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General Atomics has supported the dynamic hohlraum experiment series with the production of double-shell targets filled with deuterium, xenon, and neopentane gases. Production of a double-shell target is a process by which multiple subassemblies are fabricated, assembled, and characterized in a planned sequence. An inner capsule assembly is produced with a SiGDP conversion glass capsule stalk mounted and attached together with glass fill tube and laser-cut beryllium disk. An outer CH mandrel with a permeation barrier is then machined and each subassembly fitted together. Challenges include aligning the inner and outer glass capsules as well as filling the inner void space with known gas quantities. Information describing how we assemble the target, new hardware designed to complete the gas fills, and characterization techniques to analyze the assembly will be presented.

The neopentylidene-neopentyl complex (PNP)Ti═CHtBu(CH2tBu) (1; (PNP− = N[2-P(CHMe2)2-4-methylphenyl]2) extrudes neopentane in neat fluorobenzene under mild conditions (25 °C) to generate the transient titanium alkylidyne (PNP)Ti≡CtBu (A), which subsequently undergoes regioselective 1,2-CH bond addition of a fluorobenzene across the Ti≡C linkage to generate (PNP)Ti═CHtBu(o-FC6H4) (2). Kinetic and mechanistic studies suggest that the C−H activation process is pseudo-first-order in titanium, with the α-hydrogen abstraction being the rate-determining step and the post-rate-determining step being the C−H bond activation of fluorobenzene. At 100 °C complex 2 does not equilibrate back to A and the preference for C−H activation in benzene versus fluorobenzene is 2:3, respectively. Compound 1 also reacts readily, and in most cases cleanly, with a series of hydrofluoroarenes (HArF), to form a family of alkylidene-arylfluoride derivatives of the type (PNP)Ti═CHtBu(ArF). Thermolysis of the latter compounds generates ...

Tetrafluoromethane, CF 4 , is markedly less soluble in water than methane and neopentane around room temperature: it is a superhydrophobic solute. An analysis of the physical origin of this superhydrophobicity is performed, exploiting literature thermodynamic data covering the 5–55 °C temperature range. It results that the CF 4 –water dispersion interactions are markedly weaker in magnitude than those of a ‘hypothetical’ hydrocarbon having the same size of tetrafluoromethane, providing a smaller counterbalancing effect of the work spent to create the cavity in water. The weakness of the CF 4 –water dispersion interactions is due to the very small polarizability of CF 4 , which, in turn, is caused by the strong electronegativity of fluorine atoms.

The grafting of tetraneopentylchromium(IV) onto the surface hydroxyls of silica has been investigated by varying both the method of deposition and the nature of the silica support. Reaction of the volatile organometallic with the silica surface in vacuo is compared with reaction in solution. A faster reaction but a lower ultimate Cr loading was obtained using the solution deposition technique. The reactions of the organometallic compound with Aerosil 200, a fumed silica often used to model catalyst supports, and Sylopol 952, a silica gel used as a carrier for chromium-based ethylene polymerization catalysts, are compared. After thermal pretreatment at 200 °C, grafting on both supports yields bis(neopentyl)chromium(IV) fragments regardless of the grafting method used, suggesting that a paired arrangement of the surface hydroxyl groups exists on both types of silicas. The higher Cr loading achieved on the silica gel is attributed to its higher surface area. Thermally-induced neopentane elimination from the grafted bis(neopentyl)chromium(IV) fragments occurs at the same rate and with the same stoichiometry for both Aerosil- and Sylopol-supported materials. Consequently, interactions of the grafted organometallic fragments with nearby siloxanes appear to be unimportant in the early stages of the transformation of bis(alkyl)chromium(IV) to the alkylidene.

The thermodynamic adsorption characteristics of tetramethylsilane (TMS) molecules on graphitized carbon black (GCB) were for the first time determined experimentally and by molecular statistics methods. The potential function parameters of pair molecular interactions (φ(r)) between Si and C atoms on the basal face of graphite were calculated in the atom-atom approximation of the semiempirical molecular-statistical theory of adsorption. The contributions of Si and C atoms to thermodynamic adsorption characteristics are compared for the example of nonspecific adsorption of TMS and isostructural neopentane molecules on the flat surface of GCB.

The isotropic (n-6) Lennard-Jones temperature-dependent potential (LJTDP) together with the Hohm−Zarkova−Damyanova mixing rules is used to predict second interaction pVT virial coefficients BAB(T),...

The model reactions of neopentane hydrogenolysis and hydroisomerization on transition metal hydrides (≡ Si−O)3MIVH (1), (=eqSi−O)2MIVH2 (2), and (≡Si−O)2MIIIH (3) (M = Zr, Ti) immobilized on the surface of silica were studied by density functional theory. It was shown that the hydrogenolysis of neopentane could occur on all the three types of metal hydrides, the catalytic activity of reaction centers increasing along the series M(IV) monohydrides 1 < M(IV) dihydrides 2 < M(III) hydrides 3. At the same time, the isomerization of the hydrocarbon skeleton of neopentane observed experimentally on titanium-based systems could only be explained by the participation of Ti(III) hydrides.

CO2 reforming of methane, propane, and neopentane was investigated with a ferroelectric packed-bed and silent discharge plasma reactors in N2 at temperature from 303 to 433 K. The conversions of the substrate hydrocarbons and CO2, and the yields of H2 and CO were expressed as functions of reactor energy density irrespective of voltage waveform. The positive temperature effect on the hydrocarbon conversions and the product yields can be ascribed to the promotion of secondary decomposition of the hydrocarbons induced by radicals formed in situ because reactor power consumption was not affected by reaction temperature at the same frequencies and peak-to-peak voltages. At 303 K, the reactivity of the hydrocarbon decreased in the following order: neopentane > propane > methane. At 433 K, propane and neopentane showed the same reactivities. The molar ratio of H2 to CO was affected by hydrocarbon structure and the initial concentration ratio of CO2 to the carbon atom in hydrocarbon, but not by reaction temperature. Better carbon balances were obtained for all the hydrocarbons at 433 K than at 303 K, suggesting higher reaction efficiencies at 433 K. Carbon balance was also affected by initial gas composition, and the carbon atoms in reacted neopentane were quantitatively recovered as CO, CO2 and lighter hydrocarbons at 10 of [CO2]/[neopentane].

