- Synthesis of 2,4,6-trimethylphenylcalcium iodide and degradation in THF solution
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(Figure Presented) Heavy Grignard reagent: Despite the low reactivity of the calcium metal and the high reactivity of the resulting Ca-C bonds, the synthesis of mesitylcalcium iodide (see structure: purple I, orange Ca, red O, gray C) succeeded at very lo
- Fischer, Reinald,Gaertner, Martin,Goerls, Helmar,Westerhausen, Matthias
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- Reactions of benzyltriphenylphosphonium salts under photoredox catalysis
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The development of benzyltriphenylphosphonium salts as alkyl radical precursors using photoredox catalysis is described. Depending on substituents, the benzylic radicals may couple to form C-C bonds or abstract a hydrogen atom to form C-H bonds. A natural product, brittonin A, was also synthesized using this method.
- Boldt, Andrew M.,Dickinson, Sidney I.,Ramirez, Jonathan R.,Benz-Weeden, Anna M.,Wilson, David S.,Stevenson, Susan M.
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p. 7810 - 7815
(2021/09/28)
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- Visible-Light-Driven Self-Coupling of Methylarenes Catalyzed by Ni2P?Cd0.5Zn0.5S Nanoparticles
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The Ni2P?Cd0.5Zn0.5S nanoparticles photocatalyzed self-coupling of p-xylene was reported here, and the corresponding coupling product 1,2-di-p-tolylethane was obtained. The reaction could be extended to toluene derivatives with electron-donating and electron-withdrawing substituents. Ni2P?Cd0.5Zn0.5S nanoparticles had already been characterized by XRD, ICP-AES, SEM, TEM, UV/Vis, FL, XPS. The Mott–Schottky curves of Ni2P?Cd0.5Zn0.5S were made through electrochemical methods. An active carbon free-radical was captured through ESR measurement under irradiation. The research demonstrated this photocatalytic system feasible for the self-coupling reaction of toluene derivatives.
- Yang, Dan-Dan,Hu, Jia-Jun,Zhang, Hong,Lv, Xiao-Jun,Chen, Yong,Fu, Wen-Fu
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p. 1384 - 1392
(2020/01/08)
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- Photoredox-Catalysis-Modulated, Nickel-Catalyzed Divergent Difunctionalization of Ethylene
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Divergent synthesis that enables a catalytic reaction to selectively produce different products from common substrates will allow the charting of wider chemical space and the unveiling of distinct mechanistic paradigms. A common strategy for it employs different ligands to modulate organometallic catalysts. Dramatic developments in photocatalysis have enabled previously inaccessible transformations. In particular, photoredox catalysis modulates the oxidation state of transition-metal complexes, offering enormous opportunities for methodology development. Herein, we developed a photo-mediated divergent ethylene difunctionalization via modulating oxidation states of the nickel catalyst by using different photoredox catalysts. This work will inspire new perspectives for value-added chemical synthesis using ethylene as a feedstock and shed light on photoredox-catalyst-based divergent synthesis, which fundamentally differs from ligand-controlled transition-metal catalysis.Divergent synthesis represents a powerful strategy for directly accessing different molecular scaffolds originating from the same starting materials. Access to different end products via transition-metal catalysis is conventionally achieved by ligand control. We herein demonstrate the use of ethylene feedstock and commercially available aryl halides to accomplish the divergent synthesis of 1,2-diarylethanes, 1,4-diarylbutanes, or 2,3-diarylbutanes in a highly selective fashion through the synergistic combination of nickel and photoredox catalysis. Mechanistic studies suggest that the observed selectivity was due to different active states of Ni(I) and Ni(0) modulated by Ru- and Ir-based photoredox catalysts, respectively. The ability to access different organometallic oxidation states via photoredox catalysis promises to inspire new perspectives for synergistic transition-metal-catalyzed divergent synthesis.Functionalization of ethylene without polymerization is challenging under photo-irradiation conditions. We have demonstrated that the photo-transformation of ethylene can be controllable by merging photoredox and transition-metal catalysis. In our study, the use of different photoredox catalysts was able to modulate the oxidation state of the nickel catalyst. Through different oxidation states, the nickel-catalyzed couplings proceeded via distinct pathways to generate divergent ethylene difunctionalization products selectively from the same feedstock.
