- Photodissociation of N-(Triphenylmethyl) anilines: A Laser Flash Photolysis, ESR, and Product Analysis Study
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N-(Triphenylmethyl)anilines (Ph3C-NHPh-R, R = H, o-Me, m-Me, p-Me, p-CPh3), upon photolysis with 248- and 308-nm laser light, as well as by lamp irradiation with 254-nm light in acetonitrile and hexane solutions undergo exclusively C-N bond homolysis to give the triphenylmethyl radical in a monophotonic process. Product analysis gives as main products Ph3CH, 9-Ph-fluorene, and PhNH2. The quantum yields for the formation of Ph3C are high (0.6-0.8, 248-nm excitation) and independent of the solvent. This effective homolytic dissociation results from the low electronegativity difference between the carbon and nitrogen atoms constituting the bond to be broken, the low bond dissociation enthalpy of the C-N bond, the high excitation energy of the local chromophore (aniline), and probably from a favorable alignment of the C-N bond in a plane perpendicular to the anilino chromophore (due to the large steric requirements of the trityl group), thus enabling an effective hyperconjugative interaction with it. The above dissociation competes effectively with heterolytic cleavage, which is the pathway dominating, e.g., in the photolysis of Ph3C-Cl in MeCN under the same conditions. At high pulse intensities the trityl radicals formed above are excited by a second photon leading to either electrocyclization to 4a,4b-dihydro-9-phenylfluorenyl radical (DHPF·), or photoionization to Ph3C+, the latter only in MeCN and only on 248-nm photolysis. A new intermediate (9-Ph-4aH-fluorene) on the way to the final product 9-Ph-fluorene is identified resulting from electrocyclization, supporting a mechanism proposed earlier. The optical measurements are supported by ESR studies (irradiation with 254-nm light).
- Siskos,Zarkadis,Steenken,Karakostas,Garas
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- Direct synthesis of ligand-based radicals by the addition of bipyridine to chromium(II) compounds
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The reaction of 2,2′-bipyridine (bpy) with monomeric chromium(II) precursors was used to prepare the S = 1 complexes Cr(tBu-acac)2(bpy) (1) and (η5-Cp)(η1-Cp)Cr(bpy) (3), as well as the S = 2 compound Cr[N(SiMe3
- Zhou, Wen,Desnoyer, Addison N.,Bailey, James A.,Patrick, Brian O.,Smith, Kevin M.
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- 1,1- and 1,4-Addition Reactions with 3a,6a-Diaza-1,4-diphosphapentalene Containing Two-Coordinate and Formally Divalent Phosphorus
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3a,6a-Diaza-1,4-diphosphapentalene (DDP) reacts with halocarbons to give addition products to one or both phosphorus atoms depending on the substrate. Chlorotriphenylmethane affords a 1,4-addition product, which slowly decomposes in solution to form the Ph3C radical and the chloro-DDP coupling product with a P–P bond. Benzyl chloride is added to one phosphorus atom to form hypervalent (trivalent, four-coordinate) phosphorus with a N···P distance (nonvalent interaction) of 2.191(2) ?. A workup of the latter with GeCl2results in a complex salt containing the GeCl3–anion and cation with covalent N–P bonding.
- Kornev, Alexander N.,Galperin, Vadim E.,Sushev, Vyacheslav V.,Zolotareva, Natalia V.,Baranov, Evgenii V.,Fukin, Georgy K.,Abakumov, Gleb A.
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- Photophysics and Photochemistry of Arylmethyl Radicals in Liquids
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A series of arylmethyl radicals (including Ph2CH, 10,11-dihydro-5H-dibenzocyclohepten-5-yl (=DBHP.), Ph2CCH3, Ph2C-c-Pr, and Ph3C.) have been produced pulse radiolitically in a variety of solvents and then excited with λ=347 nm ruby laser pulses.Ph2C
- Bromberg, A.,Schmidt, K. H.,Meisel, D.
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- Evidence for a Single Electron Shift in a Lewis Acid-Base Reaction
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The Lewis acid-base reaction between a nucleophilic hafnocene-based germylene and tris-pentafluorophenylborane (B(C6F5)3) to give the conventional B-Ge bonded species in almost quantitative yield is reported. This reaction is surprisingly slow, and during its course, radical intermediates are detected by EPR and UV-vis spectroscopy. This suggests that the reaction is initiated by a single electron-transfer step. The hereby-involved germanium radical cation was independently synthesized by oxidation of the germylene by the trityl cation or strong silyl-Lewis acids. A perfluorinated tetraarylborate salt of the radical cation was fully characterized including an XRD analysis. Its structural features and the results of DFT calculations indicate that the radical cation is a hafnium(III)-centered radical that is formed by a redox-induced electron transfer (RIET) from the ligand to the hafnium atom. This valence isomerization slows down the coupling of the radicals to form the polar Lewis acid-base product. The implications of this observation are briefly discussed in light of the recent finding that radical pairs are formed in frustrated Lewis pairs.
