Synthesis reactions studied in Organic Chemistry often have a ``retro''
counterpart in energized ion decomposition chemistry. A well known
example is the retro Diels Alder reaction often observed in the mass
spectra of pesticides.
The main difference in ordinary reactions studied in Organic Chemistry and ion decomposition reactions is that one (or more) of the products of ion reactions is often a free radical. This leads to some reactions that might look 'strange' at first glance.