Fragmentation of organic ions

The manual interpretation of a mass spectrum - nature and origin of the fragmentation peaks - is a difficult but interesting exercise. Organic chemists are usually familiar with these methods of interpretation since they retrieve different types of transient ions considered to explain reaction mechanisms in condensed phases. The difference here is that these ions move in a vacuum and do not collide. The very short period of time between ion formation and ion detection (a few pis), allows to observe the existence of very unstable species that are unstable under normal conditions. 

In a second step, this resulting radical cation generally fragments. Since a mass spectrum results from the fragmentation of a sample that contains billions of molecules, it will show all possible fragmentations. As the relative probabilities of fragmentation are not the same, the fragmentation peaks will have different intensities. 

Several factors control the fragmentation procedure of M] + into daughter ions and neutrals (radicals or molecules). Two basic situations are observed  

There is a greater tendency to form stable fragments (ion or neutral) and the fragmentations with rearrangements are favoured when they involve a six-membered ring transition state leading to a hydrogen transfer at the radical cation site. 

In a hydrocarbon such as propane, the ionization of a C—C a bond will lead to the formation of the ethyl cation and a methyl radical rather than the reverse  

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Fragmentation of Organic ions and interpretation of Ei Mass Spectra... 

Fragmentation of Organic Ions and Interpretation of El Mass Spectra... 

As mentioned in the beginning of this chapter, there is by far no chance for a comprehensive treatment of the fragmentations of organic ions in this context. Nevertheless, we should not finish without having briefly addressed the mass spectrometry of heterocyclic compounds, an issue filling a book of its own. [215]... 

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