Polyacetylenes and Cumulenes,Potential Elements for Molecular Machines and Precursors of Carbon Clusters: A Theoretical Study

A recently described very simple procedure for estimating Hartree–Fock (H. F.) energy and accurate nonrelativistic energy has been used with simple hydrocarbons possessing C?C or C?C bonds and for the acetylene dimer. Experimental characteristics (heats of formation, ionization potentials, electron affinities), structural features, and reactivity have been discussed in terms of quantum‐chemistry characteristics at the H. F. level and also at a level including a part of electron correlation. Deviations from linearity with derivatives of long polyacetylenes and cumulenes are ascribed to the lowest‐energy deformation vibrations, which decrease rapidly when passing from short to long acetylenic and cumulenic chains. The role of derivatives and heteroanalogues of hydrocarbons under study in atmospheric and interstellar chemistry is briefly mentioned. Derivatives with enhanced stability represent potentially promising construction materials for molecular devices and also resources for the preparation of defined clusters of C‐atoms.     

Calculation of heat of formation :- Molecular connectivity and IOC-ω technique,a comparative study

The connectivity index has been used to evaluate the π-bond energy of alternant and non-alternant hydrocarbons. A new varient of IOC-ωtechnique has also been used for the evaluation of π-bond energy. These methods have now been used to evaluate heats of formation for both types of molecules. A comparative study reveals that the connectivity index based values are generally in better agreement with the experimental values than those obtained with the proposed new varient of the IOC-ωtechnique.     

计算模拟研究金属有机骨架材料吸附分离C2、C3烃类气体

碳氢化合物在工业生产中发挥着重要的作用,其分离纯化过程是工业生产中重要的环节。低碳烃气体的物理化学性质十分相似,仅在分子尺寸和不饱和度等方面有微小差异,分离困难。传统的精馏等分离方式能耗高、有时效率较低。金属有机骨架材料由于其优异的性能(高比表面积、高孔隙率、结构尺寸可控)在吸附分离方面发挥了重要作用。计算模拟方法能够在微观层次上描述吸附分离过程,起到实验无法替代的作用。本文综述了计算模拟用于探索金属有机骨架吸附分离低碳烃的最新研究进展,探讨了其在金属有机骨架吸附分离低碳烃研究中存在的问题,并展望了发展前景。     

A modified square well model in obtaining the surface tension of pure and binary mixtures of hydrocarbons

A model based on the perturbation theory of fluids was proposed to correlate the experimental data for surface tension of pure hydrocarbons in a wide range of temperature. The results obtained for the pure hydrocarbons were directly used to predict the surface tension for binary hydrocarbon mixtures at various temperatures. In the proposed model, a modified form of the square well potential energy between the molecules of the reference fluid was taken into account while the Lennard–Jones dispersion energy was considered to be dominant amongst the molecules as the perturbed term to the reference part of the model. In general, the proposed model has three adjustable parameters which are chain length, m, size, σ, and energy, ε/κ, parameters, but in some cases the number of parameters was reduced to two, thereby setting the chain length to be unity for pure hydrocarbons. The regressed values of these parameters were obtained using the experimental data for pure hydrocarbons at different temperatures. The results showed that these parameters can be related to the molar mass of hydrocarbons. The model was also extended to predict the surface tension of binary hydrocarbon mixtures using the parameters obtained for the pure compounds. It is worth noting that no additional parameter has been introduced into the model in the extension of the model to the mixtures studied in this work. The results showed that the proposed model can accurately correlate the surface tension of pure hydrocarbons. Also the results showed that the surface tension for binary mixture of hydrocarbons can be accurately predicted using the proposed model over a wide temperature range.     

Interaction of positively and negatively charged aromatic hydrocarbons with benzene and triphenylene: Towards a model of pure organic insulators

A theoretical study of the complexes formed by two aromatic charged hydrocarbons, cyclopropenyl cation and phenalenyl anion, with benzene and triphenylene has been carried out. The binary complexes between the charged molecules and the neutral ones have been characterized as well as the ternary systems with the neutral systems acting as insulators of the charged ones. In the ternary complex a cooperative effect is observed both in the energy and in the geometry. In general, the interaction with ions reduces the aromaticity of the insulators.     

Symmorphy transformations and operators in the repeat spaceX r(q) for additivity problems

A theoretical framework has been presented, which links two diverse molecular problems: the study of symmorphy transformations of molecular shape analysis (further developed in the present paper) and that of additivity of the zero-point vibrational energy of hydrocarbons and the total pi-electron energy of alternant hydrocarbons. The linkage, using fundamental tools of (general) topology and algebra, makes it possible to mutually introduce the methodologies used in fields hitherto separately investigated. By establishing this linkage, topological patterns described by symmorphy groups can be treated by the algebraic methods developed for the above additivity problems. The linkage also brings forth new techniques of topologizing the repeat spaceX _r(q) for the additivity problems. Moreover, this connection paves the way to analyzing molecular homologous series and their properties by means of associating sequences of molecular structures with elements of a repeat space equipped with a topology.On leave from: Institute for Fundamental Chemistry, 34-4 Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606, Japan.     