The solid-state molecular structure of centrohexaindane (1), a unique hydrocarbon comprising six benzene rings clamped to each other in three dimensions around a neopentane core, and the molecular packing in crystals of 1 center dot CHCl3 are reported. The molecular T-d-symmetry and the Cartesian orientation of the six indane wings of 1 in the solid state have been confirmed. The course and limitation of electrophilic aromatic substitution of 1 are demonstrated for the case of nitration. Based on nitration experiments of a lower congener of 1, tribenzotriquinacene 5, the six-fold nitrofunctionalisation of 1 has been achieved in excellent yield, giving four constitutional isomers, two nonsymmetrical (14 and 17) and two C-3-symmetrical ones (15 and 16), all of which contain one single nitro group in each of the six benzene rings. The relative yields of the four isomers (similar to 3 : 1 : 1 : 3) point to a random electrophilic attack of the electrophiles at the twelve formally equivalent outer positions of the aromatic periphery of 1, suggesting electronic independence of its six aromatic pi-electron systems. In turn, the pronounced conformational rigidity of the centrohexacyclic framework of 1 enables the unequivocal structural identification of the isomeric hexanitrocentrohexaindanes 14-17 by H-1 NMR spectroscopy.

The translational and rotational dynamics of neopentane adsorbed in the one-dimensional channels of MIL-47(V) has been studied by quasi-elastic neutron scattering. The rotational motion of neopentane is well-described by the rotational diffusion model, with a correlation time of 41 ps at 300 K. The translational motion of the molecule has been fitted by several models: isotropic diffusion, normal 1D and single-file diffusion. It is found that the observed line shapes can only be reproduced by the single-file diffusion model. The single-file mobility factor, F, is (8 ± 1) × 10(-14) m(2) s(-1/2) at 300 K. This is the first observation of this unusual diffusion behaviour in a MOF.

10 págs.; 8 figs.; 3 tabs., Isomerism is ubiquitous in chemistry, physics, and biology. In atomic and molecular physics, in particular, isomer effects are well known in electron-impact phenomena; however, very little is known for positron collisions. Here we report on a set of experimental and theoretical cross sections for low-energy positron scattering from the three structural isomers of pentane: normal-pentane, isopentane, and neopentane. Total cross sections for positron scattering from normal-pentane and isopentane were measured at the University of Trento at incident energies between 0.1 and 50 eV. Calculations of the total cross sections, integral cross sections for elastic scattering, positronium formation, and electronic excitations plus direct ionization, as well as elastic differential cross sections were computed for all three isomers between 1 and 1000 eV using the independent atom model with screening corrected additivity rule. No definitive evidence of a significant isomer effect in positron scattering from the pentane isomers appears to be present. ©2016 AIP Publishing LLC, G.G. and F.B. would like to acknowledge the Spanish Ministerio de Economía y Productividad (Project No. FIS2012-31230) and the European Science Foundation (COST Action Grants Nos. MP1002–Nano-IBCT and MC1301-CELINA) for financial support. Finally, L.C. thanks the Japan Society for the Promotion of Science for his fellowship.

A methodology recently introduced to describe orientational order in liquid carbon tetrachloride is extended to the plastic crystal phase of XY4 molecules. The notion that liquid and plastic crystal phases are germane regarding orientational order is confirmed for short intermolecular distances but is seen to fail beyond, as long range orientational correlations are found for the simulated solid phase. It is argued that, if real, such a phenomenon may not to be accessible with direct (diffraction) methods due to the high molecular symmetry. This behavior is linked to the existence of preferential orientation with respect to the fcc crystalline network defined by the centers of mass. It is found that the dominant class accounts, at most, for one-third of all configurations, with a feeble dependence on temperature. Finally, the issue of rotational relaxation is also addressed, with an excellent agreement with experimental measures. It is shown that relaxation is nonhomogeneous in the picosecond range, with a slight dispersion of decay times depending on the initial orientational class. The results reported mainly correspond to neopentane over a wide temperature range, although results for carbon tetrachloride are included, as well.

The interactions between an oxidic support and Pt particles were explored in a series of platinum catalysts supported on amorphous silica–alumina used for the hydrogenation of tetralin and the hydrogenolysis of neopentane. The activity of the nanosized Pt particles increased with increasing intermediate electronegativity of the support for all supports with accessible Lewis acid sites. A compensation effect between the preexponential factor and the apparent energy of activation was observed for both reactions, attributed to the stronger adsorption of the reactants and intermediates on Pt induced by the increasingly electronegative supports. The product distribution in tetralin hydrogenation also points to stronger adsorption on Pt with increasing intermediate electronegativity of the support. X-ray absorption near-edge structure (XANES) findings indicate that the stronger interaction of the reactants is related to a reduced electron density on the platinum particles.

Several different synthetic approaches to a total of 13 novel B, Al, and Sm complexes derived from the tridentate tripodal triamine ligand [N3]H3 with a neopentane, trisilylmethane, or trisilylsilane backbone and different N-substituents, as well as applications of the selected complexes to polymerization catalysis, are reported. Salt metathesis between HC[SiMe2N(CH2Ph)]3Li3(THF)2 (THF = tetrahydrofuran) and AlCl3 in Et2O/hexanes leads to complete elimination of LiCl and formation of the corresponding tripodal triamido alane HC[SiMe2N(CH2Ph)]3Al·(THF) (1). On the other hand, the reaction of {MeC[CHN(SiMe3)]3Li3}2 and AlCl3 in Et2O/hexanes yields a LiCl-containing compound MeC[CH2N(SiMe3)]3AlCl[Li(Et2O)] (2). Alkane elimination involving [N3]H3 and 1 AlMe3 produces diamido−amino aluminum methyl HC[SiMe2NHAr][SiMe2NAr]2AlMe [Ar = 4-MeC6H4 (3), CH2Ph (4)], while the reaction using ≥2 AlMe3 gives amido−amino aluminum dimethyl [ArHNMe2Si](H)C[SiMe2NAr]2(AlMe2)2 (Ar = 4-MeC6H4, 5) and [(Me3Si)HNCH2](Me)C[CH2N(S...

