The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
David Lee Phillips - One of the best experts on this subject based on the ideXlab platform.
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time resolved resonance raman study of the reaction of isoDiiodomethane with cyclohexene implications for the mechanism of photocyclopropanation of olefins using ultraviolet photolysis of Diiodomethane
Journal of Physical Chemistry A, 2001Co-Authors: Yunliang Li, King Hung Leung, David Lee PhillipsAbstract:We examine the chemical reaction of isoDiiodomethane (CH2I−I) with cyclohexene using time-resolved resonance Raman spectroscopy. Our results indicate that CH2I−I reacts with cyclohexene to produce an iodine molecule leaving group on the 5−10 ns time scale which then almost immediately forms a I2:cyclohexene complex. This in conjunction with previous results from photochemistry experiments and recent density functional theory calculations indicates that isoDiiodomethane is the methylene transfer agent mainly responsible for cyclopropanation of olefins when using ultraviolet photolysis of Diiodomethane. We present a mechanism for photocyclopropanation that is consistent with both experimental and theoretical characterization of reaction intermediates and products formed after ultraviolet photolysis of Diiodomethane in a condensed phase environment. We briefly discuss the differences and similarities in the behavior of the isoDiiodomethane and the Simmons−Smith carbenoids toward cyclopropanation reactions wi...
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isoDiiodomethane is the methylene transfer agent in cyclopropanation reactions with olefins using ultraviolet photolysis of Diiodomethane in solutions a density functional theory investigation of the reactions of isoDiiodomethane iodomethyl radical a
Journal of the American Chemical Society, 2001Co-Authors: David Lee Phillips, Weihai Fang, Xuming ZhengAbstract:We examine the chemical reactions of the isoDiiodomethane (CH2I−I), ·CH2I and CH2I+ species with ethylene using density functional theory computations. The CH2I−I species readily reacts with ethylene to give the cyclopropane product and an I2 product via a one-step reaction with a barrier height of ∼2.9 kcal/mol. However, the ·CH2I and CH2I+ species have much more difficult pathways (with larger potential barriers) to react with ethylene via a two-step reaction mechanism. Comparison of experimental results to our present calculation results indicates that the CH2I−I photoproduct species is most likely the methylene transfer agent for the cyclopropanation reaction of olefins via ultraviolet photoexcitation of Diiodomethane.
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picosecond time resolved resonance raman observation of the iso ch2i i photoproduct from the photoisomerization reaction of Diiodomethane in the solution phase
Journal of Chemical Physics, 2000Co-Authors: Wai Ming Kwok, David Lee Phillips, Anthony W Parker, Michael Towrie, Pavel Matousek, D PhillipsAbstract:We report a preliminary picosecond Stokes and anti-Stokes time-resolved resonance Raman (267 nm pump and 400 nm probe excitation wavelengths) investigation of the initial formation and vibrational cooling of the iso-CH2I–I photoproduct species produced after ultraviolet excitation of Diiodomethane in room temperature solutions. A comparison of the picosecond resonance Raman spectra with previously reported nanosecond transient resonance Raman spectra and density functional theory computations shows that the iso-CH2I–I photoproduct species is predominantly responsible for the ∼385 nm transient absorption band observed from several picoseconds to nanoseconds after ultraviolet excitation of Diiodomethane in the solution phase. Similar results were obtained in both nonpolar solution (cyclohexane solvent) and polar solution (acetonitrile) solvent. The picosecond resonance Raman spectra confirm that the iso-CH2I–I photoproduct species is formed vibrationally hot within several picoseconds and then subsequently ...
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Picosecond time-resolved resonance Raman observation of the iso-CH2I–I photoproduct from the “photoisomerization” reaction of Diiodomethane in the solution phase
Journal of Chemical Physics, 2000Co-Authors: Wai Ming Kwok, David Lee Phillips, Anthony W Parker, Michael Towrie, Pavel Matousek, Chensheng Ma, D PhillipsAbstract:We report a preliminary picosecond Stokes and anti-Stokes time-resolved resonance Raman (267 nm pump and 400 nm probe excitation wavelengths) investigation of the initial formation and vibrational cooling of the iso-CH2I–I photoproduct species produced after ultraviolet excitation of Diiodomethane in room temperature solutions. A comparison of the picosecond resonance Raman spectra with previously reported nanosecond transient resonance Raman spectra and density functional theory computations shows that the iso-CH2I–I photoproduct species is predominantly responsible for the ∼385 nm transient absorption band observed from several picoseconds to nanoseconds after ultraviolet excitation of Diiodomethane in the solution phase. Similar results were obtained in both nonpolar solution (cyclohexane solvent) and polar solution (acetonitrile) solvent. The picosecond resonance Raman spectra confirm that the iso-CH2I–I photoproduct species is formed vibrationally hot within several picoseconds and then subsequently ...
