A comparison between gas phase simulated radiolysis with low energy electrons and mercury (3P1) photosentisized dissociation: chemical effects associated with the triplet states of propene

Results on the chemical effects associated with the three known triplet states of propene at 4.4, ≈6.1 and 7.7 eV, deduced from gas phase simulated radiolysis of propene and of its isomer cyclopropane with low energy electrons, are discussed. Data of previous authors on mercury authors on mercury (³P₁) photosensitized decomposition of propene are included in the discussion.     

Gas-phase reactions of free phenylium cations with C3H6 hydrocarbons

Free, unsolvated phenylium ions formed by the spontaneous β decay of a constituent atom of multitritiated benzene have been allowed to react with gaseous propene and cyclopropane in the pressure range from 10 to 700 torr. Phenylium ions attack efficiently both the C-H and the C-C bonds of cyclopropane, yielding respectively tritiated cyclopropylbenzene and indane as the major products. Selective attack of phenylium ions on the π bond of propene is suggested by the composition of tritiated products, isomeric phenylpropenes and isopropylbenzene. The different behavior of propene and cyclopropane toward gaseous phenylium ions is consistent with the results of related radiolytic investigations concerning gaseous systems at nearly atmospheric pressure. The reactivity pattern of the isomeric C₃H₆ hydrocarbons toward gaseous phenylium ions is discussed and compared with pertinent mass spectrometric data.     

The pyrolysis of trimethylene sulfide. A unimolecular decomposition

The kinetics of decomposition of trimethylene sulfide to ethylene and thioformaldehyde was investigated in a single-pulse shock tube using the «relative rate» technique. The extent of reaction was measured in the reflected shock regime from 860° to 1170°K, but experimental difficulties limited the useful data to the temperature range of 980°–1040°K. The first-order rate constant was found to be k = 10^13.0 exp (?48,200/RT) sec^?1. This result sets an upper limit of 50 kcal/mole for the standard enthalpy of formation of CH₂S, with 35 kcal/mole as a more likely value. The isomerization of cyclopropane to propene was used for the reference reaction; in turn, this was checked, in a relative rate experiment, against the pyrolysis of cyclohexene.     

Competition between C-C and C-H insertion in prototype transition metal-hydrocarbon reactions

The competition between C-C and C-H insertion in model transition-metal reactions with cyclopropane and propene (C3H6) was studied as a function of total energy. Insertion of neutral transition metal atoms M (= Y, Zr, Nb, and Mo*) into the C-C bonds of cyclopropane led to formation of MCH2 + C2H4, whereas C-H insertion produced MC3H4 + H2. The measured product branching ratios verify the relative potential energy barrier heights for C-C and C-H insertion predicted by ab initio calculations.     

Influence of Molybdenum on Ceria Activity and CO2 Selectivity in Propene Total Oxidation

A total oxidation of propene into CO₂ is obtained on pure ceria at 673 K. However, in the presence of molybdenum, propene can be partially oxidized at room temperature. The Electron Paramagnetic Resonance (EPR) indicates changes in the oxidation state of molybdenum occurring upon interaction with propene. It has been found that the concentration of Mo(V) influences the propene conversion. The interaction between propene and molybdenum leads to the formation of surface species that, depending on the strength of their bonding to the surface, can be decomposed to ethene or coke. These results have been confirmed by infrared (FTIR) study. The oxidation reaction of propene is in competition with that of coke or ethene deposit on the catalyst surface, which can explain the decrease of the catalyst activity and selectivity in the presence of high molybdenum loadings.     

The Interaction of Walsh-Orbitols in Diademane and Related Hydrocarbons

To obtain further information concerning the interaction between Walsh-orbitols of ‘conjugated’ cyclopropane rings, the photoelectron spectra of the following compounds have been recorded: bicyclo[4.1.0]heptane 1 , cis- and trans-tricyclo[5.1.0^{3, 5}]octane 2, 3 , diademane 4 , trans-pentacyclo[3.3.2.0^{2, 9}.0^{4, 10}, 0^{6, 8}]decan 5 and bicyclo[4.1.0]heptene-2 6 . The first bands in the PE.-spectra of these compounds have been assigned on the basis of a ZDO HMO-approximation. For 2 and 4 the value for resonance integral between linked 2p atomic orbitals of two adjacent eclipsed cyclopropane rings is found to be ?1.73 eV.     