- Dong, Zhaowen,Cramer, Hanna H.,Schmidtmann, Marc,Paul, Lucas A.,Siewert, Inke,Müller, Thomas
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supporting information
p. 15419 - 15424
(2018/11/03)
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- A Phosphine-Coordinated Boron-Centered Gomberg-Type Radical
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The P-coordinated boryl radical [Ph2P(naphthyl)BMes]. (Mes=mesityl) was prepared by (electro)chemical reduction of the corresponding borenium salt or bromoborane. Electron paramagnetic resonance (EPR) analysis in solution and DFT cal
- Rosenthal, Amos J.,Devillard, Marc,Miqueu, Karinne,Bouhadir, Ghenwa,Bourissou, Didier
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supporting information
p. 9198 - 9202
(2015/08/06)
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- Reactions of phenylethynyl cuprates of lanthanides with organyl halides and synthesis of the related polyfunctional compounds
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Phenylethynyl cuprate complexes of lanthanides react with organyl halides RX, Ph3CX, R3SiX, and RC(O)X (X = Cl, I; R = alkyl) in tetrahydrofuran to give polyfunctional organic and hetero-organic compounds with high yield. The reactio
- Zhil'tsov,Druzhkova,Dydykina,Makarov
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p. 2167 - 2173
(2015/02/05)
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- Kinetic study of the hydrogen abstraction reaction of the benzotriazole-N-oxyl radical (BTNO) with H-donor substrates
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The aminoxyl radical (>N-O.) BTNO (benzotriazole-N-oxyl) has been generated by the oxidation of 1-hydroxybenzotriazole (HBT; >N-OH) with a CeIV salt in MeCN. BTNO presents a broad absorption band with λmax 474 nm and e 184
- Brandi, Paolo,Galli, Carlo,Gentili, Patrizia
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p. 9521 - 9528
(2007/10/03)
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- Chemistry of the t-butoxyl radical: Evidence that most hydrogen abstractions from carbon are entropy-controlled
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Absolute rate constants and Arrhenius parameters for hydrogen abstractions (from carbon) by the t-butoxyl radical (tBuO·) are reported for several hydrocarbons and tertiary amines in solution. Combined with data already in the literature, an an
- Finn, Meghan,Friedline, Robert,Suleman, N. Kamrudin,Wohl, Christopher J.,Tanko, James M.
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p. 7578 - 7584
(2007/10/03)
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- Phosphoryl- and thiophosphoryl-dithioformates. Part IV. Electrochemical reduction and EPR study of the radical anions
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The reduction of a number of phosphoryl- and thiophosphoryl formates, monothioformates and dithioformates has been studied by means of cyclic voltammetry and EPR spectroscopy. The reduction potentials of all dithioformates are close to -1 V vs. SCE, and i
- Alberti, Angelo,Benaglia, Massimo,Hapiot, Philippe,Hudson, Andrew,Le Coustumer, Gerard,Macciantelli, Dante,Masson, Serge
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p. 1908 - 1913
(2007/10/03)
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- Evaluation of dissociation energies of S-H bonds in thiophenols and thioalcohols on the basis of kinetic measurements
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Kinetic data on the reactions of alkyl and benzyl radicals with thiophenol C6H5SH were analyzed within the framework of the parabolic model of transition state. The values of the parameter that establishes a correlation between the activation energy of a reaction and its enthalpy were calculated for reactions of alkyl and benzyl radicals with the C6H5SH. The equations of the parabolic model were used to calculate the bond dissociation energies for 11 thiophenols and 4 thioalcohols. The activation energies for reactions of 12 thiophenoxy radicals with cumene and of C6H5S? radical with several alkyl-aromatic hydrocarbons were obtained.
