Electron transfer photochemistry of aromatic imides and phenylcyclopropane. Radical anion-radical cation cycloaddition

1986 ◽  
Vol 108 (21) ◽  
pp. 6828-6829 ◽  
Author(s):  
Paul H. Mazzocchi ◽  
Cathleen. Somich ◽  
Michael. Edwards ◽  
Tina. Morgan ◽  
Herman L. Ammon
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical

ChemInform Abstract: Electron Transfer Photochemistry of Aromatic Imides and Phenylcyclopropane. Radical Anion-Radical Cation Cycloaddition.

ChemInform ◽  
1987 ◽  
Vol 18 (11) ◽  
Author(s):  
P. H. MAZZOCCHI ◽  
C. SOMICH ◽  
M. EDWARDS ◽  
T. MORGAN ◽  
H. L. AMMON
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical

Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system

1989 ◽  
Vol 67 (4) ◽  
pp. 689-698 ◽  
Author(s):  
Donald R. Arnold ◽  
Shelley A. Mines
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Phenyl Group ◽  
Oxidation Potential ◽  
Original Position ◽  
Acetonitrile Solution ◽  
Steric Interaction ◽  
Ambident Anion

Alkenes, conjugated with a phenyl group, can be converted to nonconjugated tautomers by sensitized (electron transfer) irradiation. For example, irradiation of an acetonitrile solution of the conjugated alkene 1-phenylpropene, the electron accepting photosensitizer 1,4-dicyanobenzene, the cosensitizer biphenyl, and the base 2,4,6-trimethylpyridine gave the nonconjugated tautomer 3-phenylpropene in good yield. Similarly, 2-methyl-1-phenylpropene gave 2-methyl-3-phenylpropene, and 1-phenyl-1-butene gaveE- and Z-1-phenyl-2-butene. The reaction also works well with cyclic alkenes. For example, 1-phenylcyclohexene gave 3-phenylcyclohexene, and 1-(phenylmethylene)cyclohexane gave 1-(phenylmethyl)cyclohexene. The proposed mechanism involves the initial formation of the alkene radical cation and the sensitizer radical anion, induced by irradiation of the sensitizer and mediated by the cosensitizer. Deprotonation of the radical cation assisted by the base gives the ambident radical, which is then reduced to the anion by the sensitizer radical anion. Protonation of the ambident anion at the benzylic position completes the sequence. Reprotonation at the original position is an energy wasting step. Tautomerization is driven toward the isomer with the higher oxidation potential, which is, in the cases studied, the less thermodynamically stable isomer. The regioselectivity of the deprotonation step is dependent upon the conformation of the allylic carbon–hydrogen bond. The tautomerization of 2-methyl- 1-phenylbutene gave both 2-phenylmethyl-1-butène and 2-methyl-1-phenyl-2-butene (E and Z isomers), while 2,3-dimethyl- 1-phenylbutene gave only 3-methyl-2-phenylmethyl-1 -butene. In the latter case, steric interaction of the methyls on the isopropyl group prevents effective overlap of the tertiary carbon–hydrogen bond with the singly occupied molecular orbital, thus inhibiting deprotonation from this site. Keywords: photosensitized, electron transfer, alkene, tautomerization, radical cation.

Radical ions in photochemistry. 18. The photosensitized (electron transfer) tautomerization of alkenes; the 1,1-diphenyl alkene system

1987 ◽  
Vol 65 (9) ◽  
pp. 2312-2314 ◽  
Author(s):  
Donald R. Arnold ◽  
Shelley A. Mines
Keyword(s):  
Hydrogen Bond ◽  
Electron Transfer ◽  
Radical Cation ◽  
Radical Anion ◽  
Relative Rate ◽  
Radical Cations ◽  
Radical Ions ◽  
Back Electron Transfer ◽  
Ambident Anion ◽  
Determining Factor

The photosensitized (electron transfer) irradiation of several conjugated 1,1-diphenyl alkenes, in acetonitrile with 1,4-dicyanobenzene or 1-cyanonapthalene as electron accepting sensitizer and 2,6-lutidine as base, leads essentially quantitatively to tautomerization to the less stable unconjugated isomer(s). The proposed mechanism for this reaction involves formation of the alkene radical cation and sensitizer radical anion followed by deprotonation of the radical cation, reduction of the resulting radical to the ambident anion by back electron transfer from the radical anion, and reprotonation. There are several steps in this mechanism that could control the ratio of isomers. Evidence is provided that, at least in some cases, it is the relative rate of deprotonation from the isomeric radical cations that is the determining factor. This rate is influenced by the conformation of the radical cation; the carbon–hydrogen bond involved in the deprotonation step must overlap with the singly occupied molecular orbital.

