- Electronic and Molecular Structure of the C8H10+. Valence Isomers 1,3,5-Cyclooctatriene+. and Bicycloocta-2,4-diene+. from their Electronic Absorption Spectra in Freon Glasses
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The molecular cations of 1,3,5-cyclooctatriene (COT+.) and bicycloocta-2,4-diene (BCO+.) can be observed intact in γ-irradiated Freon glasses, as opposed to Ar matrices where ionization is accompanied by extensive rearrangements.This proves the superiority of the Freon-glass method for the generation of metastable primary cations.The electronic absorption (EA) spectra reveal a that a previous analysis of the BCO+. electronic structure on the basis of the ultraviolet photoelectron (UP) spectrum of BCO was incomplete, and b that COT undergoes planarization upon ionization, in accord with qualitative expectations and MNDO calculations.A previously proposed LCBO model was used to assess the influence of the above geometry change on the electronic structure of COT+..
- Bally, Thomas,Roth, Kuno,Straub, Rolf
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- Heats fo Formation of Solvated Annulene and Substituted Azaannulene Dianions
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It was found that the heat of solution of the potassium salt of the cyclooctatetraene (COT) dianion in tetrahydrofuran (-11.1 kcal/mol) measured calorimetrically is very different from the heat of solution determined from solubility data.This is attributed to the existence of a partially solvated solid salt (K+2COT2-*nTHF), which is the form of the COT dianion lowest in energy yet generated.This stable form of the annulene dianion is lower in energy by 393.5 kcal/mol than the gas-phase dianion with two potassium cations.Both solvation and lattice effects are rsponsible for this tremendous stabilization.Substitution of a nitrogen atom for one of the carbon atoms in the eight-member ring system results in an increase in the energy of the THF solvated dianion relative to the metal and neutral organic compound due to an increase in the electron-electron repulsion energy in the dianion.
- Stevenson, Gerald R.,Schock, Laurel E.,Reiter, Richard C.
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- Fragmentation Patterns in the Gas-Phase Pyrolysis of Some Bi- and Tri-cyclic Sulfolanes Related to the 8-Thiabicyclonon-3-ene 8,8-Dioxide Ring System
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Depending upon the degree of ring strain, the thermal breakdown of cis-8-thiabicyclonon-3-ene 8,8-dioxide 5 and related ring systems in the gas phase follows widely differing pathways.Decomposition of 5 occurs only under forcing conditions, resulting in complete fragmentation of the sulfolane ring to give a benzene and toluene, while pyrolysis of the 2,5-bridged analogues 6-8 proceeds by a retro-Diels-Alder reaction at much lower temperatures to give 1,3-dienes and the decomposition products of 3-sulfolene, buta-1,3-diene and SO2.Epoxidation of the double bond in the compounds results in a marked change in their thermal fragmentation behaviour; only SO2 is lost to produce novel divinyl epoxides.The corresponding N-ethoxycarbonylaziridines, formed by photolysis of the unsaturated sulfones in ethyl azidoformate, undergo extensive decomposition on pyrolysis and do not yield any useful products.The saturated sulfone 28 gives an expected octa-1,7-diene upon flash vacuum pyrolysis (FVP), but only under relatively severe conditions.Three isomeric diene sulfones 30-32 have also been examined and show a varied pattern of reactivity under FVP conditions.
- Aitken, R. Alan,Cadogen, J. I. G.,Gosney, Ian,Newlands, Stephen
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p. 2301 - 2308
(2007/10/02)
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- 9-Oxabicyclononynes
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Semiempirical quantum mechanics (MNDO) and force field calculations (MM 2) reveal that two diastereomeric conformations a and b of low energy exist for each of the three isomeric cis-9-oxabicyclononynes 1 - 3.Synthetically, the highly strained comp
- Mayer, Winfried,Meier, Herbert
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p. 509 - 518
(2007/10/02)
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- STRAINED CYCLOALKENYNES
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Presently known strained cycloalkynes with one, two or three additional cis- or trans-configurated double bonds are summarized in Table 3.The main topics of the article are the geometrical ring strain, the preparation or in situ generation of these compounds by fragmentation of the corresponding 1,2,3-selendiazoles, and the thermal isomerisation processes performed at room temperature or in flash pyrolysis experiments at 440-640 deg C.
- Meier, Herbert,Hanold, Norbert,Molz, Thomas,Bissinger, Hans Joachim,Kolshorn, Heinz,Zountsas, Johannes
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p. 1711 - 1720
(2007/10/02)
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- Cycloaddition of Singlet Oxygen and 4-Phenyl-4H-1,2,4-triazole-3,5-dione to 7-Substituted 1,3,5-Cyclooctatrienes
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The cycloaddition of the 7-substituted (X; Y) 1,3,5-cyclooctatrienes 3 (N3; H), 4 (OAc; H), 5 (OEt; OEt), 6 (Me; H), and 7 (iPr; H) with singlet oxygen (1O2) and 4-phenyl-4H-1,2,4-triazole-3,5-dione (PTAD) was investigated.Singlet oxygen gave w
- Adam, Waldemar,Gretzke, Nanette,Hasemann, Ludwig,Klug, Guenter,Peters, Eva-Maria,et al.
