FREE RADICALS BY MASS SPECTROMETRY: XII. PRIMARY STEPS IN THE MERCURY PHOTOSENSITIZED DECOMPOSITIONS OF ACETONE AND ACETALDEHYDE

1957 ◽  
Vol 35 (4) ◽  
pp. 305-314 ◽  
Author(s):  
F. P. Lossing
Keyword(s):  
Mass Spectrometry ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Mercury Atom ◽  
Secondary Reaction ◽  
Secondary Reactions ◽  
Tracer Experiments

The primary step in the mercury (Hg3P1) photosensitized decomposition of acetone at 55 °C. results in the formation of methyl and acetyl radicals. At least 25% of the acetyl radicals are sufficiently long-lived to suffer collision with a second excited mercury atom, the products being ketene and a hydrogen atom. The primary step in the decomposition of acetaldehyde is at least 95% to form methyl and formyl radicals. The methane found was shown by tracer experiments to be the product of a secondary reaction, probably that between methyl and formyl radicals. Other secondary reactions are discussed.

FREE RADICALS BY MASS SPECTROMETRY: XI. THE MERCURY PHOTOSENSITIZED DECOMPOSITION OF C2–C4 OLEFINS

1956 ◽  
Vol 34 (6) ◽  
pp. 701-715 ◽  
Author(s):  
F. P. Lossing ◽  
D. G. H. Marsden ◽  
J. B. Farmer
Keyword(s):  
Mass Spectrometry ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Mass Spectrometer ◽  
Cross Sections ◽  
Methyl Radicals ◽  
Allyl Radical

The mercury photosensitized (Hg3P1) decomposition of olefins has been examined using a reactor coupled directly to a mass spectrometer. The primary split of ethylene has been shown to be predominantly molecular, and that of propylene mainly into an allyl radical and a hydrogen atom. With 1-butene the split is predominantly at a C–C bond giving allyl and methyl radicals, although a rupture of a C–H bond occurs as well. With 2-butene and isobutene a C–H bond is broken. It is concluded that the allyl and methallyl radicals produced have large cross sections for reaction with excited mercury atoms.

The hydrogenation of olefines - II. The hydrogenation of butene-2 and iso butene

1959 ◽  
Vol 249 (1259) ◽  
pp. 532-546 ◽  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Hydrogen Atom ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Room Temperature ◽  
Vapour Phase ◽  
Primary Reaction ◽  
Butyl Radical ◽  
Secondary Reactions

The work on the photosensitized hydrogenation of simple olefines described in part I has been extended to some butenes. The identity of the radicals produced in the primary reaction may be determined by analysis of the octane produced by their combination. The results obtained here agree with previous investigations in that the hydrogenation of iso butene yields tert .-butyl radicals, but disagree in that sec .-butyl radicals are found to be the principal product from butene-2. Disproportionation to combination ratios have been obtained for these radicals by the methods previously described. Vapour-phase chromatography has been used to separate the products of the secondary reactions occurring in these systems and analysis of the fractions attempted by mass spectrometry. The variation of the rate of formation of some of the products with pressure has investigated and from this information hot butyl radicals has been found both to decompose in the system thus C 4 H* 9 →CH 3 + C 3 H 6 , and to abstract from the parent olefine, C 4 H* 9 + C 4 H 8 → C 4 H 10 + C 4 H 7 . Addition of a hydrogen atom to the symmetrical olefine butene-2 can yield only a sec .-butyl radical in the absence of rearrangement. The reaction has previously been studied both at room temperature, and at 300°C (Moore & Wall 1949). The results were remarkable in that only very small traces of 3, 4-dimethyl hexane were detected, while in this work it is one of the major products. The same authors, however, found a considerable amount of 3, 4-dimethyl hexane in the hydrogenation products of butene-1. A few experiments carried out here with butene-1 using v. p. c. analysis indicate that the products from either olefine are similar both with respect to molecular weight distribution and relative quantities. The mercury-photosensitized hydrogenation of iso -butene has been studied by Moore & Wall (1949) who found considerable amounts of 2, 2, 3, 3-tetramethyl butane and iso -butane as well as traces of other hydrocarbons.

FREE RADICALS BY MASS SPECTROMETRY: XIII. THE MERCURY PHOTOSENSITIZED DECOMPOSITION OF ALLENE AND BUTADIENE: THE C3H3 RADICAL

1957 ◽  
Vol 35 (8) ◽  
pp. 778-787 ◽  
Author(s):  
J. Collin ◽  
F. P. Lossing
Keyword(s):  
Mass Spectrometry ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
The Other ◽  
Methyl Radicals ◽  
Polymer Formation ◽  
Vinyl Radicals

The Hg(3P1) photosensitized decomposition of allene leads to the formation of a C3H3 radical. The reaction of this radical with added methyl radicals shows it to have the propargyl (ĊH2—C≡CH) structure rather than the alternative allenyl (CH2=C=ĊH) structure. The dissociation of 1,2-butadiene proceeds by two modes, one to give H2 + C4H4, and the other a split into CH3 and C3H3 radicals. The dissociation of 1,3-butadiene leads to the same final products, a shift of a hydrogen atom being required for the split into free radicals. No evidence was found for a dissociation of 1,3-butadiene into two vinyl radicals. Considerable polymer formation occurred with all three compounds.

Heats of formation of free radicals by mass spectrometry

1973 ◽  
Vol 95 (20) ◽  
pp. 6562-6566 ◽  
Author(s):  
D. K. Sen. Sharma ◽  
J. L. Franklin
Keyword(s):  
Mass Spectrometry ◽  
Free Radicals ◽  
Heats Of Formation

scholarly journals Thiyl and phenoxyl free radicals and NADH Direct observation of one-electron oxidation

1986 ◽  
Vol 240 (3) ◽  
pp. 897-903 ◽  
Author(s):  
L G Forni ◽  
R L Willson
Keyword(s):  
Electron Transfer ◽  
Free Radicals ◽  
Hydrogen Atom ◽  
Pulse Radiolysis ◽  
Biological Significance ◽  
Transfer Reactions ◽  
Absolute Rate ◽  
Transfer Processes ◽  
Biochemical Systems ◽  
Electron Transfer Processes

Absolute rate constants for the reaction of NADH with thiyl free radicals derived from various sulphur-containing compounds of biological significance were measured by using the technique of pulse radiolysis. These and related reactions with phenoxyl free radicals are believed to occur through one-electron-transfer processes. Further evidence comes from studies with deuterated NADH. The results support the possibility that, in biochemical systems, thiols may act as catalysts linking hydrogen-atom and electron-transfer reactions.

scholarly journals Infrared Photoactivation Reduces Peptide Folding and Hydrogen-Atom Migration following ETD Tandem Mass Spectrometry

2009 ◽  
Vol 48 (45) ◽  
pp. 8526-8528 ◽  
Author(s):  
Aaron R. Ledvina ◽  
Graeme C. McAlister ◽  
Myles W. Gardner ◽  
Suncerae I. Smith ◽  
James A. Madsen ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Hydrogen Atom ◽  
Tandem Mass Spectrometry ◽  
Peptide Folding ◽  
Tandem Mass ◽  
Atom Migration
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