Anions, equilibrium

Mixture B K[SiPh(3-fcat)2 and K[SiPh(dbcat)2] (3-fcat 2,3-dihydroxybenzaldehyde, dbcat 3,5-di-f-butylcatechol) contained two complexes with asymmetric catechols. Each complex showed the presence of two resonances due to the isomerism described above. The equilibrated mixtures showed the presence of two further species (Figure 9). These are attributed to isomers of the [SiPh(3-fcat) (dbcat)]- anion. Equilibrium was not established even after 8 weeks, whereupon decomposition prevented a more quantitative kinetic analysis. Flowever, it is apparent from the two experiments described that the kinetics of redistribution of ligands between complexes varies dramatically according to the cate-cholate involved. It is reasonable to conclude that the rate of redistribution decreases as the strength of the catecholate derivative increases. The nonstatistical distribution of complexes in a mixture indicates a thermodynamic stability of the complexes in Me2SO. The likely explanation lies in the electronic rather than the steric effects in the complex, since the live-coordination imposes little steric constraint. 

Dimeric radical anion Equilibrium constant/dm3 mol-1 Reference... 

Deprotonation of the carbocation at N( 1) [reaction (137)] is kinetically favored over the deprotonation at C(5) [reaction (136)]. Thus, isouracil is an important intermediate in these reactions. It is sufficiently long-lived to follow its reactions by pulse radiolysis. Isouracil is in equilibrium with its anion [equilibrium (138)]. This allows reactions (139) and (140) to proceed as well. However, when N(3) is substituted such as in 3MeUra, this additional pathway is no longer possible. For a compilation of rate constants see Table 10.17. 

Grzyb, K.R. (1995) NOAEM (natural organic anion equilibrium model) a data analysis algorithm for estimating functional properties of dissolved organic matter in aqueous environments Part I. Ionic component speciation and metal association. Org. Geochem., 23, 379-390. 

The following table lists the standard electrode potentials (in V) of some electrodes of the second kind.13 These consist of three phases. The metal is covered by a layer of its sparingly soluble salt and is immersed in a solution of a soluble salt of the anion. Equilibrium is established between the metal atoms and the solution anions through two partial equilibria one between the metal and its cation in the sparingly soluble salt and the other between the anion in the solid phase of the sparingly soluble salt and the anion in solution. The silver chloride electrode is preferred for precise measurements. 

To this author, the anionic equilibrium explanation seems less likely than the monomer reactivity explanation. Carbohydrate oxyanions are not normally very selective toward alkyl halides, and when conditions are set up where they can be formed in a selective manner, as with phase-transfer... 

Figure 6.50 The two conformers of ethyl anion equilibrium and methyl amine and NBO interactions of lone pair with the vicinal C-H bonds (in kcal/mol). In both cases, the overall energy between staggered and eclipsed...

Matsuo, J., Aoki, K., Sanda, F., Endo, T., 1998b. Substituent effect on the anionic equilibrium polymerization of six-membered cyclic carbonates. Macromolecules 31, 4432—4438. 

In further studies, West and Wright used a crossover experiment to establish the intramolecularity of the retro-1,2-process and also found that while rapid protic quench traps 142 as the favored side of the anionic equilibrium, alkylation proceeds slowly and occurs preferentially at carbon, shown above for conversion to 143. ... 

AB and ABA block copolymers have been prepared by the sequential addition of hexaphenyltricyclosiloxane and octaphenylcyclotetrasiloxane on a PDMS with one and two lithium silanolate chain-ends, respectively [153-157]. Some redistribution reactions occurred due to the harsh conditions required for the ROP of the perphenyl cyclic monomers. Finally, some multiblock copolymers have been prepared by the anionic equilibrium polymerization of cyclosiloxanes, which leads to a random distribution of different units-that is, diethyl, diphenyl, methylphenyl siloxy units [157], dimethyl, diphenyl siloxy units [158], and dimethyl, methylvinyl-siloxy units [159]. 

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