Doubly charged ion mass spectra: IV—chlorinated and brominated alkanes

Doubly charged ion mass spectra have been obtained for 42 chlorinated and brominated n-alkane (methyl through octyl) hydrocarbons. A double focusing Hitachi RMU-7L mass spectrometer, operated at 1.6kV accelerating voltage, has been used to measure the spectra. Molecular doubly charged ions have not been observed. Intense fragment ions have been produced from extensive H and halogen loss as well as C? C bond rupture of the parent molecule. The most abundant ions in the doubly charged ion spectra observed in this investigation resulted from reactions of [Cl]²⁺˙, [Br]²⁺˙, [CCL₂]²⁺, [C₂H₂Cl]²⁺˙, [C₃H₂]²⁺, [C₃HCl]²⁺, [C₃HBr]²⁺, [C₄H₃]²⁺˙, [C₄H₄]²⁺, [C₄H₆Br]²⁺˙, [C₄H₈Br]²⁺˙, [C₅H₂]²⁺, [C₆H₆]²⁺, [C₆H₈]²⁺ and [C₇H₈]²⁺. The prominent doubly charged fragment ions formed by electron impact of the smaller halogenated alkanes generally contained halogen, whereas ions of the type [C_nH_x]²⁺ were dominant in the spectra of higher molecular weight mono- and dihalogenated alkanes. Appearance energies of several ions have been measured. A geometry optimized quantum mechanical SCF treatment has been used to compute energies, charge densities and structures of doubly charged halogenated alkane ions.     

Kinetic regularities of the heat release during the reactions of aliphatic hydrocarbons with aqueous HNO3

The kinetics of the heat release during the reactions of aqueous HNO₃ withn-heptane andn-octadecane was studied. The kinetic regularities of the reactions of hydrocarbons C₇H₁₆−C₁₈H₃₈ with HNO₃ and the heats of the reactions were described. At all stages, except initial, the hydrocarbon reacts with NO₂ and nitric acid reproduces NO₂ in the reaction with NO. The accumulation of NO₂ results in the acceleration of the process. When the pressure of the hydrocarbon vapor is equilibrium, its reaction with NO₂ can also proceed in the gas phase. The contribution of this reaction to the total heat release was estimated. The additives of aromatic and unsaturated hydrocarbons to aliphatic hydrocarbons increase strongly the initial rate of the heat release and changes slightly the subsequent stages of the process. Naphthenic hydrocarbons have almost no effect on the kinetic parameters of the process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–40, January, 1998.     

Spin-orbit ab initio investigation of the photodissociation of C2H5Br

The photodissociation of ethyl bromide (C₂H₅Br) has been investigated by spin-orbit (SO) ab initio calculations. The vertical excitation energies of some excited states for C₂H₅Br were calculated. The potential energy curves of C₂H₅Br along the C–Br dissociation coordinate were calculated by multistate second-order multiconfigurational perturbation theory in conjunction with spin-orbit (SO) interaction through complete active space state interaction (MS-CASPT2/CASSI-SO). The calculated results clearly assigned the experimentally observed photodissociation channels leading to C₂H₅ + Br (²P_3/2) and C₂H₅ + Br*(²P_1/2).     

The doubly-charged ion mass spectra of hydrocarbons

The doubly-charged ion mass spectra of some hydrocarbons, including a variety of structural types, have been obtained by a new technique in which doubly-charged ions are charge exchanged with neutral molecules and so separated from singly-charged ions. The spectra show strong similarities, independent of hydrocarbon structure; characteristic ions include [C_mH₂]⁺⁺ (m = 2 to 5), [C_nH₆]⁺⁺(n > 6), [C₁₀H₈]⁺⁺, [C₁₂H₈]⁺⁺, [C₁₁H₁₀]⁺⁺, [C₇H₇]⁺⁺·, [C₉H₇]⁺⁺· and [C₁₃H₁₁]⁺⁺·. The fragmentation pattern of 2-phenylnaphthalene has been reconstructed, based on observed reactions of metastable doubly-charged ions to give fragment doubly-charged ions. In addition, we examined metastable ion fragmentations leading to two singly-charged ions for some of the characteristic ions, using several compounds. The value of doubly-charged ion mass spectra of hydrocarbons appears to lie in the information they provide on ion structures; this information was sufficient to permit the proposal of structures for the major ions encountered in this study.     

