Fragmentation Reactions of Negative Ions

The reaction may seem complicated but its analytical usefulness is very high. For example, some triglycerides yield, in Cl, the three protonated acids and the pseudomolecular peak (M + H)+. 

Iminium ions with short chains fragment by forming an ion-neutral complex [12], The slow step of the process is the 1,2 proton transfer leading to a secondary carbenium  

A similar mechanism could occur in other onium cases (oxonium, sulfonium, etc.). 

The reactions considered up to now were limited to those of the McLafferty classification with regard to the parity rule. The reactions of even-electron ions (EE) that do not obey the parity rule are much rarer and more difficult to predict. They are often observed in ions with extended n systems, but they often imply complex rearrangements, as is shown in the case of tropylium  

however, that the main fragmentation path of the tropylium ion is the loss of acetylene. 

---