Olefin Structure Research Articles

Embedded and DFT Calculations on the Crystal Structures of Small Alkanes, Notably Propane

A hybrid method is introduced and applied that combines second-order Moller–Plesset perturbation theory (MP2) for cluster models with density functional theory for periodic models to obtain structures and energetics for molecular crystals of the alkane species, notably propane. Calculated lattice energies elucidate the fact that propane has the lowest melting temperature of all organic compounds. The hybrid method provides an alternative to currently existing methods, which use either periodic MP2 for the determination of periodic crystals or periodic DFT+D. We also compare the hybrid method to a number of modern density functionals which are commonly used for the computation of molecular crystals. Depending on the functional used, we get a large range of lattice energies. From our QM:QM results, we can deduce that the achievements of DFT+D for computing molecular crystals largely relies on error cancellation effects between the functional and its dispersion coefficients.

Influence of the carbon atom numbers and the structure of collectors on the coal fines flotation

AbstractThis paper highlighted measuring the contact angle, the wetting heat and the IR spectrum before and after interactions between eight alkanes and coals to investigate the influence of the alkane structure and the number of carbon atoms on the coal surface hydrophobicity. The coal fines flotation tests were conducted with alkanes as collectors. The results show that after different alkanes acted on the coal samples, when the carbon numbers are same, both the contact angle and the wetting heat of isoparaffins were higher than those of the normal alkane. When the number of carbon atoms was 12, the contact angle and the wetting heat reached the maximum values after alkanes interacted with coals. The yield of the clean coal, the combustible material recovery and flotation perfect indicators of the isododecane were higher than those of the dodecane by 3.62, 4.08 and 0.96% respectively under the same condition of flotation. The ash content of the clean coal was also higher than that of the dodecane by 0.9...

Regioselectivity and Reaction Mechanism of Ru-Catalyzed Hydrogenolysis of Squalane and Model Alkanes.

The dependence of the C-C hydrogenolysis activity on reaction parameters and the structure of the substrate alkanes was investigated for Ru/CeO2 catalyst with very small (dispersion: H/Ru=0.89) Ru particles. The substrate concentration and reaction temperature did not have a significant effect on the selectivity pattern, except that methane production was promoted at high temperatures. However, the hydrogen pressure had a marked effect on the selectivity pattern. Ctertiary -C bond dissociation, terminal Csecondary -Cprimary bond dissociation, and fragmentation to form excess methane had negative reaction order with respect to hydrogen partial pressure, whereas Csecondary -Csecondary bond dissociation had an approximately zero reaction order. Therefore, a high hydrogen pressure is essential for the regioselective hydrogenolysis of Csecondary -Csecondary bonds in squalane. Ru/SiO2 catalyst with larger Ru particles showed similar changes in the product distribution during the change in hydrogen pressure. The reaction mechanism for each type of C-C bond dissociation is proposed based on reactivity trends and DFT calculations. The proposed intermediate species for the internal Csecondary -Csecondary dissociation, terminal Csecondary -Cprimary dissociation, and Ctertiary -C dissociation is alkyls, alkylidynes, and alkenes, respectively.

Prediction of water solubilities in hydrocarbons and oils using F-SAC coupled with SRK–EoS

In the present work, the F-SAC (Functional-Segment Activity Coefficient) model was used to predict the water solubility at high temperatures (and pressures) of defined hydrocarbons and non-defined oil fractions. Since in the F-SAC model no pressure effects are considered, the model was coupled with the Soave-Redlich-Kwong (SRK) equation of state by means of the Self-Consistent Mixing Rule (SCMR) in order to properly compute high-pressure data. The F-SAC parameters for hydrocarbon-water systems were revised using the combined model SRK + SCMR(F-SAC) and a data set with 648 infinite-dilution activity coefficient (IDAC), and 589 liquid-liquid equilibrium (LLE) points, including high temperature and pressure data. For defined hydrocarbon–water systems, calculated absolute average deviation (AAD) in logarithm units for IDAC and LLE were 0.12 and 0.29 respectively. The determination coefficients were close to 1.0, which indicates a strong correlation between the calculations and the experimental data. For the non-defined oil predictions, the F-SAC group fragmentation was simply determined by assuming a linear alkane structure. In spite of this crude approximation, for the studied petroleum fractions, the proposed model was capable of satisfactory represent the experimental water solubility data, with an overall AAD 0.088 for the logarithm of molar fractions.

