- Transient Kinetics and Quantum Yield Studies of Nanocrystalline α-Phenyl-Substituted Ketones: Sorting Out Reactions from Singlet and Triplet Excited States
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Recent work has shown that diarylmethyl radicals generated by pulsed laser excitation in nanocrystalline (NC) suspensions of tetraarylacetones constitute a valuable probe for the detailed mechanistic analysis of the solid-state photodecarbonylation reaction. Using a combination of reaction quantum yields and laser flash photolysis in nanocrystalline suspensions of ketones with different substituents on one of the α-carbons, we are able to suggest with confidence that a significant fraction of the initial α-cleavage reaction takes place from the ketone singlet excited state, that the originally formed diarylmethyl-acyl radical pair loses CO in the crystal with time constants in the sub-nanosecond regime, and that the secondary bis(diarylmethyl) triplet radical pair has a lifetime limited by the rate of intersystem crossing of ca. 70 ns.
- Park, Jin H.,Chung, Tim S.,Hipwell, Vince M.,Rivera, Edris,Garcia-Garibay, Miguel A.
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supporting information
p. 8192 - 8197
(2018/06/22)
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- Generation and Reactivity Studies of Diarylmethyl Radical Pairs in Crystalline Tetraarylacetones via Laser Flash Photolysis Using Nanocrystalline Suspensions
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The nanosecond electronic spectra and kinetics of the radical pairs from various crystalline tetraarylacetones were obtained using transmission laser flash photolysis methods by taking advantage of aqueous nanocrystalline suspensions in the presence of su
- Park, Jin H.,Hughs, Melissa,Chung, Tim S.,Ayitou, A. Jean-Luc,Breslin, Vanessa M.,Garcia-Garibay, Miguel A.
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supporting information
p. 13312 - 13317
(2017/10/05)
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- Supramolecular Steric Effects as the Means of Making Reactive Carbon Radicals Persistent. Quantitative Characterization of the External Surface of MFI Zeolites through a Persistent Radical Probe and a Langmuir Adsorption Isothez
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The photochemistry of tetraphenylacetone (1) adsorbed on the external surface of a MFI zeolite (the sodium form of LZ-105) has been investigated in combination with computational chemistry, surface area measurements, EPR analysis, and classical adsorption isotherms. All of the methods are consistent with a supramolecular structural model in which 1 is first adsorbed strongly through intercalation of a single benzene ring into a hole on the LZ-105 external surface (site I) followed by a weaker binding to the external framework between the holes (site II) until a monolayer of 1 is formed. From both computational and surface area measurements, it is estimated that the site I holes on the external surface will be filled at ca. 0.3-0.5 wt %/wt loading of 1/LZ-105, which corresponds to 6.5 × 1018 (ca. 10-5 mol) of holes or molecules of 1 adsorbed in holes per gram of zeolite. The supramolecular composition of ca. 0.3-0.5% of 1 on LZ-105 characterizes a "break point" for the photochemistry and the EPR measurements, since it represents the value for saturation of the site I holes with 1. These conclusions are supported quantitatively by experimental isotherms of the adsorption of 1 on LZ-105. Photolysis of 1 intercalated in the site I holes causes fragmentation into two isomeric supramolecular diphenylmethyl (DPM) radicals, one (DMP)in which is adsorbed into the internal surface and becomes strongly persistent (half-life of many weeks) and the other (DMP)ex which diffuses on the external surface and rapidly dimerizes (less than a few minutes) to produce the radical-radical combination product tetraphenylethane (2). Photolysis of 1 adsorbed on the solid external surface produces two supramolecularly equivalent DPM radicals (DMP)ex that diffuse on the external surface and rapidly dimerize to produce 2, and do not produce persistent DPM radicals. * To whom correspondence should be addressed.
- Hirano, Takashi,Li, Wei,Abrams, Lloyd,Krusic, Paul J.,Ottaviani, M. Francesca,Turro, Nicholas J.
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p. 1319 - 1330
(2007/10/03)
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- Regioselective Arylation Reactions of Biphenyl-2-ols, Naphthols, and Benzylic Compounds with Aryl Halides under Palladium Catalysis
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Biphenyl-2-ols undergo regioselective mono- and diarylation upon a treatment with aryl iodides in the presence of a palladium catalyst in DMF using Cs2CO3 as a base to produce 1,1′ : 2′,1″-terphenyl-2-ol and 2′,6′-diphenylbiphenyl-2-ol and their derivatives. The reaction of 1-naphthol selectively occurs at its 8-position to give 8-aryl-1-naphthols. In the reaction of 2-naphthol with aryl bromides, diarylated compounds, 1-(2-arylphenyl)-2-naphthols, are formed as the single major products. Under similar conditions, benzyl ketones, phenylacetonitrile, and methyl phenylacetate are arylated at their benzylic position.
