Masked anions

Joining all pieces together, the proposal involved in this explanation is that the compounds 5, 6, and 7 contain a masked anion, the hypothetical cluster [Rh3(/z-N- -tolyl)2(CO)6] , showing two coordination sites with tuneable donicity the rj -cyclohexadienyl coordination site and that provided by the two rhodium atoms of the open edged trimetallic core. The connection between these two sites should occur through the bond of one para-toXylimido ligand. Its partial double... 

Amino acid anion 1743-1729 Often masked by water deformation band near... 

Tabie 11.37 Masking Agents for Anions and Neutrai Moiecuies 11.100... 

Polymerization ofiVIasked Disilenes. A novel approach, namely, the anionic polymerization of masked disilenes, has been used to synthesize a number of poly(dialkylsilanes) as well as the first dialkylamino substituted polysilanes (eq. 13) (111,112). The route is capable of providing monodisperse polymers with relatively high molecular weight M = lO" — 10 ), and holds promise of being a good method for the synthesis of alternating and block copolymers. 

It is not necessary for a compound to depart from stoichiometry in order to contain point defects such as vacant sites on the cation sub-lattice. All compounds contain such iirndirsic defects even at the precisely stoichiometric ratio. The Schottky defects, in which an equal number of vacant sites are present on both cation and anion sub-lattices, may occur at a given tempe-ramre in such a large concentration drat die effects of small departures from stoichiometry are masked. Thus, in MnOi+ it is thought that the intrinsic concentration of defects (Mn + ions) is so large that when there are only small departures from stoichiometry, the additional concentration of Mn + ions which arises from these deparmres is negligibly small. The non-stoichiometry then varies as in this region. When the departure from non-stoichio-... 

Determination. To an aliquot of the silver(I) solution containing between 10 and 50 pg of silver, add sufficient EDTA to complex all those cations present which form an EDTA complex. If gold is present (>250 xg) it is masked by adding sufficient bromide ion to form the AuBr4 complex. Cyanide, thiocyanate or iodide ions are masked by adding sufficient mercury(II) ions to complex these anions followed by sufficient EDTA to complex any excess mercury(II). Add 1 mL of 20 per cent ammonium acetate solution, etc., and proceed as described under Calibration. 

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

The phosphonate (176) has been used for the addition to aldehydes of a masked jS-keto-ester function and applied in the synthesis of ( )-7(f),9(t)-trisporic acid B methyl ester. The isomerically pure phosphonate (177) has been used in a synthesis of dehydro-Cig juvenile hormone," the anion being generated by treatment with lithium di-isopro-pylamide in THF-HMPT at - 65 °C for 1 min. 

Figure I indicates the approach used to synthesize poly(oxyethylene)-b-poly(pivalolactone) telechelomers. An acetal capped anionic initiator, X (13) polymerizes ethylene oxide (EO) to give 2> a potassium alkoxide of a masked polyether, and this "new" initiator is to be used to polymerize pivalolactone (PVL). Since potassium alkoxides are strong nucleophiles, they can randomly attack at both the carbonyl carbon and the 3-methylene carbon in lactones, (Figure 2) such a random attack would result in a pivalolactone segment containing irregularities. Lenz (15), and Hall (16), and Beaman (17) have investigated PVL polymerization and have shown that the less nucleophilic carboxylate anion is preferable in polymerizing PVL smoothly. The weaker carboxylate anion will attack only at the methylene...

A variety of reagents could be used to carry out such a conversion (18,19). We chose to react the alkoxide ion with succinic anhydride (SA), because the alkoxide ion could be converted quantitatively to the carboxylate ion when excess of SA is used, and also because no side reactions are reported (19). The carboxylate anion, 3, thus formed was used to polymerize PVL giving the masked poly(oxyethylene)-b-po y(pivalolactone) co-polymeric salt, 4. The salt, 4, was converted to the teiechelomer, 5, by acid hydrolysis.. ... 

The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

Anionic Polymerization of Masked Disilenes Mechanism, Scope and Applications... 

The masked disilene monomers 1-5 were prepared by reaction of dichlorodisilanes of the type ClSiR1R2SiMe2Cl with the biphenyl anion radical as described before. These are composed of two regio isomers, a and b, the predominant isomer being a, as determined by H NMR NOE difference spectra. 

Table 1. Preparation and Anionic Polymerization of Masked Disilene, 1-Phenyl-7,8-disila-bicyclo[2.2.2]octa-2,5-diene...

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