A signal at a given mass in the mass spectrum may not correspond to one single structure (unless one is using sufficiently high resolution, but here only low resolution analytical mass spectrometry is being considered). In addition, even if a signal corresponds to only one structure, that structure may arise from a variety of reaction pathways. Each individual decomposition reaction pathway can be sequential combinations of simple cleavages and rearrangements, provided the sum of ion lifetimes in the sequence does not exceed the time scale of the instrument. Typically, commercial analytical mass spectrometry experiments last tens of microseconds, meaning that in general, the observed signals correspond to reactions of only a few steps.