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solvation can open the photoisomerization pathway for the direct photodissociation reaction of Diiodomethane transient resonance raman observation of the isoDiiodomethane photoproduct from ultraviolet excitation of Diiodomethane in the solution phase
Journal of Physical Chemistry A, 2000Co-Authors: Xuming Zheng, David Lee PhillipsAbstract:We report transient resonance Raman experiments that identify isoDiiodomethane as the photoproduct responsible for the ∼385 nm absorption band observed following ultraviolet excitation of Diiodomethane in liquid solutions. Comparison with previously reported gas-phase experiments and solution-phase resonance Raman and femtosecond transient absorption results suggest that solvation leads to appreciable production of the isoDiiodomethane (H2C−I−I) photoproduct via the interaction of the initially formed CH2I and I fragments with the solvent cage. The isoDiiodomethane photoproduct is likely the species or an intermediate to the species that reacts with alkenes in cyclopropanation reactions that use ultraviolet excitation of Diiodomethane in liquids.
Xuming Zheng - One of the best experts on this subject based on the ideXlab platform.
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isoDiiodomethane is the methylene transfer agent in cyclopropanation reactions with olefins using ultraviolet photolysis of Diiodomethane in solutions a density functional theory investigation of the reactions of isoDiiodomethane iodomethyl radical a
Journal of the American Chemical Society, 2001Co-Authors: David Lee Phillips, Weihai Fang, Xuming ZhengAbstract:We examine the chemical reactions of the isoDiiodomethane (CH2I−I), ·CH2I and CH2I+ species with ethylene using density functional theory computations. The CH2I−I species readily reacts with ethylene to give the cyclopropane product and an I2 product via a one-step reaction with a barrier height of ∼2.9 kcal/mol. However, the ·CH2I and CH2I+ species have much more difficult pathways (with larger potential barriers) to react with ethylene via a two-step reaction mechanism. Comparison of experimental results to our present calculation results indicates that the CH2I−I photoproduct species is most likely the methylene transfer agent for the cyclopropanation reaction of olefins via ultraviolet photoexcitation of Diiodomethane.
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solvation can open the photoisomerization pathway for the direct photodissociation reaction of Diiodomethane transient resonance raman observation of the isoDiiodomethane photoproduct from ultraviolet excitation of Diiodomethane in the solution phase
Journal of Physical Chemistry A, 2000Co-Authors: Xuming Zheng, David Lee PhillipsAbstract:We report transient resonance Raman experiments that identify isoDiiodomethane as the photoproduct responsible for the ∼385 nm absorption band observed following ultraviolet excitation of Diiodomethane in liquid solutions. Comparison with previously reported gas-phase experiments and solution-phase resonance Raman and femtosecond transient absorption results suggest that solvation leads to appreciable production of the isoDiiodomethane (H2C−I−I) photoproduct via the interaction of the initially formed CH2I and I fragments with the solvent cage. The isoDiiodomethane photoproduct is likely the species or an intermediate to the species that reacts with alkenes in cyclopropanation reactions that use ultraviolet excitation of Diiodomethane in liquids.
Jianguo Mi - One of the best experts on this subject based on the ideXlab platform.
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interfacial structures surface tensions and contact angles of Diiodomethane on fluorinated polymers
Journal of Physical Chemistry C, 2014Co-Authors: Yang Wang, David K Sang, Zhongjie Du, Chen Zhang, Ming Tian, Jianguo MiAbstract:The wetting behavior of Diiodomethane on crystalline poly(tetrafluoroethylene) (PTFE), noncrystalline PTFE, and poly(vinylidene cyanide-alt-1H,1H,2H,2H-perfluorodecyl vinyl ether) surfaces are analyzed theoretically. By combining three-dimensional reference interaction site model with three-dimensional density functional theory, the theory provides the overall density and free-energy distributions of Diiodomethane at the three surfaces. It is shown that surface roughness arising from polymer structure and configuration plays the crucial role in the surface tension and the wettability. Meanwhile, the contribution of chemical composition is also important to the surface tension by altering the intra- and intermolecular interactions and renormalizing the surface roughness. The predicted contact angles of a Diiodomethane droplet on the three surfaces are in good agreement with the available experimental values, showing the theory is able to quantitatively evaluate the cooperative contributions of chemical com...
Francisco Zaera - One of the best experts on this subject based on the ideXlab platform.