A study of molecular motion in solid cyclopropane and cyclopropane clathrate deuterate by nuclear magnetic resonance absorption and relaxation methods

Proton magnetic resonance absorption and spin-lattice relaxation measurements have been carried out for cyclopropane clathrate deuterate from 77 to 290 K together with spin—lattice relaxation measurements on solid cyclopropane from 90 to 146 K. The absorption measurement for the type I structure deuterate indicates the presence of an isotropic rotation of the cyclopropane molecule from about 230 K, while in the type II structure deuterate isotropic rotation of the enclathrated cyclopropane is present over all of the range of stability of the clathrate (~250 to 278 K). The spin-lattice relaxation measurements give an activation energy of 0.83 ± 0.03 kcal mole^?1 for the barrier to reorientation (not assigned) of the cyclopropane molecules inside the clathrate deuterate cavities. In solid cyclopropane the barrier associated with the threefold axis rotation is found to be 4.8 ± 0.2 kcal mole^?1.     

Further study of cyclopropane structural isomerization behind reflected shock waves

The homogeneous thermal isomerization of cyclopropane to propene was studied in the presence of large excesses (99.6%–99.8%) of argon or helium diluent. Reaction temperatures ranged from 1038°?1208°K, and total gas pressures were varied from 533 to 5097 torr. The comparative-rate single-pulse shock-tube method was used, with the well characterized decomposition of cyclohexene serving as the internal standard reaction. Comparison of the measured rate constants for cyclopropane isomerization with k_∞ values extrapolated from “preferred?” lower-temperature rate constants suggests that collision efficiencies for helium and argon relative to cyclopropane, under the present conditions, are β_c ≈ 0.04 and 0.05, respectively. Although the uncertainties are rather large, these results do not support the suggestion that rapidly declining β_c values are largely responsible for the anomalously low rate constants for this reaction at T≥1130°K previously reported by other workers.     

Cyclopropane chemistry. Part 5 [1,2]. Hexafluorocyclopropane as a source of difluorocarbene

Thermolysis of hexafluorocyclopropane in the presence of ethylene, propene, vinyl chloride, and vinyl bromide gives good yields of the corresponding 1,1-difluorocyclopropanes, formed by addition of difluorocarbene to the olefin. The tetrafluoroethylene formed dimerises to octafluorocyclobutane, co-dimerises with the olefin, or survives, depending on the reaction conditions. With allene, hexafluorocyclopropane gives 1-(difluoromethylene)cyclopropane, 2,2,3,3-tetrafluorospiropentane, and products derived from tetrafluoroethylene and allene.     

Multiple bond migration with participation of a protophilic agent

The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated by theab initio (RHF/6-31+G^* and MP2/6-31+G^*) methods. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide ion and between corresponding carbanions and water molecule were found on the potential energy surfaces of the proton transfer reactions. In the presence of hydroxide ion, migration of the multiple bond can occur by an “intramolecular” mechanism of the proton transfer involving the proton of hydroxide ion bound in the complex with propene or propyne molecule. For the propene system, such a mechanism seems to be quite realistic and more preferable energetically than a traditional two-stage mechanism with a passage of the proton into the medium. For the system with the triple bond, an equal expenditure of energy is required to follow any mechanism (without taking into account the effects of solvation and the interaction with a cation), whereas the formation of the stable [H₂C=C=CH·H₂O]⁻ complex can prevent further transformations. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–41, January, 1999.     

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

The hydrogen, carbon dioxide, and carbon monoxide gas adsorption and storage capacity of lithium-decorated cyclopropane ring systems were examined with quantum chemical calculations at density functional theory, DFT M06-2X functional using 6-31G(d) and cc-pVDZ basis sets. To examine the reliability of M06-2X DFT functional, a few representative systems are also examined with complete basis set CBS-QB3 method and CCSD-aug-cc-pVTZ level of theory. The cyclopropane systems can bind to one Li⁺ ion; however, the corresponding the methylated systems can bind with two Li⁺ ions. The cyclopropane systems can adsorb six hydrogen molecules with an average binding energy of 3.8 kcal/mol. The binding free energy (ΔG) values suggest that the hydrogen adsorption process is feasible at 273.15 K. The calculation of desorption energies indicates the recyclable property of gas adsorbed complexes. The same number of CO₂ and CO gas molecules can also be adsorbed with an average binding energy of −14.4 kcal/mol and −10.7 kcal/mol, respectively. The carbon dioxide showed ~3–4 kcal/mol better binding energy as compared to carbon monoxide and hence such designed systems can function as a potential candidate for the separation of these flue gas molecules. The nature of interactions in complexes was examined with atoms in molecules analysis revealed the electrostatic nature for the interaction of Li⁺ ion with cyclopropane rings. The chemical hardness and electrophilicity calculations showed that the gas adsorbed complexes are rigid and therefore robust as gas storage materials.     