Diffusion and solubility of mineral oils through ethylene-vinyl acetate copolymer

This paper reports a study of mineral oil diffusion through a filled ethylene-vinyl acetate crosslinked polymer, together with some comparisons with aliphatic linear hydrocarbons. Permeation was monitored by classical gravimetric measurements leading to values of solubility and diffusion coefficient at several temperatures ranging from 20 to 120 °C. Diffusion coefficients display a change in activation energy at at ca. 70 °C for mineral oils but not for simple hydrocarbons. The values obtained were discussed regarding available structure-diffusivity relationships and diffusion models derived from free volume theory. A relationship between penetrant evaporation temperature and its diffusivity was observed and tentatively justified.     

The destruction of atmospheric pressure propane and propene using a surface discharge plasma reactor

Surface discharge plasma reactors (SDRs) have been shown to be effective in removing a wide range of pollutants. In this study, the effectiveness of a SDR for the removal of propane and propene from an atmospheric pressure air stream was investigated. For an input energy of 100 J L-1, the conversions were found to be 16% and 68% for propane and propene, respectively. The total carbon recovery was found to increase with increasing specific input energy (SIE) for both hydrocarbons. FTIR analysis showed that CO and CO2 are the major end-products, and GC-MS identified formic acid as a significant byproduct. The effect of initial propane concentration was also investigated. The reaction chemistry involved in the oxidative plasma conversion of propane and propene is discussed.     

Microbial Degradation of Halogenated Hydrocarbons: A Biological Solution to Pollution Problems?

Chlorinated hydrocarbons are widely used because of their chemical and thermal stability as well as their fungicidal, herbicidal, and insecticidal properties. Unfortunately, it is just this stability that makes the compounds persistent in nature; half-lives of more than 15 years are not uncommon. In many countries the use of some chlorinated compounds has been prohibited, even though many such compounds (e.g., DDT) exhibit exactly the desired spectrum of effects. Surprisingly, microbiol systems that can degrade most chlorinated hydrocarbons have been found in nature. Indeed, it is possible, in many cases, to isolate pure cultures of bacteria that can utilize these compounds as the sole source of carbon and energy. Even polychlorinated compounds, such as the wood preservative and herbicide pentachlorophenol, can be utilized as a source of carbon by some bacteria. The study of the biodegradation of halogenated hydrocarbons has led to the discovery of novel catabolic pathways in which unusual and previously undescribed enzymatic activities have been detected. Bacterial enzymes have even been isolated that can replace halogen substituents in aliphatic and aromatic compounds with hydroxyl groups or hydrogen atoms. Improved understanding of the biodegradation of halogenated hydrocarbons, as described in this article, will almost certainly result in new biotechnological applications, especially in the area of waste-water treatment.     

A non-emperical LCAO MO SCF investigation of the ground and core ionized states of tetrahedrane and cyclobutadiene

Non-empirical LCAO MO SCF calculations have been carried out on the ground and localised core hole states of tetrahedrane and cyclobutadiene to investigate the suitability of ESCA as a technique for distinguishing between structurally related, isomeric hydrocarbons. Differences in energy are found to be considerably magnified in the core hole state manifold and shifts in core binding energies and shake-up structures are shown to be distinctive.     

Energy transfer in the course of triplet state quenching of aromatic hydrocarbons by nitroxyl radicals

Quenching of triplet states of aromatic hydrocarbons by nitroxyl radicals has been investigated by the flash photolysis method. There are two different mechanisms of triplet quenching: quenching occurs via enhanced intersystem crossing on exchange interaction with the radical for the triplet states of aromatic hydrocarbons which have low triplet energy (E_T < 14700 cm^?1); for very high triplet energies, energy transfer from the triplet molecule to the nitroxyl radical occurs. The energy of the excited nitroxyl radical was estimated to be 18000 cm^?1.     

Interaction of toluene,hexadecane, and water with the surfaces of random copolymers of styrene and butadiene

Molecular dynamics simulations have been used to study the interaction of toluene, hexadecane, and water with the surfaces of thin films of a random copolymer of styrene and butadiene (SB) and a random copolymer of styrene, butadiene, and acrylonitrile (SBA). Qualitatively different behavior is seen with the three small molecules. The two hydrocarbons remain on the thin films of the copolymers, but water has little affinity for the surface. Toluene has a stronger tendency to penetrate into the film than does hexadecane, which remains at the surface of the thin film. The attractive interaction of the hydrocarbons with the surfaces is dominated by van der Waals interactions. The energy of the interaction of toluene with SB is slightly smaller than the heat of vaporization of toluene at the temperature of the simulation. When expressed on a weight basis, the interaction of toluene with SB is larger than the interaction of hexadecane with the same surface. Hexadecane interacts slightly more strongly with SB than with SBA.     

