Fragmentation unimolecular decomposition

In the FFR of the sector mass spectrometer, the unimolecular decomposition fragments, and B, of tire mass selected metastable ion AB will, by the conservation of energy and momentum, have lower translational kinetic energy, T, than their precursor ... 

In a similar vein, various electron acceptors yielding anion radicals that undergo rapid unimolecular decomposition also facilitate the efficacy of Scheme 1 by effectively obviating the back-electron transfer. For example, the nitration of enol silyl ether with tetranitromethane (TNM) occurs rapidly (despite an unfavorable redox equilibrium)78 owing to the fast mesolytic fragmentation of the TNM anion radical79 (Scheme 15). 

The attachment of an electron to an organic acceptor generates an umpolung anion radical that undergoes a variety of rapid unimolecular decompositions such as fragmentation, cyclization, rearrangement, etc., as well as bimolecular reactions with acids, electrophiles, electron acceptors, radicals, etc., as demonstrated by the following examples.135"137... 

The unimolecular decompositions are nevertheless not without their complications. Consider, for example, the unimolecular decomposition of benzoyl peroxide in benzene or carbon tetrachloride, where good first-order kinetics indicate that the contribution of induced decomposition is small.58 Initial homolysis of the O—O bond leads to two benzoyl radicals (Equation 9.21), which can fragment according to Equation 9.22 to yield phenyl radicals and carbon... 

Semiempirical and ab initio techniques have been applied to the unimolecular decomposition of 2-chloropropanoic acid, which is known to form HC1, CO, and CH3CHO. In keeping with the experimental data, the results suggest that reaction proceeds by a two-step mechanism involving rate-determining formation of intermediate a-propiolactone, which then fragments to form CO and CH3CHO.47... 

Thus, both OH rotational and translational excitations are much lower with N2O-HX complexes than under bulk conditions, while the NH channel shows no such striking change. Why is there such a difference After all, like HO-X, the HN-X interaction is strongly attractive. However, for the case of HN-NO fragmentation, X-NO is also attractive, which is more favorable geometrically than HN-X once the H atom has shifted to the terminal nitrogen. Also, the HNNO lifetime may lead to sufficient HNNO -X distance at the point of fragmentation that HN-X exit channel interactions are lessened. No such unimolecular decomposition lifetime is anticipated for the OH + N2 channel. 

This analytical mode has a resolution sufficient for the fragment ions. For instance, the B/E linked scan spectrum of the unimolecular decomposition of the MH ion (m/z 259) of biotin methyl ester, produced by Cl ammonia, has a good resolution (< 1 u). The m/z 221, 241 and 243 ions are due to the elimination of neutral fragments (CH3OH, HjO and CH4), which characterize Cl mass spectra (Fig. 21). 

Warburton et al. [233] identified the diastereomeric anhydro sugars shown in Figure 84 by comparing the unimolecular decomposition spectra of the [M-OH ] [mjz 115) fragment ion (intense) in B/E linked scan spectra. In comparison to intrasource decomposition spectra - which are identical - the above method leads to characteristic spectra. 

Under these conditions, the unimolecular decomposition spectrum of molecular ions with low internal energy is rich in fragment ions, thus reflecting the facility of their formation, favoring the characterization of the polysaccharides. 

We also made molecular-dynamic simulation of thermal decomposition of some individual energetic materials, including RDX, at extremely high temperatures [93,94]. It turned out that the primary fragmentation mechanism at these conditions is entirely different from the low-temperature variant. In the case of the RDX unimolecular decomposition, it can be mentioned that elimination of NO2 group by homolysis of one N-N bond is observed for all reaction conditions whereas perhydrotriazine ring fission (depolymerization to... 

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