Fragmentations obeying the parity rule

The cleavage of the bond that is adjacent to the charged site, while observing a migration of the charge, is a common fragmentation process that occurs especially often when it allows the elimination of a small stable molecule. For example, protonated alcohols in soft ionization methods often lose water  

McLafferty [9] proposed classifying the reactions of even-electron ions that obey the parity rule (an even ion yields an even ion + neutral fragment) as follows  

2 Cleavage of a bond with cyclization and charge migration  

3 Cleavage of two bonds in a cyclic ion with charge retention  

4 Cleavage of two bonds with rearrangement and charge retention  

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