Rearrangement fragmentation

Cluster ions are also emitted from organic materials their identity and yield depend on the chemical structure of the materials. Molecular or quasi-molecular ions may be observed as well as other ions that are formed by fragmentation, rearrangement, decomposition, or reaction [52], Several typical ion formation processes are summarized in Table 3 [40]. 

Amine Characteristic Fragments Rearrangement Ions Losses from the Molecular Ion... 

The combination of the flash vacuum pyrolysis (FVP) technique169 with mass spectrometry proved to be particularly useful in identification and characterization of both the fragmentation/rearrangement patterns, intermediates and/or final products formed (see Section IV.E.l). Usually, no structures are indicated in the mass spectra, although ionization and appearance potential can, in principle, provide structural information. 

Like fragmentations, unimolecular rearrangements are always uphill at the beginning of the process, because a bond breaks. Unlike fragmentations, rearrangements are downhill at the end as a new bond forms. An example of this kind of energy profile for the Isomerization reaction of ds-2-butene appears in Figure 15-14Z). 

Scheme 8 Fragmentation, rearrangement, and solvation processes of 2-methyl-3-phenyl-3-(diphenylphosphatoxy)-2-propyl radical and associated contact ion pair...

The thermal and photochemical activations of EDA complexes by electron transfer are both enhanced when the radical ions D+- or A--(either paired or free) undergo a facile first-order (unimolecular) transformation such as fragmentation, rearrangement, bond-formation, etc., which pulls the redox equilibrium and thus renders the competition from the energy-wasting back electron transfer less effective (compare Scheme 5). Critical to the quantitative evaluation of the reaction dynamics is the understanding that the typical [D+% A--] intermediates, as described in... 

Second, rich bimolecular chemistry (attack by nucleophiles, electrophiles, oxidants, or reductants) that can be used to create reactive intermediates in solution is not generally available in the context of matrix isolation (exceptions to this rule will be discussed in the proper context below). Usually, reactive intermediates to be studied by matrix isolation must be accessible by means of unimolecular processes (fragmentations, rearrangements, ionization) induced by external sources of energy (light or other forms of radiation, discharges). 

VII. 14(13 -> 12aH)y46eosteroids (C-Nor-D-Homo Steroids) / 400 By solvolysis of 12/ -methylsulfonyloxy steroids / 400 By fragmentation-rearrangement of 12-tosylhydrazones / 402... 

Crimmins, M. T. Dudek, C. M. Cheung, W.-H. A fragmentation-rearrangement sequence of cyclobutylcarbinyl radicals. Tetrahedron Lett. 1992, 33, 181—184. 

Predict three major fragmentation/rearrangement pathways for the above compounds. For each pathway, cite the rule from Section 1.5.4 that supports your prediction. 

For each fragmentation/rearrangement pathway from exercise 1.4, show a detailed mechanism using either single barbed or double barbed arrows as appropriate. 

Boyer, J.H. and Ellis, P.S. (1979) Fragmentation-rearrangement of A3-oxadiazolin-5- and 3-ones. Journal of the Chemical Society, Perkin Transactions , (2), 483-487. 

Fig. 4.44. Formyl formation on a palladium surface (schematic), (a) Molecule fragment rearrangement on the metal surface, (b) o-Orbital interaction scheme.

Unimolecular reactions of organic radical cations are fragmentation, rearrangement and cyclizadon, as illustrated by the following generic examples. The specific details of each of these transfomiations are included in Section 7.4.6. (Note Ar and R represent aryl and alkyl groups, respectively.)... 

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