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Associated species

This chapter presents a general method for estimating nonidealities in a vapor mixture containing any number of components this method is based on the virial equation of state for ordinary substances and on the chemical theory for strongly associating species such as carboxylic acids. The method is limited to moderate pressures, as commonly encountered in typical chemical engineering equipment, and should only be used for conditions remote from the critical of the mixture. [Pg.26]

Enthalpies are referred to the ideal vapor. The enthalpy of the real vapor is found from zero-pressure heat capacities and from the virial equation of state for non-associated species or, for vapors containing highly dimerized vapors (e.g. organic acids), from the chemical theory of vapor imperfections, as discussed in Chapter 3. For pure components, liquid-phase enthalpies (relative to the ideal vapor) are found from differentiation of the zero-pressure standard-state fugacities these, in turn, are determined from vapor-pressure data, from vapor-phase corrections and liquid-phase densities. If good experimental data are used to determine the standard-state fugacity, the derivative gives enthalpies of liquids to nearly the same precision as that obtained with calorimetric data, and provides reliable heats of vaporization. [Pg.82]

Because of the uncertainties related to the parametrization of an sp C, this approach is unsuitable for the study of protomeric equilibria for structures 4 through 8. We must lay stress on the fact that this simple treatment does not include (a) medium effects which are known to be important and b) the existence of associated species (see Chapter VII, Section I. LB) whose consequences have been thoroughly studied in pyridone series (1688). [Pg.5]

The methodology for preparation of hydrocarbon-soluble, dilithium initiators is generally based on the reaction of an aromatic divinyl precursor with two moles of butyUithium. Unfortunately, because of the tendency of organ olithium chain ends in hydrocarbon solution to associate and form electron-deficient dimeric, tetrameric, or hexameric aggregates (see Table 2) (33,38,44,67), attempts to prepare dilithium initiators in hydrocarbon media have generally resulted in the formation of insoluble, three-dimensionally associated species (34,66,68—72). These precipitates are not effective initiators because of their heterogeneous initiation reactions with monomers which tend to result in broader molecular weight distributions > 1.1)... [Pg.239]

In general monomeric products are readily hydrolysed but associated species (containing 4-coordinate B) are much more stable e.g. (Mc2NBH2)2 does not react with H2O at 50° but is rapidly hydrolysed by dilute HCl at 110° because at this temperature there is a significant concentration of monomer present. [Pg.210]

For a fully dissociated salt, all techniques should give the same values of transport number, t. Transference number measurements are appropriate for electrolytes containing associated species and any technique within one of the three groups will give a similar response, but values of 7] across the groups may vary. [Pg.511]

The co-existence of tetrameric and non-associated species in a system raises the question whether the following equilibrium is maintained by a direct dissociation of tetramers ... [Pg.119]

This model is similar to the associated species model in that a chemical equilibrium is assumed between existing species, and it is different in that in the latter only a nonassociated ionic species is assumed to be the electrically conducting species. [Pg.149]

It is claimed by Minchenko and Smirnov that a correlation should exist between bulk viscosity and the bonding energy between the associated species and the ions of the second coordination sphere. [Pg.176]

The reactivity of enolates is also affected by the metal counterion. For the most commonly used ions the order of reactivity is Mg2+ < Li+ < Na+ < K+. The factors that are responsible for this order are closely related to those described for solvents. The smaller, harder Mg2+ and Li+ cations are more tightly associated with the enolate than are the Na+ and K+ ions. The tighter coordination decreases the reactivity of the enolate and gives rise to more highly associated species. [Pg.21]

An enantiotropically related pair of polymorphs was obtained for p-aminoben-zoic acid, with the system being characterized by a transition temperature of 25 °C [31]. The a-form was obtained as fibrous needles, while the /M orm was obtained in the form of prisms. The solubilities of the two forms are almost the same, indicating the existence of comparable values for AG, which in turn explained the slow transformation of the a-form into the [>-form. Nucleation of the a-form was found to be favored, which is reasonable considering that the structural motif of the a-form consists of carboxylic acid dimmers that would be expected to be stable association species in solution. [Pg.268]

