Saturated hydrocarbons, diffusion

The ultraviolet spectra of saturated hydrocarbons are usually not very informative, and are dominated by Rydberg transitions.101 They correspond to the formation of a radical cation with the ejected electron being captured in a diffuse, atomlike orbital. Bicyclo[l.1. OJbutane is the most extensively studied molecule of this group, and the Rydberg nature of the excited... 

Short-Lived Species in Fluid Solution. - In fluid solution, radical cations derived from saturated hydrocarbons are highly reactive oxidizing species and the rates of their bimolecular reactions are often determined by the frequency of diffusion collisions in solutions. It is known that the reactions of primary radical... 

A new mathematical model based on moment techniques to describe micro- and macropore diffusion is used to study the mass-transfer resistances of Ci to C4 saturated hydrocarbons in H and Na mordenites between 127° C and 272° C. The intracrystalline diffusion coefficient decreases as the number of carbon atoms increases while the energy of activation increases with the number of carbons. The contribution from individual mass-transfer resistances to the overall mass-transfer processes is estimated. 

In our calculations Boys localization procedure was applied to localize the occupied and virtual orbitals in two separate blocks. The properties of the localized virtual orbitals of normal saturated hydrocarbons are investigated in detail in [65] and for all-trans conjugated polyenes in [68], In Fig. 1 the schematic plots of ellipsoids of selected occupied and virtual orbitals of C5H12 in the 6-31G basis set are presented in the plane of the CC bonds. Only two characteristic sets of LMOs are selected, a terminal CH bond and a CC bond. The left panel shows the occupied and the right the virtual LMOs. The plots of occupied and virtual LMOs in minimal basis are very similar to case (a) and they are not presented here. We can see that the localized orbitals are well separated and their spatial extent is restricted to a small part of the molecule even for the diffuse u2 and 0 3 LMOs. The virtual LMOs are spread along the axis of chemical bonds and they are not restricted to the region between the atoms. 

Unlike the mobility of imsaturated hydrocarbons, the mobihty of saturated hydrocarbons in Na-X is, in fact, essentially unaffected by the presence of sodium cations. This has been confirmed by PFG NMR diffusion studies with benzene and -heptane in zeohte Na-X and La-X [103,151]. Since the triva-lent lanthanum ions are predominantly localized at positions in the hexagonal prisms and sodalite units, the molecules adsorbed in lanthanum-exchanged zeolites are essentially without contact to the cations. As a consequence of the specific interaction between the cations and the unsaturated hydrocarbon, the benzene mobility in Na-X was found to be two orders of magnitude smaller than in La-X, while the -heptane diffusivities were the same. 

The effect of subtle differences in certain properties of sorbate molecules on the diffusivities can be very intriguingly demonstrated in Fig. 16. With shape and size close to that of p-xylene, the long, rigid molecule, p-dichloro-benzene (p-DCB) displays an FR behaviour in silicalite-1 very similar to that of p-xylene. The flexible saturated cyclic hydrocarbons diffuse much more slowly within the channel framework of silicalite-1 than their rigid aromatic... 

Variation in the rate of anodic oxidation of normal saturated hydrocarbons with the number of carbon atoms parallels the variation in the rate of diffusion of the hydrocarbon through the electrolyte. This holds for different electrolytes (CsF/HF, H3PO4, HF, H2SO4) and electrodes (Pt-black, Raney-Pt). The rates are low for methane, highest for ethane and propane and then gradually decrease . ... 

In this study, we succeeded in the observation of Raman spectra of benzene, cyclohexane and chloroform in aqueous solution. These molecules are known to form hydrate clathrates of type M 1TH20[2], and were selected because of their high solubilities in water, relative to other saturated hydrocarbons, and because of their strong Raman lines. It may be expected that the iceberg structure formed around the solute in aqueous solution affects the rotational motion of the solute molecule. Thus the rotational diffusion constants have been determined from the linewidths of the isotropic and anisotropic Raman spectra, and the effect of the iceberg structures on the rotational motion of the solute molecules is discussed from a comparison of the rotational diffusion constants in various solutions. 

Gell B. Carol, Krishnamoorti Ramanan, Kim Eugene, Graessley W. William, and Fetters J. Lewis. Viscoelasticity and diffusion in miscible blends of saturated hydrocarbon polymers. Rheol. Acta. 36 (1997) 217-228. 

Anderson et al. showed by in situ MAS NMR spectroscopy that the main species present in the intracrystalline space are branched and saturated hydrocarbons such as isobutane and isopentane [221]. The contribution acknowledges again a role of diffusion to the formation of the first olefins structure [221]. 

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