Direct kinetic parameters for the reaction of Br atoms with neopentane

Laser flash photolysis coupled with resonance fluorescence detection of Br atoms was employed to investigate the temperature dependence of the reaction Br + neo‐C₅H₁₂ (1) between 688 and 775 K. The following Arrhenius preexponential factor and activation energy were determined (±1 σ): A₁ = (6.89 ± 2.27) 10¹⁴ cm³ mol⁻¹ s⁻¹ and E_A,1 = 57.61 ± 2.05 kJ mol⁻−¹ The only other kinetic parameters reported for the reaction of Br atoms with neo‐C₅H₁₂ were obtained from competitive kinetic experiments relative to Br + C₂H₆. Comparison with our direct results is hampered by uncertainties in the kinetic data for the reference reaction that may need reinvestigation. The standard enthalpy of formation for the neo‐C₅H₁₁ radical was estimated to be 34.7 and 41.6 kJ mol⁻¹, depending on the value of the activation energy assumed for the reverse reaction neo‐C₅H₁₁ + HBr (−1). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 49–55, 2001     

Probing the exohedral magnetic properties of C20 derivatives by through space NMR shieldings (TSNMRS)

The through space NMR shieldings (TSNMRS) of dodecahedrane C₂₀H₂₀, of the isomeric hydrocarbons C₂₀H₁₂, of the ions C₂₀H₁₂²⁺ and C₂₀H₁₂^2?, of the fluxional fullerene C₂₀ and of its dication C₂₀²⁺ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G1 geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved π-conjugation in the compounds studied could be quantified.     

On optically detected ESR spectra from radical cations of liquid hydrocarbon solvents

The optically detected electron spin resonance (OD ESR) method has been employed to study the origin of radical-cation ESR signals in some saturated hydrocarbons with small amounts of 2.5-diphenyloxazol or p-terphenyl under radiolysis. In cyclohexane, the ESR, signal with resolved hyperfine structure was ascribed to c-C₆H₁₀⁺/PPO^? radical-ion pairs produced from primary c-C₆H₁₂⁺/PPO^? ones by monomolecular decay, of cyclohexane radical cations to cyclohexene radical cations. Cis- and trans-decalin under radiolysis accumulate 9,10-octalin which captures solvent holes and form 9,10-octalin radical cations giving a resolved OD ESR spectrum. 9,10-octalin is present in non-irradiated commercial decalin as an impurity. The OD ESR technique has been shown to be very sensitive to some impurities in hydrocarbon solvents.     

Ethylene and propylene adsorption and the formation of hydrocarbon complexes with NO2 upon interaction of adsorbed olefins with an NO + O2 mixture over HZSM-5 and CuZSM-5 zeolites studied by TPD and ESR

Adsorption of C₂H₄ and C₃H₆ on copper in oxidized samples of CuZSM-5 is found to increase with the copper concentration; simultaneously, olefin adsorption on the Br?nsted acid sites decreases. The Cu²⁺ cations in the square-planar coordination exhibit higher reactivity in olefin adsorption than copper cations in the square-pyramidal coordination. Thermal treatment of CuZSM-5 with hydrogen results in regeneration of the Br?nsted acid sites for olefin adsorption and the disappearance of Cu²⁺ cations, the active sites of adsorption, due to the reduction of Cu²⁺ to Cu⁺ and Cu⁰. Desorption peaks appear in the TPD spectra upon the interaction between the adsorbed hydrocarbons and NO₂. These peaks are not observed upon separate adsorption of the reactants, and they are likely due to decomposition of NO₂-hydrocarbon complexes over both the Br?nsted and copper-containing sites of the zeolite     

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C₂H₂, C₂H₄, C₂H₆) on the surface of a sorbent containing Ag⁰, Ag^δ+, and AgO sites. The dynamics of change in the structural characteristics of Ag _n (n ≤ 10) is analyzed and the adsorption of oxygen on Ag₈ and Ag₁₀ is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag₈, Ag₁₀, Ag ₁₀ ⁺ , Ag₁₀O, and Ag₁₀O₂ clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C₂H₂ increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Ag^δ+) but also to bind C₂H₂ and C₂H₄ directly to the sorbent’s surface.     