Boron as a Powerful Reductant: Synthesis of a Stable Boron-Centered Radical-Anion Radical-Cation Pair

2014 ◽  
Vol 54 (1) ◽  
pp. 359-362 ◽  
Author(s):  
Philipp Bissinger ◽  
Holger Braunschweig ◽  
Alexander Damme ◽  
Christian Hörl ◽  
Ivo Krummenacher ◽  
...  
Keyword(s):  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical

The regiochemistry of trapped radical anion-radical cation pairs from aryl substituted phthalimides

1981 ◽  
Vol 22 (42) ◽  
pp. 4189-4192 ◽  
Author(s):  
Paul H. Mazzocchi ◽  
Frederick Khachik
Keyword(s):  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical

Absorption spectra and reaction kinetics of the radical anion, radical cation and OH adduct(s) of 3,5-dinitroanisole studied by pulse radiolysis

2010 ◽  
Vol 98 (5) ◽  
pp. 305-315 ◽  
Author(s):  
Johannes J. Tamminga ◽  
Cornelis A. M. van den Ende ◽  
John M. Warman ◽  
Andries Hummel
Keyword(s):  
Reaction Kinetics ◽  
Absorption Spectra ◽  
Radical Cation ◽  
Radical Anion ◽  
Anion Radical ◽  
Pulse Radiolysis ◽  
Kinetics Of

Substituent effects in oxime radical cations. 1. Photosensitized reactions of acetophenone oximes

2003 ◽  
Vol 81 (6) ◽  
pp. 575-585 ◽  
Author(s):  
HJ Peter de Lijser ◽  
Jason S Kim ◽  
Suzanne M McGrorty ◽  
Erin M Ulloa
Keyword(s):  
Electron Transfer ◽  
Steady State ◽  
Radical Cation ◽  
Radical Anion ◽  
Substituent Effects ◽  
Radical Cations ◽  
Ionization Potentials ◽  
Semiquinone Radical ◽  
Am1 Calculations ◽  
Iminoxyl Radical

A variety of ortho-, meta-, and para-substituted (-H, -F, -Cl, -CF3, -CN (meta and para only), -CH3, -OCH3, and -NO2) acetophenone oximes were synthesized and studied using laser flash photolysis (LFP) and steady-state photolysis experiments in acetonitrile with chloranil as the photosensitizer. In addition, semi-empirical (AM1) calculations were performed on the neutral species, the radical cations, and the corresponding iminoxyl radicals. The data was analyzed in terms of the electrochemical peak potentials of the oximes, the quenching rates of triplet chloranil (LFP), the calculated ionization potentials, and the measured conversions of the oximes in the steady-state photolysis experiments. Photolysis of the oximes in the presence of chloranil results in the formation of the chloranil radical anion, which reacts rapidly with the oxime radical cation to form the semiquinone radical and an iminoxyl radical. Evidence for the formation of the chloranil radical anion and the semiquinone radical was obtained from LFP studies. The measured quenching rates from the LFP studies represent the rates of electron transfer from the oximes to triplet chloranil. This data was correlated to various radical and polar substituent constants. The Hammett studies suggest that steric, polar, and radical effects are important for ortho-substituted acetophenone oximes, polar effects are important for para-substituted oximes, and radical stabilization is more important than polar effects for the meta-substituted substrates. The calculated ionization potentials of the oximes show an excellent correlation with the measured quenching rates supporting the electron transfer pathway. On the basis of calculated charge densities, we conclude that the measured substituent effects are transition state effects rather than ground state effects. At this point all of the available data suggests that the conversion of the oximes is controlled by two energetically opposing reactions, namely oxidation of the neutral oxime, which is favorable for oximes with electron-donating substituents, and deprotonation of the oxime radical cation, which is favorable for oximes with electron-withdrawing substituents. The overall result is a reaction with little selectivity as far as substituent effects are concerned.Key words: oxime, radical cation, iminoxyl radical, electron transfer, substituent effect.

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