing collisions.

Electron Gain and Electron Loss Radicals Stabilized on the Purine and Pyrimidine of a Cocrystal Exhibiting Base-Base Interstacking: ESR-ENDOR of X-Irradiated Adenosine:5-Bromouracil

Abstract: KAR L., AND BERNHARD, W. A. Electron Gain and Electron Loss Radicals Stabilized on the Purine and Pyrimidine of a Cocrystal Exhibiting Base-Base Interstacking: ESR-ENDOR of XIrradiated Adenosine:5-Bromouracil. Radiat. Res. 93, 232-253 (1982). The predominant free radicals trapped in cocrystals of adenosine:5-bromouracil X-irradiated at 12?K were identified by ESR-ENDOR spectroscopy and the radical reactions were followed upon annealing to 480?K. The dominant electron abstraction and electron addition products stabilized on the bases at 12?K are observed to be the bromouracil 7r-cation and the adenine rcation and 7r-anion. The formation of an anion on bromouracil is inferred from the presence of a radical formed by deuterium addition to C6 of bromouracil at higher temperatures. Above 40?K the bromouracil 7r-cation appears to decay by recombination and is reduced to undetectable levels at - 170?K. Both adenine ir-ions are also observed to decay within the same temperature range. Above 200?K hydrogen adducts are stabilized on the bases. Experiments using partially deuterated cocrystals indicate that the H-adducts are formed via both hydrogen addition and protonation of the respective anions. Two hydrogen abstraction radicals stabilized on the sugar residue are detectable at temperatures above 200?K, but these may be present at much lower temperatures. The results presented here question the generally accepted hypothesis that, in the presence of purine:pyrimidine stacking interactions, holes are predominantly transferred to the purines while electrons are predominantly transferred to the pyrimidines.

Aminyle, 7. Über Diarylaminyle

Abstract: Die Diarylaminyle 1b–22b und die heterocyclischen Aminyle 23b und 26b wurden durch thermische oder photolytische Dissoziation der entsprechenden Hydrazine oder durch Wasserstoffabstraktion aus den entsprechenden Aminen erzeugt und wie die entsprechenden Nitroxide 1c–26c ESR-spektroskopisch untersucht. Der Einflus der Substitution auf die Eigenschaften des Diphenylaminyl-Systems und auf das Dissoziationsverhalten der Tetraarylhydrazine wird diskutiert. Aminyls, 7. Diarylaminyls The diarylaminyls 1b–22b and the heterocyclic aminyls 23b and 26b were generated by thermal or photolytic dissociation of the corresponding hydrazines or by hydrogen abstraction of the corresponding amines and studied by e.s.r. as were the corresponding nitroxides 1c–26c. The influence of substitution on the properties of the diphenylaminyl system and on the dissociation of the tetraarylhydrazines is discussed.

Dynamics of the O(1D)+CH4 reaction: Atomic hydrogen channel vs molecular hydrogen channel

Abstract: The O(1D)+CH4 reaction has been investigated using a new universal crossed molecular beam apparatus. Both the atomic hydrogen channel (CH3O/CH2OH+H) and the molecular hydrogen channel (H2CO/HCOH+H2) have been experimentally observed in this reaction. The experimental results suggest that the main atomic hydrogen channel in the O(1D)+CH4 reaction should be CH2OH (hydroxymethyl)+H, while the CH3O (methoxy)+H channel is at most a minor process. From the product angular distribution measurements, it is clear that the radical products (CH2OH and/or CH3O) in the hydrogen atom channel are only slightly backward scattered relative to the O(1D) beam direction, indicating that this product channel mainly goes through a long-lived intermediate pathway. The slightly backward scattered products are possibly due to other reaction mechanisms. For the molecular hydrogen channel, the product angular distribution obtained from simulation also seems isotropic, implying that this channel also likely goes through a long-lived...

Theoretical Prediction of a Perepoxide Intermediate for the Reaction of Singlet Oxygen with trans-Cyclooctene Contrasts with the Two-Step No-Intermediate Ene Reaction for Acyclic Alkenes

Abstract: B3LYP/6-31G* and CASMP2 calculations have been employed to study the ene reaction of singlet oxygen with trans-cyclooctene. These methods predict that the reaction involves a perepoxide intermediate, whereas alkenes such as tetramethylethylene are predicted by the same methods to occur by a two-step no-intermediate mechanism, with no perepoxide intermediate. The change in mechanism arises because the trans-cyclooctene imposes a substantial strain in the transition state for hydrogen abstraction. The perepoxide is formed through a polarized diradical intermediate that can lead to the observation of alkene isomerization. The polarized diradical also becomes a minimum because of the barrier to abstraction.