- Li, Jiesheng,Luo, Yixin,Cheo, Han Wen,Lan, Yu,Wu, Jie
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supporting information
p. 192 - 203
(2019/01/21)
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- Nondirecting Group sp3 C?H Activation for Synthesis of Bibenzyls via Homo-coupling as Catalyzed by Reduced Graphene Oxide Supported PtPd@Pt Porous Nanospheres
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The use of heterogeneous bimetallic Pd-based nanocatalyst for directing the inactivated sp3 C?H coupling has been scarcely explored. This work reported the formation of symmetrical C?C bonds from the inactivated sp3 C?H bonds catalyzed by employing reduced graphene oxide supported PtPd@Pt porous nanospheres. The reaction of sp3 C?H activation proceeded under mild conditions without any solvent, ligand or directing group. It is a higher atom-, step- and cost-effectiveness strategy for developing heterogeneous catalysts in the synthesis of bibenzyls with various functional groups (e. g. aryl, alkyl, methoxyl, halogen, ester, and pyridyl). (Figure presented.).
- Wang, Zheng-Jun,Lv, Jing-Jing,Yi, Rong-Nan,Xiao, Min,Feng, Jiu-Ju,Liang, Zhi-Wu,Wang, Ai-Jun,Xu, Xinhua
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supporting information
p. 932 - 941
(2018/01/05)
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- Dimerization of Benzyl and Allyl Halides via Photoredox-Mediated Disproportionation of Organozinc Reagents
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Benzyl and allyl halides undergo homocoupling when treated with zinc in the presence of a catalytic amount of a cationic iridium(III) complex under irradiation with 400 nm light-emitting diodes. The reaction proceeds through the intermediate formation of an organozinc reagent, which disproportionates to a free radical and elemental zinc under photoredox conditions.
- Levin, Vitalij V.,Agababyan, Daniil P.,Struchkova, Marina I.,Dilman, Alexander D.
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p. 2930 - 2935
(2018/05/28)
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- An unprecedented oxidative intermolecular homo coupling reaction between two sp3C–sp3C centers under metal-free condition
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An unprecedented formation of benzylic sp3C–sp3C coupled dibenzylic products has been illustrated. The reactions have been carried out in the presence of three oxidizing reagents, i.e., diacetoxy-iodobenzene (IBDA), N-fluorobenzenesulfonimide (NFSI), and pyridine (Py) using toluene derivatives.
- Sahoo, Santosh K.
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supporting information
p. 3476 - 3480
(2016/07/15)
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- Photochemical Reductive C–C Coupling with a Guanidine Electron Donor
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The metal-free photoinduced reductive C–C coupling reactions of a number of substituted benzyl halides (15 examples) with the organic electron-donor 2,3,5,6-tetrakis(tetramethylguanidino)pyridine are evaluated. Depending on the substituents at the benzyl group, a C–C coupling product yield in the range 50–95 % is achieved. The photochemical benzyl-radical formation by homolytic N–C bond cleavage of the initially formed benzyl-pyridinium salts is the rate-determining step of these reactions. Electron-withdrawing as well as -donating substituents at the phenyl group increase the reaction rate. Quantum chemical computations did not reveal any correlation between either the enthalpy or Gibbs free energy of the N–C bond cleavage step and the experimentally determined first-order rate constants. Instead, the structural difference between the excited state generated by irradiation and the electronic ground state of the pyridinium ions could be used to rationalize the differences in the reaction rates.
- Wiesner, Sven,Walter, Petra,Wagner, Arne,Kaifer, Elisabeth,Himmel, Hans-J?rg
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p. 5045 - 5054
(2016/10/26)
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- Use of mixed Li/K metal TMP amide (LiNK chemistry) for the synthesis of [2.2]metacyclophanes
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A new two-step general approach to [2.2]metacyclophane synthesis from substituted m-xylenes is described. The strategy employs a selective benzylic metalation and oxidative C-C bond formation for both synthetic operations. Regioselective benzylic metalati
- Blangetti, Marco,Fleming, Patricia,O'Shea, Donal F.