Vapor–Liquid Equilibria for (n-Hexane, n-Octane, Cyclohexane, or 2,3-Dimethylpentane) + Toluene + {[4empy][Tf2N] (0.3) + [emim][DCA] (0.7)} Mixed Ionic Liquids

Recently, the study about the use of ionic liquids (ILs) in the aromatic extraction is focused in the selective separation of the hydrocarbons and the solvent in order to propose a whole alternative process involving ILs. As a consequence, the vapor–liquid equilibria (VLE) for the hydrocarbons + ILs systems are required. In this work the VLE for several alkane + toluene systems in the presence of the 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) (0.3) + 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) (0.7) binary IL mixture were determined. In addition to extend the experimental VLE information, this work is aimed at the alkane structure evaluation: linear alkanes (n-hexane and n-octane), cyclic alkanes (cyclohexane), and branched-chain alkanes (2,3-dimethylpentane) have been used. All systems have been studied at 323.2, 343.2, and 363.2 K over the whole range of composition within the miscibility region. The NRTL thermodynamic model was used to adjust the VLE for all ...

NO formation in premixed flames of C1–C3 alkanes and alcohols

The influence of alkane and alcohol molecular structures on nitric oxide (NO) pollutant formation trends is investigated through the study of C1–C3 alkanes and alcohols in premixed stagnation flames at atmospheric pressure. The flame diagnostics consist of one-dimensional (1-D) Planar Laser-Induced Fluorescence (PLIF) for measurements of NO and CH concentrations, 1-D NO-LIF thermometry, and 1-D Particle Tracking Velocimetry (PTV) for the determination of flame reactivity and burning rates. The results show that alcohols produce less NO than their alkane equivalents. This behaviour is linked to the lower flame temperatures of alcohol flames and the tendency of alcohols to produce lower concentrations of the CH radical, due to inhibition of the formation of methyl groups. These trends are captured in the available thermochemical models; however, there are discrepancies regarding the formation pathways of NO and its intermediates which are linked to variability in model rate coefficients. Further adjustments to all of the thermochemical models are needed to accurately capture the nature of NOx pollutant formation in premixed alkane and alcohol flames, and this experimental study provides target data for this effort.

Effect of Alkyd Varnish on the Thermal Stability and Static Smoke Properties of Decorative Wood

The effect of alkyd varnish on thermal stability and static smoke properties of decorative wood were analysed by using thermo-gravimetric (TG) analyzer, differential scanning calorimeter and plastic smoke density tester. The TG results show that maximum mass loss of the wood and alkyd varnish occurs in the range of 200-500°C. At the pyrolysis stage, the alkyd varnish exhibits an obvious endothermic process, while the wood exhibits an obvious endothermic process and then an exothermic one. The infrared analysis and smoke density test show that the olefin structure and benzene ring structure of alkyd varnish increase both the special optical density and mass optical density of the decorative wood consisted alkyd varnish. Meanwhile, the higher external heat flux and application of an ignition source decrease the special optical density and mass optical density of the decorative materials.

Structure of olefin-imidacloprid and gas-phase fragmentation chemistry of its protonated form.

