Bromobenzene mass spectrum

A student performed a reaction in which bromobenzene was converted to the corresponding Grignard reagent, which was then reacted with methyl benzoate (Eq. 8.20). Mass spectra (Figs. 8.61-8.63) were obtained of three components of the reaction mixture, which were expected to be triphenylmethanol (25), benzophenone (26), and biphenyl (27). Confirm that these products were indeed formed by assigning the appropriate mass spectrum to each compound. For each spectrum, (a) specify the parent and base peaks (b) identify the compound represented by the mass spectrum and (c) predict the structure of the ion for each of the peaks for which a value of m/z is provided. 

Figure 8.53 Electron ionization mass spectrum of (a) bromobenzene and (b) dichloromethane.

Compounds containing bromine also give a characteristic pattern. Bromine has two isotopes, Br and Br, that are almost equally abundant in nature (50.7% and 49.3%i respectively). Compounds containing bromine will therefore have a characteristic peak at (M+2) that is approximately the same height as the molecular ion peak. For example, consider the mass spectrum of bromobenzene (Figure 15.27). 

In the mass spectrum of bromobenzene (Figure 15.27), the base peak appears at m/z=77. 

---