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supporting information; experimental part
p. 1249 - 1254
(2011/11/05)
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- The 1,2,4-triazolyl cation: Thermolytic and photolytic studies
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The generation of the 1,2,4-triazolyl cation (1) has been attempted by the thermolysis and photolysis of 1-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridinium tetrafluoroborate (2) and the thermolysis of 1- and 4-diazonium-1,2,4-triazoles, using mainly mesitylene as the trapping agent. Thermolysis of 2 gave mostly 1,2,4-triazole, together with 3-(1,2,4-triazol-4-yl)-2,4,6-trimethylpyridine, 4-(1,2,4-triazol-4-ylmethyl)-2,6-dimethylpyridine, and 4-(2,4,6-trimethylbenzyl)-2,6-dimethylpyridine. Thermolysis, of each of the diazonium salts in the presence of mesitylene again gave mainly triazole together with very low yields of 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene and the corresponding -4-yl isomer in about the same ratio. On the other hand, photolysis of 2 in mesitylene gave mainly 1-(1,2,4-triazol-1-yl)-2,4,6-trimethylbenzene. A photoinduced electron transfer from mesitylene to 2 has been observed and preliminary laser flash photolyses of 2 and the corresponding 2,4,6-triphenylpyridinium salt have been carried out. The observed transients are explained as arising from the first excited states of the pyridinium salts rather than from 1. Ab initio MO calculations are reported and indicate that the predicted electronic ground-state of the triazolyl cation is a triplet state of B1 symmetry with five π electrons, which corresponds to a diradical cation (1c). Possible mechanisms for the formation of the various products are proposed.
- Abramovitch,Beckert,Gibson Jr.,Belcher,Hundt,Sierra,Olivella,Pennington,Sole
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p. 1242 - 1251
(2007/10/03)
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- Photoinduced Substitution of 1,3,5-Tricyanobenzene by Toluene
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Irradiation of a solution of 1,3,5-tricyanobenzene in acetonitrile in the presence of toluene gives 1-benzyl-3,5-dicyanobenzene and 1-benzyl-3,5,6-tricyanobenzene.In a toluene solution only bibenzyl is obtained.On the basis of results using 2H8>toluene (i.e. deuterium incorporation only in the benzyl and not in the cyanoaromatic moiety) a series of reactions which involves photoinduced electron-transfer, removal of proton from the radical cation, and then coupling of the radical anion and the radical formed is postulated.It is also suggested that for the coupling reaction to take place then the reduction potential for radical anion to dianion on the cyanoaromatic species might play an important role.
- Ohashi, Mamoru,Aoyagi, Nobuyuki,Yamada, Shuzo
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p. 1335 - 1338
(2007/10/02)
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- CYANOETHYLATION OF HYDROCARBONS, INITIATED BY AUTOOXIDATION
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Oxygen was used as an initiator of the free-radical cyanoethylation of alkylbenzenes (toluene, o-, m-, and p-xylenes, mesitylene, ethylbenzene, p-cymene) and tetralin (0.25-0.66 liter of oxygen to 1 liter of the hydrocarbon) The reactions were carried out in an autoclave at 150-350 deg C with a carbon-acrylonitrile ratio of 100:1.The initiation evidently results mainly from homolytic dissociation of the hydroperoxide formed during the autooxidation of the hydrocarbons.The effectiveness of oxygen for the initiation of the cyanoethylation of hydrocarbons depends on the oxidizability of the hydrocarbons.
- Galust'yan, G. G.
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p. 811 - 815
(2007/10/02)
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- The Role of Aroyloxyl Radicals in the Formation of Solvent-derived Products in Photodecomposition of Diaroyl Peroxides. The Reactivity of Substituted Cyclohexadienyl Radicals and Intermediacy of ipso Intermediates
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Photolyses of bis(2-thiophenecarbonyl)peroxide (TPO) in benzene and toluene afforded, among free-radical products, biphenyl and dimethylbiphenyls, respectively, which were solely derived from the aromatic solvents.The yields of biphenyls depended upon the rate with which the radical intermediates were generated from the peroxides in sufficiently high concentrations for their dimerization.Photolyses of TPO and dibenzoyl peroxide in 1,3,5-trimethylbenzene afforded also a solvent-derived products, 2,3',4,5',6-pentamethyldiphenylmethane.Its formation provides clear evidence for participation of cyclohexadienyl radicals bearing the aroyloxyl group on the methyl-substituted ipso carbon atom.
