Chlorobenzene mass spectrum

The peak at m/z 77 m the mass spectrum of chlorobenzene m Figure 13 41 is attributed to this fragmentation Because there is no peak of significant intensity two atomic mass units higher we know that the cation responsible for the peak at m/z 77 cannot contain chlorine... 

Figure 13.41 presents the mass spectrum of chlorobenzene. There are two prominent... 

A third source of error is associated with the fragmentation pattern caused by dissociation of the molecular ions formed in the source region of the spectrometer. Under severe conditions these processes may proceed with substantial isotopic fractionation, and this obscures the measurements of isotopic composition at the collector. To some extent careful standardization of the instrumental conditions may ensure that errors from fragmentation are systematic, and thus cancel (at least to some extent). Alternatively, softer ionization methods can be used to prevent most or all of the fragmentation. The bottom spectrum in Fig. 7.7 illustrates this approach it shows the mass spectrum of chlorobenzene obtained by photoionization. Only the parent molecular ions are observed. It should be kept in mind, however, that softer ionization usually yields smaller ion currents and consequently statistical counting errors increase. 

Figure 13.41 presents the mass spectrum of chlorobenzene. There are two prominent molecular ion peaks, one at mlz 112 for C6H535C1 and the other at mlz 114 for C6H537C1. The peak at mlz 112 is three times as intense as the one at mlz 114. 

The mass spectrum of chlorobenzene (PhCl, CfiH Cl) is very simple. There are two peaks at 112 (100%) and 114 (33%), a peak at 77 (40%), and veiy little else. The peaks at 112/114 with their 3 1 ratio are the molecular ions, while the fragment at 77 is the phenyl cation (Ph+ or C5H5 ). 

FIGURE 9. Reactions of chlorobenzene radical cations with ammonia (a) mass spectrum of the ions produced within the quadrupole collision cell (the intensity of the m/z 112 peak is reduced by a factor of 25), and (b) high energy (8 keV, nitrogen collision gas) of the so-produced m/z 94 ions. Spectrum (c) corresponds to the reactions of the m/z 11 phenyl cation, formed in the ion source, with ammonia (the intensity of the m/z 77 peak is reduced by a factor of 40)... 

Figure SAia shows the mass spectrum of chlorobenzene. The peaks at miz 112 and miz 114 in approximately a 3 1 intensity ratio are a clear indication that chlorine atoms are present. An miz 77 peak for the phenyl cation fragment is evident, as well.

Figure 29.26 The mass spectrum of chlorobenzene, showing the [M + 2] peak. (Note that there are also tiny [M +1] and [M + 3] peaks corresponding to in the molecule.)...

Apart from the need for isotopic enrichment and synthesis there are other problems in applying whole molecule mass spectrometry to measure isotope ratios. Assume, for example, that we want to determine isotopic composition of chlorine from the spectrum of chlorobenzene presented in Fig. 7.7. The peaks at 114 and... 

Observations of the UV absorption" attributable to benzyne in the vapor phase, evidence from time-resolved mass spectrometry, and more rei ntly of the IR spectrum of benzyne in a matrix at very low temperature leave no doubt as to the existence of such a transient intermediate. Its lifetime in solution is extended when benzyne is supported on a polymer phase. Results of competitive trapping experiments, when benzyne is generated from different precursors, and the classical experiments of Roberts et al. on cine-substitution in the amination of chlorobenzene confirm the formation of benzyne as an intermediate. ... 

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