Synthesis of diamantane from new polycyclic hydrocarbons C14 under the action of ionic liquids

Diamantane was obtained by skeletal rearrangement of three new polycyclic hydrocarbons C₁₄H₁₈, C₁₄H₂₀ and C₁₄H₂₂ under the action of aluminate ionic liquids. For the successful isomerization of hydrocarbon C₁₄H₂₂ containing two hydrogen atoms more, the addition of Pd/C to the reaction medium is necessary.     

Ab initio and density functional study of substituent effects in halogenated cations of alkenes

A theoretical study of the halogenated cations of mono-, di-, tri- and tetramethyl-substituted ethylenes, C₃H₆X⁺, C₄H₈X⁺, C₅H₁₀X⁺ and C₆H₁₂X⁺, X=F, Cl, Br, have been studied at the ab initio MP2 and density functional B3LYP levels of theory implementing 6-311++G(d,p) basis set. The potential energy surfaces of all molecules under investigation have been scanned and the ¹³C and ¹H NMR chemical shifts for all the bridged halonium ions studied have been calculated using the GIAO method at the B3LYP level. The calculated halogen binding energies in the halonium ions have been correlated with the experimental rates of chlorination and bromination of the corresponding alkenes. The computed hydride affinities and the NICS values for the bridged cations show that the bromo cations are more stable than the analogous chloro and fluoro cations.     

The formation of the anilinium ion from the ammonium ion in the ammonia chemical ionization of substituted benzenes

Compounds C₆H₅X(X ? F, Cl, Br, NO₂, CN, OCH₃) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C₆H₅NH₃]⁺ (m/z 94). [NH₄]⁺ reacts with C₆H₅X(X ? F, Cl, Br) to yield m/z 94 but C₆H₅X (X ? CN, NO₂) forms this ion only by reactions involving either [NH₃]⁺ or [C₆H₅X]⁺. C₆H₅OCH₃ does not form m/z 94.     

氢、碳氢燃料对向扩散火焰

A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffu-sion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH₄ to C₁₆H₃₄. The basic diffusion flame struc-tures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The de-tailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory(LLNL) are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H₂ has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.     

Positive ion–molecule reactions in OCS/hydrocarbon mixtures

The positive ion–molecule reactions of OCS have been investigated in an ion cyclotron resonance spectrometer. A variety of reactions in OCS/hydrocarbon mixtures have been investigated for various C₁? C₄ hydrocarbons—alkanes, alkenes and alkynes. The formation of organosulfur ions is found in reactions in OCS/hydrocarbon (C_n) mixtures with n <4. Formation of organosulfur ions is observed from hydrocarbon ions reacting with OCS and [OCS]⁺˙ and S⁺˙ reacting with the hydrocarbons. The proton affinity of OCS has been determined to be 688.7±8 kJ mol^?1 while that of CS₂ is measured to be 712.1±8 kJ mol^?1. Comparison with the proton affinity of CO₂ shows that the proton affinity increases as sulfur is substituted for oxygen.     

Verification of the interstitial carbide hydrolysis mechanism by a radioanalytical method

The hydrolytic products of manganese carbide Mn₇C₃ are hydrogen and a number of paraffins of the series CH₄, C₂H₆, C₃H₈, etc., whose concentrations characteristically decrease with increasing number of carbon atoms in the hydrocarbon molecule. A radioanalytical method applied after Mn₇C₃ hydrolysis by tritium, oxide has revealed that an analogous series of olefins in trace concentrations is formed as well. It has been confirmed that the sum of the concentrations of hydrocarbons higher than C₄ corresponds to the trend of the series. A stoichiometric and structurally consistent radical mechanism of Mn₇C₃ hydrolysis is proposed as derived from the composition of the hydrolytic products. The initial components of the radical reactions could be CH ₂ ^¨ and CH ₃ ^· radicals. The statisical and combinatorial aspects of the mechanism are also discussed.     

Thermodynamic functions of gaseous beryllium,titanium and germanium organometallic molecules

The thermal functions S⁰_T, -(G⁰_T-H⁰_O)/T and (H⁰_T-H⁰_O) have been calculated from structural and spectroscopic data for the gaseous organometallics C₅H₅BeX (X = Cl, Br and BH₄), C₅H₅MX₃ (M = Ti and Ge; X = Cl, Br and I) and CH₃TiX₃ (X = Cl, Br and I). The rotational barriers of the C₅H₅ and CH₃ groups have been evaluated and discussed.     

