- Solvent perturbs the reactivity of tert-butylcarbene
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Two different sources of tert-butylcarbene are used to generate this reactive intermediate in a variety of solvents. Two products, 1,1- dimethylcyclopropane and 2-methyl-2-butene are formed. Solvents able to form an ylid or complex with the carbene strongly favor the alkene product.
- Ruck, Rebecca T.,Jones Jr., Maltland
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- tert-BUTYLCARBENE FROM 1,1-DIIODONEOPENTANE
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When 1,1-diiodoneopentane is passed through a hot tube containing methyllithium-coated Pyrex chips, 1,1-dimethylcyclopropane and 2-methyl-2-butene are produced in near quantitative yield.The ratio of products indicates that the intermediate carbene is the same as is produced from thermal or photosensitized decomposition of tert-butyldiazomethane but different from that formed by direct irradiation of the diazo compound.
- Fukushima, Motoo,Jones, Maitland,Brinker, Udo H.
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- Generation of methylene by the liquid phase oxidation of isobutene with nitrous oxide
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The application of nitrous oxide as an alternative oxidant provides new opportunities for selective oxidation of olefins. Here, we studied for the first time the thermal oxidation of isobutene with N2O in the liquid phase. The study revealed that the oxidation proceeds via 1,3-dipolar cycloaddition of N2O to the C[dbnd]C bond by two routes forming unstable 4,5-dihydro-[1,2,3]-oxadiazole intermediates. The main route (the contribution of 91%) includes the addition of the N2O oxygen to the second carbon atom in olefin. In this case, the oxadiazole decomposes with the C–C bond cleavage yielding acetone, methylene (:CH2), and N2. The methylene then readily reacts with isobutene and benzene (solvent). The minor route involves the addition of the N2O oxygen to the first carbon atom and the oxadiazole decomposition with a hydrogen shift leading to isobutanal and N2. The main distinctive feature of the studied reaction is the formation of methylene in high yield.
- Semikolenov, Sergey,Ivanov, Dmitry,Babushkin, Dmitry,Malykhin, Sergey,Kharitonov, Alexander,Dubkov, Konstantin
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- Azo-coupling and reduction of cyclopropanediazonium ions in the reactions with polyhydroxyarenes and aminophenols
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A reaction of cyclopropanediazonium ion, generated by decomposition of N-cyclopropyl-N-nitrosourea upon treatment with potassium or cesium carbonates, with various poly-hydroxyarenes and aminophenols has been studied. The reaction of azo-coupling proceeds with phloroglucinol, resorcinol, 3-methoxy- and 3-aminophenol giving rise to mono-, bis-, and tris(cyclopropylazo)arenes as the major products. Oxidizable phenols such as hydro-quinone, 2-methoxy-, 4-amino-, and 2-aminophenol give products of radical transformations with participation of cyclopropyl radical.
- Shulishov,Klimenko,Korolev,Kostyuchenko,Okonnishnikova,Tomilov
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experimental part
p. 1703 - 1711
(2011/04/23)
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- Rate coefficients of hydroxyl radical reaction with dimethyl ether and methyl tert-butyl ether over an extended temperature range
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Rate coefficients of the reaction of hydroxyl (OH) radicals with CH3OCH3 (k1) and CH3OC(CH3)3 (k2) over an extended temperature range are reported. Measurements were performed using a laser photolysis-laser-induced fluorescence technique under slow flow conditions at a total pressure of 740±10 Torr. Arrhenius plots of the data exhibited significant curvature and were fitted in the form of k(T) = ATB exp(-C/T). The resulting modified Arrhenius expressions (error limits ±2σ) that best described these extended temperature measurements and prior low-temperature measurements were (in units of cm3 molecule-1 s-1) k1(295-650 K) = (1.05±0.10)×10-17T2.0 and exp[(328±32)/T] and k2(293-750 K) = (1.15±0.11)×10-17T2.04 exp-[(266±41)/T]. Comparison of our measurements for k1 with previous, overlapping low-temperature measurements indicated generally good agreement. Our measurements for k2, although consistent with previous room temperature measurements, exhibited a larger temperature dependence than previously reported. High-temperature oxidation mechanisms for these oxygenated fuel components are proposed. Support for the mechanisms is presented in the form of product analysis studies in high-temperature tubular flow reactors. For CH3OC(CH3)3, these studies suggest that H abstraction from the tert-butyl group is an important high-temperature oxidation pathway.