The neopentylidene-neopentyl complex (PNP)Ti=CH(t)Bu(CH2(t)Bu) (2; PNP(-) = N[2-P(CHMe2)(2-)4-methylphenyl]2), prepared from the precursor (PNP)Ti[triple bond]CH(t)Bu(OTf) (1) and LiCH2(t)Bu, extrudes neopentane in neat benzene under mild conditions (25 degrees C) to generate the transient titanium alkylidyne, (PNP)Ti[triple bond]C(t)Bu (A), which subsequently undergoes 1,2-CH bond addition of benzene across the Ti[triple bond]C linkage to generate (PNP)Ti=CH(t)Bu(C6H5) (3). Kinetic, mechanistic, and theoretical studies suggest the C-H activation process to obey pseudo-first-order in titanium, the alpha-hydrogen abstraction to be the rate-determining step (KIE for 2/2-d(3) conversion to 3/3-d(3) = 3.9(5) at 40 degrees C) with activation parameters DeltaH = 24(7) kcal/mol and DeltaS = -2(3) cal/mol.K, and the post-rate-determining step to be C-H bond activation of benzene (primary KIE = 1.03(7) at 25 degrees C for the intermolecular C-H activation reaction in C6H6 vs C6D6). A KIE of 1.33(3) at 25 degrees C arose when the intramolecular C-H activation reaction was monitored with 1,3,5-C6H3D3. For the activation of aromatic C-H bonds, however, the formation of the sigma-complex becomes rate-determining via a hypothetical intermediate (PNP)Ti[triple bond]C(t)Bu(C6H5), and C-H bond rupture is promoted in a heterolytic fashion by applying standard Lewis acid/base chemistry. Thermolysis of 3 in C6D6 at 95 degrees C over 48 h generates 3-d(6), thereby implying that 3 can slowly equilibrate with A under elevated temperatures with k = 1.2(2) x 10-5 s(-1), and with activation parameters DeltaH = 31(16) kcal/mol and DeltaS = 3(9) cal/mol x K. At 95 degrees C for one week, the EIE for the 2 --3 reaction in 1,3,5-C6H3D3 was found to be 1.36(7). When 1 is alkylated with LiCH2SiMe3 and KCH2Ph, the complexes (PNP)Ti=CHtBu(CH2SiMe3) (4) and (PNP)Ti=CHtBu(CH2Ph) (6) are formed, respectively, along with their corresponding tautomers (PNP)Ti=CHSiMe3(CH2tBu) (5) and (PNP)Ti=CHPh(CH2tBu) (7). By means of similar alkylations of (PNP)Ti=CHSiMe3(OTf) (8), the degenerate complex (PNP)Ti=CHSiMe3(CH2SiMe3) (9) or the non-degenerate alkylidene-alkyl complex (PNP)Ti=CHPh(CH2SiMe3) (11) can also be obtained, the latter of which results from a tautomerization process. Compounds 4/5 and 9, or 6/7 and 11, also activate benzene to afford (PNP)Ti=CHR(C6H5) (R = SiMe3 (10), Ph (12)). Substrates such as FC6H5, 1,2-F2C6H4, and 1,4-F2C6H4 react at the aryl C-H bond with intermediate A, in some cases regioselectively, to form the neopentylidene-aryl derivatives (PNP)Ti=CHtBu(aryl). Intermediate A can also perform stepwise alkylidene-alkyl metatheses with 1,3,5-Me3C6H3, SiMe4, 1,2-bis(trimethylsilyl)alkyne, and bis(trimethylsilyl)ether to afford the titanium alkylidene-alkyls (PNP)Ti=CHR(R') (R = 3,5-Me2C6H2, R' = CH2-3,5-Me2C6H2; R = SiMe3, R' = CH2SiMe3; R = SiMe2CCSiMe3, R' = CH2SiMe2CCSiMe3; R = SiMe2OSiMe3, R' = CH2SiMe2OSiMe3).

Hydrocarbons are the main components in natural gases. Although the molecular distribution has been often used to study the origin of hydrocarbon, the occurrence of pentane and hexane isomers has not been discussed for natural gases. This study first reports controlling factors of pentane and hexane isomer ratios of natural gases from Akita, Niigata and Hokkaido in Japan. For the samples from Akita and Niigata, pentane and hexane isomer ratios such as neopentane/isopentane and 2,2-dimethylbutane/2,3-dimethylbutane show positive correlations with δ13C (ethane), suggesting that the ratios are affected by the generation temperature. Relation between kerogen type and isobutane/n-butane ratio is also discussed. By the comparison between Akita and Niigata gases that originated from type II kerogen and Hokkaido gases that originated from type III kerogen, the gases from type III kerogen show a higher isobutane/n-butane ratio compared with those originated from type II kerogen. Although carbon isotopic ratios of ethane and propane are good parameters for the gas generation temperature, this study indicates that combinations among pentane isomer ratios and hexane isomer ratios also provide good parameters for the gas generation temperature.

We report the results of molecular dynamics simulations of the interaction thermodynamics of group I cations with hydrophobic molecules in water using a variety of nonpolarizable force fields. Surprisingly, we find that the Li(+) ion is predicted to form thermodynamically favorable interactions with methane and neopentane using a new mode of recognition that is intermediate between a direct contact and a solvent-separated complex. Further simulations show that this favorable interaction is only predicted by ion parameter sets that correctly reproduce Li(+)'s experimental hydration number.

