34467-53-3Relevant articles and documents
Reactions of selected molecular anions with oxygen
Knighton,Bognar,Grimsrud
, p. 557 - 562 (2007/10/02)
An investigation of the gas-phase reactions of molecular oxygen with the molecular anions of 17 compounds formed by resonance electron capture was undertaken using a pulsed e-beam high-pressure mass spectrometer. The molecular anions of sulphur hexafluoride, perfluromethylcyclohexane, cis- and trans-perfluorodecalin, m-chloronitrobenzene, o, m-and p-fluoronitrobenzene and o-, m- and p-dinitrobenzene were found to be unreactive towards oxygen. Those of o- and p-chloronitrobenzene, penta- and perchlorobenzene, perfluorobenzene, and perfluoratoluene were found to react readily with oxygen The second-order rate constants for these reactions are shown to bear so inverse dependence on temperature. The reactions involving o- and p-chloronitrabenezene and penta-and perchlorobenzene proceed via a branched mechanism by which an ion of the type [M + O - Cl]- and Cl- ion are simultaneously produced. A greater variety of negative ions are formed in the reactions of the molecular anions of perfluorobenzene and perfluorotoluene with oxygen The electron affinities of pentachlorobenzene (0.7 eV) and perchlorobenzene (1.0 eV) are also reported for the first time.
Resonance Electron Capture Rate Constants for Substituted Nitrobenzenes
Knighton, W. B.,Mock, R. S.,McGrew, D. S.,Grimsrud, E. P.
, p. 3770 - 3776 (2007/10/02)
We report here a new method for the determination of electron capture (EC) rate constants that utilizes a pulsed electron beam mass spectrometer.The method is first tested by measurements of the known dissociative electron capture rate constants for several halogenated methanes that have been extensively studied by other techniques.The resonance electron capture (REC) rate constants of nitrobenzene (NB) and 23 substituted nitrobenzenes (SNB's) are then determined for the first time at 125 deg C in 10 Torr of methane buffer gas.The SNB's studied here include several sets of closely related structural isomers whose electron affinities (EA's) have been previously determined.It is shown that the REC rate constants of these compounds bear little systematic relationship with the EA's of these compounds.The REC rate constants of the SNB's are also compared with other previously reported characteristics associated with the negative ionization of these compounds, including their entropies of negative ionization, the lifetimes against autodetachment of their initially formed molecular anions, and the rates of autodetachment from electronically excited states of their molecular anions.
Kinetic models for gas-phase electron-transfer reactions between nitrobenzenes
Han, Chau-Chung,Wilbur, James L.,Brauman, John I.
, p. 887 - 893 (2007/10/02)
Rate constants for gas-phase electron-transfer reactions between substituted nitrobenzenes have been measured using ion cyclotron resonance spectroscopy. On the basis of the assumption that these reactions occur through the formation of an intermediate complex, a statistical model is used to interpret the reaction kinetics. The intersecting parabolas quantum mechanical model provides an alternative description of the energy surface. Energy barriers are found to be consistent for the two methods. The results for exothermic reactions are consistent with a Marcus theory analysis, but suggest that a zero-order potential energy surface may not be completely adequate for quantitative prediction of reaction rates.
Entropy Changes and Electron Affinities from Gas-Phase Electron-Transfer Equilibria: A(-) + B = A + B(-)
Chowdhury, Swapan,Heinis, Thomas,Grimsrud, Eric P.,Kebarle, Paul
, p. 2747 - 2752 (2007/10/02)
By measuring the electron-transfer equilibria 1, A(-) + B = A + B(-), at 150 deg C with a pulsed electron high-pressure mass spectrometer we determined the ΔGo1 values involving 12 new compounds.Measurements of the temperature dependence of K1 for 21 reactions involving some of the new compounds and many compounds whose ΔGo1 had been determined previously led, via van't Hoff plots, to ΔHo1 and ΔSo1 values.These were interconnecting such that ΔHo and ΔSo continuous scales (ladders) were obtained.These were anchored to SO2 whose electron affinity is accurately known.Available geometries and vibrational frequencies for SO2 and SO2(-) permit the evaluation of So(SO2(-)) - So(SO2).Through the ΔSo scale the So(B(-)) - So(B) for the other compounds B could be obtained also.Certain regularities in the So(B(-)) - So(B) data permitted entropy estimates to be made also for compounds for which no van't Hoff plots were made.In this manner a table of ΔHo, ΔSo, and ΔGo data for the electron capture e + B = B(-) was obtained, which contains some 50 compounds B.Most of the compounds are substituted benzenes, quinones, conjugated acid anhydrides, and perfluorinated organics.