Charge stripping mass spectra: A method for identifying isomeric [C5H8]+˙ and [C3H6]+˙ ions

Charge stripping (collisional ionization) mass spectra are reported for isomeric [C₅H₈]⁺˙ and [C₃H₆]⁺˙ ions. The results provide the first method for adequately quantitatively determining the structures and abundances of these species when they are generated as daughter ions. Thus, loss of H₂O from the molecular ions of cyclopentanol and pentanal is shown to produce mixtures of ionized penta-1,3- and -1,4-dienes. Pent-1-en-3-ol generates [penta-1,3-diene]⁺˙. [C₃H₆]⁺˙ ions from ionized butane, methylpropane and 2-methylpropan-1-ol are shown to have the [propene]⁺˙ structure, whereas [cyclopropane]⁺˙ is produced from ionized tetrahydrofuran, penta-1,3-diene and pent-1-yne.     

Decomposition of 1,1‐dimethyl‐1‐silacyclobutane on a tungsten filament—evidence of both ring C?C and ring Si?C bond cleavages

The decomposition of 1,1‐dimethyl‐1‐silacyclobutane (DMSCB) on a heated tungsten filament has been studied using vacuum ultraviolet laser single photon ionization time‐of‐flight mass spectrometry. It is found that the decomposition of DMSCB on the W filament to form ethene and 1,1‐dimethylsilene is a catalytic process. In addition, two other decomposition channels exist to produce methyl radicals via the Si? CH₃ bond cleavage and to form propene (or cyclopropane)/dimethylsilylene. It has been demonstrated that both the formation of ethene and that of propene are stepwise processes initiated by the cleavage of a ring C? C bond and a ring Si? C bond, respectively, to form diradical intermediates, followed by the breaking of the remaining central bonds in the diradicals. The formation of ethene via an initial cleavage of a ring C? C bond is dominant over that of propene via an initial cleavage of a ring Si? C bond. When the collision‐free condition is voided, secondary reactions in the gas‐phase produce various methyl‐substituted 1,3‐disilacyclobutane molecules. The dominant of all is found to be 1,1,3,3‐tetramethyl‐1,3‐disilacyclobutane originated from the dimerization of 1,1‐dimethylsilene. Copyright © 2010 John Wiley & Sons, Ltd.     

Structures of decomposing and non-decomposing gas-phase [C4H6O]+· radical cations,and their [C2H2O]+· and [C3H6]+· product ions

The structures of gas-phase [C₄H₆O]^+· radical cations and their daughter ions of composition [C₂H₂O]^+· and [C₃H₆]^+· were investigated by using collisionally activated dissociation, metastable ion measurement, kinetic energy release and collisional ionization tandem mass spectrometric techniques. Electron ionization (70 eV) of ethoxyacetylene, methyl vinyl ketone, crotonaldehyde and 1-methoxyallene yields stable [C₄H₆O]^+· ions, whereas the cyclic C₄H₆O compounds undergo ring opening to stable distonic ions. The structures of [C₂H₃O]^+· ions produced by 70-eV ionization of several C₄H₆O compounds are identical with that of the ketene radical cation. The [C₃H₆]^+· ions generated from crotonaldehyde, methacrylaldehyde, and cyclopropanecarboxaldehyde have structures similar to that of the propene radical cations, whereas those ions generated from the remainder of the [C₄H₆O]^+· ions studied here produced a mixed population of cyclopropane and propene radical cations.     