International audience; The determination of the absolute configuration of chiral molecules is at the heart of asymmetric synthesis.Here we probe the spectroscopic limits for chiral discrimination with NMR spectroscopyinchiral aligned media and with vibra-tional circular dichroism spectroscopyofthe sixfold-deuter-ated chiral neopentane.The study of this compound presents formidable challenges since its stereogenicity is only due to small mass differences.For this purpose,weselectively prepared both enantiomers of 2H6-1 through aconcise syn-thesis utilizing multifunctional intermediates.While NMR spectroscopyinchiral aligned media could be used to characterize the precursors to 2H6-1,the final assignment could only be accomplished with VCD spectroscopy, despite the fleetingly small dichroic properties of 1.Both enantiomers were assigned by matching the VCD spectra with those computed with density functional theory.

In this chapter, we report AaeAPO catalyzed alkane hydroxylations with H2O2 as the sole oxidant. High selectivity for alcohols, high efficiency of H2O2 utilization, high regioselectivity and stereospecificity were observed. The scope of the alkane substrates includes linear, branched and cyclic hydrocarbons, further expanding to gaseous ethane, propane and neopentane. Metabolites of several drug molecules were also analyzed and compared with P450s metabolites. Combining with coenzymes or cofactors, AaeAPO can also utilize the environmentally desirable oxidant O2 to perform C–H oxidation. All these various reactions suggest that AaeAPO has potential practical application as an industrial biocatalyst.

Molecular processes, ranging from hydrophobic aggregation and protein binding to mesoscopic self-assembly, are typically driven by a delicate balance of energetic and entropic non-covalent interactions. Here, we focus on a broad class of such processes in which multiple ligands bind to a central solute molecule as a result of solute–ligand (direct) and/or ligand–ligand (cooperative) interaction energies. Previously, we described a weighted random mixing (WRM) mean-field model for such processes and compared the resulting adsorption isotherms and aggregate size distributions with exact finite lattice (FL) predictions, for lattices with up to n = 20 binding sites. Here, we compare FL predictions obtained using both Bethe–Guggenheim (BG) and WRM approximations, and find that the latter two approximations are complementary, as they are each most accurate in different aggregation regimes. Moreover, we describe a computationally efficient method for exhaustively counting nearest neighbors in FL configurations, thus making it feasible to obtain FL predictions for systems with up n = 48 binding sites, whose properties approach the thermodynamic (infinite lattice) limit. We further illustrate the applicability of our results by comparing lattice model and molecular dynamics simulation predictions pertaining to the aggregation of methane around neopentane.

This chapter overviews protein aggregation pathways followed by a discussion of protein interactions with cosolvents and then protein?protein interactions. It covers the recent developments in the understanding of protein interactions with salts, and to a much lesser extent, with other excipients such as sugars, glycerol, or amino acids. Understanding how protein?cosolvent interactions impact upon protein?protein interactions is only possible by using simplistic descriptions of proteins, such as Deryaguin, Landau, Verwey, and Overbeek (DLVO) theory. A simulation study on the pair potential of mean force for either methane or neopentane in salt solutions found that the ion specific effects correlated well with the effect of salt on the hydrogen bonding network in bulk water. The interactions of salt ions and protein charged groups are best rationalized in terms of the law of matching water affinities (LMWA).

The heats of formation (HOFs) were calculated for a series of neopentyl difluoroamino compounds by using density functional theory (DFT) method with 6-311G∗∗ basis set, as well as semi-empirical methods. In the isodesmic reactions designed for the computation of HOF, the neopentane was chosen as a reference compound. The HOFs increase smoothly as –ONO2 groups being replaced by –NF2 and –NO2. However, HOFs increase dramatically as –ONO2 groups being replaced by –N(NO2)CH3 and –N3 groups. The variations of HOFs are different with different substituents. The semi-empirical MO (MNDO, AM1, and PM3) methods did not produce accurate and reliable results for the HOFs of the title compounds. The relative stability of the title compounds was evaluated based on the calculated HOFs, the energy gaps between the frontier orbitals and the bond order of C–R bond (C–NF2, C–ONO2, C–NO2 and C–N3). The magnitudes of intramolecular group interactions were predicted through the disproportionation energies. Thermal stabilities were evaluated via bond dissociation energies (BDE) at the B3LYP/6-311G∗∗ level. These results provide basic information for the molecular design of novel high energetic density materials.

Catalysis Letters, 110 (3-4), ISSN:1011-372X, ISSN:1572-879X

The hydrogen/deuterium exchange reaction of 2,2-dimethylpropane (neopentane) over D(2)O-exchanged zeolites (MOR, FAU, BEA, MFI) using a batch recirculation reactor was studied by means of gas chromatography coupled with mass spectrometer. In the temperature range 473-573 K, H/D exchange proceeds without side reaction such as cracking at short contact times. Indeed the C-H bond has appeared favorably involved in the activation of neopentane compared to the less accessible C-C bond. The transition state allowing hydron exchange is most likely a carbonium species (pentacoordinated carbon) as in the case of the H/D exchange between methane and solid acid. The activation energies of the H/D exchange between neopentane and zeolites are the same for all zeolites indicating a common carbonium ion type transition state. On the basis of previous results in the case of the exchange between methane and liquid superacids, the deuterium exchange rates in neopentane were tentatively related to the acidity of the solids. However the order of activity MORMFIBEAFAU seems to be related to the size of the pores, which may suggest the involvement of a confinement effect in the zeolites cavities. Moreover we found that H/D exchange takes also place between neopentane and deuterated sulfated zirconia (SZ) emphasizing its strong acidity.

Multiwalled carbon nanotube (MWCNT) samples were obtained by purification and ball-milling of a MWCNT sample synthesized by catalytic chemical vapor decomposition. These samples were oxidized with KMnO4–H2SO4 solution. A heat treatment was employed to decompose the oxygenated groups created by the oxidation treatment. The samples were characterized by transmission electron microscopy (TEM), adsorption of nitrogen, pore size distribution, and by thermogravimetric analysis combined with mass spectroscopy (TG-MS). The dynamics of 2,2-dimethyl-propane (neopentane) sorption was studied by frequency-response (FR) spectroscopy. The FR spectra obtained clearly demonstrate the effect of (a) the ball-milling, (b) the oxidative treatment and (c) the heat treatment on the sorption uptake processes involved in these treated samples.

