Stoichiometrical dependence

The first step is carbon-metal bond formation via coordination. This process may be followed by one or more steps, leading to transformation of ligands and/or reaction between ligands. In a final step, the metal is removed from the organic moiety. Reactions are catalytic or stoichiometric, depending on whether or not the metal is eliminated in its original oxidation state. The following is a broad classification of these processes. 

This is consistent with the relative ease of dissociation of poly(styryl)lithium in the presence of bases and also with the concentration dependence of enthalpy versus R plot (Fig. 4) with a break observed at an R value of ca. 1.0. These calorimetric results are also in agreement with the stoichiometric dependencies observed by Helary and Fontanille 92> from their kinetic and spectroscopic studies. For example, they reported that the UV wavelength of maximum absorption of poly(styryl)lithium shifted upon additions of TMEDA until an R value of 1.0 and then was constant. They also observed that TMEDA additions increased or decreased the rate of polymerization, depending on [PSLi] the increase or decrease in the rate leveled off at an R value of ca. 1.0. All... 

It has been observed that the concentrated solution viscosity decreases upon addition of TMEDA to solutions of poly(isoprenyl)lithium 93). This would be consistent with the process shown in Eq. (17) or (20) and not with Eqs, (18) or (19). The decrease in viscosity would be consistent with interaction of TMEDA to form an unassociated complex (Eq. (20)), but this does not seem to be in accord /with the stoichiometry observed by calorimetry. It is noteworthy that the break observed by calorimetry at R = 0.5 is consistent with the stoichiometric dependence of spectral, kinetic and microstructure effects 90). Again this shows that these kinetic effects are related to the stoichiometry of formation of base-organolithium adduct, i.e. that they are ground-state solvation effects. 

We have two stoichiometrically independent routes in the thermodynamic basis and three independent routes in the kinetic basis of this mechanism. It follows that one route of the kinetic basis is stoichiometrically dependent. If we assume that the third route is stoichiometrically dependent, two opportunities exist for making Mr equal to Mf ... 

Flame Speeds. Overall, the calculated flame speeds agree well with experiment. Flame speed calculations as a function of diluent concentration with 0=0.8 (the peak of the stoichiometric dependence) are shown in Figure 1. The calculated flame speeds are less temperature dependent than experiment. Considering the stoichiometric dependence of the flame speeds, the calculations of flame speed are in greater error away from the peak (0=0.8) and exceed the experimental error at both rich and lean limits. 

In complex reactions, the singular reaction steps are interconnected, that is, singular components participate in different reactions, with the consequence that a part of the reactions is stoichiometrically dependent. Only the independent reactions can be determined from the change in the number of moles. The solution to the problem of stoichiometric dependence can be found... 

Clegg W, Dunbar L, Horsburgh L, Mulvey RE. Stoichiometric dependence of the long-established reaction of butyUithium with pyridine a hidden secondary reaction that produces a pyridine adduct of a lithiodihydropyridine. Angew Chem Int Ed Engl. 1996 35 753-755. 

Fig. 27 Stoichiometric dependence of benzene deprotonation by magnesiate TMEDA Na(TMP) (nBu)Mg(TMP)...

Duralink HTS 1,6-hexamethylenebissodium thiosulphate (Flexsys America) was used as a post-vulcanisation stabiliser in the sulphur vulcanisation of an NR compound. The effects of this additive on the cure characteristics and on the tensile properties and tear strength of vulcanisates were investigated. The improved reversion resistance, network sulphur rank analysis on overcure and the stoichiometric dependence of activation energy on HTS level supported the conclusion that the active sulphurating species was altered. Improvements in tear strength at equal modulus were consistent with the formation of a bimodal network. 16 refs. 

The fiinctional dependence of tire reaction rate on concentrations may be arbitrarily complicated and include species not appearing in the stoichiometric equation, for example, catalysts, inliibitors, etc. Sometimes, however, it takes a particularly simple fonn, for example, under certain conditions for elementary reactions and for other relatively simple reactions ... 

This is the situation exploited by the so-called isolation method to detennine the order of the reaction with respect to each species (see chapter B2.1). It should be stressed that the rate coefficient k in (A3,4,10) depends upon the definition of the in the stoichiometric equation. It is a conventionally defined quantity to within multiplication of the stoichiometric equation by an arbitrary factor (similar to reaction enthalpy). 

The breaking up of azeotropic mixtures. The behaviour of constant boiling point mixtures simulates that of a pure compound, because the composition of the liquid phase is identical with that of the vapour phase. The composition, however, depends upon the pressure at which the distillation is conducted and also rarely corresponds to stoichiometric proportions. The methods adopted in practice will of necessity depend upon the nature of the components of the binary azeotropic mixture, and include —... 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

A rational classification of reactions based on mechanistic considerations is essential for the better understanding of such a broad research field as that of the organic chemistry of Pd. Therefore, as was done in my previous book, the organic reactions of Pd are classified into stoichiometric and catalytic reactions. It is essential to form a Pd—C cr-bond for a synthetic reaction. The Pd— C (T-bond is formed in two ways depending on the substrates. ir-Bond formation from "unoxidized forms [1] of alkenes and arenes (simple alkenes and arenes) leads to stoichiometric reactions, and that from oxidized forms of alkenes and arenes (typically halides) leads to catalytic reactions. We first consider how these two reactions differ. 

TT-Aliylpalladium chloride reacts with a soft carbon nucleophile such as mal-onate and acetoacetate in DMSO as a coordinating solvent, and facile carbon-carbon bond formation takes place[l2,265], This reaction constitutes the basis of both stoichiometric and catalytic 7r-allylpalladium chemistry. Depending on the way in which 7r-allylpalladium complexes are prepared, the reaction becomes stoichiometric or catalytic. Preparation of the 7r-allylpalladium complexes 298 by the oxidative addition of Pd(0) to various allylic compounds (esters, carbonates etc.), and their reactions with nucleophiles, are catalytic, because Pd(0) is regenerated after the reaction with the nucleophile, and reacts again with allylic compounds. These catalytic reactions are treated in Chapter 4, Section 2. On the other hand, the preparation of the 7r-allyl complexes 299 from alkenes requires Pd(II) salts. The subsequent reaction with the nucleophile forms Pd(0). The whole process consumes Pd(ll), and ends as a stoichiometric process, because the in situ reoxidation of Pd(0) is hardly attainable. These stoichiometric reactions are treated in this section. 

Normality makes use of the chemical equivalent, which is the amount of one chemical species reacting stoichiometrically with another chemical species. Note that this definition makes an equivalent, and thus normality, a function of the chemical reaction in which the species participates. Although a solution of 1T2S04 has a fixed molarity, its normality depends on how it reacts. 

The lower equivalent weight of magnesium hydroxide compared to caustic soda, hydrated lime, and soda ash reduces the stoichiometric amounts necessary to neutralize a given amount of acid. Depending on relative alkah costs, magnesium hydroxide can offer the advantage of lower chemical costs. 

With as httie as 0.5% hydrolysis of the sulfone monomer, the polymerization stoichiometric balance is sufficientiy upset to prevent high molecular weight polymer from being achieved. The dependence of maximum attainable PSF molecular weight on water content during polymerization can be inferred from Figure 1. 

Chemical Properties. Stoichiometric vitreous sihca contains two atoms of oxygen for every one of sihcon, but it is extremely doubtful if such a material really exists. In general, small amounts of impurities derived from the starting materials are present and various stmctural defects can be introduced, depending on the forming conditions. Water is incorporated into the glass stmcture as hydroxyls. 

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