- Takahara, Shigeru,Urano, Tishiyuki,Kitamura, Akihide,Sakuragi, Hirochika,Kikuchi, Osamu,et al
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p. 688 - 697
(2007/10/02)
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- Thermolysis of Highly Congested Tri-tert-alkylmethanols: Strain Energies of Bridgehead Alkyl Radicals
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The rate constants and the products of the thermolysis of tertiary alcohols, R1R2R3COH, where Ri is tert-butyl, 1-adamantyl, 1-bicyclooctyl, or 1-norbornyl, have been determined.Apart from the usual secondary alcohols and ketones, the products include new ketones, formed by ring opening of the 1-norbornyl group, and solvent-incorporated alcohols.The activation energies for (t-Bu)-C, Ad-C, Oc-C, and, in one case, Nor-C cleavage are compared with the molecular mechanics calculated strain-energy changes, Δstrain.These latter are based on a simple model of the reaction intermediate where the bridgehead radicals are represented by the corresponding alkanes.Taking the ΔG(excit.)(200 deg C)/Δstrain correlation for t-Bu-radical formation as a reference, one can show that the deviations, ΔΔstrain, of the data for the formation of the other radicals (Ad, 2.4; Oc, 4.0; Nor, 7.7 kcal mol-1) indicate the real difference between the strain energies of the radicals and the alkanes.Analogous ΔΔ(excit.) data for other reactions considered to involve rate-determining radical formation correlate with ΔΔstrain, the slopes ranging from 0.16 to 1.13.The ΔΔstrain values also correlate with solvolysis rate constants of tert-alkyl tosylates, with a slope (ΔΔstrain/ΔG(excit.)(70 deg C)) of 0.36; tentative values for the strain energies of other bridgehead radicals are proposed and compared with the predictions of a radical force field.
- Lomas, John S.
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p. 4291 - 4299
(2007/10/02)
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- OXIDATIVE PHOSPHONYLATION OF AROMATIC COMPOUNDS
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Aryl phosphonates can be prepared in good yield from the respective arenes and tri- or dialkylphosphites by either chemical or anodic oxidation.The anodic oxidation proceeds either via phosphinium radical cations, which then attack the arenes electrophilically, or via arene radical cations, which add the trialkylphosphite as nucleophile.Aryl phosphonates are also obtained in good yield by chemical oxidation with peroxodisulfate/AgNO3 in acetonitrile/water or glacial acetic acid.The diethylphosphinium radical cation, formed from diethylphosphite by oxidation with Ag(II), is supposed to be the reactive species in this process.Raising the silver salt concentration leads to an increase in polyphosphonylation.Selectivity ratios were determined for the oxidative phosphonylation process.
- Effenberger, Franz,Kottmann, Hariolf
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p. 4171 - 4182
(2007/10/02)
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- INTERMEDIACY OF CYCLOHEXADIENYL RADICALS WITH AN AROYLOXY GROUP ON THE METHYL-SUBSTITUTED IPSO CARBON ATOM IN PHOTOLYSES OF BIS(2-THIOPHENECARBONYL) AND DIBENZOYL PEROXIDES IN 1,3,5-TRIMETHYLBENZENE
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Investigation of the products arising from photolyses of bis(2-thiophenecarbonyl) and dibenzoyl peroxides in 1,3,5-trimethylbenzene provided clear evidence for participation of cyclohexadienyl radicals with the aroyloxy group on the methyl-substituted ipso carbon atom in formation of 2,3',4,5',6-pentamethyldiphenylmethane through recombination with 3,5-dimethylphenylmethyl radicals.
- Takahara, Shigeru,Kitamura, Akihide,Sakuragi, Hirochika,Tokumaru, Katsumi
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p. 1315 - 1318
(2007/10/02)
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- PHOTOCHEMICAL OXIDATION AND DIMERIZATION OF ALKYLBENZENES. SELECTIVE REACTIONS OF THE ALKYL SIDE GROUPS
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Irradiations of alkylbenzene compounds in an oxygen atmosphere result exclusively in oxidation reactions, while in a less oxidative environment dimerization processes predominate.Under all conditions studied, the reactions took place only at one benzyl position.