Gentle thermolysis of the bis(neopentyl) complex Cp*W(NO)(CH 2 CMe 3 ) 2 (1) at 70 °C in various substituted benzenes results in the loss of neopentane and the generation of the transient alkylidene complex Cp*W(NO)(=CHCMe 3 ) (A), which subsequently effects single C-H bond activations of the benzenes. These activations exhibit a pronounced selectivity for the C-H linkages ortho to the benzene substituents. Thus, thermal reactions of 1 with C 6 H 5 X lead to the preferential formation of the corresponding Cp*W-(NO)(CH2CMe3)(o-C6H4X) complexes, the ortho-selectivity, i.e., X = F > OMe > Cl > Br > C≡CPh, diminishing as the steric demands of the substituents increase. Consistently, thermolyses of 1 in o-C 6 H 4 X 2 afford Cp·W(NO)(CH2CMe3)(2,3-C6H3X2) complexes with 98% selectivity when X = F and 82% selectivity when X = Cl. Similarly, the principal organometallic products resulting from the thermolyses of 1 in m-C 6 H 4 X 2 are the ortho-para-activated isomers Cp*W(NO)(CH 2 CMe 3 )(2,4-C 6 H 3 X 2 ) with 84% selectivity when X = F and 89% selectivity when X = Cl. Finally, thermolyses of 1 in para-disubstituted benzenes p-C 6 H 4 XY (X = F or OMe, Y = Cl or OMe) again reveal that the ortho-directing abilities of the substituents diminish in the order F > OMe > Cl. Some mechanistic insights into these activation processes have been obtained by monitoring of the early stages of the thermolysis of 1 in chlorobenzene by 1 H NMR spectroscopy. This monitoring reveals that the selectivity of the alkylidene intermediate A for forming the ortho-activated isomer is thermodynamic rather than kinetic in nature. Thus, the meta-and para-activated isomers are formed initially, but then convert to the ortho-activated product. The principal organometallic complexes resulting from ortho-C-H activations are formally 16-electron species in which there are no interactions between the tungsten centers and the Lewis-basic benzene substituents. Instead, the Lewis-acidic tungsten centers engage in intramolecular agostic interactions with the methylene C-H bonds of their neopentyl ligands to acquire some additional electron density. Being coordinatively and electronically unsaturated, these tungsten complexes react readily with added Lewis bases. Thus, treatment of Cp*W(NO)(CH 2 CMe 3 )(o-C 6 H 4 F) with Et 4 NCN and CO produces [Et 4 N] + [Cp*W(NO)(CH 2 -CMe 3 )(CN)(o-C 6 H 4 F)] - and Cp*W(NO)(η 2 -C(=O)CH 2 CMe 3 )(o-C 6 H 4 F), respectively, and the solid-state molecular structure of the latter complex has also been established by a single-crystal X-ray crystallographic analysis.

Roles of CO 2 and H 2 O as oxidants are discussed based on the data on the substrate conversions and the product distributions in the nonthermal plasma reforming of aliphatic hydrocarbons such as methane, propane, and neopentane from 303 K to 433 K. Only small effects of initial concentrations of hydrocarbons and types of oxidants are observed on hydrocarbon conversions, and the initial chemical interaction between hydrocarbons and the oxidants unlikely occurs. CO 2 and H 2 O have shown the comparable oxidation powers in the hydrocarbon reforming. Two molar excess of CO 2 or H 2 O to methane is required to oxidize methane carbon atoms to CO and CO 2 , and larger amounts of CO 2 or H 2 O for propane and neopentane. The different natures of CO 2 and H 2 O are reflected in the synthesis gas composition as in the ordinary catalytic reforming processes at higher temperatures: higher H 2 yields and higher H 2 to CO ratios on addition of H 2 O.

The reaction of Hf(CH2tBu)4 with a silica surface treated at 800 °C affords a unique surface organometallic species in only one surface environment, (⋮SiO)Hf(CH2tBu)3 (1-SiO2-(800)). In contrast, with SiO2-(500) two surface species, (⋮SiO)Hf(CH2tBu)3 (1-SiO2-(500)) and (⋮SiO)2Hf(CH2tBu)2 (2−SiO2-(500)), in a molar ratio of 70:30 are obtained. Thermal treatment of 1-SiO2-(800) at increasing temperatures leads to the successive evolution of neopentane, isobutene, and isobutane as well as several alkanes varying from C1 to C5. Polyisobutenes are also formed on the surface. The mechanism by which such decomposition occurs suggests a succession of γ-H eliminations with formation of neopentane followed by β-methyl transfer and formation of isobutene and [Hf]−Me. This isobutene is reinserted into [Hf]−Me with formation of isopentene and [Hf]−H. A comparison of the analytical data of 1-SiO2-(800) and (⋮SiO)Zr(CH2tBu)3 indicated the hafnium complex exhibits in EXAFS shorter Hf−C and Hf−O bonds and a larger Hf−Cα−C...

In a preceding project, functional forms for “short” Helmholtz energy equations of state for typical nonpolar and weakly polar fluids and for typical polar fluids were developed using simultaneous optimization. In this work, the coefficients of these short forms for the equations of state have been fitted for the fluids acetone, carbon monoxide, carbonyl sulfide, decane, hydrogen sulfide, 2-methylbutane (isopentane), 2,2-dimethylpropane (neopentane), 2-methylpentane (isohexane), krypton, nitrous oxide, nonane, sulfur dioxide, toluene, xenon, hexafluoroethane (R-116), 1,1-dichloro-1-fluoroethane (R-141b), 1-chloro-1,1-difluoroethane (R-142b), octafluoropropane (R-218), 1,1,1,3,3-pentafluoropropane (R-245fa), and fluoromethane (R-41). The 12 coefficients of the equations of state were fitted to substance specific data sets. The results show that simultaneously optimized functional forms can be applied to other fluids out of the same class of fluids for which they were optimized without significant loss of a...

