Alkanes fragmentation

In the case of alkanes with tertiary or quaternary carbon atoms the characteristic decomposition mode is usually the fragment alkane elimination (Sec. 2.6) and its yield can be used to estimate G(S i) values. Based on the fragment alkane elimination yield Pitchuozhkin et al. [162] calculated a singlet G value of 3.3 1 for 2,2,4-trimethylpentane. 

Some classes of compounds are so prone to fragmentation that the molecular ion peak IS very weak The base peak m most unbranched alkanes for example is m/z 43 which IS followed by peaks of decreasing intensity at m/z values of 57 71 85 and so on These peaks correspond to cleavage of each possible carbon-carbon bond m the mol ecule This pattern is evident m the mass spectrum of decane depicted m Figure 13 42 The points of cleavage are indicated m the following diagram... 

For linear alkanes, the initial fragment lost is an ethyl group (never a methyl group), followed by propyl, butyl, and so on. An intense peak at mass 43 suggests a chain longer than butane. 

Nepeta (Lamiaceae) is a genus of perennial or annual herbs found in Asia, Europe and North Africa. About 250 species of Nepeta are reported of which, 67 species are present in Iran. Some species of this genus are important medicinal plants and their extracts have been used for medicinal purposes. Aerial parts of Nepeta sintenisii Bornm. was subjected to hydrodistillation and the chemical composition of isolated essential oil has been analyzed by GC/MS method for first time. Identification of components of the volatile oil was based on retention indices relative to n-alkanes and computer matching with the Wiley275.L library, as well as by comparison of the fragmentation patterns of the mass spectra with those reported in the literature. 

Five-membered ring systems are also formed on transfer of single-skeletona-tom fragments, usually in a stepwise process CR2 from diazo alkanes [28], NH from azourude (hydrazoic acid) [134], O from peroxy acids [/ii], S from phos-... 

Compound 123 (R = R = H) oxidatively adds chloroform and gem-dichloro-alkanes (940M4153). With methyl iodide, trans addition occurs and species 147 is formed. With dichloromethane, the route is three-fragment and four-electron, and the result is species 148 (R = H). Dichloromelhylbenzene and methyl dichloro-ethanoate give 148 (R = Ph and COOMe, respectively). Simultaneously, the... 

Cracking (Chapter 3 Focus On) A process used in petroleum refining in which large alkanes are thermally cracked into smaller fragments. 

The molecular ion intensity decreases with increased branching, therefore the molecular ion peak may be nonexistent. The loss of 15 Daltons from the molecular ion indicates a methyl side chain. The mass spectra of branched alkanes are dominated by the tendency for fragmentation at the branch points, and hence are difficult to interpret. 

Duffield and coworkers65 studied the El- induced mass spectra of five arene- (215-219) and four alkane sulfonylthioureas (220-223) and observed two rearrangement processes, namely loss of S02 from 215-219 and the elimination of ArS02 and RS02 with the thione sulfur atom from 215-223. The other fragmentations involved simple bond cleavages with and without hydrogen transfer (equation 48). The loss of H2S was evident for all the compounds studied except 221 and 222. It was, however, found to be a thermal and not an ionization process. 

This catalytic reaction has been named alkane a-bond metathesis since alkyl fragments of alkane mixtures are exchanged. For example, propane is... 

With only few exceptions, most log P programs refer to the octanol-water system. Based on Rekker s fragmental constant approach, a log P calculation for aliphatic hydrocarbon-water partitioning has been reported [96]. Another more recent approach to alkane-water log P and log D is based on the program VolSurf [97]. It is believed that these values may offer a better predictor for uptake in the brain. 

The most recent catalysts that operate under thermal conditions were then based on the premise that a Cp M fragment with ligands that dissociate under thermal conditions could be a catalyst for alkane borylation. After a brief study of Cp IrH4 and Cp Ir(ethylene)2, Dr. Chen studied related rhodium complexes. Ultimately, he proposed that the Cp Rh(ri" -C6Me6) complex would dissociate CeMce as an iimocent side product, and that Cp Rh(Bpin)2 from oxidative addition of pinBBpin (pin=pinacolate) would be the active catalyst. The overall catalytic... 

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