- Arif,Dellinger,Taylor
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p. 2436 - 2441
(2007/10/03)
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- A Photochemical Source of Real Alkylcarbenes
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Treatment of 7,7-dibromodibenzobicycloheptane with di-tert-butylcuprate or dibutylcuprate, followed by quenching with water, led to exo- and endo-7-monoalkyldibenzobicycloheptanes.Photolysis through either quartz or Pyrex gave the products of intramolecular reactions of the corresponding alkylcarbenes.The temperature dependence of the products formed from tert-butylcarbene was verified, and butylcarbene was trapped intermolecularly. - Keywords: carbenes, retrocycloadditions, insertion reactions.
- Glick, HC,Likhotvorik, Igor R.,Jones, Maitland
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p. 5715 - 5718
(2007/10/02)
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- Synthesis, structure, and reactions of heterobinuclear μ-methylene complexes
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Sources of the reactive fragment Cp2Ti==CH2 react with a variety of late-transition-metal complexes containing μ-halides [Cl-MLn]2 to yield early-late binuclear complexes containing μ-CH2, and μ-Cl ligands. Complexes containing Rh, Ir, Pt, Pd, and Au have been prepared and characterized. The X-ray structure of the complex Cp2Ti-CH2-RhCl(COD) (COD = 1,5-cyclooctadiene) prepared from Cp2Ti-CH2C-(CH3)2-CH2 and [Cl-Rh(COD)]2 has been determined. Crystallographic data: space group Pbcm; Z = 4; a = 8.268 (2) A?, b = 16.409 (4) A?, c = 12.604 (3) A?; V = 1710 (1) A?3. The structure was refined to a final R of 0.069 and R3σ of 0.048 for the 1061 reflections that had Fo > 3σ(Fo).
- Mackenzie, Peter B.,Coots, Robert J.,Grubbs, Robert H.
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- Intermolecular activation of C-D bonds in benzene-d6 by trans-neopentyl(trifluoromethanesulfonato)bis(trimethyl-phosphine) platinum (II)
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trans-(Me3P)2Pt(CH2C(CH3) 3)(SO3CF3) (L2PtNpTf, 1) reacts with benzene-d6 at 133°C and gives trans-(Me3P)2Pt(C6D5)(SO 3CF3) (2) and neopentane-d1 as the major products. When this reaction is carried out in concentrated solutions ([1]0 ≥ 0.04 M), small quantities of neopentane-d0 (8-17%) and 1,1-dimethylcyclopropane (1-3%) are also detected; larger quantities of neopentane-d0 are produced (32-45%) when the initial concentration of 1 is low ([1]0 = 0.01-0.03 M). The rate of reaction is decreased by the addition of Bu4N+Tr- and increased by the addition of Bu4N+BF4-. A competitive kinetic isotope effect was estimated by allowing 1 to react with C6D5H and comparing the relative yields of neopentane-d0 and neopentane-d1: kH/kD is large, but its quantitative value is uncertain because of experimental ambiguities. The mechanism for this reaction seems to involve generation of L2PtNp+ as an essential intermediate. This intermediate appears to react with benzene by direct oxidative addition of a C-H bond, but electrophilic attack on the benzene ring cannot be rigorously excluded.
- Brainard, Robert L.,Rodger Nutt,Randall Lee,Whitesides, George M.
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p. 2379 - 2386
(2008/10/08)
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- Preparation and properties of metallacyclobutanes of nickel and palladium
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Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes.Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carb
- Miyashita, Akira,Ohyoshi, Mayumi,Shitara, Hiroaki,Nohira, Hiroyuki
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p. 103 - 112
(2007/10/02)
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- Synthesis of metallacyclobutanes and metallacyclobutabenzenes of molybdenum and tungsten
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Reactions of 1,3-bis(bromomagnesio)-2,2-dimethylpropane or 1-magnesacyclobutabenzene with either dichloromolybdenocene or dichlorotungstenocene have given the corresponding four-membered metallacycles of both metals.
- Boer, H.J.R. de,Heisteeg, B.J.J. van de,Schat, G.,Akkerman, O.S.,Bickelhaupt, F.
