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.

Etch-pit initiation by dissolved oxygen on terraces of H-Si(111)

Abstract: Dissolved oxygen in 40% aqueous ammonium fluoride solution initiates the formation of etch pits in the terraces of the otherwise ideal H-Si(111) surface. The etch pits are observed byex situ scanning tunneling microscopy in an argon atmosphere following emersion from the aqueous fluoride solution. Removal of O2 from the fluoride solution by sparging with argon substantially reduces the initiation of etch pits. We propose the following mechanism of etch-pit initiation. Oxygen molecules are reduced to superoxide anion radicals at the negative open-circuit potential of the silicon surface. A small fraction (less than 0.4%) of these superoxide anions abstract hydrogen atoms from the H-Si(111) terraces to form silicon radicals (dangling bonds), which are then susceptible to etching in neutral to basic aqueous solutions. Hydrogen atom abstraction by aqueous superoxide anion radical also explains the known enhancement by water of oxide growth on hydrogen-terminated silicon surfaces.

Extent of charge transfer in the photoreduction of phenyl ketones by alkylbenzenes.

Abstract: Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs), acetophenones (APs), and ..cap alpha..,..cap alpha..,..cap alpha..-trifluoroacetophenones (TFAs) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements. The relative amounts of primary and tertiary radicals formed by reaction of the same ketones with p-cymene have also been measured. For all three types of ketones, rate constants correlate well with triplet ketone reduction potentials. The magnitude of the kinetic isotope effects observed with toluene-d/sub 8/ and p-xylene-d/sub 10/ diminishes as the ketones become easier to reduce. All of the ketone triplets react with alkylbenzenes primarily by a charge-transfer mechanism, with the rate-determining step changing from complexation to hydrogen transfer as the ketones become harder to reduce. The least reactive AP triplets probably react significantly via simple hydrogen atom abstraction as well. Those ketones with n,..pi..* lowest triplets (all BPs and some APs) react with p-cymene to give primary/tertiary radical ratios that vary no more than a factor of 2 from the 0.40 value displayed by tert-butoxy radicals; those with ..pi..,..pi..* lowest triplets (TFAs and some APs) give ratios that favor primary radicals and that vary by an order of magnitude withmore » the triplet ketone reduction potential. The variation in cymene product ratios reflects different orientations for attack on cymene by n,..pi..* and ..pi..,..pi..* triplets and differing degrees of partial electron transfer within the exciplexes, which are not tight radical ion pairs.« less

Picolinyl esters as derivatives for the structural determination of long chain branched and unsaturated fatty acids

Abstract: 3-Picolinyl esters were prepared from n-, iso-, anteiso- and unsaturated long chain fatty acids and were examined by gas chromatography and mass spectrometry The spectra contained ions which were diagnostic of the position of both the methyl branching and the double bond, and could be rationalized by assuming hydrogen abstraction from the chain by the nitrogen of the pyridine ring and cleavage at the resulting radical site The derivatives were easy to prepare and gave more informative spectra than the previously used pyrrolidides