Cations counterions

Of the cations (counterions) associated with polar groups, sodium and potassium impart water solubiUty, whereas calcium, barium, and magnesium promote oil solubiUty. Ammonium and substituted ammonium ions provide both water and oil solubiUty. Triethanolammonium is a commercially important example. Salts (anionic surfactants) of these ions ate often used in emulsification. Higher ionic strength of the medium depresses surfactant solubihty. To compensate for the loss of solubiUty, shorter hydrophobes ate used for appHcation in high ionic-strength media. The U.S. shipment of anionic surfactants in 1993 amounted to 49% of total surfactant production. 

An additional method for investigating the interactions in the system consisting of cation, counterion and monomer could have been the calculation of a supermolecule... 

The mechanism for the stereoselective polymerization of a-olefins and other nonpolar alkenes is a Ti-complexation of monomer and transition metal (utilizing the latter s if-orbitals) followed by a four-center anionic coordination insertion process in which monomer is inserted into a metal-carbon bond as described in Fig. 8-10. Support for the initial Tt-com-plexation has come from ESR, NMR, and IR studies [Burfield, 1984], The insertion reaction has both cationic and anionic features. There is a concerted nucleophilic attack by the incipient carbanion polymer chain end on the a-carbon of the double bond together with an electrophilic attack by the cationic counterion on the alkene Ti-electrons. 

The idea that the stereochemical outcome of an intramolecular enolate alkylation is determined by chelation in the transition state was recently demonstrated by Denmark and Henke, who observed a marked preference for a "closed transition state (coordination of the cationic counterion to an enolate and the developing alcohol) resulting in a syn product. For example, the highest syn anti ratio (89 11) was obtained in toluene and the lowest syn.anti ratio (2 98) was obtained with a crown ether. These observations parallel the facial selectivities described herein and in ref 11 on the intramolecular SN2 reaction see (a) Denmark, S. A. Henke, B. R. J. Am. Chem. Soc. 1991, 113, 2177. (b) Denmark, S. A. Henke, B. R. J. Am. Chem. Soc. 1989, 111, 8022. 

Table 4 Anionic and Cationic Counterions Useful in Reverse-Phase HPLC...

Marszall (1988) studied the effect of electrolytes on the cloud point of mixed ionic-nonionic surfactant solutions such as SDS and Triton X-100. It was found that the cloud point of the mixed micellar solutions is drastically lowered by a variety of electrolytes at considerably lower concentrations than those affecting the cloud point of nonionic surfactants used alone. The results indicate that the factors affecting the cloud point phenomena of mixed surfactants at very low concentrations of ionic surfactants and electrolytes are primarily electrostatic in nature. The change in the original charge distribution of mixed micelles at a Lxed SDS-Triton X-100 ratio (one molecule per micelle), as indicated by the cloud point measurements as a function of electrolyte concentration, depends mostly on the valency number of the cations (counterions) and to some extent on the kind of the anion (co-ion) and is independent of the type of monovalent cation. 

The second approach involves the addition of a chelated form of the transition metal, for example, Ci2-dien plus zinc(II) (where Ci2-dien is 4-dodecyldiethylenediamine), into the mobile phase (Fig. 2.7). In this example, the triamine chelate binds strongly to the metal ion, forming a complex cationic counterion. The metal chelate represents a conformationally semirigid structure with a local polarized charge center. As such, not only is there the typical electrostatic attraction of anions for the positively charged... 

Similarly, the counterion in the mobile phase during run can affect the partition ratios. Figure 9.9 shows an example of a separation of organic acids at pH 4.4 in which the only variable was the cation counterion— K+ in Figure 9.9a and Na+ in Figure 9.9b. Because K+ is more strongly held than Na+, and it competes with the analytes for ionic sites on the resin, the overall retention times in Figure 9.9a are shorter. A secondary effect in this case is the alteration in the elution order. 

Gas hydrates crystallized from saline solution, as in the hydrate desalination process, may contain anionic host lattices with the cationic counterions in the smaller voids. 

FIGURE 10.16 Diagram of electrosteric stabilization (a) negatively charged particles surrounded by cationic counterions with nonionic polymers adsorbed, (b) positively charged polymers called polydectrolytes intermingled with anionic counterions attached to uncharged particles. 

The carbonate minerals, characterized by the presence of the COj anion unit, are dominated petrologically by calcite (CaCOj) and the isos-tructural phases magnesite (MgCOj) and dolomite [CaMgfCOjlj]. The calcite structure is illustrated in Fig. 5.23, and in this phase, as in all the mineral carbonates, the CO3 groups are linked by the intermediate (Ca +) cations (counterions). The mineral carbonates have been reviewed by Reeder (1983). 

The structure of the cation (counterion) in the anionic polymerization of e, g. styrene is of paramount importance for the kinetics of propagation. This was amply demonstrated by the works of warc Schulz , Bywater a. o. 

Termination may also take place by dissociation of the macrocarbo-cation-counterion complex where a proton is lost to the counter ion. Termination can also take place by the reaction of a growing chain end with traces of water or other protonic reagents. 

M + Protonated base or cationic counterion to conjugate base... 

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