One of the major insect metabolites of the widely used neonicotinoid insecticide imidacloprid, 1 (1-[(6-chloro-3-pyridinyl)methyl]-N-nitro-1H-imidazol-2-amine), is the olefin 2. To better understand how the structure of olefin 2 relates to the gas-phase fragmentation of its protonated form, 2H(+), X-ray crystallography, tandem mass spectrometry experiments and DFT calculations were carried out. Olefin 2 was found to be in a tautomeric form where the proton is on the N(1) position of the imidazole ring and forms a hydrogen bond to one of the oxygen atoms of the coplanar nitroamine group. Under conditions of low-energy collision-induced dissociation (CID) in a linear ion trap, 2H(+), formed via electrospray ionization (ESI), fragments via a major loss of water, together with minor competing losses of HNO2 and NO2•.This contrasts with 1H+, which mainly undergoes bond homolysis via NO2• loss. Thus, installation of the double bond in 2 plays a key role in facilitating the loss of water. DFT calculations, carried out using the B3LYP/6-311G++(d,p) level of theory, revealed that loss of water was energetically more favourable compared to HNO2 and NO2• loss. Three multistep, energetically accessible mechanisms were identified for loss of water from 2H(+), and these have the following barriers: (I) direct proton transfer from N(5) of the pyridine to O(1) on the NO2 group (119 kJ mol(-1)); (II) rotation of the N(2)-N(4) bond (117 kJ mol(-1)); (III) 1,3-intramolecular proton transfer between the two oxygen atoms of the NO2 group (145 kJ mol(-1)). Given that the lowest barrier for the losses of HNO2 and NO2• is 156 kJ mol(-1), it is likely that all three water loss mechanisms occur concurrently.

Study on combustion and ignition characteristics of ethylene, propylene, 1-butene and 1-pentene in a micro flow reactor with a controlled temperature profile

Weak flames of four alkenes (ethylene, propylene, 1-butene and 1-pentene) were observed using a micro flow reactor with a controlled temperature profile to investigate their combustion and ignition characteristics. Weak-flame based investigation which enables to elucidate general ignition property of each fuel was conducted. One-dimensional computations with detailed reaction mechanisms were conducted to compare and analyze experimental results. Single luminous zone of hot flame was observed for all four alkenes. The order of weak flame position was ethylene, 1-pentene, 1-butene and propylene from the lower temperature side and thus the reactivity of those fuels are higher in the same order. Computational results captured the order of the experimental weak flame position. Alkene results were compared with alkane results in terms of carbon number and the order of weak flame position agreed between the alkene and alkane results. Weak flame structures of alkenes were analyzed using the computations. A similar overall flame structure was obtained for the four alkenes from the mole fraction profiles of major species. Rate of consumption was investigated to clarify fuel consumption of alkenes. Reactions with O, H and OH radicals proceed in the fuel consumption of alkenes. H-atom addition reaction of alkene where the reaction occurs at the double bond of the alkene is a unique reaction compared with the alkane and consumes a significant amount of the fuel. H-atom abstraction reaction with OH, which is important in alkane, is also important in the alkene consumption. Reaction path analysis was conducted to examine the high reactivity of ethylene. OH production through HO2 in the initial stage of oxidation is important against the weak flame position. Ethylene has a high rate of HO2 production compared with the other alkenes through HCO + O2 <=> CO + HO2, C2H5 + O2 <=> C2H4 + HO2 and C2H3 + O2 <=> C2H2 + HO2, which results in a high reactivity.

ChemInform Abstract: Oxidation of Olefins with Benzeneseleninic Anhydride in the Presence of TMSOTf.

A new oxidizing system for olefins, consisting of benzeneseleninic anhydride and trimethylsilyl triflate, was studied. The highly reactive benzeneseleninyl cation is presumably formed under these conditions. It has been shown that different products are formed with this species depending on the specific structure of olefin. The 1,1-disubstituted olefins afforded mostly α,β-unsaturated carbonyl compounds. The sterically encumbered tri- or tetrasubstituted olefins yielded 1,2- or 1,4-dihydroxylated products, presumably via four-membered cyclic intermediates.

Oxidation of Olefins with Benzeneseleninic Anhydride in the Presence of TMSOTf.

A new oxidizing system for olefins, consisting of benzeneseleninic anhydride and trimethylsilyl triflate, was studied. The highly reactive benzeneseleninyl cation is presumably formed under these conditions. It has been shown that different products are formed with this species depending on the specific structure of olefin. The 1,1-disubstituted olefins afforded mostly α,β-unsaturated carbonyl compounds. The sterically encumbered tri- or tetrasubstituted olefins yielded 1,2- or 1,4-dihydroxylated products, presumably via four-membered cyclic intermediates.