Any association between two solute species (molecules and/or ions) in solution can be considered as constituting complexation. Whenever a compound is capable of forming an associated species with another dissolved solute molecule, the complexation of the two can profoundly influence the solubility of the system. The simplest type of complex that may be formed between a drug entity (denoted in the following discussion as D) and an interacting substrate or ligand (which will be identified as S) is the species in which they combine in a 1 1 stoichiometric ratio ... [Pg.341]

The reaction product of (diphenylmethyleneimino)triinethylsilane with 2,2<-biphenylene-fluoroborane is an associated species as illustrated by (XII). [Pg.54]

Associated ions in this context means an association species held together (albeit transiently) via electrostatic interactions. [Pg.313]

Further work is needed to be able to predict the properties of the cross-dimers and thus reduce the number of adjustable parameters in cases where cross-association must be considered. More complex associated species may have to be postulated to improve the results. [Pg.431]

Blowfly maggots that infest or blow the wool of sheep are especially common in warm humid areas, but occur wherever sheep are raised. Several species are involved, but the most troublesome species in Africa is Lucilia cuprina. The flies are attracted either to open wounds or to fermenting wool, the latter a condition that arises when sheep in full fleece are subjected to frequent rains during warm weather. While Lucilia cuprina apparently confines its attack mostly to the wool and the serous fluid that exudes from the skin of infested sheep, some of the associated species may attack the skin and flesh with serious or fatal result. Lucilia sericata has been observed to penetrate the abdominal wall and enter the peritoneal cavity. [Pg.99]

Since the electrolyte may contain associated species, we choose to define the general term current fraction as Is /Io, assuming that interfacial resistances, which may change during the course of an experiment, have been allowed for. Because the steady state current is not a linear function of the applied potential difference above some undefined potential, the above parameter is generally potential-dependent. However, because electrolytes display a linear, steady state, current-applied potential difference response up to at least 20 mV we may define a limiting current fraction, f+, as... [Pg.157]

Field surv have confirmed oxidant injury to ponderosa pine and associated species at numerous locations in the Sierra Nevada foothills east and southeast of Fresno. Oxidant measurements at ground stations and by instrumented aircraft show late-aftemoon peaks of transported oxidant on the western slopes of the Sierras. Limited measurements by instrumented aircraft suggest the development of a layer of oxidant approaching the forested mountain slopes between 610 and 1,829 m during the late afternoon. A very weak inversion or isothermal layer may serve as a reservoir of oxidant, which is advected to the mountain slope in the southern coastal air basin, as suggested by Edinger. Considerable concern has been registered about air quality in the Lake Tahoe basin, where local development may cause adverse oxidant concentrations. ... [Pg.597]

Coolia monotis is another related, macro-algal associated species which also spreads into more temperate waters where it is commonly associated with Ulva. It is not very toxic, with only slight hemolytic activity found in a strain from Okinawa (51). [Pg.90]

Organolithium compounds tend to associate into dimers, higher oligomers and polymers of two types Complexes where the Li atoms are linked to each other by a chain of one or more atoms of other elements (C, N, O etc.), and complexes where the Li and other metallic atoms are close to each other, forming clusters. Section V presents examples of application of instrumental methods—mainly NMR and XRD—to structural elucidation of these associated species. [Pg.322]

A function closely related to QCC is the Li quadrupolar splitting constant (QSC), defined as QSC = (1 -h/7 /3) x( Li), where r is the asymmetry parameter. The Li QSC values can be estimated from the Li and C(para) spin-lattice relaxation times. The QSC values are correlated with the effects of structure, solvent and temperature on association in solution for aryllithium compounds (155, 171, 172). Conclusions can be drawn about the structure of the associated species in cases where no supporting XRD evidence is available. ... [Pg.361]


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See also in sourсe #XX -- [ Pg.5 ]

See also in sourсe #XX -- [ Pg.5 ]




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