Ionic fragmentation reaction

Photoisomerization of c/.y-stilbene 191 Ionic fragmentation reaction 191 Cyclopropyl radical ring-opening 192 Ionic molecular rearrangement 193 Ene reaction 196 Thermal denitrogenation 198 Unimolecular dissociation 199 Sn2 reaction 200... 

The mass spectrum and thermochemistry of salicilaldehyde 26) shows many parallels to the case above. The major ionic fragmentation reactions of salicilaldehyde, 23, are illustrated in Eq. (11). The thermal fragmentation pattern of the same molecule is illustrated in Eq. (12).26) The ionic fragmentation that proceeds from mje 121, Eq. (11), directly parallels the thermal reactivity of salicilaldehyde, Eq. (12) whereas the ions at mje 107 and... 

The pyrolytic generation of benzyne in parallel to ionic fragmentation reactions has received considerable attention in the literature. One of the procedures that has been used for benzyne generation is the pyrolysis of biphenylene. °>54)Thebenz5me ion (mjelG) has a relative intensity of 25% as compared to the biphenylene molecule ion at 70 eV. Under pyrolytic conditions biphenylene pelds a small amount of benz5uie although most of... 

Somewhat surprisingly, the pressure dependence of quantum yields from the photolysis of NO at 1236 A, where the primary process is almost entirely photoionization199, is very similar to that observed for 1470-1650 A198. Clearly, recombination of the ionic fragments must lead to an excited state of NO which predissociates upon collision. However, the neutralization reaction... 

In designing preparative radical ionic chain reactions, including the fragmentation approach to alkene radical cations, careful choice of the radical... 

Aliphatic onium ions such as immonium, oxonium, and sulfonium ions have been introduced as even-electron ionic products of the a-cleavage occurring from molecular ions of amines, alcohols, and ethers or thiols and thioethers, respectively (Chap. 6.2.5). All these and analogous onium ions are capable of further fragmentation reactions, the majority of which are alkene losses [141] yielding fragments of high relevance for structure elucidation. 

Harrison, A.G. Finney, C.D. Sherk, J.A. Factors Determining Relative Ionic Abundances in Competing Fragmentation Reactions. Org. Mass Spectrom. 1971, 5, 1313-1320. 

Although stable and neutral bimetallic complexes were obtained from the dicat-ionic fragments and 129 or 130 there was the possibility that reactions with two molar equivalents of a metal-ligand monocation should give rise to trimetallic species. However, reactions of 130 with sources of the cations M (CO)3 (M = Mn, Re), namely [Mn(NCMe)3(CO)3][PF6] and [ReBr(THF)2(CO)3], yielded as products [N(PPh3)2][l,3,6- M (CO)3 -3,6-(p-H)2-l,l,l-(CO)3-2-Ph-c/ow-l,2-ReCBgHT] [M = Mn (156), Re (157)], respectively (Chart 27). ° In these molecules, the exo-polyhedral M (CO)3 moiety is almost certainly bonded to the cluster via two non-equivalent B-H M interactions with an Re-M bond completing... 

The sole gas-phase study on a cationic magnesium cluster examined the photodissociation spectrum of the Mg2(CH4)+" complex . Mg2 is only a minor product (equation 66) while Mg is the main ionic fragment and may arise via either of the processes shown in equations 67 and 68. The latter reaction is predicted to only be slightly more endothermic. 

In summary, the electron transfer reactions of amines offer an interesting variety of pathways, involving free radical or ionic intermediates and leading to two-electron oxidation as well as coupling and fragmentation reactions. In many systems, however, the most important reaction involves electron return from the acceptor radical anion, i.e. quenching of an excited state without net chemical change. 

Figure 13.6 Schematic setup of Assion et al. experiment [43], Femtosecond laser pulses are modified in a computer-controlled pulse shaper. Ionic fragments from molecular photodissofy ciation are recorded with a reflection time of flight mass spectrometer. This signal is used directly as feedback in the controlling evolutionary computer algorithm to optimize branching ratios of photochemical reactions. (Taken from Fig. 1, Ref. [43].)...

Another significant aspect of the approach of Parry and Edwards was based on the types of reactions most easily participated in by the various classes of boranes. Species which contain a BH2 unit (which included B2H6 and the series BnHn+6) all reacted with nucleophiles to generate either molecular or ionic fragments. These two reaction modes were described as symmetrical and non-symmetrical cleavage respectively. The two modes of cleavage are illustrated in Figure 2 for... 

In the next chapter you will meet, among many other reactions, more fragmentations, but they will be radical fragmentations rather than ionic fragmentations, and involve homolytic cleavage of C-C bonds. 

Thermolysis and photolysis reactions are both more selective than ionic fragmentation processes. This is because there is genrally more energy available to ions in a mass spectrometer and the activation energies for the... 

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