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p. 197 - 200
(2007/10/02)
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- Cyclometallation Reactions in Neopentyl and Trimethylsilylmethyl Systems of Rhodium(III) and Iridium(III). Formation and X-Ray Crystal Structures of the Four-membered Metallacycles and
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The interaction of 5-C5Me5)(PPh3)> with Mg(CH2CMe3)Cl in pentane gives the rhodacyclobutane (2).The analogous reaction of 5-C5Me5)-(PPh3)> (M = Rh or Ir) with Mg(CH2SiMe3)Cl allows the isolation of the dialkyl derivatives 5-C5Me5)(PPh3)>.Thermolysis of 5-C5Me5)(PPh3)> in cyclohexane leads to the iridasilacyclobutane derivative (6).The mechanism of formation of the metallacyclobutane derivatives is discussed.The X-ray crystal structures of (2) and (6) have been determined.The two metallacycle compounds give isostructural crystals belonging to the P21/n space group with four molecules in the unit cell of dimensions for (2): a = 17.199(6), b = 10.987(4), c = 16.06495) Angstroem, β = 109.54(2)deg; (6): = 17.098(7), b = 11.294(5), c= 15.977(7) Angstroem, β = 108.17(2)deg.Their crystal structures refined to R = 0.0441 and 0.0389 for (2) and (6) respectively, are built up of deformed 'three-legged piano stools', one leg being the M-P bond , the other two being the M-C ? bonds of the metallacyclobutane ring with C-Rh-C = 66.8(2) and C-Ir-C = 77.3(4)deg.These rings are puckered: angle between M-C...C and E-C...C = 16.5(4) and 18.9(6)deg for (2) (E = C) and (6) (E = Si), respectively.
- Andreucci, Luca,Diversi, Pietro,Ingrosso, Giovanni,Lucherini, Antonio,Marchetti, Fabio,et al.
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p. 477 - 488
(2007/10/02)
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- The high pressure photochemistry of alkenes. III. The 184.9 nm photoisomerization processes in acyclic alkenes
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We have made a systematic study of the 184.9 nm photoisomerization of the gaseous acyclic alkenes.Apart from the cis-trans isomerization (geometric isomerization), we have also observed the formation of products arising from the 1,3-hydrogen and methylene shifts (structural isomerization). 1-Alkenes do not show evidence of structural isomerization.This kind of isomerization increases with an increase in the number of alkyl substituents around the double bound.These observations, combined with those from the literature, may be explained on the basis of the following: (a) the 1?,?* state is involved in cis-trans isomerization process; (b) the 1?,R(3s) state is responsible for the methylene shifts; (c) another singlet state is required for the 1,3-hydrogen shift; (d) this last state is either at an energy level higher than that of the Rydberg state or the hot ground state.Finally, the photoexcited molecules, through internal conversion, may convert from one state to another, and their lifetime is long enough to be stabilized by collision.
- Collin, Guy J.,Deslauriers, Helene
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p. 1424 - 1430
(2007/10/02)
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- Chemical Activation Study of the Reactions of Methylene with Oxetan and 3,3-Dimethyloxetan
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Methylene (singlet) formed by the photolysis of ketene (313 nm) reacts with oxetan to yield 2-methyl- and 3-methyloxetans by insertion in the C-H bonds and probably also tetrahydrofuran.These products are formed chemically activated and undergo unimolecular decomposition unless collisionally stabilized.Using perfluoropropane as the bath gas, the results obtained with 2-methyloxetan have been interpreted using RRKM theory and a step-ladder model with a most probable step size of ca. 9 kJ mol-1.Using 206 nm radiation yields methylene with excess energy, some of which is still present when it reacts, and results in the production of 2-methyloxetan with an average lifetime approximately one-half that of the energised molecule produced when 313 nm radiation is used.Similarly methylene reacts with 3,3-dimethyloxetan to yield chemically activated 3-ethyl-3-methyloxetan and 2,3,3-trimethyloxetan.A third compound tentatively identified as 3,3-dimethyltetrahydrofuran is also formed.The decomposition of these 3 molecules has been followed and in the case of the ethylmethyloxetan the average energy transferred in collision with 3,3-dimethyloxetan has been found to be ca. 6.5 kJ mol-1.Some deductions can be made about the Arrhenius parameters for the thermal decomposition of the (as yet unreported) trimethyloxetan and the dimethyltetrahydrofuran.
- Frey, Henry M.,Pidgeon, Ivy M.
