Isomerization of hydrocarbon ions. VI—parameters determining the isomerization of aliphatic hydrocarbon ions

The radical or non-radical character of aliphatic hydrocarbon ions determines the extent to which these ions equilibrate to a mixture of interconverting structures prior to decomposition. It is suggested that the radical (odd electron) ions have both lower thresholds for decomposition and higher barriers for isomerization that non-radical (even electron) ions, thus explaining their reduced tendency for isomerization. Moreover, the molecular size seems to be a major influencing factor for the isomerization of unsaturated hydrocarbon molecular ions. With decreasing molecular size isomerization prior to decomposition becomes more pronounced. Collisional activation spectra of fragment ions (formed by loss of H₂O from the corresponding alcohols) and of [C₅H₁₀]⁺ and [C₄H₈]⁺ molecular ions are reported in support of these conclusions.     

3-Neopentylallyllithium II. Reactions in hydrocarbon media

Product distributions are reported for several reactions in hydrocarbon solvent of 3-neopentylallyllithium, the 1,4-addition product of tert-butyllithium and 1,3-butadiene. Protolysis with several agents yields predominately the “normal” products [(Ia) and (Ib)] with less than 6% of the terminal olefin observed. The ratio of the cis/trans isomers [(Ia) and (Ib)] parallels the ratio of the lithiated forms before protolysis. Reaction with chlorotrimethylsilane also shows no “rearranged” product. Carboxylation and ketone addition reactions, however, proceed with marked rearrangement unless the ketone is very hindered. Di-tert-butyl ketone and benzophenone give no rearranged product. Addition of a second mole of butadiene also results in predominant (60%) rearrangement of the neopentylallyl group. Bromination with molecular bromine and 1,2-dibromoethane yields a mixture of dibromo-derivatives in the former case and C₁₆-diolefin coupling products in the later case. Tentative mechanisms for protolysis and addition reactions are discussed.     

Pyrolyses of azoalkanes. photoelectron spectra of some hydrocarbon radicals

The pyrolyses of azocyclobutane (=1)and azocyclopropylmethane (=2) have been used to generate C₄H₇ radicals. The photoelectron spectra at various temperatures are presented and the results compared with the data obtained by pyrolyses of the corresponding methylnitrites.     

Fluoro-ketones. I reactions of hydrocarbon grignards with perfluoroalkylacid fluorides

The reaction between Grignard reagents and perfluoroacid fluorides provides a convenient synthesis procedure for ketones R_fOR_fC(O)R′, where R_fOR_f is perfluoroalkylether group and R' is either an aromatic or aliphatic group. Reaction temperature is an important factor in producing higher yields of ketones. Meta and para-bromophenyl Grignard reagents, which thus far have not been prepared as pure mono Grignards, present secondary competing reactions which detract from their synthetic utility.     

Chemiluminescence of hydrocarbon polymers

The thermal oxidation of some hydrecarbon polymers differing by their degree of branching was studied simultaneously by chemiluminescence and infrared spectrophotometry. In the case of isotactic polypropylene, measurements were made at various temperatures ranging from 140 to 180°C. The other polymers—ethylene–propylene copolymer, low and high density polyethylene—were studied only at 160°C. In all cases, the induction times of chemiluminescence coincide with those of carbonyl growth. The previously proposed mechanisms of light emission are not consistent with the kinetic data or with the structure effects on luminescence, which seems directly related with the presence of tertiary hydrogens. A hypothetical mechanism based on the β scission of tertiary alkoxyls is proposed.     

Thermal activation of hydrocarbon C-H bonds by tungsten alkylidene complexes.