Molecular dynamics simulation on volume swelling of CO2–alkane system

The microscopic mechanism of the volume swelling of CO2–alkane (decane, octane, hexane and cyclohexane) systems and the effects of temperature, pressure and alkane structure on the volume swelling of CO2–alkane systems are investigated by performing molecular dynamics simulation. It is shown that the increase in pressure, the reduction in temperature and the straight-chain structure of the alkane are of benefit to the volume swelling of CO2–alkane systems by calculating the volume swelling coefficient; CO2 in supercritical state plays a dominant role in the volume swelling of CO2–alkane systems. The microscopic process of the volume swelling of CO2–decane system shows that the increase in the average separation distance between decane molecules and the stretch of decane molecules result in the volume swelling of decane as CO2 dissolve into decane. The calculations of interaction energies in CO2–decane system indicate that the interaction between CO2 and decane molecules is responsible for the volume swelling of CO2–alkane system. Further study on the interaction between CO2 and decane molecules shows that the dispersion interaction, resulting in the different solubility of CO2 in alkanes, is the essence of the volume swelling for CO2–alkane system. This work is a good start on understanding the mechanism of alkane swelling influenced by CO2 at the molecular level and provides useful information for guiding CO2 enhancing oil recovery.

Structure and transport properties of liquid alkanes in the vicinity of α-quartz surfaces

Abstract Structure and mass transport properties of several liquid n-alkanes, methane, decane and tetracosane, in the vicinity of α-quartz surfaces of three crystal planes have been investigated by using molecular dynamics simulations. Solid α-quartz surfaces were terminated with –H and –OH groups to create hydrophobic and hydrophilic surfaces, respectively. It was observed that adsorption of the liquid alkane molecules is more noticeable near the (0 0 1) crystal plane when compared with other two planes (0 1 1) and (1 0 0). For a given alkane, the number of molecules adsorbed near a α-quartz wall marginally depends upon the crystal plane and type of surface termination. Ordering parameter and radius of gyration for liquid molecules were examined in the interface region to gain the knowledge about molecular alignment and chain configuration in the interface region. Liquid molecules in the first adsorption layer near the hydrophilic and hydrophobic surfaces are more parallel to the interface in the following order (0 0 1), (0 1 1) and (1 0 0). Portions of decane and tetracosane liquid molecules tend to enter into the H-terminated side with an orientation in the parallel direction to the interface and into the OH-terminated side with an orientation in the perpendicular direction for (1 0 0) crystal plane. Molecules are flattened in the direction perpendicular to the interface and are elongated in the other direction in the interface region for decane and tetracosane. It is observed that the in-plane self-diffusion coefficient of liquids, the self-diffusion coefficient according to the migration of molecules in the directions parallel to the interface, is smaller in the vicinity of the solid surface and approaches to the bulk liquid value away from the interface. For methane, decane and tetracosane, the in-plane diffusion in the first adsorption layer near the smoother silica surface (0 0 1), which has molecularly smoother surface than the other two surfaces (0 1 1) and (1 0 0), for both of the terminations is higher as compared with the other two surfaces (0 1 1) and (1 0 0). It was found that the diffusion coefficients in the two directions of the 2-D in-plane diffusion are different significantly and this anisotropic nature is resulted by the topology of the solid surface. At the same reduced temperature, a tendency was observed that the in-plane diffusion near the H-terminated and OH-terminated surfaces for three crystal planes increases with an increase in the chain length of the liquid alkanes.

