Interpreting Mass Spectra Base peak in mass spectrum of 2,2-dimethylpropane is at m/z 57 m/z=57 corresponds to t-butyl cation Molecular ion fragments to give most stable carbocation CH3 CH3 H3C-C-CH3 H3C-C+ .CH3 CH3 CH3 m/z=57▪ Base peak in mass spectrum of 2,2-dimethylpropane is at m/z = 57 ▪ m/z = 57 corresponds to t-butyl cation ▪ Molecular ion fragments to give most stable carbocation Interpreting Mass Spectra