Synthesis, X-ray diffraction and computational study of the crystal packing of polycyclic hydrocarbons featuring aromatic and perfluoroaromatic rings condensed in the same molecule: 1,2,3,4-tetrafluoronaphthalene, -anthracene and -phenanthrene

We have synthesised some planar polycyclic compounds, in which unsubstituted aromatic rings are condensed with perfluorinated aromatic rings, and have carried out a combined X-ray diffraction and computational study to analyse their self-recognition behaviour in crystalline phases. We compare our results with the parent hydrocarbons and with other compounds that have a variable degree of fluorination. Whereas the molecular planes in crystals of hydrocarbons with mono- or difluorinated aromatic rings or of perfluorinated compounds arrange themselves in V-shaped configurations, our present results show that perfluorinated rings tend to stack over unsubstituted rings even when these two moieties coexist in a condensed system, producing crystalline materials with parallel molecular layers with the arene-perfluoroarene recognition pattern. Our analysis shows that the packing energy of all these crystals is dispersion-dominated and that coulombic terms are selective rather than quantitatively predominant in crystals with arene-perfluoroarene interactions. No compelling proof of a special role of C-H...F interactions has been found.     

Direct Non-oxidative Methane Conversion by Non-thermal Plasma: Modeling Study

The direct non-oxidative conversion of methane to higher hydrocarbons in dielectric barrier discharges has been investigated theoretically at atmospheric pressure. Preliminary modeling of the results is presented, based on a well-stirred reactor model to determine the spatially and time-averaged species composition through the solution of balance equations for species, mass, gas and electron energy. The results show good quantitative agreement between model predications and experimental measurements by considering the glow and after-glow regions. Moreover, the model has predicted that there exists a transition where the main product of ethane will transform to acetylene by increasing the specific energy. The dominant reaction paths and the possibility of selective to C₂ hydrocarbons have been discussed. A list of gas-phase reactions has been compiled for modeling methane conversion in non-thermal plasma and can be employed in more sophisticated two- or three-dimensional plasma simulations.     

Rate coefficients of H-atom abstraction from ethers and isomerization of alkoxyalkylperoxy radicals

Group rate expressions for the hydrogen(H)-atom abstraction reactions from ethers by hydrogen atoms and hydroxyl(OH) radicals and the intramolecular hydrogen-transfer isomerization reactions of alkoxyalkylperoxy radicals, which result from the H-abstraction from ethers followed by the addition of O(2), have been evaluated based on the quantum chemical calculations and experimental data. With the relative method proposed in the present study, it was shown that the rate coefficients of the reactions, for which only poor experimental information is available, can be reliably evaluated by calculating and extracting the difference from the well-established reactions of alkane hydrocarbons. The major features on the H-abstraction reactions from O-adjacent sites of ethers compared to those from alkanes were the suppression of the activation energy due to the decrease of the C-H bond dissociation energy and non-next neighbor substituent effect from the alkyl group on the counter side of -O-. For the hydrogen transfer isomerization reactions, similar suppression of the activation energy as well as the change in the ring strain energy was found as a major feature.     

The interaction curve of non-bonded carbon and hydrogen atoms and its application

A universal interaction curve of non-bonded carbon and hydrogen atoms has been proposed. This curve has been successfully applied to determine numerous properties of various saturated and unsaturated hydrocarbons such as the equilibrium of molecular conformation, the strain energy of molecules, the sublimation heat of organic crystals and so on.     

Quadrupole type mass spectrometric study of the abstraction reaction between hydrogen atoms and ethane

The reactions of photochemically generated deuterium atoms of selected initial translational energy with ethane have been investigated. At each initial energy the relative probability of the atoms undergoing reaction or energy loss on collision with ethane was investigated, and the phenomenological threshold energy was measured as 30+/-5kJmol(-1) for the abstraction from the secondary C-H bonds. The ratio of relative yields per bond, secondary:primary was approximately 3 at the higher energies studied. The correlation of threshold energies with bond dissociation energies, heats of reaction and activation energies is discussed for abstraction reactions with several hydrocarbons.     

Formation of HO2 radicals from the 248 nm two-photon excitation of different aromatic hydrocarbons in the presence of O2

The excitation energy dependence of HO(2) radical formation from the 248 nm irradiation of four different aromatic hydrocarbons (benzene, toluene, o-xylene, and mesitylene) in the presence of O(2) has been studied. HO(2) has been monitored at 6638.20 cm(-1) by cw-CRDS, and the formation of a short-lived, unidentified species, showing broad-band absorption around the HO(2) absorption line, has been observed. For all four hydrocarbons, the same HO(2) formation pattern has been observed: HO(2) is formed immediately on our time scale after the excitation pulse, followed by a formation of more HO(2) on a much longer time scale. Taking into account the absorption of the short-lived species, the yields of both types of HO(2) radicals are in agreement with a formation following 2-photon absorption by the aromatic hydrocarbons. The yields do not much depend on the nature of the aromatic hydrocarbon. For practical use in past and future experiments on aromatic hydrocarbons, an empirical value is given, allowing the estimation of the total concentration of HO(2) radicals formed at 40 Torr He in the presence of around [O(2)] = 1 × 10(17)cm(-3) as a function of the 248 nm excitation energy: [HO(2)]/[aromatic hydrocarbon] ≈ 2 × 10(-6) × E(2) (with E in mJ cm(-2)).