Reaction of ions

Ciary D C, Smith D and Adams N G 1985 Temperature dependence of rate coefficients for reactions of ions with dipolar molecules Chem. Phys. Lett. 119 320-6... 

The electric field-jump method is applicable to reactions of ions and dipoles. Application of a powerful electric field to a solution will favor the production of ions from a neutral species, and it will orient dipoles with the direction of the applied field. The method has been used to study metal ion complex formation, the binding of ions to macromolecules, and acid-base reactions. 

The possibility of a barrier which inhibits a reaction in spite of the attractive ion-dipole potential suggests that one should make even crude attempts to guess the properties of the potential hypersurface for ion reactions. Even a simple model for the long range behavior of the potential between neutrals (the harpoon model ) appears promising as a means to understand alkali beam reactions (11). The possibility of resonance interaction either to aid or hinder reactions of ions with neutrals has been suggested (8). The effect of possible resonance interaction on cross-sections of ion-molecule reactions has been calculated (25). The resonance interaction would be relatively unimportant for Reaction 2 because the ionization potential for O (13.61 e.v.) is so different from that for N2 (15.56 e.v.). A case in which this resonance interaction should be strong and attractive is Reaction 3 ... 

A necessary condition for ion-molecule reactions that has not been considered thus far is that of continuity between reactant and product potential energy surfaces. Many reactions of ions and molecules take place with / a transition from one potential energy surface to another. If no suitable crossings between the respective surfaces exist, then obviously orbiting ion-molecule collisions cannot produce chemical reac-... 

Table II. Total Cross-Sections for Reactions of Ions with Ethylene...

Low energy ion-molecule reactions have been studied in flames at temperatures between 1000° and 4000 °K. and pressures of 1 to 760 torr. Reactions of ions derived from hydrocarbons have been most widely investigated, and mechanisms developed account for most of the ions observed mass spectrometrically. Rate constants of many of the reactions can be determined. Emphasis is on the use of flames as media in which reaction rate coefficients can be measured. Flames provide environments in which reactions of such species as metallic and halide additive ions may also be studied many interpretations of these studies, however, are at present speculative. Brief indications of the production, recombination, and diffusion of ions in flames are also provided. 

The first systematic measurements of the reactions of ions with molecules in the gas phase were initiated largely by workers associated with analytical mass spectrometry.4-6 It was the rapidly expanding area of ion-molecule reactions which led to the origin of Gas-Phase Ion Chemistry as a distinct field.7 The discovery that ion-molecule equilibria in the gas phase can be determined by mass spectrometric techniques8 led to an explosion of thermochemical measurements based on determination of equilibria by a variety of techniques.9 Significantly, for the first time, information could be obtained on the thermochemistry of reactions which had solution counterparts of paramount importance such as acidities and basicities. These were obtained from proton transfer equilibria such as,... 

Once the energy E0 for the dissociation reaction has been established, the enthalpy change for the reaction at a given temperature T (such as the standard temperature T = 298 K) can be obtained from a thermodynamic cycle involving the reaction at 0 K and at T K. Thus, for the dissociation reaction of ion M+ and ligand L,... 

Follow-up reactions of ion radicals as critical (reactive) intermediates 228... 

The reaction of ions with peroxyl radicals appears also in the composition of the oxidation products, especially at the early stages of oxidation. For example, the only primary oxidation product of cyclohexane autoxidation is hydroperoxide the other products, in particular, alcohol and ketone, appear later as the decomposition products of hydroperoxide. In the presence of stearates of metals such as cobalt, iron, and manganese, all three products (ROOH, ROH, and ketone) appear immediately with the beginning of oxidation, and in the initial period (when ROOH decomposition is insignificant) they are formed in parallel with a constant rate [5,6]. The ratio of the rates of their formation is determined by the catalyst. The reason for this behavior is evidently related to the fast reaction of R02 with the... 

The chemical behavior of ions, ion pairs, and polarizable molecules partakes of the same indistinctness as the definitions of these species. Any attempt to make a complete catalog of the reactions of ions will almost certainly include borderline reactions whose intermediates are in fact ion-pairs or even covalent molecules. For many purposes the identification of a reaction as carbonium ion-like, or what the Germans would call Krypto-ionenreaktion, is as useful as the certain knowledge that the intermediate is actually a carbonium ion. Many of the ionic reaction mechanisms in the literature do not represent actual free ions and were not so intended by their authors. The ionic representation is often merely a convenient simplification if it is an oversimplification it is one that is easily rectified when the pertinent data become available. The value of such approximate mechanisms is that... 