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p. 3357 - 3379
(2007/10/02)
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- The Symmetrical Cyclooctadienynes: 1,5-Cyclooctadien-3-yne and 1,3-Cyclooctadien-6-yne
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Starting with 1,5-cycloctadiene (1) and cyclooctatetraene (2), respectively, the title compounds 16 and 17, highly strained members of the C8H8-series, can be generated in six or seven steps and isolated in pure state.Their stability and their chemical behaviour is discussed.Di- and oligomerisations on the one hand and Diels-Alder reactions on the other are mainly concerned. 16 and 17 are very reactive dienophiles; moreover 17 can also be used as a diene.
- Echter, Toni,Meier, Herbert
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p. 182 - 197
(2007/10/02)
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- The Reductive Decyclizations of Semibullvalene
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Reduction of semibullvalene (5) with potassium more closely resembles deprotonation of tetrahydropentalenes by n-butyl-lithium-potassium t-pentoxide than it does the reduction of (5) with lithium; the former processes both provide the cyclo-octatetraenyl dianion (4), plausibly via the intermediate bicyclooctadienediyl dianion (3).
- Goldstein, Melvin J.,Wenzel, Timothy T.
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p. 1654 - 1655
(2007/10/02)
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- An Azocine Anion Radical and Heats of Formation of Azocine Dianions
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3,8-Dimethyl-2-methoxyazocine was reduced to its anion radical in hexamethylphosphoramide (HMPA).The ESR spectrum of the DMMA anion radical resembles one recorded from a monosubstituted cyclooctatetraene anion radical where the substituent is an electron-withdrawing group.Calorimetric techniques were utilized to study the thermodynamic stability of the DMMA dianion.This dianion is more stable relative to the metal and neutral molecule than is either the cycloocatetraene (COT) or tert-butoxycycloocatetraene dianion.The unexpected stability of DMMA2- is attributed to strong interactions between the cation (Na+) with the oxygen and/or nitrogen atoms.This same interaction shifts the disproportionation of DMMA-. to the right in solvents where ion association is prevalent.
- Stevenson, Gerald R.,Schock, Laurel E.,Reiter, Richard C.,Hansen, John F.
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p. 6078 - 6082
(2007/10/02)
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- The Metallation-Elimination Reaction, II. Monocyclic Anions and Polyanions
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Equimolar mixtures of n-butyllithium and potassium tert-amyloxide effect metallation and metal hydride elimination of cyclic olefins directly to give conjugated anions and polyanions in a single operation. 1-Methyl-1-cycloalkenes or methylenecycloalkanes are particularly well suited and give highly unsaturated products.Odd-membered rings eliminate better than their even-membered counterparts, and eight-membered rings eliminate particularly slowly.Reactions with methyl iodide and trimethylsilyl chloride proceed smoothly in high yield.
- Wilhelm, Dieter,Clark, Timothy,Friedl, Thomas,Schleyer, Paul von Rague
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p. 751 - 760
(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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- Polyacene Dianion Crystal Lattice Energies and Thermodynamic Stabilities: The Quantitative Effect of Aromaticity
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A calorimeter interfaced with a data acquisition system has been used to measure the heats evolved from the reactions of solid sodium polyacene dianion salts with water.These heats were utilized in a thermochemical cycle to obtain the thermodynamic stabilities (heats of formation) of the salts.For all of the polyacene dianion salts including those from anthracene, tetracene, pentacene, etc., the heats of formation from the polycene and sodium metal were found to be negative.Electron-electron repulsion energies (E(rep)) were calculated for each of the dianions.The calculated results could then be used with the experimental heats of formation to obtain the actual crystal lattice energies for the salts.For all of the systems studied the crystal lattice energies were found to be between 400 and 440 kcal/mol.Assuming a similar crystal lattice energy for the sodium benzene dianion (Na+2Bz2-), its heat of formation from benzene and sodium metal was found to be very endothermic (+96 kcal/mol).Much of this endothermicity is due to the antiaromatic nature of the benzene dianion.The enthalpy of transferring two electrons from the benzene dianion to the antiaromatic (planar) cyclooctatetraene neutral molecule to form benzene and the cyclooctatetraene dianion is about -177 kcal/mol.
- Stevenson, Gerald R.,Zigler, Steven S.,Reiter, Richard C.
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p. 6057 - 6061
(2007/10/02)
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- Heats of Formation of the Annulene Dianion and Neutral Molecule
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The enthalpy of reaction of the disodium salt of annulene with water and the heat of combustion of neutral annulene were both measured calorimetrically.These measurements were utilized in a thermochemical cycle to yield the heat of reaction of sodium metal with annulene to give the solid dianion salt.The enthalpy of reaction of the dianion with water (-10.9 kcal/mol) is much less exothermic than that for the dianion of annulene.The results indicate that the annulene dianion is greatly stabilized via aromatization.Further, its relative thermodynamic stability over that of the annulene dianion has been attributed to a reduced electron-electron repulsion force in the larger annulene dianion.The combustion measurements indicate that the neutral annulene does not possess any conjugative stability.The heat of combustion of annulene (-2182.2 kcal/mol) is more exothermic by 9 kcal/mol than that for two annulenes.
- Stevenson, Gerald R.,Forch, Brad E.
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p. 5985 - 5988
(2007/10/02)
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- SYNTHESIS AND PHOTOCHEMISTRY OF 2,3,8,9-TETRAHYDROINDENONE-1
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The novel β,γ,δ,ε-unsaturated ketone (2) was prepared and all its photoproducts were identified, following wavelength dependent, irradiation-induced transformations.
- Abramson, Sarah,Fuchs, Benzion
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p. 1165 - 1168
(2007/10/02)
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