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Alkenes fragmentation mass

In mass spectrometry, the loss of an alkene fragment by a cyclic rearrangement of a carbonyl compound having y hydrogens, (p. 826)... [Pg.869]

Coke deposits were studied using mass spectra obtmed from the probe El and Cl analyses of the deactivated catalysts arising from the various feed streams. Alkane and alkene fragments were observed to dominate the individual mass spectra (particularly, m/z 57, 71 and 55, 69, respectively, in the El mode). Although alkylaromatics were evident for the catalyst from the tests with n-hexadecane and the n-hexadecane/phenanthrene mixture PACs are only present in trace quantities. Quinoline addition gave rise to much less intense ions from the deactivated catalyst due to its lower carbon content and the reduced sensitivity made it difBcult to observe the aromatic fragments. Indeed, the most intense peak was from quinoline itself (m/z 129 El, 130 Cl). [Pg.318]

C-8 hydroxyl group and the C-2 of the ring B alkene. The mass spectroscopic fragmentation pattern and a careful assignment of the NMR spectrum allowed the formulation of several part structures from which the final structure was deduced. [Pg.103]

The determination of the position of the double bond in linear alkenes by oxyselena-tion and GC-mass spectrometry was described by Francis and Tande [265]. Mixed ethers containing oxygen and selenium, formed by single-step conversion of alkenes, showed mass spectral fragmentation characteristics that depend on the original doublebond position. [Pg.303]

The mass spectra of phosphines (other than the simple methylphosphines) generaUy result in the observation of an M+ peak and fragmentation that occurs produces daughter ions that have come about by loss of an alkene fragment. [Pg.213]

The alkene fragment has an even mass. In contrast, most radical fragments encountered thus far have an odd mass (M-15 for loss of a methyl group, M—29 for loss of an ethyl group, M 3 for loss of a propyl group, etc.). Therefore, the mass spectrum of a ketone or aldehyde often contains a peak at M—x, where x is an even number. Some of the most common fragments are listed in Table 15.3. [Pg.704]

Ion series Consecutive alkene fragments of the type of CnH2n i or C H2n.30 (for both m/z 41, S3, 69,...) with maxima due to alkyl loss alter ring opening next to the carbonyl group and H transfer. Prominent even-mass maxima by elimination of substituents at position 2 or 6 as alkenes via sterically favored McLafferty rearrangements. [Pg.430]

Branched and internal alkenes fragment similarly at allylic bonds. Figure 11-29B shows the mass spectrum of 2-hexene, in which the base peak at m/z = 55 corresponds to formation of the resonance-stabilized 2-butenyl cation. [Pg.469]

The majority of marine isonitriles are sesquiterpenes with the molecular formula, C16H25N. Often cyclic, these are alkanes or alkenes possessing only a single isocyano-related functional group. In the mass spectrum, they exhibit a molecular ion at w/z 231, or an intense fragment ion at m/z 204, indicative of M+-HCN. Some are crystalline (see Table 2). With few exceptions most of the isothiocyano and formamido analogs are minor noncrystalline metabolites (see Table 3). [Pg.50]

Veith, H.J. Gross, J.H. Alkene Loss From Metastable Methyleneinunonium Ions Unusual Inverse Secondary Isotope Effect in Ion-Neutral Complex Intermediate Fragmentations. Org. Mass Spectrom. 1991,26, 1097-1105. [Pg.63]

Note Extensive isomerization prior to or between single steps of fragmentation makes the mass spectra of isomeric alkenes become very similar. [Pg.256]

As pointed out, carbenium ions make up the largest portion of alkane mass spectra and dissociate further by alkene loss. This type of fragmentation is rather specific, nevertheless isomerizations of the carbenium ion can happen before. Generally, such processes will yield a more stable isomer, e.g., the tcrt-butyl ion instead of other [C4H9] isomers (Fig. 6.19). [Pg.260]


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Mass fragmentation

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