The carbon-13 nuclear magnetic resonance spectra of some α-spirocyclopropyl ketones and related cyclohex-2-en-1-ones and 2-ethylidenecyclohex-3-en-1-ones

The ¹³C NMR spectra of a series of β,γ-unsaturated α-spirocyclopropylcyclohexanones and saturated α-spirocyclopropylcycloalkanones have been analyzed and compared with the spectra of diethyl cyclopropanedicarboxylate and a corresponding spiro acylal. The chemical shifts of the cyclopropane methylene carbons are correlated with spiroactivation of the cyclopropane ring to nucleophilic attack. In the case of the saturated spiro ketones these chemical shifts can also be correlated with their photochemistry. In the SFORD spectra of the spiro ketones the signals of the cyclopropane methylene carbons appear as complex multiplets: this is attributed to second-order coupling resulting from strong coupling between the vicinal cyclopropane protons. The ¹³C NMR spectra of a series of related cyclohex-2-en-1-ones and 2-ethylidenecyclohex-3-en-1-ones have also been analyzed; the chemical shift assignments for the latter corroborate the configurational assignments made on the basis of ¹H NMR spectroscopy.     

Supported silica-molybdena catalysts for olefin metathesis activated by photoreduction

Cyclopropane (CP) or methylcyclopropane (MCP) chemisorption on silica-molybdena catalysts photoreduced in CO was found to result in a sharp increase (by one order of magnitude) of specific activities for olefin metathesis (propene, 1-hexene, ethyl oleate). IR and UV-VIS spectroscopic studies revealed that promoting effect of CP and MCP treatment was associated with the formation of the thermally stable carbene complexes Mo = CH₂ and Mo=CH-CH₃, arising from CP and MCP interaction with low coordinated MO⁴⁺ ions in photoreduced Mo/SiO₂ IR data showed fast reversible transformation of Mo=CH₂ to Mo=CH-CH₃ thus providing the first direct spectroscopic confirmation of a chain carbene mechanism of propene metathesis. A general scheme for CP and MCP interaction with photoreduced Mo/SiO₂ was proposed.     

Heats of solution of gaseous hydrocarbons in water at 15, 25, and 35°C

Calorimetrically measured heats of solution of eleven hydrocarbon gases into water are reported at 15 and 25°C. Gases studied are methane, ethane, propane, n-butane, 2-methylpropane, 2,2-dimethylpropane, cyclopropane, ethene, propene, 1-butene, and ethyne. These values in combination with previous results are used to derive heat capacity changes at 25°C. Comparison of enthalpy and heat capacity values with those from other studies shows satisfactory agreement. Correlation of the heat capacity change with the number of water molecules in the first solvation shell of the solute suggests that the observed heat capacity changes are primarily due to changes in the water molecules in this solvent shell.     

Spectroscopic calculation of CH bond dissociation energies for the bromo derivatives of alkanes,alkenes, and arenes

The CH bond dissociation energies were determined for the bromo derivatives of methane, ethane, propane, cyclopropane, ethane, propene, and benzene by the spectroscopic and quantum-chemical methods. The spectroscopic values of the CH bond dissociation energies were obtained from the fundamental absorption bands by the variational method in an anharmonic approximation using the Morse-harmonic basis. Quantum-chemical calculations were performed using the 6-311G(3df, 3pd)/B3LYP basis. The resulting tendencies of variation of the bond dissociation energies due to changes in the molecular structure are discussed.     

Enantioselective cyclopropanation reaction using a conformationally fixed pyridinium ylide through a cation-π interaction

Using a chiral pyridinium ylide with a fixed conformation through a cation-π interaction performs enantioselective cyclopropanation of electron-deficient olefins. ¹H NMR, X-ray structural analysis and DFT calculations elucidated the self-complexation and the face-to-face arrangement between the pyridinium and the phenyl rings. The absolute configuration of the product was determined after conversion into a bicyclic cyclopropane derivative.     

Linear combination of walsh orbitals in tris-σ-homobenzenes : Photoelectron spectroscopy and model calculations

The applicability of the cyclopropane Walsh orbital model to a series of tris-σ-homobenzenes is investigated by means of photoelectron (PE) spectroscopy and molecular orbital (MO) theory, with particular emphasis on an understanding of the conformational dependence of the conjugative interaction between Walsh orbitais of linked 3-membered rings. The shifts of the first three PE bands in the series diademane (1), trans-pentacyclo[3.3.2.0^2.9.0^4.10.0^6.8]decane (2), trans-tris-σ-homobenzene (3) and its 3,3,6,6,9,9-hexamethyl derivative (4) are well described in terms of a “Linear Combination of Walsh Orbitals” (LCWO) model, provided “radially” oriented contributions to the cyclopropane Walsh orbitais are included. The results imply that the highest occupied MO in 2,3 and 4 is localized in the s-cis-bicyclopropyl fragment of these species.