Testing secondary organic aerosol models using smog chamber data for complex precursor mixtures: influence of precursor volatility and molecular structure

Abstract. We use secondary organic aerosol (SOA) production data from an ensemble of unburned fuels measured in a smog chamber to test various SOA formation models. The evaluation considered data from 11 different fuels including gasoline, multiple diesels, and various jet fuels. The fuels are complex mixtures of species; they span a wide range of volatility and molecular structure to provide a challenging test for the SOA models. We evaluated three different versions of the SOA model used in the Community Multiscale Air Quality (CMAQ) model. The simplest and most widely used version of that model only accounts for the volatile species (species with less than or equal to 12 carbons) in the fuels. It had very little skill in predicting the observed SOA formation (R2 = 0.04, fractional error = 108%). Incorporating all of the lower-volatility fuel species (species with more than 12 carbons) into the standard CMAQ SOA model did not improve model performance significantly. Both versions of the CMAQ SOA model over-predicted SOA formation from a synthetic jet fuel and under-predicted SOA formation from diesels because of an overly simplistic representation of the SOA formation from alkanes that did not account for the effects of molecular size and structure. An extended version of the CMAQ SOA model that accounted for all organics and the influence of molecular size and structure of alkanes reproduced the experimental data. This underscores the importance of accounting for all low-volatility organics and information on alkane molecular size and structure in SOA models. We also investigated fitting an SOA model based solely on the volatility of the precursor mixture to the experimental data. This model could describe the observed SOA formation with relatively few free parameters, demonstrating the importance of precursor volatility for SOA formation. The exceptions were exotic fuels such as synthetic jet fuel that expose the central assumption of the volatility-dependent model that most emissions consist of complex mixtures with similar distribution of molecular classes. Despite its shortcomings, SOA formation as a function of volatility may be sufficient for modeling SOA formation in chemical transport models.

Pd-catalyzed aerobic direct olefination of polyfluoroarenes

The first example of Pd-catalyzed aerobic direct olefination of polyfluoroarenes has been developed. The reaction makes use of molecular O2 as terminal oxidant, and provides a cost-efficient and environmentally benign access to polyfluoroarene–alkene structures that are of interest in life and material sciences.

Secondary organic aerosol yields of 12-carbon alkanes

Abstract. Secondary organic aerosol (SOA) yields were measured for cyclododecane, hexylcyclohexane, n-dodecane, and 2-methylundecane under high-NOx conditions, in which alkyl proxy radicals (RO2) react primarily with NO, and under low-NOx conditions, in which RO2 reacts primarily with HO2. Experiments were run until 95–100% of the initial alkane had reacted. Particle wall loss was evaluated as two limiting cases using a new approach that requires only suspended particle number-size distribution data and accounts for size-dependent particle wall losses and condensation. SOA yield differed by a factor of 2 between the two limiting cases, but the same trends among alkane precursors were observed for both limiting cases. Vapor-phase wall losses were addressed through a modeling study and increased SOA yield uncertainty by approximately 30%. SOA yields were highest from cyclododecane under both NOx conditions. SOA yields ranged from 3.3% (dodecane, low-NOx conditions) to 160% (cyclododecane, high-NOx conditions). Under high-NOx conditions, SOA yields increased from 2-methylundecane &lt; dodecane ~ hexylcyclohexane &lt; cyclododecane, consistent with previous studies. Under low-NOx conditions, SOA yields increased from 2-methylundecane ~ dodecane &lt; hexylcyclohexane &lt; cyclododecane. The presence of cyclization in the parent alkane structure increased SOA yields, whereas the presence of branch points decreased SOA yields due to increased vapor-phase fragmentation. Vapor-phase fragmentation was found to be more prevalent under high-NOx conditions than under low-NOx conditions. For different initial mixing ratios of the same alkane and same NOx conditions, SOA yield did not correlate with SOA mass throughout SOA growth, suggesting kinetically limited SOA growth for these systems.

Synthesis of 2-Pyridones by Cycloreversion of [2.2.2]- Bicycloalkene Diketopiperazines

A general strategy for the conversion of [2.2.2]-diazabicyclic alkene structures to 2-pyridone aromatic heterocyclic products is reported. The reaction sequence starts from 2,5-diketopiperazine (DKP) derivatives, is compatible with both aromatic and aliphatic aldehyde components, and can intercept either intra- or intermolecular cycloaddition manifolds. Priming of one aza-bridging function in the intermediate [2.2.2]-DKP scaffold permits cycloreversion (microwave heating) and selective extrusion of cyanate derivatives leading to the formation of 2-pyridone structures. Progress toward the synthesis of louisianin A and B, antiproliferative 2-pyridone natural products, is also disclosed.

