1- Bromobutane mass spectrum

Figure 22-8 Electron ionization mass spectrum (70 eV) of 1-bromobutane. [From A. lilies, R B. Shevlin, G. Childers, M. Peschke, and J. Tsai, Mass Spectrometry for Large Undergraduate Laboratory Sections," J. Chem. Ed. 1995, 72, 717. Referee from Maddy Harris.]...

Ions containing Cl or Br have distinctive isotopic peaks shown in Figure 22-7.11 In the mass spectrum of 1-bromobutane in Figure 22-8, two nearly equal peaks at mlz 136 and 138... 

A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC-MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here. 

The electron ionization mass spectrum of 1-bromobutane in Figure 21-15 has two peaks of almost equal intensity at miz 136 and 138. The peak at miz 136 is the molecular ion C4H9 Br. Because bromine has almost equal abundance of the isotopes Br and Br, the second peak of almost equal intensity is C4H9 Br. Any molecule or fragment containing just one Br will have pairs of peaks of nearly equal intensity in its mass spectrum. Other major peaks at m/z 107, 57, and 41 are explained by rupture of the bonds of 1-bromobutane in Figure 21-16. The peak at 107 has an equal-intensity partner at 109, so it must contain Br. Peaks at 57 and 41 do not have equal-intensity partners, so they cannot contain Br. 

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