Fragmentation of molecular ions

There are several more or less strict approaches to describe the processes of formation and fragmentation of molecular ions. Unfortunately none of them is able to predict... 

Purposeful fragmentation of molecular ion peaks can be used to provide structural information. This technique has been exploited using ESI ionisation in conjunction with LC/MS for the identification of peptide and proteins. 

Fragmentation of molecular ions (or any odd-electron ion) may occur by cleavage of bonds in two ways heteroly tic or homoly tic. 

Reimann, C.T., Quist, A.P., Kopniczky, J., Sundqvist, B.U.R., Erlandsson, R., Teng-vall, P. (1994) Impacts of Polyatomic Ions on Surfaces - Conformation and Degree of Fragmentation of Molecular-ions Determined by Lateral Dimensions of Impact Features. Nucl. Instrum. Meth. B 88 29-34. 

In Section 14.3, we saw several examples of fragmentation of molecular ions to give resonance-stabilized cations. Make a list of these resonance-stabilized cations and write important contributing structures of each. Estimate the relative importance of the contributing structures in each set. 

Only ions appear in a mass spectrum. However, the fragmentations of molecular ions also produce neutral species, molecules, and radicals that are not detected but participate nevertheless in the thermochanistry of dissociation reactions. Figure 9.19 shows the alpha cleavages (see Section 9.3.1) possible from 3-hexanamine ionized by electron ionization. 

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