Switching reactions

Fragmentation occurs because the repeller voltage increases the kinetic energy of the ions, not only making collision-induced dissociation (CID) more likely but also allowing endothermic ion-molecule and solvent-switching reactions to occur. 

It was noted that the isomeric ion species was unlikely to be the weakly bonded CH3-0-0+ since switching reactions such as,... 

Observation132 that switching reactions can be driven by solvation represented an important finding in the early field of cluster ion reactions. An especially significant study was that of the hydration of NO+ ... 

F. Insights into Competition Between Ion Core Transformations, Ligand Switching Reactions, and Association Reactions... 

Cluster Formation and Switching Reactions of Ligated Metallic Atomic Ions... 

Such monosolvated ions are of interest themselves, for thermochemical reasons. The solvent-switching reactions just described can be carried out in an equilibrium fashion, as shown in reactions (14) and (15). 

While the alkyl group switching reaction is not observed in the gas phase, secondary and tertiary alcohols give rise to a totally different reaction with esters. Typical examples are shown in (79) and (80). These reactions display a reverse reactivity compared to the acids, viz., t-C4H9OH > i-C3H7OH > primary alcohols (Table 9). In fact, these reactions have not been detected for primary alcohols. 

Such reactions, together with binary switching reactions of the kind... 

Following reactions (55) and (56), the weakly bonded ions 02 02 and 02 N2 undergo fast binary switching reactions with other abundant atmospheric gases e.g. 

A detailed study of these switching reactions has been made by Adams et al.76 who determined the relative bond strengths of a series of molecules to both 02 and 02 and recognised that the 0 J NO ion formed in reaction (59) is not the stable nitrate ion, NOJ, but the more reactive peroxy isomer which reacts with NO ... 

So the above ternary association reactions and binary switching reactions convert the 02 ions to the stable N02 and NO3 ions. Other parallel (but probably less significant) reaction schemes which have been proposed involve the production of HCOJ and COJ (e.g. from the 03 and C02 reaction186 ). Significantly, however, CO3 reacts with NO and N02 to produce N02 and N03 respectively. 

As another example of hybrid simulation touched upon above, Haseltine and Rawlings (2002) treated fast reactions either deterministically or with Langevin equations and slow reactions as stochastic events. Vasudeva and Bhalla (2004) presented an adaptive, hybrid, deterministic-stochastic simulation scheme of fixed time step. This scheme automatically switches reactions from one type to the other based on population size and magnitude of transition probability. 

A somewhat different approach was used by Vincent in phase-switching reactions using pyridyl-labelled substrates and products. The pyridyl-containing tag is here thought of as a masked phase tag, which allows for phase switching with the help of a heavy fluorous copper(ll)-carboxylate complex. Comparison with a non-fluorous system indicated that a problem of release of the strongly coordinating pyridine linker was avoided in the fluorous approach. ... 

Smith D., Adams N.G. and Alge E., Ion-ion mutual neutralization and ion-neutralization and ion-neutral switching reactions of some stratospheric ions. Planet. Space Sci. , 29, 449 (1981). 

Another transformation of one aromatic compound to another is the Stone-Wales rearrangement of pyracyclene (113), which is a bond-switching reaction. The rearrangement of bifluorenylidene (114) to dibenzo[g,p] chrysene (115) occurs at temperatures as low as 400° C and is accelerated in the presence of decomposing iodomethane, a convenient source of methyl radicals. This result suggested a... 

Chemical reagents have been used in solution to footprint sites of interaction in noncovalent complexes. Only a limited set of studies have been performed in the gas phase using ion—molecule reactions between a charged noncovalent complex and various neutral reagents [72,73]. They can be classified into two areas H/D exchange reactions [72] and ligand switching reactions [73]. Recent results in these two areas are discussed below. 

W.E. Rudzinski, L. Lozano and M. Walker, The effects of pH on the polyaniline switching reaction, J Electrochem. Soc., 1990, 137, 3132 D. Moon, T. Maruyama, K. Osakada and T. Yamamoto, Chemical oxidation of polyaniline by radical generating reagents, 02, H202-FeCl3 catalyst, and dibenzoyl peroxide, Chem. Lett., 1991, 1633. 

Cluster ions can be formed by photon or electron interaction with a neutral cluster produced in a supersonic expansion [1321. Another process restricted to clusters is ligand-switching or the replacement of one ligand for another. Often exothermic ligand-switching reactions take place at rates near the gas kinetic limit, especially for small values of n [72, 133]. Chemical-reactivity studies as a function of cluster size show a variety of trends [93, 127. 133]. Proton-transfer reactions are often unaffected by solvation, while nucleophilic-displacement reactions are often shut down by as few as one or two solvent molecules. 

Because of space limitations, we have limited ourselves to reactions of positive ions and have omitted processes like collisional dissociation which, so far as multiple collisions are concerned, are strongly related to vibrational excitation and deexcitation, and we have also omitted isotopic exchange processes, which show many similarities to proton-transfer reactions, isomerization processes, and switching reactions. 

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