Ion pairs because

The reduced species is the radical R the activity coefficient of which, yQx, is close to unity. The oxidised species, at any rate in the organic solvents, is not the lone carbenium ion R+, but one that is part of an ion-pair because of the relatively high ionic strength... 

The present author has developed a novel method called ion-association method. This is also a simple and versatile method for the preparation of ion-based organic dye nanoparticles in pure aqueous solution by the ion association approach [23]. It utilizes the control of hydrophilicity/hydrophobicity of the ionic material itself via ion-pair formation for example, addition of a cationic target dye solution into aqueous solution containing a certain kind of hydrophobic anions forms an electrically neutral ion-pair because of the strong electrostatic attraction, followed by aggregation of ion-pair species originated from van der Waals attractive interactions between them to produce nuclei and the subsequent nanoparticles (Fig. 3). In this case, hydrophobic but water-soluble anions, such as tetraphenyl-borate (TPB) or its derivatives (tetrakis(4-fluorophenyl)borate (TFPB), tetrakis [3,5-... 

An aspect of general interest in organometallic chemistry is the equilibrium between contact and solvent-separated ion pairs, because metal cations which are sun ounded by an individual solvent cage are expected to show different reactivity towards basic centres than those closely attached to carbanions or amines. At the same time, the anionic centre is less shielded in an SSIP than in a CIP and thus expected to be more reactive. In solution, the differentiation by NMR methods between both structural motifs relies in most cases on chemical shift interpretations and, if possible, on heteronuclear Overhauser (NOE) measurements. The latter method is especially powerful in the case of lithium organic compounds, where H, Li or even H, Li NOE can be detected by one- and two-dimensional experiments. ... 

Calculations have shown that the lowest-energy isomer of Ng is azidopentazole (Cs symmetry), which is characterized as a five-membered ring with a three-atom nitrogen tail [3,35,63]. Three low-energy local minima including the bicyclic Da, structure, are also located on the potential energy surface of Ns and are about 200 kcal/mol lower in energy than cubic N8. Bartlett and co-workers [14] considered a possible Ng ion pair but they concluded that the [N5+ N3 ] salt cannot exist as an ion pair because of the unbalance between EA (6.04 eV, EOM-CCSD level) of N5+ and IP (2.53 eV, EOM-CCSD level) of N3 . 

Moreover, the only solute descriptor for ion-pair effect was the analyte charge, but it was shown that the analyte charge status did not explain (1) different experimental curves when k is plotted as a function of the stationary phase concentration of the IPR for various IPRs (2) the dependence of the ratio of the retention of two different analytes on IPR concentration (3) the dependence of the k/ ko ratio on the analyte nature if experimental conditions are the same [16,17] and (4) ion-pairing of peptides [12]. The model makers realized that the charge may have been a too-simple solute descriptor for ion-pairing because it did not exhibit the hydrophobic effect, but they did not devise a better descriptor. Section... 

Two points, however, should be noted. First, the concentration of Ca from which [Ca ] is obtained by multiplying it by an activity coefficient is somewhat less than the total calcium determined analytically (hereafter denoted as Ca) because of the existence of Ca-containing ion pairs. Because the concentration of such ion pairs and hence the concentration of Ca is a function of several variables, including the pH and the concentration of other ions in solution, Ca is a better indicator of the calcite solution and precipitation history of the water. 

The active center in this reaction is presumably a carbonium ion ion pair, as shown above, which can vary in structure and reactivity from a free carbonium ion at one extreme to a contact ion pair (or even a readily dissociated covalent compound) at the other. The initiator, which consists of the catalyst shown in the equation and generally a cocatalyst, has a controlling effect on the structure of the ion pair because it provides the counterion, Y, for the active center. Hence, small changes in the composition of the initiator as well as in monomer structure, reaction solvent, and temperature can cause profound changes in both the rates of the propagation and termination reactions and in the structure of the polymer formed. For this reason, polymerization reactions have been referred to as "chemical amplifiers" in that the polymer molecule is formed by hundreds or thousands of propagation reactions followed by one termination reaction. 

In pyridine, ionized species will be present mainly as solvent-separated ion pairs because pyridine is a strong EPD medium, but a weak dissociating medium. DMSO is both a strong EPD and a strong dissociating medium and therefore ionized species will be present as free ions to a much greater extent 64, 49, 50, 97). 

The specific microwave effect was absent because the difference between the polarity of the GS and TS is very small. The reactive species in GS comprise very loose ion-pairs, because of delocalization of the negative charge in the malonate ion (Eq. 72) ... 

The onium salt is present in the aqueous phase in equilibrium with the ion pair Because of the relative hydrophobic character of, it is effectively... 

A technique often used in the analysis of ionic molecules is the formation of ion pairs" because this permits the separation of substances that are too ionized to separate by means of adsorption-partition methods, but are too... 

The rare gas halide species are the brightest ultraviolet light soufces available. They all share common molecular heritage, which is that their excited stales are ionic in nature and are short-lived excited state analogs to the ground state alkali halides [5] (see Fig. 1). For example, the XeQ laser at 308 nm, which tends to be the most widely used of these devices, has an upper laser level that is a set of excited states corresponding to bound Xe+Q ion pairs. Because of quantum... 

Among the many available ionic species, charged organic structures can afford numerous ion pairs because of their extensive diversity. For example, bulky geometries of both cation and anion constituents enable effective production of ionic liquids... 

A severe consequence of the overestimation of the intermolecular distance at the Hartree-Fock level of theory is evident in the potential curve for proton transfer. At the longer distances, Hartree-Fock potential curves often exhibit two distinct minima, corresponding to traditional A-H- -B hydrogen bonds and to hydrogen-bonded A - - - H-B ion pairs. Because early studies which examined proton transfer in hydrogen-bonded complexes between second-period elements A and B were carried out at the Hartree-Fock level, models for proton transfer were developed which include double minima along the proton transfer coordinate. However, more recent calculations at the MP2 level indicate that only a single... 

The polymerization of styrene in liquid ammonia, initiated by potassium amide was one of the first anionic polymerization reactions studied in detail. It is of particular interest because propagation takes place through free ions rather than by ion-pairs because of the high dielectric constant of liquid ammonia. The reaction takes place at 240 K (-33°C). Initiation consists of two processes. The first is the breakdown of initiator into ions... 

Supercritical fluid extraction with CO2 containing at least 10% methanol is effective for removing distearyldimethylammonium chloride from sediment and sewage sludge as an ion pair. Because anionic surfactants are already present in sludge, no anion need be added to insure ion pair formation. SEE is not more complete than conventional liquid-solid extraction with methanolic HCl, but is more rapid. There is some indication that less of materials other than cationic surfactants is extracted by SEE compared to conventional extraction (150,151). 

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