Adsorption isotherms of nitrogen, carbon dioxide, methanol, dichloromethane, benzene and neopentane were determined on a range of molecular sieve and super-activated carbons with the objective of establishing the range of validity of the Theory of Volume Filling of Micropores (TVFM) in terms of the ratio of pore width to molecular diameter, Lo/σ. It is shown that, in the absence of molecular-sieving effects, both the characteristic curve concept and the DR equation are valid over the whole of the micropore range, corresponding to values of Lo/σ less than or equal to 5 and to at least a slight enhancement in the characteristic energy, E0, of the adsorbent when compared with the corresponding value obtained with non-porous carbon blacks. On the other hand, estimation of the mean micropore width was only possible for values of Lo/σ up to ca. 2.3, corresponding to at least a two-fold enhancement in E0. Results obtained using N2 at 77 K showed some significant differences to those obtained with organic adsorptives at higher temperature.

By the substitution of one methyl group in Neopentane C(CH3)4 with a methylchlorid group the globular sphere is expanded in 1-chloro-2,2-dimethylpropane (CH3)3C(CH2Cl). With the aid of DSC measurements, X-ray powder diffraction, 1H NMR and 35Cl NQR measurements two orientationally disordered (plastic) phases were established. The low temperature structure was solved and a structural model of phase II is proposed. A mechanism to describe the reorientation in the different phases is given as well as a connectivity scheme between the phases is discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Molybdenum carbide is a promising catalyst in many reactions. Its formation was investigated by XRD for two different active carbons:commercial one (NC100) and made out of expanded graphite. They were impregnated by MoCl 5 from vapor phase and carbonized in a stream ofhydrogen. XRD studies were performed both in ex situ and in situ conditions. Formation of different crystallographic carbide phases (stable,hexagonal Mo 2 C and/or unstable cubic molybdenum carbide) was observed depending on the conditions of carbidization. The reported earliercatalytic behavior at low temperatures were rationalized in terms of formation of these phases and oxy- or oxyhydrocarbides.# 2005 Elsevier B.V. All rights reserved. Keywords: Molybdenum carbide; Activated carbons; Catalyst characterization; X-ray diffraction 1. IntroductionThermodynamically stable binary carbides are only formedby the transition metals in group IV (Ti, Zr, Hf), V (V, Nb, Ta),VI (Cr, Mo, W) and by Mn in group VII. Transition metalcarbides possess electronic properties similar to preciousmetals [1]. They were first obtained in a classical way ofmetallurgical process at high temperatures and the obtainedmaterial was of rather high particle sizes and low specificsurface area. The elaboration of the thermo-programmed (TP)method of carbides synthesis [2,3] was, due to possibility ofbalancing between sintering and synthesis rate and obtainingcarbides with high specific surface areas, significant improve-ment into catalytic application of the carbides. Transition metalcarbides have attracted considerable attention for catalyticapplications since Levy and Boudart [4] first published resultson Pt-like behavior of WC in the neopentane izomerizationreaction. Nowadays the highly dispersed (nanometric) molyb-denum carbides as substitutes for currently applied preciousmetals (Pt, Pd) are considered to be prospectus catalysts inhydrodesulphurization (HDS) and hydrodenitrogenation(HDN) processes. Therefore a great effort is directed towardsstudies of interrelation between the observed catalytic proper-ties and structure of the active phase. In the Mo–C system thereexistsa series ofcarbide phases [5].Thereare at least twoMo

Force field based simulations have been employed to model the structure, and mechanical and mass transport properties of the all-silica zeolite MFI (ZSM5—Si96O192). Undeformed and deformed MFI subject to uniaxial loading in each of the three principal directions were investigated. The mechanical properties are predicted to include negative on-axis Poisson's ratios (auxetic behaviour) in the x 1–x 3 plane of the undeformed structure, and are strain-dependent. Transformation from positive-to-negative Poisson's ratio behaviour, and vice versa, is predicted for most on-axis Poisson's ratios at critical loading strains. Simulations of the simultaneous sorption of neopentane and benzene guest molecules onto the undeformed host MFI framework indicate a low neopentane-to-benzene loading ratio, consistent with experimental observation. The sorption of these two molecular species onto deformed MFI is Poisson's ratio- and strain-dependent. Uniaxial tensile loading along a direction containing a negative on-axis Pois...

CO/sub 2/ reforming of methane, propane, and neopentane was investigated with a ferroelectric packed-bed reactor (FPR) in N/sub 2/ at temperatures ranging from 298 K to 433 K. The reaction behavior of the hydrocarbons was greatly affected by their chemical structures and reaction temperature. At ambient temperature, hydrocarbon conversion decreased in the following order: neopentane/spl Gt/propane>methane. With an increase in reaction temperature, hydrocarbon reactivity was enhanced with only a slight difference in the conversions of the above hydrocarbons. CO/sub 2/ deoxygenation was a clean reaction irrespective of reaction temperature, but CO was formed not only from CO/sub 2/ but also from hydrocarbons. No chemical interaction between CO/sub 2/ and the hydrocarbons in nonthermal plasma was observed. Temperature effect on the H/sub 2/ yield depended on the hydrocarbon structure. Higher H/sub 2/ yields were obtained for neopentane and propane than for methane. Product composition and carbon balance were also affected by the hydrocarbon structure, relative concentrations of hydrocarbons to CO/sub 2/, and temperature.

Neopentane and TMS are used as model M(CH3)4 systems to investigate intramolecular interactions. The nonbonded site−site potential between two proximal hydrogen atoms on different methyl groups, Vnb(dHH), is not Lennard−Jones- or Morse-like but is found to be pseudolinear in hydrogen−hydrogen internuclear separation, dHH, for both neopentane and TMS. The Morse potential is found to be a poor basis in which to expand Vnb(dHH). The nonbonded site−site potential is conformation-dependent and not transferable between molecules. The individual contributions to Vnb(dHH) are presented. The local mode parameters for neopentane and TMS are calculated ab initio for a variety of molecular conformations. The ab initio values of the local mode frequency and local mode anharmonicity are increasingly blue-shifted with increasing steric hindrance. Electron correlation is found to be increasingly important with decreasing internuclear separations, dHH.

