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Hydrocarbon structures dimerization

Deprotonation of OsH4(PMe2Ph)3 with excess KH in thf at 70°C leads to lipophilic K+[/ac-OsH3(PMe2Ph)3]-. In the solid state, this has a dimeric structure with phenyl rings helping it present a hydrocarbon-like exterior to solvents (Os-H 1.66-1.69 A, Os-P 2.271-2.28 A) [166]. [Pg.64]

Another type of interaction is the association of radical ions with the parent compounds. Recently (118), a theoretical study was reported on the interaction of butadiene ions with butadiene. Assuming a sandwich structure for the complex, the potential curve based on an extended Hiickel calculation for two approaching butadienes (B + B) revealed only repulsion, as expected, while the curves for B + and B + B" interactions exhibit shallow minima (.068 and. 048 eV) at an interplanar distance of about 3.4 A. From CNDO/2 calculations, adopting the parameter set of Wiberg (161), the dimer cation radical, BJ, appears to be. 132 eV more stable than the separate B and B species, whereas the separate B and B species are favored by. 116eV over the dimer anion radical, BJ. This finding is consistent with experimental results formation of the dimer cation radical was proved in a convincing manner (162) while the attempts to detect the dimer anion radical have been unsuccessful. With other hydrocarbons, the reported formation of benzene dimer anion radical (163) represents an exceptional case, while the dimeric cation radical was observed... [Pg.368]

It should be noted that in forming this dimeric channel structure all the hydrogen bonds are parallel to the channel axis and that the inner surface is lined with the polar polypeptide groups. In addition the various lipophilic side chains coat the outer wall of the structure and are thus in contact with the lipid hydrocarbon chains. The resulting gramicidin A channel is a most efficient means of ion transport with approximately 107 sodium ions traversing the channel per second, under conditions of 1 M NaCl, 100 mV applied potential and a temperature of 25 °C 225). The detailed mechanism by which this can be achieved is under active study 226). [Pg.187]

The black explosive powder previously described as Se4N2 is now assigned this structure. It is very sensitive when dry and handling it damp with an hydrocarbon is recommended. There is brown dimer, also explosive [2]. [Pg.1428]

Anodic oxidation in inert solvents is the most widespread method of cation-radical preparation, with the aim of investigating their stability and electron structure. However, saturated hydrocarbons cannot be oxidized in an accessible potential region. There is one exception for molecules with the weakened C—H bond, but this does not pertain to the cation-radical problem. Anodic oxidation of unsaturated hydrocarbons proceeds more easily. As usual, this oxidation is assumed to be a process including one-electron detachment from the n system with the cation-radical formation. This is the very first step of this oxidation. Certainly, the cation-radical formed is not inevitably stable. Under anodic reaction conditions, it can expel the second electron and give rise to a dication or lose a proton and form a neutral (free) radical. The latter can be either stable or complete its life at the expense of dimerization, fragmentation, etc. Nevertheless, electrochemical oxidation of aromatic hydrocarbons leads to cation-radicals, the nature of which is reliably established (Mann and Barnes 1970 Chapter 3). [Pg.90]

An investigation of lithium diisopropyl amide (LDA) by solid state NMR led to the observation of dramatic differences between the spectra of the solid polymer and the complex crystallized from THF. Li as well as "C and "N MAS spectra showed large sideband patterns in the former case and only a few sidebands in the latter. For both materials X-ray data are available and establish a helix structure for the polymeric material, which is insoluble in hydrocarbon or ethereal solvents, and a dimer structure of the THF complex (25, 26, Scheme 4). The obvious difference between both structures, apart from the solvent coordination in the THF complex, is the magnitude of the structural N-Li-N angle, which is close to 180° in the first case and close to 90° in the second (176° and 107°, respectively). Thus, a large difference for the electric field gradient around the Li cation is expected for the different bonding situations. [Pg.175]

A variable-temperature Li, C, NMR spectroscopy study was carried out on the ligand structure and association behavior of [ Li, N]-enriched lithium bis(trimethylsilyl)-amide in hydrocarbon solntion. The system behaves as shown, for example, in equation 38, with the solnte adopting a dimeric form (209), which tnms to the monomeric 210 on... [Pg.367]


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See also in sourсe #XX -- [ Pg.731 ]




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Dimeric structures

Hydrocarbon structure

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