Decane mass spectrum

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... 

FIGURE 13 42 The mass spectrum of decane The peak for the molecular ion is extremely small The most prominent peaks arise by fragmentation... 

Example The El mass spectrum of n-decane is typical for this class of hydrocarbons (Fig. 6.18a). Branching of the aliphatic chain supports cleavage of the bonds adjacent to the branching point, because then secondary or tertiary carbenium ions and/or alkyl radicals are obtained (Fig. 6.18b,c). This allows for the identification of isomers to a certain degree. 

Temperature Effects. The chemical ionization spectra of three paraffins (n-decane, 2,2,3,3-tetramethylhexane (compound 13), and 2,2,5,5-tetramethylhexane (compound 14) have been determined at several different temperatures of the mass spectrometer ionization chamber, and the relative intensities obtained for the MW — 1 ions are give in Table VII. The relative intensities decrease for all three compounds as the temperature increases, in accordance with the behavior found for the chemical ionization spectrum of ethyl-/3-chloropropionate... 

A closer look at the spectrum of K-decane also reveals fragment ions at m/z 84, 98, and 112, i.e., rearrangement ions at even mass number. The origin by loss of H from the accompanying carbenium ions at m/z 85, 99, and 113, respectively, can be excluded by application of the even-electron rule. Instead, alkane molecular ions may undergo alkane loss, [76] e.g.,... 

For example, full-scan mass spectra of buspirone contain an abundant [M+H]+ ion signal with little detectable fragmentation. The product ion spectrum reveals product ions and neutral losses associated with diagnostic substructures of buspirone (Figure 6.25). The product ion at mlz 122, for example, is indicative of the pyrimidine substructure. The presence of this ion in the product ion spectrum of a metabolite indicates a structure that contains the pyrimidine substructure. Similarly, the mlz 180 product ion is diagnostic of the azaspirone decane substructure, and the neutral loss of 164 (producing the mlz 222 product ion) is diagnostic of the butyl azaspirone decane dione substructure. 

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