Anion defined

Another point which needs to be clarified from the start is the nomenclature of metalated silanes We will frequently use the term silyl anion in this chapter when we talk about metalated silanes. Although the term anion defines, literally taken, an ionic compound, this expression, when used by us, does not necessarily imply that the compound in question is of ionic nature, but covers, as well, in analogy to the use of the term carbanion , silicon compounds with a polarized covalent silicon-metal bond. 

In this arrangement the terminal sulfur atoms of the two Cp (CO)2Fe 38i38g anions define a distorted octahedron which is centered on a Na cation (Na4). Each of the remaining Na" cations (Nal-Na3) is coordinated by three exocyclic sulfur atoms, an endocyclic sulfur atom and a THF molecule. As a consequence of crystallographic disorder, the positions of Na2 show half occupancy. 

The alkylzinc anions, defined as ate complexes (see Ate Complexes), are heterodimetallic systems which can be divided in two different classes, namely, the trialkylzincates of general formula M+R3Zn and the tetraalkylzincates of general formula M +R4Zn. The first zincate derivatives, that is, NaZnEts and KZnEts, were prepared by Wanklyn in 1858 from the reaction of metalhc sodium or potassium with diethylzinc (equation 38). In spite of this early discovery, many of the efforts to study this class of compounds are... 

Figure 9.18 Mass spectrometry of glycerides, phospholipids and fatty adds, (a) origin of main fragmentation ions as illustrated (b) (c) Example of negative ion FAB MS/MS CID mass spectrum of indicated fatty acid. The main fragment ions visible are homologation fragment anions. Mass differences between consecutive fragment anions define fatty acid CH2-length (

In general, anions are less strongly hydrated than cations, but recent neutron diffraction data have indicated that even around the halide ions there is a well defined primary hydration shell of water molecules, which, in... 

Hence, acids can be defined as substances producing cations characteristic of the solvent (solvo-cations, for example NH4, NO ), and bases as substances producing anions characteristic of the solvent (solvo-anions, for example OH , NH, NO3). This concept has been applied to solvents such as liquid sulphur dioxide, liquid hydrogen chloride and pure sulphuric acid. 

A fuzzier atom type participating in these descriptors has been defined that is pharmacologically relevant - the physicochemical type at near-neutral pH [24], which is one of the following seven binding property classes 1 = cation 2 = anion 3 = neutral hydrogen-bond donor 4 = neutral H-bond acceptor ... 

The extra charge defines whether the current molecular system is aneiitral system, positively charged system (caiioiT), ornegaiively charged system (anion). 

The operation of the nitronium ion in these media was later proved conclusively. "- The rates of nitration of 2-phenylethanesulphonate anion ([Aromatic] < c. 0-5 mol l i), toluene-(U-sulphonate anion, p-nitrophenol, A(-methyl-2,4-dinitroaniline and A(-methyl-iV,2,4-trinitro-aniline in aqueous solutions of nitric acid depend on the first power of the concentration of the aromatic. The dependence on acidity of the rate of 0-exchange between nitric acid and water was measured, " and formal first-order rate constants for oxygen exchange were defined by dividing the rates of exchange by the concentration of water. Comparison of these constants with the corresponding results for the reactions of the aromatic compounds yielded the scale of relative reactivities sho-wn in table 2.1. 

The selectivity relationship merely expresses the proportionality between intermolecular and intramolecular selectivities in electrophilic substitution, and it is not surprising that these quantities should be related. There are examples of related reactions in which connections between selectivity and reactivity have been demonstrated. For example, the ratio of the rates of reaction with the azide anion and water of the triphenylmethyl, diphenylmethyl and tert-butyl carbonium ions were 2-8x10 , 2-4x10 and 3-9 respectively the selectivities of the ions decrease as the reactivities increase. The existence, under very restricted and closely related conditions, of a relationship between reactivity and selectivity in the reactions mentioned above, does not permit the assumption that a similar relationship holds over the wide range of different electrophilic aromatic substitutions. In these substitution reactions a difficulty arises in defining the concept of reactivity it is not sufficient to assume that the reactivity of an electrophile is related... 

One of the major factors in determining the structures of the substances that can be thought of as made up of cations and anions packed together is ionic size. It is obvious from the nature of wave functions that no ion has a precisely defined radius. However, with the insight afforded by electron... 

A solution s ionic balance is defined as the ratio of the total cation charge to the total anion charge. Determine the ion balance for this sample of water, and comment on whether the result is reasonable. 

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

Phosphoric acids and the phosphates maybe defined as derivatives of phosphoms oxides where the phosphoms atom is in the +5 oxidation state. These are compounds formed in the M2O—P20 system, where M represents one cation equivalent, eg, H", Na", 0.5 Ca ", etc. The molecular formula of the phosphoms(V) oxide [1314-56-3] is actually P O q, but this oxide is commonly referred to in terms of its empirical formula, P2O5. StmcturaHy, four phosphoms—oxygen (P—O) linkages are arranged in an approximate tetrahedral configuration about the phosphoms atom in the phosphate anion. Compounds containing discrete, monomeric PO ions are known as orthophosphates or simply as phosphates. 

Silicates in Solutions. The distribution of sdicate species in aqueous sodium sdicate solutions has long been of interest because of the wide variations in properties that these solutions exhibit with different moduli (23—25). Early work led to a dual-nature description of sdicates as solutions composed of hydroxide ions, sodium ions, coUoidal sdicic acid, and so-called crystaHoidal sdica (26). CrystaHoidal sdica was assumed to be analogous to the simple species then thought to be the components of crystalline sdicate compounds. These include charged aggregates of unit sdicate stmctures and sdica (ionic micelles), and weU-defined sdicate anions. 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

Direct dyes are defined as anionic dyes substantive to ceUulosic fibers (cotton, viscose, etc), when applied from an aqueous bath containing an electrolyte. Before the discovery of Congo Red in 1884, only mordanted cotton could be dyed. Congo Red [573-58-0] (62) (Cl Direct Red 28 Cl 22120) a primary symmetrical disazo dye, which is made readily from bisdiazotized benzidine and naphthionic acid [84-86-6] (4-arnino-l-naphthalenesulfonic acid), was the precursor of a most important line of dyes, including all shades, derived from benzidine and its homologues. Today, no benzidine dye is produced because benzidine is carcinogenic. 

---