Thermal activation of CpW(NO)(CH(2)CMe(3))(2) (1) in neat hydrocarbon solutions transiently generates the neopentylidene complex, CpW(NO)(=CHCMe(3)) (A), which subsequently activates solvent C-H bonds. For example, the thermolysis of 1 in tetramethylsilane and perdeuteriotetramethylsilane results in the clean formation of CpW(NO)(CH(2)CMe(3))(CH(2)SiMe(3)) (2) and CpW(NO)(CHDCMe(3))[CD(2)Si(CD(3))(3)] (2-d(12)), respectively, in virtually quantitative yields. The neopentylidene intermediate A can be trapped by PMe(3) to obtain CpW(NO)(=CHCMe(3))(PMe(3)) in two isomeric forms (4a-b), and in benzene, 1 cleanly forms the phenyl complex CpW(NO)(CH(2)CMe(3))(C(6)H(5)) (5). Kinetic and mechanistic studies indicate that the C-H activation chemistry derived from 1 proceeds through two distinct steps, namely, (1) rate-determining intramolecular alpha-H elimination of neopentane from 1 to form A and (2) 1,2-cis addition of a substrate C-H bond across the W=C linkage in A. The thermolysis of 1 in cyclohexane in the presence of PMe(3) yields 4a-b as well as the olefin complex CpW(NO)(eta(2)-cyclohexene)(PMe(3)) (6). In contrast, methylcyclohexane and ethylcyclohexane afford principally the allyl hydride complexes CpW(NO)(eta(3)-C(7)H(11))(H) (7a-b) and CpW(NO)(eta(3)-C(8)H(13))(H) (8a-b), respectively, under identical experimental conditions. The thermolysis of 1 in toluene affords a surprisingly complex mixture of six products. The two major products are the neopentyl aryl complexes, CpW(NO)(CH(2)CMe(3))(C(6)H(4)-3-Me) (9a) and CpW(NO)(CH(2)CMe(3))(C(6)H(4)-4-Me) (9b), in approximately 47 and 33% yields. Of the other four products, one is the aryl isomer of 9a-b, namely, CpW(NO)(CH(2)CMe(3))(C(6)H(4)-2-Me) (9c) ( approximately 1%). The remaining three products all arise from the incorporation of two molecules of toluene; namely, CpW(NO)(CH(2)C(6)H(5))(C(6)H(4)-3-Me) (11a; approximately 12%), CpW(NO)(CH(2)C(6)H(5))(C(6)H(4)-4-Me) (11b; approximately 6%), and CpW(NO)(CH(2)C(6)H(5))(2) (10; approximately 1%). It has been demonstrated that the formation of complexes 10 and 11a-b involves the transient formation of CpW(NO)(CH(2)CMe(3))(CH(2)C(6)H(5)) (12), the product of toluene activation at the methyl position, which reductively eliminates neopentane to generate the C-H activating benzylidene complex CpW(NO)(=CHC(6)H(5)) (B). Consistently, the thermolysis of independently prepared 12 in benzene and benzene-d(6) affords CpW(NO)(CH(2)C(6)H(5))(C(6)H(5)) (13) and CpW(NO)(CHDC(6)H(5))(C(6)D(5)) (13-d(6)), respectively, in addition to free neopentane. Intermediate B can also be trapped by PMe(3) to obtain the adducts CpW(NO)(=CHC(6)H(5))(PMe(3)) (14a-b) in two rotameric forms. From their reactions with toluene, it can be deduced that both alkylidene intermediates A and B exhibit a preference for activating the stronger aryl sp(2) C-H bonds. The C-H activating ability of B also encompasses aliphatic substrates as well as it reacts with tetramethylsilane and cyclohexanes in a manner similar to that summarized above for A. All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 4a, 6, 7a, 8a, and 14a have been established by X-ray diffraction methods.     

Water/hydrocarbon interfaces: effect of hydrocarbon branching on single-molecule relaxation

Water/hydrocarbon interfaces are studied using molecular dynamics simulations in order to understand the effect of hydrocarbon branching on the dynamics of the system at and away from the interface. A recently proposed procedure for studying the intrinsic structure of the interface in such systems is utilized, and dynamics are probed in the usual laboratory frame as well as the intrinsic frame. The use of these two frames of reference leads to insight into the effect of capillary waves at the interface on dynamics. The systems were partitioned into zones with a width of 5 A, and a number of quantities of dynamical relevance, namely, the residence times, mean squared displacements, the velocity auto correlation functions, and orientational time correlations for molecules of both phases, were calculated in the laboratory and intrinsic frames at and away from the interface. For the aqueous phase, translational motion is found to be (a) diffusive at long times and not anomalous as in proteins or micelles, (b) faster at the interface than in the bulk, and (c) faster upon reduction of the effect of capillary waves. The rotational motion of water is (a) more anisotropic at the interface than in the bulk and (b) dependent on the orientation of the covalent O-H bond with respect to the plane of the interface. The effect of hydrocarbon branching on aqueous dynamics was found to be small, a result similar to the effect on the interfacial water structure. The hydrocarbon phase shows a larger variation for all dynamical probes, a trend consistent with their interfacial structure.     

Metal-catalysed hydrocarbon oxidations

This brief review describes recent findings by the author and his co-workers in the field of catalytic systems for the oxidation of saturated and aromatic hydrocarbons with molecular oxygen (from air), hydrogen peroxide and some other compounds. These systems are based on metal complexes as catalysts and often include obligatory co-catalysts, such as amino acids, nitrogen-containing bases or weak carboxylic acids. Some of these reactions can be considered as biomimetic models of corresponding oxidation processes occurring in living cells. In some cases, aerobic oxidations considered here occur in some cases under the action of light. Some features of these reactions and their mechanisms are presented and discussed. To cite this article: G.B. Shul'pin, C. R. Chimie 6 (2003).     

