Anions anion effect

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 5 Carboxylic acids are much stronger acids than alcohols because of the electron withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge m the carboxylate anion (resonance effect)... 

Schemes 110-113 outline the most common general methods for accomplishing the synthesis of thiiranes by formation of a C—S bond (75RCR138,66CRV297, 64HC(19-1)576). The methods in Schemes 111-113 are variations of Scheme 110 they differ in the details of the generation of the thiolate anion which effects the ring closure by a displacement reaction. The methods of converting oxiranes to thiiranes, to be discussed separately (Section 5.06.4.3), involve a displacement like thafof Scheme 110 as the final step.

S ts can be used to precipitate proteins by salting out effects. The effectiveness of various salts is determined by the Hofmeister series, with anions being effective in the order citrate > PO4" > SO4" > CH3COO > Cl > NO3 , and cations according to NH4 > > Na ... 

The pA of 1,3-dithiane is 36.5 (Cs" ion pair in THF). The value for 2-phenyl-1,3-dithiane is 30.5. There are several factors which can contribute to the anion-stabilizing effect of sulfur substituents. Bond dipole effects contribute but carmot be the dominant factor because oxygen substituents do not have a comparable stabilizing effect. Polarizability of sulfur can also stabilize the carbanion. Delocalization can be described as involving 3d orbitals on sulfur or hyperconjugation with the a orbital of the C—S bond. MO calculations favor the latter interpretation. An experimental study of the rates of deprotonation of phenylthionitromethane indicates that sulfur polarizability is a major factor. Whatever the structural basis is, there is no question that thio substituents enhance... 

Table 3.1-2 [EMIM]X salts and melting points, illustrating anion effects.

If the cation has been unchanged, its ability to act as a hydrogen-bond donor has been unchanged, so why is an effect seen at all I propose that there is competition between the anion and the Reichardt s dye solute for the proton. Thus, the values of the ionic liquids are controlled by the ability of the liquid to act as a hydrogen bond donor (cation effect) moderated by its hydrogen bond acceptor ability (anion effect). This may be described in terms of two competing equilibria. The cation can hydrogen bond to the anion [Equation (3.5-2)] ... 

Comparison of Ca3(POi)2, Ca(C204), and Mg3(P04)2. The effects of cation and anion composites were tested by comparing the dissolution of Ca3(P04)2, Ca(C204), andMg3(P04)2 at pH 7 (Table 10). The dissolution of Ca3(P04)2 is achieved more effectively with X than with EDTA. However, when the anion is oxalate, the dissolution of Ca2+ is drastically reduced with X. EDTA can dissolve Ga(C204) to the same extent as Ca3(P04)2, i.e. the anion effect is insignificant. A better separation of Ca2+ from oxalate anion may be achieved by EDTA. 

NOTE It is also apparent that the ferric ion (Fe3+) should chelate most readily. In practice, however, under strongly alkaline conditions, the preferred reaction is to instantaneously form ferrous hydroxide and then to slowly revert to ferric hydroxide (competing anion effect). 

NOTE If the BW contains phosphate, the preferred reaction is for calcium to precipitate as hydroxyapatite, rather than to chelate with EDTA or NTA (a further competing anion effect). Consequently, there would seem to be no valid reason to produce combined phosphate-chelant programs, with the chelant acting as a reserve against unforeseen hardness incursions caused by a softener leakage, or other source. In practice, the chelant acts to solubilize existing deposits, producing a very clean boiler. 

NOTE Although control over transported iron is critical in larger power boilers, as discussed earlier, control by the chelation of ferric iron is not possible (because of the competing anion effect). Consequently, Fe203 and Fef04 are essentially unaffected by chelants. However, it is well known that where an iron chelate (chelonate) is formed, it is stable and will not be destroyed by hydrolysis at high temperature. 

If the alkalinity is too low, iron corrosion may take place. If the alkalinity is too high, there is a further competing anion effect, with magnesium precipitated as Mg(OH)2, rather than chelated. 

The mechanism of the reaction was interpreted in terms of equilibria (265) and (266) with the second step at least partially rate-determining in view of the acceleration observed with added anions, the effect of base being envisaged as in (XXXIX). 

The effect of surface deformation in the Helmholtz layer should also be involved in Eq. (35). In consideration of specific adsorption of anions, such effects can be expressed by the potential gradient Lj y, z, as follows,... 

The N—>P dative bonds are weak and different in lengths (1.800 A on average), and the triflate anions are effectively extended to consider interaction with the counter ion. Again the phosphorus atom is strongly pyramidalized and features the aspects of an inert nonbonding electron pair. 

The study of the MEEP/PEO-(LiX)n and MEEP/PPO-(LiX)n complexes, (X= BF4, CIO4) by Li NMR spectroscopy, DSC and X-ray diffraction showed that they were multiphase with amorphous MEEP and crystalhne PEO phases. Strong cation-anion association effects were also observed [612]. 

To sum up, in addition to the electronic stabilization and solvation, classical steric congestion caused by either the cation or anion moieties effectively controls the ease of ionic dissociation of the carbon-carbon a bond in hydrocarbons. 

Since the rate does not display an inverse dependence on Hg(II) concentration, the oxidation of Hg atoms, in equilibrium with mercury(l) and mercury(II), can be discounted, although Hg atoms are kinetically important in the reduction of thallium(IIl) by mercury(I) . It seems likely that the acid-dependent path (A ) involves CoOH. Anion effects were not investigated. 

Then, substitution of the sulfur atom of Cys with an oxygen would greatly decrease the rate of reaction, because nucleophilicity, anion-stabilizing effect and proton-donating ability of OH group are far smaller than that of an SH group. 

These last examples illustrate the effecte of heavy cations on anionic stability. The opposite case of an anionic effect is also possible. Thus diazonium salts are hardly stable but not dangerous when the anion is a chloride ion, whereas they become dangerous when the anion is a sulphide or carboxylate. 

Nanofiltration membranes are negatively charged and reject multivalent anions at a much higher level than monovalent anions, an effect described as Donnan exclusion. Nanofiltration membranes have MgS04 retention and water permeability claims. 

Wang JX, Markovic NM, Adzic RR. 2004. Kinetic analysis of oxygen reduction on Pt(ll 1) in acid solutions Intrinsic kinetic parameters and anion adsorption effects. J Phys Chem B 108 ... 

Housmans THM, Koper MTM. 2005b. CO oxidation on stepped Rh[n(lll) x (111)] single-crystal electrodes Anion effects on CO surface mobility. Electrochem Commun 7 581-588. 

Markovic NM, Lucas CA, Rodes A, Stamenkovic V, Ross PN. 2002. Surface electrochemistry of CO on Pt(lll) Anion effects. Surf Sci 499 L149-L158. 

The anion electronic effect in a recent analysis of the inhibition effect of bisulfate and comparison with the effect of OH adsorption (Pt-OH formation), Wang and co-workers found that the electronic effect must also be operative [Wang et al., 2004]. 

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