Dynamics for the reactions of ion pair intermediates of solvolysis, 39, 1 Dynamics of guest binding to supramolecular systems techniques and selected examples, 42, 167... 

By varying conditions such as the cathode temperature, we can produce metal ions in several electronic states this will be discussed in Section II.E. Cooks et al. (48) discussed the reaction of ions with organic surfaces but the emphasis of the review was on the processes occurring rather than the production of ions. 

In this section, there will be a discussion of the gas-phase reactions of ions containing one metal atom. The approach will be to highlight coordination changes, reactivity, redox behavior, and where possible there will be an attempt to try to explain the comparative reactivity of similar ions. Unfortunately, there is too much material in this area to have a comprehensive review of all metal-ion reactions. 

Electrochemical considerations. There is so much evidence from electrical and also from non-electrical studies for the existence of ion-pairs in solvents of low polarity, that it cannot be ignored in discussing the reactions of ions in such systems [136]. The most detailed and comprehensive discussion of ion-pairs and related concepts has been given by Szwarc [137]. The next step after the recognition of the existence of ion-pairs is the estimation of their concentration as a function of the various experimental parameters, so that their importance relative to the free ions can be assessed. In order to do this, the dissociation constant of the ion-pairs under the relevant conditions is required. 

This selection of reactions, by way of example, is not meant to imply that, for instance, a second-order termination reaction of ion-pairs, say... 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

The fast reactions of ions between aqueous and mineral phases have been studied extensively in a variety of fields including colloidal chemistry, geochemistry, environmental engineering, soil science, and catalysis (1-6). Various experimental approaches and techniques have been utilized to address the questions of interest in any given field as this volume exemplifies. Recently, chemical relaxation techniques have been applied to study the kinetics of interaction of ions with minerals in aqueous suspension (2). These methods allow mechanistic information to be obtained for elementary processes which occur rapidly, e.g., for processes which occur within seconds to as fast as nanoseconds (j0. Many important phenomena can be studied including adsorption/desorption reactions of ions at electri fied interfaces and intercalation/deintercalation of ions with minerals having unique interlayer structure. 

In this paper, a review of the mechanistic information that has been obtained in chemical relaxation studies of reactions of ions with metal oxide minerals in aqueous suspensions is discussed. The... 

Their starting point was the fundamental hypothesis that the reactions of organic chemistry are reactions of ions, that is, that at the moment of reaction,... 

Interest within the physical organic community on the mechanism for the formation and reaction of ion-pair and ion-dipole intermediates of solvolysis peaked sometime in the 1970s and has declined in recent years. The concepts developed during the heyday of this work have stood the test of time, but these reactions have not been fuUy characterized, even for relatively simple systems. Richard and coworkers have prepared a short chapter that summarizes their recent determinations of absolute rate constants for the reactions of these weak association complexes in water. This work provides a quantitative basis for the formerly largely qualitative discussions of competing carbocation-nucleophile addition and rearrangement reactions of ion and dipole pairs. 

A Global scheme for solvolysis 2 Clocks for reactions of ion pairs 3 Addition of solvent to carbocation-anion pairs i Protonation of a carbocation-anion pair 11 Isomerization of ion pair reaction intermediates Reorganization of ion pairs in water 13 Internal return of isotopically labeled ion pairs Racemization of ion pairs 22 Concluding remarks 24 Acknowledgements 24 References 24... 

In retrospect, it should have been clear to me - as I am sure it was to Bill Jencks -that the rate and equilibrium constants for addition of solvent to 1-phenylethyl carbocation intermediates of solvolysis of 1-phenylethyl derivatives would serve as the first step in the characterization of the dynamics of the reactions of their ion pair intermediates. Therefore, this earlier work has served as a point of departure for our experiments to determine relative and absolute barriers to the reactions of ion pair intermediates of solvolysis. 

Contact- and solvent-separated ion pairs form whenever solvolysis proceeds to the free carbocation. However, these intermediates are generally only thought of as significant when their formation can be detected by experiment. We have focused on several different reactions of ion pairs that leave detectable signatures. 

We have focused on determining partition rate constant ratios for a variety of reactions of ion pairs, and of absolute rate constants from these ratios. This has been accomplished by use of one of the rate constants from this product ratio as a clock for the second reaction. 

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