- Denisov
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p. 238 - 241
(2007/10/03)
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- Sterically Hindered Free Radicals. 18. Stabilization of Free Radicals by Substituents As Studied by Using Triphenylmethyls
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The relative stabilization of 10 4-mono- and 24 4,4'-disubstituted triphenylmethyl radicals 1 has been measured by recording the degree of dissociation of the corresponding quinonoid dimers 2 by means of ESR.The following substituents or combinations of t
- Neumann, Wilhelm P.,Penenory, Alicia,Stewen, Ulrich,Lehnig, Manfred
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p. 5845 - 5851
(2007/10/02)
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- Sterically Hindered Free Radicals, XIX. - Stable 4,4',4''-Trisubstituted Triphenylmethyl Radicals
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The title radicals (4-R-C6H4)3C. (1), R = F, Cl, Ph, OMe, NO2, tBu, OEt, SMe, CN, CF3, have been prepared, the latter four for the first time, and the ESR spectra have been recorded. aoH, amH, and as
- Duennebacke, Dieter,Neumann, Wilhelm P.,Penenory, Alicia,Stewen, Ulrich
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p. 533 - 536
(2007/10/02)
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- Chemistry of heavy carbene analogues R2M (M = Si, Ge, Sn). 12. Concerted and nonconcerted insertion reactions of the germylene Me2Ge into the carbon-halogen bond
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During the reaction of Me2Ge with CCl3X (X = Cl, Br), PhCH2X (X = Br, I), and Ph2CHCl, 1H CIDNP is observed in the products of net insertion of Me2Ge into the carbon-halogen bond and in Me2GeX2 (X = Cl, Br). It is concluded that a two-step radical reaction takes place by an abstraction-recombination mechanism. No reaction takes place with alkyl halides that have a C-X bond dissociation energy of more than about 70 kcal/mol. Me2Ge is generated thermally at 70-95°C or photochemically from the 7-germabenzonorbornadiene 1 and reacts in both cases in the singlet state. The activation energy for forming Me2Ge from 1 is 19 kcal/mol for the reaction with CCl4. Insertion products are also formed with the alkenyl halides CH2=CHCH2X, PhCH=CHX (X = Cl, Br), and 2-bromobut-2-ene, but without showing CIDNP effects. Since Me2GeX2 was not found either, Me2Ge reacts in these cases in a nonradical manner. It does not react with 1-chlorocyclohexene, but it does react with Me2GeX2 under formation of digermanes and/or oligogermanes without CIDNP.
- K?cher, Jürgen,Lehnig, Manfred,Neumann, Wilhelm P.
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p. 1201 - 1207
(2008/10/08)
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- Sterically Hindered Free Radicals, XV The First Unsymmetrical Dimer from Two Different Stable Radicals: 3-(tert-Butylphenylmethylene)-6-(triphenylmethyl)-1,4-cyclohexadiene from tert-Butyldiphenylmethyl and Triphenylmethyl
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The quinonoid title compound 6 is formed in an equilibrium to 95percent and can be isolated, when the two title radicals 1 and 3 are generated in solution.The reason for this is the sterically less strained position of the bulky tBu group at the sp2
- Neumann, Wilhelm P.,Stapel, Ralf
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p. 2006 - 2012
(2007/10/02)
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- Sterically Hindered Free Radicals, XIII. Wittig's Radical 4-Benzoyltriphenylmethyl and Analogous Mono-4-substituted Trityl Radicals
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The mono-4-R-triphenylmethyl radicals 1, 8b-f, R = tBu, CF3, COMe, COPh, CN, Me, or their quinonoid dimers 4, 9b-f are prepared, most of them for the first time.The degree of dissociation of the latter at 25 deg C is surprisingly high (=/ 33percent, 0.01 M), donors and acceptors being effective here likewise.ESR data are given and discussed.
- Zarkadis, Antonios K.,Neumann, Wilhelm P.,Uzick, Wolfram
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p. 1183 - 1192
(2007/10/02)
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- PHOTOPHYSICS OF ARYLMETHYL RADICALS AT 77 K. STRUCTURE-PHOTOREACTIVITY CORRELATION
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Five arylmethyl radicals, Ph2CH(.), DBHP(.), Ph2C(.)CH3, Ph3C(.), and Ph2C(.)-c-Pr were generated in glassy matrices at 77 K and their absorption, excitation, and emission spectra were studied in detail.Under similar conditions, fluorescence quantum yield
- Bromberg, A.,Meisel, Dan
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p. 2507 - 2513
(2007/10/02)
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- Kinetic Applications of Electron Paramagnetic Resonance Spectroscopy. 42. Some Reactions of the Bis(trifluoromethyl)aminoxyl Radical
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Absolute rate constants have been determined in Freon solvents over a temperature range from ca. 190 to 300 K for H atom abstraction by (CF3)2NO. from 11 substrates and for the addition of this radical to CH2=CCl2.Some values found for log A (M
- Doba, T.,Ingold, K. U.
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p. 3958 - 3963
(2007/10/02)
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- Evidence of Single Electron Transfer in the Reduction of Various OrganicSubstrates by Lithium Tetrakis(N-dihydropyridyl)aluminate
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Aromatic ketones, polynuclear hydrocarbons, and alkyl halides with LiAl(PyH)4 by a single electron transfer process.
- Ashby, E.C.,Goel, A.B.
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p. 3934 - 3936
(2007/10/02)
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- Evidence for Single Electron Transfer in the Reactions of Alkali Metal Amides and Alkoxides with Alkyl Halides and Polynuclear Hydrocarbons
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Evidence for single electron transfer as the major pathway in reactions previously considered to be classic SN1 and SN2 pathways has been obtained.In this connection, the reaction of KOBu-t with trityl bromide has been shown to proceed through the trityl radical, and the reaction of LiN(i-Pr)2 with a primary alkyl iodide probe gave evidence of proceeding by single electron transfer, as indicated by the cyclized nature of the product as a result of a radical intermediate.
- Ashby, E. C.,Goel, A. B.,DePriest, R. N.
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p. 2429 - 2431
(2007/10/02)
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