Common fragmentation lost

Common Fragmentation Patterns of Families of Organic Compounds Common Fragments Lost... 

Some Common Fragments Lost in Mass Spectra... 

There are two types of mass spectroscopy rules that concern (1) common fragment ions and (2) common fragments lost. Both of these rules can be defined in the same type of data structure. The components of the data structure are ... 

Table 10.5 lists common fragments detected and Table 10.6 lists common fragments lost. More extensive tables have been published [6,8,9]. 

For molecules containing heteroatoms (O, N, Cl, Br, etc., a very common fragmentation is the cleavage of the a,P-bond (often referred to as cleavage (3 to the heteroatom). In such molecules, the lone pairs on the heteroatom will be the least tightly bound in the molecule, and it will be one of these electrons which is lost upon electron impact (Scheme 5.9), leading to cleavage P to the heteroatom. 

Hard ionisation techniques commonly fragment molecular ions, leading to the loss of neutral species and the formation of fragmentation ions. Some common species lost in mass spectra, and possible chemical inferences that can be drawn from this information, are shown in Table 13.10. In contrast, examples of common fragment ions that are formed are listed in Table 13.11. 

Mass spectra of arsilidene complexes, [Cp Mn(CO)2]2AsR, 17-24 (Table 3), contain molecular ion peaks. The most common fragment ions correspond to elimination of 2CO, R and Cp Mn(CO)2. The abundances of these ions depend strongly on the R substituent at the As atom (Table 4). Substituents R such as F, I, OCS, NCS and N3 are easily eliminated directly from the molecular ion. Loss of Ph, however, occurs only after elimination of all carbonyl ligands, and R = H, R = c-Hex are not lost at all. Only compounds with R = Ph, H and c-Hex have mass spectra which display peaks corresponding to (M—2CO) and (M-4CO) ". The formation of (M — R — nCO) (n = 2,4) ions is characteristic of complexes containing R = I, OCS, NCS and N3. The complex having R = F is intermedi-... 

COMMON MASS SPECTRAL FRAGMENTS LOST Thomas J. Bruno and Paris D. N. Svoronos... 

If the elemental composition of the fragment lost can be deduced, this gives an even more powerful test. For example, the presence of a major (M — 15) ion is common, but a major (M — NH) ion is probably an anomalous ion the loss of 35 is logical only if chlorine is present. 

Compound A produces a predominant fragment at miz 264, which corresponds to a neutral loss of 175, which in this case corresponds to the loss of 4-trifluo-romethylbenzylamine [37]. This neutral loss can be used to monitor the presence of other species sharing this common feature. Radioactively labelled compound A was incubated in rat liver microsomes, analysed by LC-MS-MS and the TIC for the neutral loss of a mass of 175 (Figure 6.20a) was obtained. When compared with the radioactivity profile in Figure 6.20b, two extra components were detected in the TIC. This was due to the loss of the radiolabel during metabolism. LC-MS-MS is very useful as a complementary detection method where the radiolabel is lost during metabolism or in situations where a radiolabel is not available. 

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