Olefinic hydrocarbons resonances

The side-chain alkylation reaction of aromatic hydrocarbons has also been studied using unsaturated aromatic olefins, especially styrene. Pines and Wunderlich 43) found that phenylethylated aromatics resulted from the reaction of styrenes with arylalkanes at 80-125° in the presence of sodium with a promoter. The mechanism of reaction is similar to that suggested for monoolefins, but addition does not take place to yield a primary carbanion a resonance stabilized benzylic carbanion is formed [Reaction (23a, b)j. 

The above type of bonding is assumed to occur in other metal-olefin and metal-acetylene complexes (172). Acetylenes have two mutually perpendicular sets of ir-orbitals and are therefore capable of being bonded to one or to two metal atoms both types of complexes are known. When the hydrocarbon is a nonconjugated polyolefin e.g., cyclo-octa-1,5-diene, each C C bond interacts independently with the metal atom. In complexes of conjugated polyolefins, e.g., cyclopentadiene, infrared and nuclear magnetic resonance studies (99) indicate that it is not yet possible to distinguish between structure (IV), in which each C C bond independently contributes two --electrons to the metal-olefin bonding, and structure (V), in which... 

The physical and chemical properties of the X -phosphorins 118 and 120 are comparable to those of phosphonium ylids which are resonance-stabilized by such electron-pulling groups as carbonyl or nitrile substituents Thus they can be viewed as cyclic resonance-stabilized phosphonium ylids 118 b, c, d). As expected, they do not react with carbonyl compounds giving the Wittig olefin products. However, they do react with dilute aqueous acids to form the protonated salts. Similarly, they are attacked at the C-2 or C-4 positions by alkyl-, acyl- or diazo-nium-ions Heating with water results in hydrolytic P—C cleavage, phosphine oxide and the hydrocarbon being formed. 

Figure 19 shows the C CP/MAS NMR spectra recorded lOmin to 53 h after adsorption of [ C-l]-l-octene on zeolite HZSM-5. The spectra indicate that the C-labeled terminal olefinic =Cll2 groups evident in the spectra at ca. 113 ppm are transformed into terminal C-labeled paraffinic CH3 groups, evident at 14.3 ppm. Furthermore, the selective label penetrates into internal -CH2- groups of the octene hydrocarbon skeleton, characterized by resonances occurring at 33.0 ppm. 

Here a surface Lewis acid (denoted by j) abstracts a hydride ion from the methylene group adjacent to the double bond. This mechanism is in accord with the essential Lewis acid nature of the silica-alumina surface and is consistent with the previously demonstrated ability of this surface to abstract hydride ions from tertiary hydrocarbons. Since an alkenyl carbonium ion is stabilized by resonance to a greater extent than is a saturated carbonium ion, it may well be the most stable species which could form in the chemisorption of an aliphatic olefin or its precursor. It seems reasonable, therefore, to presume that such species may be involved in heterogeneous acid catalysis to a greater extent than has been generally recognized. This chemisorption process does not, of course, exclude the more conventional acid addition to the double bond which may occur under suitable circumstances but rather, it introduces an alternate path which may well exert a considerable influence on the overall course of catalytic reactions. Thus, for example, since a substituted ally lie carbonium ion may be converted to a conjugated diene by loss of a proton, it may be an important intermediate in the formation... 

An exception to the straightforward correspondence between C shifts in zeolites (or other catalysts) and solution values occurs when the structure of the compound is significantly perturbed on the catalyst. The most common example is protonation equilibria on acidic catalysts. Indeed, there have been a number of reports of the use of protonation shifts of amines 151,521, phosphines (151, and phosphine oxides (531 as probes of catalyst acidity. Similar effects are (x ca-sionally encountered in in situ experiments when a basic molecule is formed as an intermediate or product. An interesting case is the conversion of acetone to hydrocarbons on zeolites, which may involve the intermediacy of diacetone alcohol, mesityl oxide, phorone, and isophorone—all ketones. The chemical shifts of the carbonyl carbons of all these species in acidic zeolites were found to be up to 10 ppm downfield of the corresponding values in reference compilations. Furthermore, although the chemical shifts of the olefinic carbons a to the carbonyl were in reasonable agreement with values for CDCI solutions, the resonances of the olefinic carbons p to the carbonyl were very broad and shifted 20-30 ppm downfield 54. ... 

Cyclic Olefins. Molecular orbital calculations show that the trend of downfield shift for CO and upheld shift for hydrocarbon C resonances in the series... 

ASTM Test Method D5292, Aromatic Carbon Contents of Hydrocarbon Oils by High Resolution Nuclear Magnetic Resonance Spectroscopy, permits determination of aromatic hydrogen and aromatic carbon content of gas oils, lubricating oils, and other hydrocarbon fractions that are completely soluble in chloroform and carbon tetrachloride at ambient temperatures. Concentrations as low as 0.1 mol-% hydrogen and 0.5 mol-% carbon can be determined. Olefins and phenolic compounds above 1 mass-% interfere. 

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