Examples of cations

The alkaline earth ions have fairly diffuse adsorption edges which cover a wide pH range, e.g. 7-11.5 for (Ali and Dzombak, 1996) and 7-11 for Sr on 

Oxide Cation Surface complex Stability constant Reference 

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In their polymerization, many individual alkene molecules combine to give a high molecular weight product Among the methods for alkene polymerization cationic polymerization coordination polymerization and free radical polymerization are the most important An example of cationic polymerization is... 

The polymerizations of tetrahydrofuran [1693-74-9] (THF) and of oxetane [503-30-0] (OX) are classic examples of cationic ring-opening polymerizations. Under ideal conditions, the polymerization of the five-membered tetrahydrofuran ring is a reversible equiUbtium polymerization, whereas the polymerization of the strained four-membered oxetane ring is irreversible (1,2). 

Cationic, anionic, and amphoteric surfactants derive thek water solubiUty from thek ionic charge, whereas the nonionic hydrophile derives its water solubihty from highly polar terminal hydroxyl groups. Cationic surfactants perform well in polar substrates like styrenics and polyurethane. Examples of cationic surfactants ate quaternary ammonium chlorides, quaternary ammonium methosulfates, and quaternary ammonium nitrates (see QuARTERNARY AMMONIUM compounds). Anionic surfactants work well in PVC and styrenics. Examples of anionic surfactants ate fatty phosphate esters and alkyl sulfonates. 

Electrochemical studies, in combination with EPR measurements, of the analogous non-chiral occluded (salen)Mn complex in Y zeoUte showed that only a small proportion of the complex, i.e., that located on the outer part of the support, is accessible and takes part in the catalytic process [26]. Only this proportion (about 20%) is finally oxidized to Mn and hence the amount of catalyst is much lower than expected. This phenomenon explains the low catalytic activity of this system. We have considered other attempts at this approach using zeolites with larger pore sizes as examples of cationic exchange and these have been included in Sect. 3.2.3. 

The first examples of cationic exchange of bis(oxazoline)-metal complexes used clays as supports [49,50]. Cu(II) complexes of ligands ent-6a, 6b, and 6c (Fig. 15) were supported on three different clays laponite (a synthetic clay), bentonite, and montmorillonite KIO. The influence of the copper salt from which the initial complexes were prepared, as well as that of the solvent used in the cationic exchange, was analyzed. 

Some excellent examples of cationic polycyclizations, especially in the field of steroid synthesis, were described in Chapter 1. However, these polycyclizations can also be performed using a radical as initiator. Such reactions can be divided into those based on serial 6-mdo-trig cyclizations from polyene acyl precursors [92], radi-... 

There are numerous examples of cations of the interhalogens, and a great deal is known about the behavior of such species. The species that have been more fully studied involve only one type of halogen such as I3+, Br3+, and Cl3+. In general, the production of these species requires rather stringent conditions that may include nonaqueous solvent systems. For example, a reaction that takes place in anhydrous sulfuric acid can be used to produce I3 +. ... 

Examples of cations that are present in significantly lower concentrations than the simple cations are iron, manganese, zinc, copper, nickel, and cobalt. Except for cobalt, these have multiple oxidations states in soil as shown in Table 6.1. Because of their multiple oxidation states, they may be present as many more species than the simple cations. Typically, the higher oxidation states predominate under oxidizing conditions, while the lower oxidation states predominate under reducing conditions. However, it is common to find both or all oxidation states existing at the same time in either aerobic or anaerobic soil [7,8],... 

Give examples of cations including oxy and hydroxy cations common in soil. 

In some examples of cationic polymerisation, the degree and the rate of polymerisation increase as the temperature decreases. This can be explained as follows. 

There are only a few examples of cationic clusters, which is in keeping with the postulated electron-sink effect of the system of metal-metal bonds. This hypothesis is supported by examination of some properties of the clusters Co3(CO)9(/i3-CR) as reported previously207 209. ... 

While cyclopentanes have also been produced by antibody-catalysed cyclization (Appendix entry 15.2) (Li et al., 1996), much the most striking example of cationic cyclization by antibodies is the formation of the decalins [79], [80] and [81] (Fig. 29). The rra/w-decalin epoxide [82] (tu2 100 h at 37°C) was employed as a mixture of two enantiomeric pairs of diastereoisomers as a TSA to raise antibodies, among which HA5-19A4 emerged as the best catalyst for cyclization of substrate [83] (Appendix entry 15.4) (Hasserodt et al., 1997). 