High‐temperature kinetics of the reaction between CN and hydrocarbons using a novel high‐enthalpy flow tube

More than 70 molecules of varied nature have been identified in the envelopes of carbon‐rich stars through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals, and a significant number are unique to the circumstellar medium. The determination of relevant laboratory kinetics data is critical to keep up with the development of the high spectral and spatial resolution observations and of the refinement of chemical models. Neutral–neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures and deserve a detailed laboratory investigation. The approach we have developed aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high‐enthalpy source with a flow tube and a pulsed laser photolysis–laser‐induced fluorescence system to probe the undergoing chemical reactions. The high‐enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane (C₃H₈), propene (C₃H₆), allene (C₃H₄), 1,3‐butadiene (1,3‐C₄H₆), and 1‐butyne (C₄H₆) over a temperature range extending from 300 to 1200 K. All studied reactions of CN with unsaturated hydrocarbons are rapid, with rate coefficients greater than 10^?10 cm³ · molecule^?1 · s^?1 and exhibit slight negative temperature dependence above room temperature. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 753–766, 2012     

Molecular Structures of Dibromo[(E)2‐bromo‐2‐phenylvinyl]‐(phenyl) tellurium (IV) and Dibromo [(Z)‐2‐bromo‐2‐phenyl‐vinyl] (p‐tulyl) tellurium (IV) hydrate methanolate

The structures of title compounds, [TeBr₂(C₈H₆Br)(C₆H₅)] (I) and [TeBr₂(C₈H₆Br)(C₇H₉)](H₂O)(CT₃OH) (II), have been determined by X‐ray diffraction. The structures confirm that E‐ or Z‐type configuration of vinylic telluride depends on the polarity of solvent employed. In either structure, Te atom is in a trigonal dipyramide configuration with the lone pair of electrons in the equatorial position.     

Diagnosis of Active Species in Reactive Acetylene Plasma by Laser-Ionization Molecular-Beam Time-of-Flight Mass Spectrometry

This work reports a new laser molecular beam time-of-flight mass spectrometry (LMB-TOFMS) instrument built at Plasma Spectroscopy Lab in Dalian University of Technology (DUT). The preliminary investigation of the intermediate species distribution of acetylene plasma in an atmospheric-pressure fast-flow nanosecond-pulsed dc-discharge has been carried out. The C_xH₂ species (x = 4,6,8), believed to be the dominant source of negative ions in C₂H₂ plasma, have been detected with relatively intense peak signals and some complex radical species like C₇H₇, C₉H₅, C₁₀H₅ are also observed. The addition of Ar gas significantly influenced the detection of the intermediate species. This is might be due to the metastable Ar^* with energies of 11.5 and 11.7 eV and a long lifetime. The potentialities of LMB-TOFMS for hydrocarbon plasmas diagnosis have been discussed.     

Hydrocarbon and fluorocarbon solubility and dilation in poly(dimethylsiloxane): Comparison of experimental data with predictions of the Sanchez–Lacombe equation of state

Sorption and dilation isotherms are reported for a series of gases (N₂, O₂, CO₂), hydrocarbon vapors (CH₄, C₂H₆, C₃H₈), and their fluorocarbon analogs (CF₄, C₂F₆, C₃F₈) in poly(dimethylsiloxane) (PDMS) at 35°C and pressures up to 27 atmospheres. The hydrocarbons are significantly more soluble in hydrocarbon-based PDMS than their fluorocarbon analogs. Infinite dilution partial molar volumes of both hydrocarbons and fluorocarbons in PDMS were similar to their partial molar volumes in other hydrocarbon polymers and in organic liquids. Except for C₂H₆ and C₃H₈, partial molar volume was independent of penetrant concentration. For these penetrants, partial molar volume increased with increasing concentration. The Sanchez–Lacombe equation of state is used to predict gas solubility and polymer dilation. If the Sanchez–Lacombe model is used with no adjustable parameters, solubility is always overpredicted. The extent of overprediction is more substantial for fluorocarbon penetrants than for hydrocarbons. Very good fits of the model to the experimental sorption and dilation data are obtained when the mixture interaction parameter is treated as an adjustable parameter. For the hydrocarbons, the interaction parameter is approximately 0.96, and for the fluorocarbons, it is approximately 0.87. These values suggest less favorable interactions between the hydrocarbon-based PDMS matrix and the fluorocarbon penetrants than between PDMS and hydrocarbons. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3011–3026, 1999