Catalytic, enantioselective, intramolecular carbosulfenylation of olefins. Preparative and stereochemical aspects.

The first catalytic, enantioselective, intramolecular carbosulfenylation of isolated alkenes with aromatic nucleophiles is described. The combination of N-phenylsulfenylphthalimide, a chiral selenophosphoramide derived from BINAM, and ethanesulfonic acid as a cocatalytic Brønsted acid induced an efficient and selective cyclofunctionalization of various alkenes (aliphatic and aromatic) tethered to a 3,4-methylenedioxyphenyl ring. Under these conditions, 6-phenylthio-5,6,7,8-tetrahydronaphthalenes are formed diastereospecifically in good yields (50-92%) and high enantioselectivities (71:29-97:3 er). E-Alkenes reacted much more rapidly and with much higher selectivity than Z-alkenes, whereas electron-rich alkenes reacted more rapidly but with comparable selectivity to electron-neutral alkenes and electron-deficient alkenes. The Brønsted acid played a critical role in effecting reproducible enantioselectivity. A model for the origin of enantioselectivity and the dependence of rate and selectivity on alkene structure is proposed along with a rationale for the site selectivity in reactions with monoactivated arene nucleophiles.

Effect of chemical structure on secondary organic aerosol formation from C&amp;lt;sub&amp;gt;12&amp;lt;/sub&amp;gt; alkanes

Abstract. The secondary organic aerosol (SOA) formation from four C12 alkanes (n-dodecane, 2-methylundecane, hexylcyclohexane, and cyclododecane) is studied in the Caltech Environmental Chamber under low-NOx conditions, in which the principal fate of the peroxy radical formed in the initial OH reaction is reaction with HO2. Simultaneous gas- and particle-phase measurements elucidate the effect of alkane structure on the chemical mechanisms underlying SOA growth. Reaction of branched structures leads to fragmentation and more volatile products, while cyclic structures are subject to faster oxidation and lead to less volatile products. Product identifications reveal that particle-phase reactions involving peroxyhemiacetal formation from several multifunctional hydroperoxide species are key components of initial SOA growth in all four systems. The continued chemical evolution of the particle-phase is structure-dependent, with 2-methylundecane SOA formation exhibiting the least extent of chemical processing and cyclododecane SOA achieving sustained growth with the greatest variety of chemical pathways. The extent of chemical development is not necessarily reflected in the oxygen to carbon (O : C) ratio of the aerosol as cyclododecane achieves the lowest O : C, just above 0.2, by the end of the experiment and hexylcyclohexane the highest, approaching 0.35.

Quantum Chemical Challenges for the Binding of Simple Alkanes to Supramolecular Hosts

Binding of hydrocarbon guests to supramolecular hosts can lead to unusual geometric changes such as bending or coiling of guests upon encapsulation. Cucurbiturils (CBs) are classic cation binders that were recently used for the selective binding of small-membered hydrocarbons with a very high association constant (Ka ≈ 10(6) M(-1)). In this study, we have systematically investigated the binding of some alkanes to CB-[6] using a series of quantum chemical methods. The calculated binding free energies are very strong and are largely influenced by guest orientations inside the host and reorganization of host and guests. The computed (1)H NMR chemical shifts of the encapsulated alkanes agree with the experimental estimates thus confirming guest encapsulation. Further, we have shown that although binding of both cyclopentane and neopentane have very strong binding affinities (>20 kcal mol(-1)), the selectivity of cyclopentane to neopentane at CB-[6] is a kinetically driven process through the computation of approximate transition state structures of both alkanes to CB-[6]. The calculated binding affinities with dispersion corrected density functionals (DFs) are very close to the experimental estimates, whereas DFs that lack dispersion correction predict that alkane binding to CB-[6] is largely unfavorable. Finally, we have investigated the binding of some long chain alkanes to several supramolecular hosts using dispersion corrected semiempirical methods which cannot be routinely studied through density functional theory methods due to the larger size of the system.