- Satoh, Tetsuya,Inoh, Jun-Ichi,Kawamura, Yoshiki,Kawamura, Yuichiro,Miura, Masahiro,Nomura, Masakatsu
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p. 2239 - 2246
(2007/10/03)
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- Palladium-catalyzed regioselective mono- and diarylation reactions of 2-phenylphenols and naphthols with aryl halides
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Not only monoarylation but also diarylation of 2-phenylphenols with aryl iodides proceeds effectively and regioselectively when a palladium catalyst and an appropriate base are employed. The products are 1,2-diphenyl- and 1,2,3-triphenylbenzene derivative
- Satoh,Kawamura,Miura,Nomura
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p. 1740 - 1742
(2007/10/03)
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- Y-Conjugated Dianions. A 13C Nuclear Magnetic Resonance Study
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Tris(diphenylmethylene)methane dianion (12-), tetraphenylacetone dianion (22-), and diphenylacetate dianion (32-) were generated in dimethyl sulfoxide or tetrahydrofuran solutions by deprotonation of the appropriate carbon acid.Chemical shifts, carbon-carbon spin coupling constants, and other spectroscopic evidence indicated an sp2-hybridized central atom for all dianions, as well as D3 symmetry for the all-carbon dianion.The one-bond CC spin coupling constant for 12- (62 Hz) increased upon consecutive replacements of diphenylmethylene by the groups, i.e., to 69 Hz for 22- and 76.7 Hz for 32-,2K+ (86.0 Hz for the Li+ salt) reflecting charge localization at oxygen.An empirical model for the residual charge on phenyl-substituted resonance-stabilized carbanions that allows comparison of dissimilarly substituted carbanions was developed.
- Rajca, Andrzej,Tolbert, Laren M.
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p. 871 - 876
(2007/10/02)
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- The Chemistry of Pentavalent Organobismuth Reagents. Part 7. The Possible Role of Radical Mechanisms in the Phenylation Process for Bismuth(V), and Related Lead(IV), Iodine(III), and Antimony(V) Reagents
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The phenylation reactions of bismuth(V), lead(IV), and iodine(III) have been examined to test the presence or absence of phenyl radicals.In the case of several bismuth(V) reactions the presence of phenyl radicals has been detected, but it has been shown, by use of a large excess of radical trapping agent, that these radicals have nothing to do with the phenylation process.In the same way, the other phenylation reactions fail to respond to a large excess of a radical trap.
- Barton, Derek H. R.,Finet, Jean-Pierre,Giannotti, Charles,Halley, Frank
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p. 241 - 250
(2007/10/02)
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- Exploratory Study of the Intermolecular Reactivity of Excited Diphenylmethyl Radicals
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A series of intermolecular reactions of excited diphenylmethyl radicals has been examined with laser flash photolysis techniques.The radicals, Ph2CH(.), were generated by 308-nm photodecomposition of 1,1,3,3-tetraphenylacetone or diphenyldiazomethane.In the latter system the radicals result from reaction of diphenylcarbene with hydrogen-donor solvents.The radicals were then excited with the 337-nm pulses from a nitrogen laser, leading to the formation of the readily detectable excited state of the radical, Ph2CH(.) (λmax 355 nm).The excited radical is an excellent electron donor, reacting with methyl viologen with kq=1.3*1010 M-1s-1 in wet acetonitrile and leading to the formation of methyl viologen radical cation.Ph2CH(.) is readily quenched by amines, but no evidence for full electron transfer could be obtained, e.g., for triethylamine kq = 5.2*108 M-1 s-1 in cyclohexane.The excited radical is 14 times more reactive toward oxygen than its ground state, but the process seems to involve a different mechanism, probably leading to singlet oxygen generation.Halogenated substrated react readily with Ph2CH(.); for example, for CCl4 kq = 1.6*108 M-1 s-1 and leads to Ph2CHCl in a process that is presumed to involve charge transfer.Excited diphenylmethyl is not a good hydrogen abstractor in spite of the fact that its hydrogen abstraction reactions would be more exothermic than those of phenyl radicals.
- Scaiano, J. C.,Tanner, M.,Weir, D.
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p. 4396 - 4403
(2007/10/02)
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- Studies on the Reaction of 3,3,4,4-Tetraphenylthietan-2-one
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The chemical reactivity of 3,3,4,4-tetraphenylthietan-2-one (3,3,4,4-tetraphenyl-β-thiolactone, 5) toward nucleophilic, reducing, and oxidizing reagents has been investigated.Compound 5 is relatively inert toward nucleophiles (1-butanethiol, sodium hydroxide, sodium methoxide).The only product obtained from these reactions which cannot be readily attributed to initial thermal fragmentation of the ring is tetraphenylethylene (10).Treatment of 5 with the strong reducing reagent LiAlH4 gave four products upon workup: 2,2,3,3-tetraphenyl-1-propanol (19), 2,2,3,3-tetraphenylpropyl acetate (20), 1,1,3,3-tetraphenyl-2-propanone (7), and 1,1,3-triphenyl-2-indanone (21).The substituted acetone 7 was also obtained when DIBAL was added to 5.Desulfurization experiments with Raney nickel and cobalt catalysts consistently gave 10 in varying amounts.In addition to the alkene 10, compounds 7, 21, and 2,2,3-triphenyl-4,5,6,7-tetrahydro-1-indanone (26) were also isolated with W-2 Raney nickel.Finally, oxidation of 5 with m-chloroperbenzoic acid gave the novel mixed carboxylic-sulfinic acid anhydride (32).This molecule is of particular interest in light of the previous difficulty encountered in the preparation of this class of compounds.Many of the products obtained in these reactions are not those expected based upon previous studies of β-thiolactones.Potential pathways for the origin of the compounds obtained are suggested.
- Charumilind, P.,Kohn, Harold
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p. 4359 - 4365
(2007/10/02)
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