Fragmentation patterns of organic molecules

In Summary Molecules can be ionized by an electron beam at 70 eV to give radical cations that are accelerated by an electric field and then separated by the different deflections that they undergo in a magnetic field. In a mass spectrometer, this effect is used to measure the molecular masses of molecules. At high resolution, the mass of the molecular ion permits the detennination of the molecular formula. The molecular ion is usually accompanied by less massive fragments and isotopic satellites, owing to the presence of less abundant isotopes. In some cases, such as with Cl and Br, more than one isotope may be present in substantial quantities. 

Fragmentation is more likely at a highly substituted center 

CHAPTER 11 Alkenes Infrared Spectroscopy and Mass Spectrometry 

Cleavage of C-C bonds to give more stable carbocations is the main fragmentation mode seen for alkanes in the mass spectrometer. C-H bonds, which are stronger (Table 3-2), cleave less readily. 

Fragmentations also help to identify functional groups 

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