Infrared spectroscopy of polycyclic aromatic hydrocarbon cations. 1. Matrix-isolated naphthalene and perdeuterated naphthalene

Ionized polycyclic aromatic hydrocarbons (PAHs) are thought to constitute an important component of the interstellar medium. Despite this fact, the infrared spectroscopic properties of ionized PAHs are almost unknown. The results we present here derive from our ongoing spectroscopic study of matrix isolated PAH ions and include the spectra of the naphthalene cation, C10H8+, and its fully deuterated analog, C10D8+, between 4000 and 200 cm-1. Ions are generated in situ Lyman-alpha photoionization of the neutral precursor. Bands of the C10H8+ ion are observed at 1525.7, 1518.8, 1400.9, 1218.0, 1216.9, 1214.9, 1023.2, and 758.7 cm-1. Positions and relative intensities of these bands agree well with those in the available literature. The 758.7 cm-1 band has not previously been reported. C10D8+ ion bands appear at 1466.2, 1463.8, 1379.4, 1373.8, 1077.3, 1075.4, and 1063.1 cm-1. Compared to the analogous modes in the neutral molecule, the intensities of the cation's CC modes are enhanced by an order of magnitude, while CH modes are depressed by this same factor. Integrated absorption intensities are calculated for the strongest bands of C10H8 and for the observed bands of C10H8+. Absolute intensities derived for the naphthalene cation differ from earlier experimental results by a factor of approximately 50, and from theoretical predictions by a factor of approximately 300. Reasons for these discrepancies and from the astronomical implications of PAH cation spectra are discussed.     

Photo-ionization of aromatic hydrocarbon negative ions in ethers. The biphenyl anion

On the basis of Marcus' theory of electron transfer the mechanism and kinetics of electron ejection from lower excited states of aromatic hydrocarbon negative ions in liquid ethers are discussed.The application of the theory to the photo-ionization of biphenyl^? in glymes by nanosecond ruby laser pulses studied by Makkes van der Deyl et al. leads to a free energy of electron ejection for the ground state ion, ΔG⁰_e ≈ 12000 cm^?1.     

Hydrophobic encapsulation of hydrocarbon gases

[reaction: see text] Encapsulation data for hydrophobic hydrocarbon gases within a water-soluble hemicarcerand in aqueous solution are reported. It is concluded that hydrophobic interactions serve as the primary driving force for the encapsulation, which can be used for the design of gas-separating polymers with intrinsic inner cavities.     

Properties of amorphous and crystallizable hydrocarbon polymers. III. Studies of the hydrogenation of polybutadiene

Three methods for hydrogenating anionically prepared polybutadiene (containing about 8% vinyl double bonds) were investigated: homogeneous catalysis (alkylated transition metal salts), heterogeneous catalysis (nickel on kieselguhr; paladium on calcium carbonate), and stoichiometric reaction with in situ generated diimide. The products were characterized by intrinsic viscosity, gel permeation chromatography, infrared spectroscopy, and melt viscosity. Only the heterogeneous catalysts were found to yield completely hydrogenated products without incorporation of foreign groups and without significant change in the large-scale molecular structure of the chain. The 195°C melt viscosity of linear polybutadiene hydrogenated with heterogeneous catalysts is virtually identical with that of linear polyethylene with the same intrinsic viscosity in trichlorobenzene at 135°C. The solid state properties of hydrogenated polybutadiene, containing about 20 ethyl branches/1000 main chain atoms, closely resemble those of commercial branched polyethylene.     

Head-group-influenced mixed micellization of sodium deoxycholate with conventional hydrocarbon surfactants of identical hydrocarbon tails

Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state.     

Liquid-liquid equilibria for ternary acetonitrile-ethanol-saturated hydrocarbon and acetonitrile-1-propanol-saturated hydrocarbon mixtures

Isothermal vapour-liquid equilibrium data for acetonitrile-1-propanol at 45° C were measured by use of a recirculating still. The liquid-liquid equilibria of (acetonitrile-etha-nol)-(n-hexane or n-heptane or n-octane) and those of (acetonitrile-1-propanol)-(cyclohexane or n-hexane or n-heptane) were obtained from measurements of tie-lines. The experimental results were compared with those calculated from the UNIQUAC associated-solution model.