Ion pairs, types

Intermolecular interaction of ions has been roughly categorized in terms of contact ion pairs (CIP) and solvent-separated ion pairs (SSIP) (Fuoss and Accascina, 1959 Davis, 1962 Szwarc, 1972, 1974 Gordon, 1975), as in (11), though doubtlessly a myriad of ion-pair types exist with varying interionic separations. 

In aqueous solution the addition (via 6) and the electron transfer product (via 7) do not exclude each other, i.e., (6) and (7) can occur simultaneously [18]. This has been explained in terms of an electron-transfer/addition mechanism involving an ion-pair-type transition state with subsequent competition between combination of the ions (to give addition) and separation by solvent (leading to electron transfer) [15]. 

In order to explain the field effects observed for the cationic polymerizations, we have earlier proposed a kinetic scheme based on the two-state polymerization mechanism and on the field-facilitated dissociation hypothesis (11). Though the assumptions involved in the proposed interpretation turn out to be partly invalid in the light of the experimental data accumulated most recently (15), it is still necessary to give an outline of the scheme. We assumed that, by the initiation reaction between initiator molecules (C) and monomer molecules (M), active species of an ion-pair type (My) are produced, a portion of which dissociates into active species of a free ion type (Mf) and gegenions (C ). The propagation, monomer transfer and termination can be effected by the free ions and ion pairs. A dissociation equilibrium is established between the free ions and ion pairs, which can be characterized by a dissociation constant K. Then we have ... 

Fig. 33. Arrhenius plot of kp vs. T The k values are the highest in the whole temperature range, JE"( are slightly lower, and + c are the lowest. The dependence is linear. When one ion pair type is transformed to another at the changing temperature [fe(+ fe(+ )s] the dependence ceases to be linear. (I) Dioxane, (2) oxepane, (3) cumyl methyl ether. See p. 524 of ref. 19 and ref. 375.

Mescaline can be analysed by using a number of HPLC methodologies. Most of these involve reversed-phase systems based upon ion-pairing-type separations [2, 10]. 

During the period when theorists were addressing the question as to the possible existence of ion pairs, there was a good deal of experimental inquiry as well. The neutral pair nature of H3N" HC1 was confirmed in the gas phase by its rotational spectrum. The intermole-cular distance derived from the spectral data was noted to be in remarkable agreement with an earlier ab initio computation with MP2 correlation. The following year saw the measurement of the microwave spectrum of H N—HBr, and this complex too had the characteristics of a neutral pair. Nor are any of the complexes pairing a hydrogen halide with HjP of the ion-pair type. 

Figure 1. Schematic diagram of the energies of the anion ground state (M S), the lowest covalent state (M-S ), ion-pair state (M S ) and cation ground state (M+S ) versus /j M = alkali metal atom S = solvent molecules). The ion-pair state is expected to correlate with the ground state of the solvated electron plus the solvated M+ ion in bulk fluids. The ground-state electronic character of the neutral cluster changes from covalent to ion-pair type at a certain critical size.

The type of counterion, chloride or methylsulfate, has little influence [36], A more or less extensive ion exchange probably takes place in the rinse liquor with the anionic surfactants coming from the detergent carryover and the anions of water hardness. As a result, it is very likely that no strong difference exists between the two actives once on fabrics [26], This is not in line with other results showing that anionic counterions of the surfactant are present on the fibers, which suggest an ion pair type adsorption [30], For instance, iodide is much more substantive than chloride [98],... 

We can ask the question what happens if one of the two ions becomes irreversibly retained on the neutral stationary phase by any of the possible mechanisms Most probably, the remaining ion will elute in the form of a corresponding acid (or base). However, the eluting peak should be expected to be rather broad, since the moving ion must be retarded for a certain time by the immobihzed counter ion. This ion-pair-type retention can explain the taffing of the ammonia peak in Fig. 12.17. 

Secondly, as Professor House discussed in his book and papers, the importance of the nature of intermediary metal enolate in the acylation reaction should be taken into consideration. Thus the procedure for the preferable formation of a contact ion pair type of metal enolate by adding magnesium salt to the lithiated solution should be preferred for the acylation on carbon over oxygen. Thirdly, recent introduction of cyanoformate as soft electrophile would be preferable because C-16 plays as soft nucleophile while oxygen of carbonyl group as hard nucleophile. 

An article by Kormosh et al. compares the properties of various electrodes for determination of indomethacin a classic electrode with a polymer membrane, a solid-state electrode, and a Wood alloy in PVC tube, in which membranes were prepared using PVC and graphite [81]. The active ingredient applied was an ion-pair type complex of indomethacin with Rhodamine B. The optimum sensor turned out to be the solid-state one based on PVC. By comparing it with another solid-state sensor (BMSA type electrode)... 

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