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p. 1237 - 1248
(2007/10/02)
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- Reductive Elimination of a Carbon-Carbon Bond from Bis(trialkylphosphine)-3,3-dimethylplatinacyclobutanes Produces Bis(trialkylphosphine)platinum(0) and 1,1-Dimethylcyclopropane
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The thermal decompositions of several platinacyclobutanes-bis(triethylphosphine)-(1), bis(triisopropylphosphine)-(2), and bis(tricyclohexylphosphine)-3,3-dimethylplatinacyclobutane (3) -have been examined in cyclohexane solution.Decomposition of 1 proceeds heterogeneously: it products platinum metal, neopentane, 1,1-dimethylcycloprorane, and ethilene and seems to be autocatalytic.Decompositions conducted using reaction mixtures containing mercury(0) proceed homogeneously and produce predominately 1,1-dimethylcyclopropane; any platinum metal produced is apparently amalgamated by Hg(0) and rendered catalytically inactive.Thermal decompositions of 2 and 3 proceed homogeneously, even in the absence of Hg(0), and yield 1,1-dimethylcyclopropane, bis(trialkylphosphine)platinum(0), and small quantity of neopentane.The rates of the decomposition decreases by addition of trialkylphosphine, and a study of these dependence of the rate on concentration of added phosphine for 2 indicates that one phosphine dissociates to produce a three-coordinate platinum(II) intermediate prior to reductive elimination of 1,1-dimethylcyclopropane.The Arrhenius activation parameters for decomposition of 2 and 3 are respectively Ea=46+/-3 kcal mol-1, log A=23+/-2 and Ea=42+/-2 kcal mol-1, log A=21+/-1.Substitution of deuterium for hydrogen in the triisopropylphosphine groups of 2 produces no change in the rate of the reaction.We cannot distinguish between mechanisms in which reductive elimination of 1,1-dimethylcyclopropane occurs directly from the three-coordinate intermediate and those in which oxidative addition of a C-H bond to platinum bycyclometalation of the phosphine produces a Pt(IV) intermediate in a step preceding rate-limiting reductive elimination of 1,1-dimethylcyclopropane.
- DiCosimo, Robert,Whitesides, George M.
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p. 3601 - 3607
(2007/10/02)
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- C(sp3)-H and C(sp2)-H Bond Activation in the (Pentamethylcyclopentadienyl)rhodium(III) System: Formation of (2,2-Dimethylpropane-1,3-diyl)(pentamethylcyclopentadienyl)(triphenylphosphine)rhodium and Neopentyl(pentamethylcyclopentadie
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The rhodacyclobutane and the ortho-metallated compound are formed in the reaction of 5-C5Me5)(PPh3)> with LiCH2CMe3 or XMgCH2CMe3.
- Diversi, Pietro,Ingrosso, Giovanni,Lucherini, Antonio,Fasce, Daniela
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p. 945 - 946
(2007/10/02)
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- The Spiropentyl Radical and Some Homolytic Reactions of Spiropentane
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Spiropentyl radical was generated by Hydrogen abstraction from spiropentane by t-butoxyl radical and its e.s.r. spectrum obtained.The experimental e.s.r. parameters were compared with computational results obtained using semi-empirical SCF MO methods.The spiropentyl radicals do not undergo β-scission in the observable temperature range (T H2 attack by the halogen atom to give 1-(halogenomethyl)cyclopropylmethyl radicals.The β-scission of these latter radicals has been inves tigated by e.s.r. spectroscopy and by the reduction of 1,1-bisbromomethylcyclopropane with tri-n-butyltin hydride.
- Kennedy, Alan J.,Walton, John C.,Ingold, Keith U.
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p. 751 - 757
(2007/10/02)
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- Coupling of Organic Halides electrocatalyzed by the NiII/NiI/Ni0-PPh3 System. A Mechanistic Study based on an Electroanalytical Approach
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The coupling of the organic halides bromobenzene, 1-iodobutane, 1-iodo-2,2-dimethylpropane, and benzyl chloride has been carried out by electrochemically generating and continuously recycling the nickel(0) complex promoter .This species undergoes oxidative addition by organic halides leading to ?-bonded organometallic nickel(II) derivatives.In these complexes the metal-carbon bond can be cleaved either by a straightforward thermal decomposition or by a cathodic reduction, depending upon whether the co-ordinated organic group is an alkyl or an aryl one.In the former case a high yield of the coupling product is obtained only by employing organic halides not bearing hydrogen atoms in the β position; when a β-elimination reaction can occur, the yield of the coupling product is, on the contrary, very low and can be significantly improved only by carrying out the reductive process at more negative potentials, at which a proposed nickel hydride intermediate can be reduced.When the co-ordinated organic group is an aryl one, reductive elimination of the organic group does not occur by thermal decomposition and the coupling product can be formed only by means of a cathodic reduction of the relevant organometallic nickel(II) derivative.An overall mechanism is proposed which is consistent with the data.
