Cationization, influence charge types

Equations (8)—(16) indicate that substituents in the homocyclic ring of quinolinium, benzopyrylium, benzothiopyrylium, and isobenzothiopyrylium cations influence pKR for pseudobase formation in the heterocyclic ring via p values in the range 4.9-6.9. The particular type of charge neutralization upon pseudobase formation is the major determinant of the magnitude of p. The observed p values are considerably larger than p = 2.81 for the acid dissociation of ring-substituted anilinium ions (31)148 which can be considered as the simplest... 

From the results of an investigation of the effects of hexadecyltri-methylammonium iodide, hexadecylpyridinium bromide, and sodium hexadecylsulfonate on the protonation equilibria of a large number of indicators of different charge types (Table 12), Hartley (1934) proposed a sign rule to account for the observed shifts in the equilibria. Considering only electrostatic interactions and the valence changes of the indicators, Hartley s rule states that cationic micelles are not expected to influence the equilibria of the -I- -I- -I- type, and likewise... 

On the other hand, if HA is an uncharged acid z = — V, e.g. CH3—CO2H), the right-hand side of Eq. (4-10) involves the sum of two reciprocal radii (zha = 0) and a strong influence of the relative permittivity on the ionization equilibrium is expected. Because in acid/base reactions of this charge type, neutral molecules are converted into anions and cations, which attract each other, reaction (4-5) will shift to the right with an increase in relative permittivity of the solvent in which HA is dissolved. Ionization increases when increases. This rule is qualitatively verifiable for water and alcohols as... 

The equilibrium constant for (31) at 100 C decreases by a fraction of ca. 10 on transfer from DMAC to 88 % MeOH-HgO. This is because the Sif2 anion-cation reaction is much more strongly influenced by solvent transfer than the back reaction between polar molecules. The large change in equilibrium constant for a process of this charge type with solvent transfer warns us that acid-base indicator systems of this charge... 

The influence of a cyclopropane ring on an adjacent cationic centre continues to be examined. The cations derived from 4-substituted bicyclo[3,l,0]hex-2-enes and their benzo analogues (359) exist, under stable ion conditions, as cyclopentyl-like cations with charge delocalization into the three-membered ring, but with no homoantiaromatic or Mobius-type character. Dibenzotropylium ion (384 = cyclopropyl = H) and the dibenzocycloheptadiene counterpart both show considerable... 

The type of catalyst influences the rate and reaction mechanism. Reactions catalyzed with both monovalent and divalent metal hydroxides, KOH, NaOH, LiOH and Ba(OH)2, Ca(OH)2, and Mg(OH)2, showed that both valence and ionic radius of hydrated cations affect the formation rate and final concentrations of various reaction intermediates and products.61 For the same valence, a linear relationship was observed between the formaldehyde disappearance rate and ionic radius of hydrated cations where larger cation radii gave rise to higher rate constants. In addition, irrespective of the ionic radii, divalent cations lead to faster formaldehyde disappearance rates titan monovalent cations. For the proposed mechanism where an intermediate chelate participates in the reaction (Fig. 7.30), an increase in positive charge density in smaller cations was suggested to improve the stability of the chelate complex and, therefore, decrease the rate of the reaction. The radii and valence also affect the formation and disappearance of various hydrox-ymethylated phenolic compounds which dictate the composition of final products. 

In the photochemical one-electron oxidation of aromatic sulfides, dimer radical cations were formed in rapid equilibrium with monomeric radical cation (59). The complex formation of a- and tt-types has been shown to be sensitive to the steric and electronic influence of substituent. For the case of jo-(methylthio)anisole the formation of TT-type dimer was shown to be reduced due to steric hindrance of two methyl groups. No formation of dimer radical cation was observed for jo-(methoxy)thioanisole and diphenyl disulfide where the corresponding monomer radical cations are stabilized by the delocalization of positive charge on the sulfur atom. Density-functional calculations supported the experimental results. The intramolecular formation of similar radical... 

The configuration of near sohd phase water can be altered in close proximity to the phyUosilicate. The siloxane surface influences the character of the water due to the nature of their charge distribution and the complexes formed between the cation and the surface functional groups. Both the type of charge and degree of charge localization, as well the valence and size of the complexed cations, confiol the characteristics of the water molecules near the surface. 

In the antiferromagnetic state, the spins are oriented parallel to the c-axis. Moss-bauer studies have indicated that the number and type of subsites in the magnetic structure may be influenced by the halide concentration, the nature of the halide and the level of excess protons vhich balance the halide charge. When chloride is present in the structure, there are tv o different Fe " sites, vhereas for fluoride-containing akaganeite, the number of non-equivalent cation sites may be greater. 

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