Hydrocarbons protonation

The formation of protonated H+(H20)n species can affect the acidity of the non-solvated protonic sites. Therefore, as the acid strength of the protonic sites in zeolites plays a key role in the hydrocarbon transformation reactions, driving the rate of the hydrocarbon protonation [4-6], the presence of water vapor among the reactants can modify reaction rates of the individual reactions involving in the hydrocarbon transformations. 

As observed, aromatic hydrocarbons gave products of protonation on dissolution in hydrofluoric acid. Oxidation into aromatic cation-radicals did not take place (Kon and Blois 1958). Trifluoro-acetic acid is able to transform aromatics into cation-radicals. This acid is considered a middle-powered one-electron oxidant (Eberson and Radnor 1991). Its oxidative ability can be enhanced in the presence of lead tetraacetate. This mixture, however, should be used carefully to avoid oxidation deeper than the one-electron removal. Thus, oxidation of 1,2-phenylenediamine by the system Pb(OCOCH3)4 -I- CE3COOH -P CH2CI2 leads to the formation of either primary or secondary cation-radicals. The primary product is the cation radical of initial phenylenediamine, whereas the secondary product is the cation radical of dihydrophenazine (Omelka et al. 2001). Sulfuric acid is also used as an one-electron oxidant, especially for aromatic hydrocarbons. In this case, generation of cation radicals proceeds simultaneously with the hydrocarbon protonation and sulfonation (Weissmann et al. 1957). 

Interpretation of the NMR Spectra of Membranes. Let us first consider a model system of lysolecithin and serum albumin (74), shown in Figure 12. Lysolecithin in D20 is shown in Figure 12A, while the effect of increasing amounts of bovine serum albumin is shown in Figures 12B and 12C. When no protein is present, the lines for both the methylene protons on the lysolipid tails and the quaternary ammonium methyl protons on the choline moiety of the polar heads are narrow. Thus, the polar ends of the molecules are free to move, and the apolar hydrocarbons within the detergent micelles are in a liquid-like state (24). When protein is added, the hydrocarbon proton line broadens and shifts upfield slightly, but neither the width nor area of the quaternary ammonium line... 

For biological membranes the situation is more complex. The results from erythrocyte ghosts and lipids (13) suggest nonpolar association through lipid hydrocarbon chains. As a test of the technique a membrane in which the bilayer conformation has been demonstrated by some independent technique is desirable. I have argued earlier from calorimetric evidence that the membrane of M. laidlawii is such a system. NMR spectra of M. laidlawii membranes taken in this laboratory do not, however, show discernible hydrocarbon proton resonance. We must consider, then, why the two techniques of calorimetry and NMR do not agree. 

Although the majority of the lipids in M. laidlawii membranes appear to be in a liquid-crystalline state, the system possesses the same physical properties that many other membranes possess. The ORD is that of a red-shifted a-helix high resolution NMR does not show obvious absorption by hydrocarbon protons, and infrared spectroscopy shows no ft structure. Like erythrocyte ghosts, treatment with pronase leaves an enzyme-resistant core containing about 20% of the protein of the intact membrane (56). This residual core retains the membrane lipid and appears membranous in the electron microscope (56). Like many others, M. laidlawii membranes are solubilized by detergents and can be reconstituted by removal of detergent. Apparently all of these properties can be consistent with a structure in which the lipids are predominantly in the bilayer conformation. The spectroscopic data are therefore insufficient to reject the concept of a phospholipid bilayer structure or to... 

The identifiable compounds in coke-oven and petroleum pitches are mainly polynuclear aromatic hydrocarbons. Proton magnetic resonance spectra of solvent-soluble fractions of these materials show that over 90 of the protons are attached to aromatic rings. Under the conditions of carbonization it would... 

The material tenaciously holds hydrocarbons, such as pentane, hexane, and petroleum ether, which cannot be removed even under high vacuum. The solvated crystals show hydrocarbon protons in the NM and exhibit a broad melting point. However, we have found that cyclohexane is not retained in the crystals. 

Hydrocarbon protonations by catalysts have been modeled theoretically. BLYP/6-31G calculations suggest protonation of the C-C bonds, followed by collapse to alkane and alkene. The acidic catalyst site is regenerated by transfer of a proton to an adjacent oxygen. This model, which is summarized in Figure 4.15, undoubtedly oversimplifies the picture, but probably contains the fundamental aspects of the catalysis. 

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