- Schiavon, Gilberto,Bontempelli, Gino,Corain, Benedetto
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p. 1074 - 1081
(2007/10/02)
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- The photolysis of tetrahydrofuran and of some of its methyl derivatives at 185 nm
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The uv photolysis of tetrahydrofuran, 1, 2-methyltetrahydrofuran, 2, cis-2,5-dimethylterahydrofuran, 3, trans-2,5-dimethyltetrahydrofuran, 4, and 2,2,5,5-tetramethyltetrahydrofuran, 5, has been investigated by product analysis in the liquid phase, and quantum yields have been determined.The photolysis of tetrahydrofuran itself was also studied in the gas phase at pressures ranging from 1 to 120 atm (pressurizing gas N2); and very little difference was found between the photolytic behaviour of the vapour at 120 atm and that of the liquid.The major products are in all cases the cyclopropanes and the corresponding carbonyl compounds, as well as the olefinic alcohols and the carbonyl compounds that are isomeric with the starting material.These products are considered to be formed by the two primary processes and . The cyclopropanes formed in reaction retain some excess energy (apparently more then is needed to realize the trimethylene form), and in the photolysis of tetrahydrofuran vaapour the hot cyclopropane rearranges to a considerable extent into propene.The propene to cyclopropane yield ratio falls strongly with increasing pressure, to a value of 0.065 at 120 atm.A similar value is observed in the liquid phase photolysis.The five-membered oxyl alkyl diradical from reaction is the likely intermediate in the cis-trans photoisomerization that is observable with the 2,5-dimethyltetrahydrofurans (Φ(cis -> trans) ca. Φ(trans -> cis) ca. 0.2).The photolysis of these compounds also demonstrates that steric factors have a strong bearing on the course of the reaction, e. g. the quantum yield of methylcyclopropane from the cis compound is 0.22, vs. 0.08 from the trans compound.Molecular hydrogen is produced if the tetrahydrofurans carry hydrogen in α-position.Its production is enhanced if the α-position is shared with a methyl group (1 gives a hydrogen quantum yield of 0.07, 2 of 0.17, 3 of 0.27, 4 of 0.29, and 5 of zero).
- Kizilkilic, Nuray,Schuchmann, Heinz-Peter,Sonntag, Clemens Von
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p. 2819 - 2826
(2007/10/02)
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- (E-Z)-ISOMERISATION OF CHLOROOLEFINS
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Equilibrium constants for the (E-Z)-isomerisation of the compounds R-CH=CH-Cl were determined and the experimental values compared with energy differences, calculated by the CNDO/2 method.
- Prochazka, Milos,Adamcova, Jindriska,Palecek, Milos
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p. 1388 - 1400
(2007/10/02)
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- Ion-Molecule Complexes in Unimolecular Fragmentations of Gaseous Cations. Alkyl Phenyl Ether Molecular Ions
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A decomposition pathway that bears a formal resemblance to first-order elimination in solution is demonstrated for parent ion fragmentations of alkyl phenyl ethers under electron impact (EI) and chemical ionization (CI).The sequence of steps in the gas phase, parent ion -> ion-molecule complex -> fragments, is analogous to first-order elimination in solution (which goes through ion pairs).Such a mechanism for expulsion of PhOH+. from molecular ions has been tested by examing neutral products from 70-eV electron bombardment of neopentyl phenyl ether in a specially constructed electron bombardment flow (EBFlow) reactor.The C5H10 isomers 2-methyl-1-butene (2) and 2-methyl-2-butene (3) are recovered in the same ratio (2/3=1.14) as is produced by gas-phase deprotonation of tert-amyl cation.This result is validated by a mass spectrometric study of deuterated analogues, for which the ratio of γ-transfer (corresponding to product 2) to α-transfer (corresponding to product 3) is calculated to be 1.46.Intermediacy of an ion-molecule complex, PhOCH2C(CH3)3+. -> .CH3CH2(CH3)2C+> -> PhOH+. + 2 or 3, predicts this outcome, where the species in brackets represents an electrostatically bound comlex of the neutral phenoxyl radical and an alkyl cation.This mechanism explains the published mass spectrometric (EI an CI) and EBFlow results for n-propyl and n-butyl phenyl ethers.Several confirmatory experiments support the intermediacy of an ion-molecule complex and rule out other interpretations of the experiment data.
- Morton, Thomas Hellman
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p. 1596 - 1602
(2007/10/02)
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