Mechanisms for H-transfer from 1,1-dimethylallyl (DMA) to neopentyl (CH 2 t-Bu) in the complex Cp*W(NO)(CH 2 t-Bu)(η 3 -DMA) are examined by B3LYP-DFT calculations. Either the mid-H or the methyl H on the DMA can transfer tothe W-bound neopentyl to generate neopentane (2,2-dimethylpropane) and Cp*W(NO)(η 2 -1,1-dimethylallene) or Cp*W(NO)(η 2 -2-methylbuta-1,3-diene) intermediates, respectively. The open coordination site created by the neopentane loss is the site of the subsequent C-H bond activation of alkanes and arenes. The similarities in the overall enthalpic barriers for these mechanisms, 23-24 kcal/mol, explain the observed deuterium distribution (65% on the mid-carbon and 35% on the methyls of the DMA) when benzene-d 6 reacts as substrate.

Kinetic acidities are reported for methane, ethane, propane, cyclopropane, isobutane, neopentane, tetramethylbutane, norbornane, nortricyclene, and adamantane by tritiodeprotonation or deuteriodeprotonation in cyclohexylamine catalyzed by cesium cyclohexylamide.

We have acquired high-resolution carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of methane, ethane, propane, isobutane, and neopentane. These experimental measurements are complemented by high-quality ab initio calculations, performed with the improved virtual orbital approximation. The degree and character of Rydberg-valence mixing in the preedge of the NEXAFS spectra of these species is explored. Significant Rydberg-valence mixing only occurs when there are excited states of valence sigma(C-H) character that have the appropriate symmetry to interact with excited states of Rydberg character. Our results show that this mixing is only present when there are C-H bonds to the core excited carbon atom.

Acetylene was pyrolyzed in a flow system at pressures between 104 and 403 Torr and temperatures between 854 and 971 K. Products were analyzed by gas chromatography with flame ionization and mass spectrometric detection. In some experiments the reactor was placed in the chromatographic oven to limit condensation. Twenty-four products were detected, of which fifteen were found to be primary. Orders and Arrhenius parameters were found for thirteen products. The results were interpreted in terms of a radical mechanism with 24 reactions for pure acetylene. Radical addition to acetylene produced chemically activated radicals, which could either eliminate a hydrogen atom or add more acetylene. If the radical contained five or more atoms, cyclization to form cyclopentadiene or an aromatic compound, respectively, was also possible. It was suggested that radical recombination could produce chemically activated intermediates that could cyclize to form cyclohexadienes. Addition of neopentane introduced methyl radicals, which could participate in another series of ten chemically activated acetylene addition and hydrogen elimination reactions to form propyne, cyclopentadiene and toluene. Five quotients of rate constants were calculated for competitive reactions.

The Xe nuclear magnetic resonance chemical shift differences that afford the discrimination between various biological environments are of current interest for biosensor applications and medical diagnostic purposes. In many such environments the Xe signal appears close to that in water. We calculate average Xe chemical shifts (relative to the free Xe atom) in solution in eleven liquids: water, isobutane, perfluoro-isobutane, n-butane, n-pentane, neopentane, perfluoroneopentane, n-hexane, n-octane, n-perfluorooctane, and perfluorooctyl bromide. The latter is a liquid used for intravenous Xe delivery. We calculate quantum mechanically the Xe shielding response in Xe-molecule van der Waals complexes, from which calculations we develop Xe (atomic site) interpolating functions that reproduce the ab initio Xe shielding response in the complex. By assuming additivity, these Xe-site shielding functions can be used to calculate the shielding for any configuration of such molecules around Xe. The averaging over configurations is done via molecular dynamics (MD). The simulations were carried out using a MD technique that one of us had developed previously for the simulation of Henry's constants of gases dissolved in liquids. It is based on separating a gaseous compartment in the MD system from the solvent using a semipermeable membrane that is permeable only to the gas molecules. We reproduce the experimental trends in the Xe chemical shifts in n-alkanes with increasing number of carbons and the large chemical shift difference between Xe in water and in perfluorooctyl bromide. We also reproduce the trend for a given solvent of decreasing Xe chemical shift with increasing temperature. We predict chemical shift differences between Xe in alkanes vs their perfluoro counterparts.

Steam reforming of aliphatic hydrocarbons such as methane, ethane, propane, and neopentane was investigated with two types of barrier discharge plasma reactors. With a ferroelectric packed-bed reactor ( FPR) in N/sub 2/, almost the same conversions were obtained for ethane, propane, and neopentane, but methane was less reactive than these hydrocarbons. Hydrogen gas yield decreased in the order: methane/spl ap/ethane>propane>neopentane. The molar ratio of H/sub 2/ to CO {[H/sub 2/]/[CO]} exceeded 3.5 for all the hydrocarbons. [H/sub 2/]/[CO] did not change in the range of H/sub 2/O content from 0.5% to 2.5%. At the volumetric ratio of H/sub 2/O to Hydrocarbon=2.0, carbon balances were poor for ethane, propane, and neopentane, but almost all of the carbon atoms in the reacted methane were recovered as CO and CO/sub 2/. The mole fractions of CO and CO/sub 2/ depended on the chemical structures of the substrate hydrocarbons. It is considered that the water-gas-shift reaction proceeds backward for the reaction systems of the hydrocarbons with higher hydrogen atom densities per molecule. FPR maintained the same performance for 10 h in the steam reforming of methane. The efficiency of a silent discharge plasma reactor was much lower than that of FPR.

Rate coefficients for the reactions of ethane, propane, n-butane, isobutane, and neopentane with Ta atoms and Ta clusters consisting of up to 30 Ta atoms have been measured in a fast-flow reactor. A near-monotonic dependency of the rate coefficients on cluster size is observed for each of these hydrocarbons, with the exception of Ta 1 1 , which exhibits rate coefficients that are several times that observed for the analogous reaction with Ta 1 0 and Ta 1 2 , for propane, n-butane, and isobutane. Modeling the general trend in the rate coefficients using transition state theory is found to require a relatively loose transition state with free rotation of the hydrocarbon about the bonding point on the cluster, consistent with the rate-determining step being cluster removal by an association reaction process. It is demonstrated that, in general, metal cluster reactions with reagents that can form strongly bound association complexes may exhibit little evidence of cluster-size-based selectivity in the rate of cluster removal, despite exhibiting significant selectivity in terms of the extent of the dehydrogenation reaction involved.

