Fragmentation mass spectra

Phosphorus tribromide, 426 Photochemical rearrangement, of 4-hydroxy-thiazolium innersalt, 375 Photochemistry, mass spectra fragmentation analogy with, of 2-imino-4-thia-zolines, 27... 

Pyrolysis of polyisoprene takes place by a free radical mechanism and generates mainly isoprene (MW=68), a dimer of isoprene (DL-limonene, MW=138), and several other unsaturated hydrocarbons (see Sections 2.6 and 6.1). The mass spectra fragmentation (generating fragments with specific mass/charge (m/z) ratios) of a model molecule simulating polyisoprene (isoprene oligomer) occurs by the mechanisms as indicated below ... 

Typical mass spectra fragments from saccharides are likely to have the following structures ... 

The formation of the mass spectra fragments can be explained by a variety of mechanisms. For example, the formation of the ion m/z 163 for the trisaccharide with the spectrum shown in Figure 3.6,2 can be explained as follows ... 

The presence of free radicals in pyrolytic reactions seems to be a common event, as seen by the increase in certain more stable species as the pyrolysis temperature increases. At elevated temperatures, higher levels of aromatic compounds, polynuclear aromatic compounds, or small molecules tend to be formed. These compounds were not seen in the mass spectra fragments, where only intramolecular rearrangements are more common. 

Attachment at the 14 -position in the eburnamyl portion is established, not only by the above mass spectrometric and synthetic evidence, but also by the fact that in the hepta- and octadeuteriodihydroebumamenine mass spectra fragments c and d retain all the deuterium atoms. Since two of these must have been introduced through reversible imine-enamine interconversion and two by reduction of an enamine double bond the only reasonable distribution is that shown in CCCLXVIII and the pleiocarpinine linkage is therefore at C-14. The axial proton at C-14 in eburnamine (CCCLXI) appears at 5.4 ppm (J = 5 and 10 cps). Similar couphng constants observed for a one proton absorption at 5.0 ppm in the spectrum of pleiomutine (CCCLVI) may be attributed to the C-14 hydrogen atom which is thus axial 5). 

These calculations show that the ratio of CO2/ CO amounts to 7.25/3.35=2.16, which is two times larger than that calculated without taking into account the properties of the mass spectra (fragmentation, probability of ionization) obtained in the TA-MS system used. 

To test this hypothesis, feeding experiments were performed with (5S)- and (5i )-[2- C, 5- Hi] mevalonate to cultures of Claviceps sp. strain SD58. Based on the mass spectra fragmentation patterns of the elymoclavine produced under these conditions the authors concluded that This experiment thus suggests that the scrambling of C from C-2 of mevalonate between C-7 and C-17 of elymoclavine and that of from C-5 of mevalonate between the two allyUc hydrogen positions of the the isoprenoid unit occur independently of each other (although not necessarily in different reaction steps). ... 

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