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thermal chemistry of Diiodomethane on ni 1 1 0 surfaces i clean and hydrogen covered
Surface Science, 2003Co-Authors: Francisco ZaeraAbstract:The thermal chemistry of Diiodomethane on Ni(1 1 0) single-crystal surfaces was studied by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Diiodomethane was chosen as a precursor for the formation of methylene surface species. I 3d and C 1s XPS data indicated that, indeed, adsorbed Diiodomethane undergoes the C–I bond dissociations needed for that transformation, and detection of iodomethane production in TPD experiments pointed to the stepwise nature of those reactions. Significant amounts of methane are produced from further thermal activation of the chemisorbed methylene groups. This involves surface hydrogen, both coadsorbed from background gases and produced by dehydrogenation of some of the adsorbed Diiodomethane, and can be induced at temperatures as low as about 160 K, right after the C–I bond breaking steps. Unique to this system is the detection of significant amounts, up to 10% of the total CH2I2 adsorbed, of heavier hydrocarbons, including ethene, ethane, propene, propane, and butene. Deuterium labeling experiments were used to provide support for a mechanism where the initial hydrogenation of some adsorbed methylene to methyl moieties is followed by a rate-limiting methylene insertion step to yield ethyl intermediates. Facile subsequent b-hydride elimination and reductive elimination with coadsorbed hydrogen account for the formation of ethene and ethane, respectively, while a second and third methylene insertions lead to C3 and C4 production. Based on the final product distribution, the methylene insertion was estimated to be approximately 20 times slower than the following hydrogenation–dehydrogenation reactions. Normal kinetic isotope effects were observed for most of the hydrogenation and dehydrogenation reactions involved. � 2003 Elsevier B.V. All rights reserved.
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thermal chemistry of Diiodomethane on ni 1 1 0 surfaces ii effect of coadsorbed oxygen
Surface Science, 2003Co-Authors: Francisco ZaeraAbstract:Abstract The effect of coadsorbed oxygen on the thermal chemistry of Diiodomethane on Ni(1 1 0) single-crystal surfaces was studied by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). I 3d and C 1s XPS data indicated that adsorbed Diiodomethane undergoes two sequential C–I bond scission steps to ultimately produce methylene surface species, the same as on clean Ni(1 1 0). Moreover, significant amounts of methane and other heavier hydrocarbons are produced after further thermal activation of those chemisorbed methylene groups. The production of alkanes and alkenes, which is accounted for by a chain growth mechanism where the initial hydrogenation of some adsorbed methylene to methyl moieties is followed by a rate-limiting methylene insertion step to yield ethyl intermediates, is inhibited but not fully blocked by the coadsorbed oxygen. New reaction pathways are also opened up by the presence of oxygen in this system, including a direct coupling of two methylene groups to ethene, the insertion of an oxygen atom into a nickel–methylene group to produce formaldehyde, and a parallel methylene insertion chain growth sequence starting from a CH 2 I ads intermediate to ultimately yield C 3 H 5 and C 4 H 7 unsaturated gas-phase radicals.
Oksang Jung - One of the best experts on this subject based on the ideXlab platform.
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host guest conversion transformation of Diiodomethane within 1d ensemble suprachannels into triiodide iodine channel via photoreaction
Crystal Growth & Design, 2018Co-Authors: Seo Young Hwang, Malenahalli Halappa Naveen, Yoonbo Shim, Oksang JungAbstract:Self-assembly of ZnBr2 with 2,7-bis(isonicotinoyloxy)naphthalene (L) yields one-dimensional (1D) zigzag chains of [ZnBr2L] composition. This 1D chain ensemble forms unique suprachannels of 4.0 × 4.2 A2 size via weak C–H···π and π···π interactions. A 350 nm ultraviolet irradiation affects host–guest conversion. Diiodomethane molecules within the suprachannel structure of CHCl3·CH2I2@[ZnBr2L] were transformed into an unprecedented triiodide–iodine channel skeleton, HL+@[I3·I2]−. Specifically, two clear, quasi-reversible redox peaks were observed at +0.33 and +0.70 V versus Ag/AgCl in the anodic scan and at +0.19 and +0.62 V in the cathodic scan in acetonitrile for HL+@[I3·I2]−.
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Host–Guest Conversion: Transformation of Diiodomethane within 1D-Ensemble Suprachannels into Triiodide–Iodine Channel via Photoreaction
Crystal Growth & Design, 2018Co-Authors: Seo Young Hwang, Malenahalli Halappa Naveen, Yoonbo Shim, Oksang JungAbstract:Self-assembly of ZnBr2 with 2,7-bis(isonicotinoyloxy)naphthalene (L) yields one-dimensional (1D) zigzag chains of [ZnBr2L] composition. This 1D chain ensemble forms unique suprachannels of 4.0 × 4.2 A2 size via weak C–H···π and π···π interactions. A 350 nm ultraviolet irradiation affects host–guest conversion. Diiodomethane molecules within the suprachannel structure of CHCl3·CH2I2@[ZnBr2L] were transformed into an unprecedented triiodide–iodine channel skeleton, HL+@[I3·I2]−. Specifically, two clear, quasi-reversible redox peaks were observed at +0.33 and +0.70 V versus Ag/AgCl in the anodic scan and at +0.19 and +0.62 V in the cathodic scan in acetonitrile for HL+@[I3·I2]−.