The monolayer of C(CH 3 ) 4 molecules adsorbed upon a highly homogeneous MgO powder surface has been studied by means of neutron diffraction techniques at the temperature 210 K. The structure of the monolayer presents a strong commensurability c(2 × 4) with the MgO(0 0 1) surface. The results of potential calculations support the proposed structure.

Hydroxyl groups of MCM-41 dehydroxylated under vacuum at 500 °C react with tetraneopentyl zirconium, leading to the evolution of neopentane and the formation of organometallic species with the mean formula (SiO) 2 ZrNp 2 which were fully characterized by physicochemical methods such as solid-state NMR, infrared spectroscopy, quantification of evolved gases and microanalysis. Decomposition of the resulting materials under vacuum, oxygen, water and hydrogen has been studied. The acid properties of the Zr-MCM-41 solids obtained by this way compare well to those of Zr-MCM-41 materials obtained by direct synthesis.

The fundamental spectrum and the parameters of the potential function of a number of saturated hydrocarbon molecules are calculated in an anharmonic approximation. The calculation is performed by the variational technique using a minimal Morse-harmonic basis. The potential function is taken as the sum of the Morse function for CH bonds and the harmonic function for the skeletal and deformation vibrations. The initial approximation for the potential function is found by ab initio calculations in a 6-31G basis and refined by solving the inverse problem. The calculated CH bond dissociation energies depend significantly on the molecular structure and on the position of CH bonds in the molecule. These energies correlate well with the experimental cleavage energies of these bonds. The changes in the dipole moment of the molecule induced by vibrations were found by ab initio calculations in a 6-31G basis. The calculated IR transmission curves are in good agreement with the experimental curves.

The momentum-transfer cross sections for positronium (Ps)–gas molecule scattering in the low energy region are determined by analysing the thermalization process of ortho-positronium (o-Ps) in various gases. The momentum distributions of Ps in Ne, H2, CH4, N2, C2H4, n-C4H10, i-C5H12 and neopentane are measured as functions of mean lifetime, by using the one-dimensional angular correlation of annihilation radiation method. The average energies obtained for o-Ps with mean lifetimes of 3–90 ns are analysed, to yield the momentum-transfer cross sections for the Ps–gas molecule scattering. The cross sections thus determined are σm = (20 ± 8) × 10−16 cm2 for Ne, (16 ± 3) × 10−16 cm2 for H2, (17 ± 6) × 10−16 cm2 for CH4, (37 ± 10) × 10−16 cm2 for N2, (35 ± 8) × 10−16 cm2 for C2H4, (100 ± 30) × 10−16 cm2 for n-C4H10, (110 ± 50) × 10−16 cm2 for i-C5H12 and (180 ± 60) × 10−16 cm2 for neopentane, in the Ps energy range below 0.3 eV. The Ps is thermalized mainly through elastic scattering with diatomic and polyatomic molecules, as in the case of scattering with inert gases.

This is the first of two papers aimed at understanding, from an atomistic perspective, hydrophobicity at different length scales and how properties such as local densities and angular profiles change for hydrophobic solutes of different sizes. In a subsequent publication we will describe the hydrophobic hydration and hydrophobic interaction of platelike molecules of nanoscale size. Molecular dynamics is used to compute radial and orientational distribution functions of water around three different molecules: argon, methane, and neopentane. In addition, the potential of mean force between two neopentane molecules is computed. The results for the full OPLS/AA1 force field are compared with the solute−solvent WCA truncated OPLS/AA force field for these systems. This work addresses the question of whether a molecule of the size of neopentane is large enough to induce a hydrophobic response similar to that of large hydrophobic molecules or paraffin walls. We answer this question in the affirmative. The orient...

Applying the G3 and G3(MP2) models and using both the isodesmic and atomization schemes, the heats of formation (ΔHf) at 0 and 298 K are calculated for mono-tert-butylmethane (2,2-dimethylpropane or neopentane, abbreviated as mono-TBM), di-tert-butylmethane (di-TBM), tri-tert-butylmethane (tri-TBM), and tetra-tert-butylmethane (tetra-TBM). Upon examining the results, it is found that all of the calculated ΔHf298 values are well within ±10 kJ mol-1 of the available experimental data for the first three compounds. Hence, for tetra-TBM, a compound that has not yet been synthesized, the G3(MP2) results reported in this work should be reliable estimates. Moreover, we have found that the atomization scheme is slightly more suitable for the study of the smaller molecules, while the isodesmic scheme is more suitable for the larger molecules. Structurally, it is found that the equilibrium structures of mono-TBM, di-TBM, tri-TBM, and tetra-TBM have Td, C2, C1, and T symmetry, respectively. The energy-minimized stru...

The adsorption and reaction of alkanes on/with metal single crystal surfaces are reviewed in this report. A comprehensive treatment of the structures and binding of molecular alkanes on metals is first presented. A detailed discussion of the current state of understanding of the dynamics of alkane trapping at surfaces then follows, including the most recent treatments of the roles of both intrinsic and extrinsic precursor states and the influence of preadsorbed species on trapping. The progress in the use of molecular dynamics simulations to predict trapping probabilities is thoroughly discussed. The current states of both the dynamics and the kinetics of dissociative adsorption on a variety of metal surfaces are elaborated.

Adsorption isotherms of C(CH3)4 on uniform MgO(1 0 0) surface have been measured in a wide range of temperature 190 6 T 6 273 K and a coverage corresponding to the two first layering transitions.A detailed study of the first transition is performed.Heat of adsorption, two-dimensional critical temperature and other experimental values of thermodynamic quantities are reported and compared to those related to C(CH3)4 adsorbed on graphite and boron nitride.On the other hand some structural investigations are given to support the thermodynamic analysis. 2003 Elsevier Science B.V. All rights reserved.