Mass spectral fragmentation hydrocarbons

Because mass-spectral fragmentation patterns are usually complex, it s often difficult to assign structures to fragment ions. Most hydrocarbons fragment in many ways, as the mass spectrum of hexane shown in Figure 12.4 demonstrates. The hexane spectrum shows a moderately abundant molecular ion at m/z = 86... 

Mass spectra of the cis- and /ram-isomers of the pyrimido[2,TA [l,3]thiazin-6-ones 294 and 295 were studied. Retro-Diels-Alder fragmentation of the hydrocarbon ring was of medium to low stereospecificity. A number of highly selective processes were discovered allowing differentiation between stereoisomers <1996RCM721>. The mass spectral fragmentation pattern of 296 was studied in detail <1996PS(113)67>. 

The rationale used in the interpretation of the mass spectra of methylalkanes has been presented in several reports 2- vs. 4-methylalkanes (Baker et al., 1978 Scammells and Hickmott, 1976 McDaniel, 1990 Bonavita-Cougourdan et al., 1991) 2,X- and 3,X-dimethylalkanes (Nelson et al., 1980 Thompson et al., 1981) and internally branched mono-, di- and trimethylalkanes (Blomquist et al., 1987 Pomonis et al., 1980). In the majority of reports, identification is based on GC and MS data, but the conclusions are not confirmed with standards or synthesis of the proposed structures. However, there are reports of chemical ionization (Howard et al., 1980) and electron impact of synthetic methyl-branched hydrocarbons (Carlson et al., 1978, 1984 Pomonis et al., 1978, 1980) and these have been very useful in confirming mass spectral fragmentation patterns with chemical structures. 

Further work on the free and ester-bound triterpenoid alcohols in cellular subtractions of Calendula officinalis flowers has appeared. An investigation of the mass spectral fragmentation of pentacyclic hydrocarbons in petroleum has been published. ... 

How did our understanding of the mass spectral fragmentations of alkanes improve with this revolution of the instrumental capacities One has to take note that most of these improvements went into an enlargement of the number of classes of substances that could be measured with these instruments, the hydrocarbons having become somewhat the poor parent of mass spectrometry, the fragments containing two to four carbon atoms forming a notable exception because of their widespread abundance in all mass spectra and the possibility to make ab initio or semi-empirical calculations of new, hitherto unknown structures. 

To establish unambiguously the length of a hydrocarbon chain or the position of double bonds, mass spectral analysis of lipids or their volatile derivatives is invaluable. The chemical properties of similar lipids (for example, two fatty acids of similar length unsaturated at different positions, or two isoprenoids with different numbers of isoprene units) are very much alike, and their positions of elution from the various chromatographic procedures often do not distinguish between them. When the effluent from a chromatography column is sampled by mass spectrometry, however, the components of a lipid mixture can be simultaneously separated and identified by their unique pattern of fragmentation (Fig. 10-24). 

Mass spectral results are consistent with the proposed structures and are given in Tables 4 and 5. Almost all of the major ion fragments are derived from the simple degradation of the hydrocarbon backbone. Ion fragments can be grouped together with respect to the number of carbons present within the particular ion fragment cluster and are reported as such in Tables 4 and 5. 

Mass spectral papers include another compilation of monoterpenoid alcohol spectra, a comparison of fragmentation patterns for camphor and menthone with their oxime, semicarbazone, and nitrophenylhydrazone derivatives, and a comparison of collisional activation mass spectra of ten related acyclic, monocyclic, and bicyclic monoterpenoid hydrocarbons together with derived 7119 ions. ... 

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