Another example of cation control excimer formation will be given in Section 2.2A.3 dealing with calixarenes. 

Figure 2 Examples of cationic lipids, differing in the head group structure (mono/ poly cationic) and the nonpolar lipid anchor (Chol/hydrocarbon chains). Abbreviations DOTAP, A-[l-(2,3-dioleoyloxy)propyl]-A,A,7V-trimethyl-ammoniumchloride DOTMA, A-[l -(2,3-dioleyloxy)propyl]-A A, A-trimethylammoniumchloride DC-Chol, 3 P"[A-(A, A -dimethylaminoethyl)carbamoyl]-cholesterol DOGS, A, A-dioctodecyl-amidoglycylspermin DORI, A-(l, 2-dioleoyloxypropyl)-A,A-dimethyl-A-hydroxyethyl-ammoniumbromide SpdC, spermidin-cholesterol.

Examples of cation-radical deprotonation-fragmentation of alcohols also deserve a separate consideration. Hammerum and Audier (1988) described the following reactions ... 

Butyl rubber, polyisobutylene, is an example of cationic polymerization with an acid. Review Chapter 14, Section 2.3. A small amount of isoprene is added to enable cross-linking during vulcanization through the allylic sites. 

Another example of cation control over borate structure is found in the recently elucidated structure of the industrially important synthetic zinc borate Zn[B304(0H)3] [2 ZnO 3 B3O3 3 H2O], shown in Fig. 12 [45]. This compound has a polytriborate structure reminiscent of that found in colemanite (Fig. 7a) [29]. Yet, due to the different coordination requirements of the Ca and Zn cations, the anionic polyborate chains in these two compounds have different spatial arrangements. In the case of colemanite, parallel triborate chains are linked together into extended sheets by coordination with interstitial (and H2O). These sheets are bound... 

The cations of the ionic liquid include organic and inorganic cations. Examples of cations include dialkylimidazolium ion, tetra-alkylphosphonium ion, etc. and these cations can be associated with a number of different anions (Fig. 1). The anion includes organic and inorganic anions such as PFg, CF3S03, CF3C00, etc. and Lewis acids such as AlCU", GaC, etc. 

Figure 2.1-1 Examples of cations commonly used for the formation of ionic liquids.

Cationic photoinitiators are compounds that, under the influence of UV or visible radiation, release an acid, which in turn catalyzes the desired polymerization process. Initially, diazonium salts were used, but they were replaced by more thermally stable iodonium and sulfonium salts. Examples of cationic initiators are in Table 4.3. 

Examples of cationic emulsifiers are quaternary ammonium salts, amine hydrochlorides, etc... 

This section will be quite short in that we are unaware of any examples of cations which display bishomoantiaromatic character. There are several potential candidates including derivatives of 102 and 103 in which a bishomocyclopentadienyl-type delocalization could occur. Examples of these cations are known however, there is no evidence for any significant degree of cyclic delocalization217222. 

Common examples of cationic Lewis acids are metal ions, such as Al3+ and Cu2+. Hydration of the Al3+ ion, for example, is a Lewis acid-base reaction in which each of six H20 molecules donates a pair of electrons to Al3+ to form the hydrated cation A1(H20)63+ ... 

Considering the observation743 that the stabilizing effect of donor substituents decreases in the order NH2 > SH, OH > Cl, it is not surprising that examples of cations with oxygen as directly attached donor atoms, such as cation 297, are scarce.744 Cation 298 with sulfur as an intramolecular w-donor is the only example of its kind.745... 

A rare example of cationic polymerization of emulsified epoxy resins has been reported by Walker et al.973 Polymerization of water emulsion of epoxy resins with a variety of superacids (triflic acid, HCIO4, HBF4, HPF6) results in polyols with two glycidyl units (294) in contrast to commercial epoxy resins with one unit separating the aromatic moieties. The level of residual glycidyl ether and Bisphenol-A units is also much lower than in conventional epoxy resins. 

The acid-catalysed hydrolysis of 5-methoxyacenaphthylene 1,2-oxide was shown to proceed via the carbocation (76).149 This cation reacted with water to give an approximately 3 2 ratio of cis.trans diols, despite the trans-diol being substantially more stable. Hence, transition state effects, and not thermodynamic stability, determine the products. A computational investigation examined carbocations derived from oxidized benzo aJanthraccncs.150 Examples of cations considered are (77), derived by epoxi-dation and ring opening, and (78), derived by methyl oxidation and subsequent C—O bond heterolysis. 

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