Consecutive ion — molecule reactions

Both this and previous studies demonstrate the existence of rather long chains of consecutive ion-molecule reactions in methane, ethylene, and acetylene, and thus they provide direct evidence for ionic mechanisms of condensation or polymerization in these gases. Polymers have been found in relatively high yields among the radiolysis products of these... 

Most of the studies of ions formed by charge transfer have been concentrated on the unimolecular reactions of M+ ions formed in well-defined internal-energy states (e.g., fragmentation patterns6) and more recently have been concerned with rate-coefficient measurements.118 Some work has also been reported on consecutive ion-molecule reactions of M+ ions produced in well-defined internal states (mostly... 

I. Szabo, Consecutive ion-molecule reactions in ethylene investigated by means of positive ion-impact, Arkiv Fysik 33, 57-71 (1967). 

I.Szabo, Theoretical analysis of consecutive ion-molecule reactions. I. The mechanisms in a tandem mass spectrometer of perpendicular type. II. The mechanisms in a tandem mass spectrometer of longitudinal type, Int. J. Mass Spectrom. Ion Phys. 3, 103-129, 169-188(1969). 

Table V. Consecutive Ion-Molecule Reactions in Ethylene Observed in a Tandem Mass Spectrometer (Fig. 3) with Incident Ar+ Ions "...

Beginning with the ionization of N2, consecutive ion-molecule reactions eventually lead to the formation of [(H20) -i-H] cluster ions ... 

Here, a primary ion P+ formed by the radiation field reacts with a gas molecule M to give an intermediate complex [PM +] which can either dissociate to a secondary species S + and a neutral fragment N or react with another molecule to produce another complex [PM2 + ]. The latter then dissociates into a tertiary ion T+ or propagates the chain by forming a third intermediate [PM3 + ]. A quaternary ion Q+ may result from dissociation of [PM3 + ], or the chain may continue through reaction of [PM3 + ]. Wexler and Jesse (38), on the other hand, have suggested a model which states that reactive intermediate complexes are not involved in the propagation, but rather the polymerization proceeds by chains of simple consecutive and competitive ion-molecule reactions,... 

Owing to the advent of powerful techniques for the investigation on ion-molecule reactions ne.ii 7) processes like (38) can in fact be directly measured in the gas phase. The direct observation of these reactions has, among others, the inherent advantage over solution experiments that no artificial separation into contributions of cations and anions needs to be performed, and that only well-defined supermolecular entities participate. Reaction (38) may be replaced by a series of consecutive steps to build up the cluster-ion AS ... 

MS/MS. The capability of trapping ions for long periods of time is one of the most interesting features of FTMS, and it is this capability that has made FTMS (and its precursor, ion cyclotron resonance) the method of choice for ion-molecule reaction studies. It is this capability that has also lead to the development of MS/MS techniques for FTMS [11]. FTMS has demonstrated capabilities for high resolution daughter ion detection [42-44], and consecutive MS/MS reactions [45], that have shown it to be an intriguing alternative to the use of the instruments with multiple analysis stages. Initial concerns about limited resolution for parent ion selection have been allayed by the development of a stored waveform, inverse Fourier transform method of excitation by Marshall and coworkers [9,10] which allows the operator to tailor the excitation waveform to the desired experiment. 

Such behaviour clearly contrasts with the case of 4-iodoaniIine, where protonation in a chemical ionization source occurred not only on the ring but also on the nitrogen atom . Nitrogen protonation was indicated by ion-molecule reactions with dimethyl disulphide consecutive to collisional dehalogenation (FT-ICR experiments) or by an increase in the intensity of the peak at mjz 76 following high-energy collisional activation . 

Two water molecules are oxidized by four consecutive charge-separation reactions through photosystem II to form a molecule of diatomic oxygen and four hydrogen ions. The outcoming electron in each step is transferred to a redox-active tyrosine residue followed by the reduction of a photoxidized... 

The alkylation of isobutane with C3-C5 olefins involves a series of consecutive and simultaneous reactions with carbocation species as the key intermediates. Scheme 6.10.2 shows the reaction of 2-butene and isobutane as a typical example. In the initial step, proton addition to 2-butene affords a sec-butyl cation. This sec-butyl cation can either isomerize or accept a hydride from a molecule of isobutane, giving n-butane and the thermodynamically more stable fert-butyl cation. These initiation reactions are required to generate a high level of ions in the start-up phase of alkylation but become less important under steady state conditions. 

Genera/. The central goal of fundamental electrochemical kinetics is to find out what electrons, ions, and molecules do during an electrode reaction, hr this research, one is not only concerned with the initial state (Le., the metal and the reactants in the solution next to the electrode surface before the reaction begins) and the final product of the reaction, one also has to know the intermediate species formed along the way. Thus, all practical electrode reactions (say, the electro-oxidation of methanol to C02) consist of several consecutive and/or parallel steps, each involving an intermediate radical, e.g., the adsorbed C-OH radical. I Iowcver, one finds that intermediates can be classed into two types. 

They proposed a polymerization scheme closely related to other well-known chemical reactions of metal alkoxide with carbonyl compounds (20). In Scheme 2, complex [A] is converted to [B] by hydride ion transfer from the alkoxyl group to the carbon atom of aldehyde (Meerwein-Ponndorf reduction). Addition of one molecule of monomer to the growing chain requires transfer of the alkoxide anion to the carbonyl group to form a new alkoxide [C]. Repetition of these two consecutive processes, i.e., coordination of aldehyde and transfer of the alkoxide anion, constitutes the chain propagation step. 

The observations described prompted a study of the reaction between the 2-cyanoallyl anion and tetrafluoroethylene, since this system has the merit that the charge may be accommodated in the nitrile group of the reaction intermediate in the [2 + 3] atom cycloaddition (54). Elimination of two HF molecules indeed occurs, presumably in a consecutive way, although the product ions resulting from loss of one molecule of HF from the collision complex have not been observed (Dawson and Nibbering, 1980). However, reaction (54) has not yet been studied with specifically deuterated 2-cyanoallyl anions, so that at present an end-on addition process (55) cannot be excluded. 

---