Electron Affinities from Electron-Transfer Equilibria : A(-) + B = A + B(-)
Grimsrud, Eric P.,Caldwell, Gary,Chowdhury, Swapan,Kebarle, Paul
, p. 4627 - 4634 (2007/10/02)
Determination of the equilibrium constants K1 for gas-phase electron-transfer equilibria with a pulsed electron beam high ion source pressure mass spectrometer led to the electron affinities of 34 compounds with EA's between 0.5 and 3eV.The compounds are mostly substituted nitrobenzenes, substituted quinones, and conjugated molecules containing oxygen atoms.The EA of smaller molecules like SO2, NO2, CS2, and CH3NO2 also were determined.The method is very well suited for rapid, accurate, routine determinations of electron affinities.A comparison with EA's determined with other gas-phase methods and EA's evaluated from polarographic half-wave reduction potentials and charge-transfer spectra in solution is made.The rate constants for a number of exothermic electron-transfer reactions were determined.Most of these proceed at near collision rates.Electron-transfer reactions involving perfluorinated compounds like perfluoromethylcyclohexane, perfluorocyclohexane, and sulfurhexafluoride do not follow this behavior.While the perfluoro compounds have high thermal electron capture cross sections, they do not accept electrons from A(-) of compounds A with lower electron affinity.The perfluoro anions do transfer electrons to compounds A with higher electron affinity, and the rate constants increase with EA(A) - EA(perfluoro compound).
One-Electron Reduction of Nitrobenzenes by α-Hydroxyalkyl Radicals via Addition/Elimination. An Example of an Organic Inner-Sphere Electron-Transfer Reaction
Jagannadham, V.,Steenken, S.
, p. 6542 - 6551 (2007/10/02)
The reaction in aqueous solution of α-hydroxyalkyl radicals with para-substituted nitrobenzenes were studied by using product analysis, electron spin resonance, and pulse radiolysis techniques.At neutral pH the α-hydroxyalkyl radicals are quantitatively oxidized to yield the corresponding ketones or aldehydes and H+, and the nitrobenzenes are reduced to the radical anions.The mechanism of this redox reaction depends strongly on the substituents on the α-hydroxyalkyl radical (the electron donor) and on the nitrobenzene (the electron acceptor).In case of α-hydroxymethyl radical, the reaction proceeds by addition to the nitro group to produce an alkoxynitroxyl radical which can undergo an OH--catalyzed heterolysis to give formaldehyde and the radical anion of the nitrobenzene.With the α-hydroxyethyl radical, both addition and "electron transfer" take place, the fraction of electron transfer increasing with increasing electron-withdrawing power of the substituent.The nitroxyl-type adducts undergo a spontaneous unimolecular heterolysis to give acetaldehyde, H+, and nitrobenzene radical anion.The rate constants ks (from 2 to 5*104 s-1) for this heterolysis increase with increasing electron-withdrawing strength of the substituent if it is on the benzene, and they decrease if the substituent is on the methyl carbon of the nitroxyl.The heterolysis reaction is characterized by low (5-10 kcal/mol) activation enthalpies and strongly negative (-5 to -25 eu) activation entropies, which originate from hydration of a proton in the transition state.From the effect on the activation parameters exerted by substituents on the electron acceptor and on the electron donor parts of the nitroxyl radical it is concluded that the heterolysis reaction proceeds by a push-pull mechanism and is entropy controlled.In the α-hydroxyprop-2-yl radical with substituted nitrobenzenes, the lifetimes of potential adducts of the nitroxyl type are s=2.1*103 s-1.The heterolysis reaction can also be slowed down by making the solvent less polar than water: in 95percent propan-2-ol/5percent water ks=1.5*104 s-1 for R=CN as compared to >106 s-1 in water.
Relative Electron Affinities of Substituted Nitrobenzenes in the Gas Phase
Fukuda, Elaine K.,McIver, Robert T.
, p. 2993 - 2995 (2007/10/02)
Using pulsed ion cyclotron resonance mass spectrometry, we have determined the relative electron affinities of 12 substituted nitrobenzenes in the gas phase by measuring equilibrium constants for electron transfer reactions of the type C6H5NO2- + X-C6H4NO2 = X-C6H4NO2- + C6H5NO2, where X is a substituent group.An excellent correlation is found between the relative electron affinities of the substituted nitrobenzenes and the relative gas-phase acidities of substituted anilines and phenols.