- Pasternak, Mordechai,Morduchowitz, Abraham
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p. 4275 - 4278
(2007/10/02)
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- Substituent Effects on the C-C-Bond Strength, 3. The Thermal Stability of 2,2-Disubstituted Malononitriles
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The products, the rate constants and the activation parameters of the homolytic thermal decomposition of a series of malononitriles 8a - e were determined.A linear correlation is found between ΔG* (300 deg C) and the strain enthalpies Hsp of 8 as deduced from force field calculations (MM2 force field).From this correlation and a comparison with the corresponding relationship for Cq-Cq alkanes 9.2 kcal*mol-1 resonance energy of 1,1-dicyanoalkyl radicals 10 is estimated.The relationships between strain enthalpy Hsp, structure and barriers to internal rotation for the compounds 8 are discussed briefly.
- Barbe, Werner,Beckhaus, Hans-Dieter,Ruechardt, Christoph
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p. 1058 - 1069
(2007/10/02)
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- PHOTOCHEMICAL REACTION OF 3-ARYL-2-ISOXAZOLINES WITH METHYLATED BENZENES
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Irradiation of 3-aryl-2-isoxazolines (1b and 1c) results in a hydrogen abstraction reaction from toluene, xylene or mesitylene by the carbon-nitrogen double bond to give isoxazolidine derivatives.
- Kumagai, Tsutomu,Kawamura, Yasuhiko,Mukai, Toshio
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p. 2279 - 2282
(2007/10/02)
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- Substituent Effects on the C-C-Bond Strength, 2. The Thermal Stability of Tetrasubstituted Succinonitriles
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Rate constants and activation parameters for the thermolysis reaction of ten, partly cyclic tetraalkylsuccinonitriles and of meso-2,3-dimethyl-2,3-diphenylsuccinonitrile were determined.Relationships between ΔG* (300 deg C), ΔH* and ΔS* of the thermolysis reaction on the one hand and the change in strain enthalpy during bond dissociation on the other are pointed out.A force field procedure for the estimation of the strain in α-cyanoalkyl radicals is presented.A quantitative separation of the steric and resonance effects responsible for the thermal dissociation pro cess was achieved successfully.A resonance energy of 5.3 kcal*mol-1 was deduced for tertiary α-cyanoalkyl radicals in agreement with the most recent literature data.
- Barbe, Werner,Beckhaus, Hans-Dieter,Ruechardt, Christoph
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p. 1042 - 1057
(2007/10/02)
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- Chemistry of the tert-Butyl Radical: Polar Character, ρ Value for Reaction with Toluenes, and the Effect of Radical Polarity on the Ration of Benzylic Hydrogen Abstraction to Addition to Aromatic Rings
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We have reexamined the reactions of tert-butyl radicals with toluenes and have obtained a ρ value of 0.49 +/- 0.04 at 80 deg C.The new, independent system involves the quantification of all of the principal products from the reaction of tert-butyl radicals with mixtures of toluene and substituted toluene.Five major products contain benzyl fragments and are formed in significant yields: two symmetrical bibenzyls, the cross bibenzyl, and the two neopentylbenzenes that result from combination of tert-butyl and the two benzyl radicals.Attack on the side chain is a major reaction of free tert-butyl radicals and is the only significant reaction that they undergo other than cage and termination reactions. tert-Butyl radicals do not add to the ring of toluenes.Data on the relative rates of addition to benzenes and hydrogen abstraction from toluenes are collected for a series of radicals including hydrogen atoms; methyl, isopropyl, and tert-butyl radicals; and p-nitrophenyl, p-bromophenyl, and phenyl radicals.The data demonstrate that more electrophilic radicals have a larger tendency to add to rings whereas more nucleophilic radicals have a larger tendency to abstract benzylic hydrogens.
- Pryor, William A.,Tang, Felicia Y.,Tang, Robert H.,Church, Daniel F.
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p. 2885 - 2891
(2007/10/02)
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