Stoichiometric control

The function of the oxygen sensor and the closed loop fuel metering system is to maintain the air and fuel mixture at the stoichiometric condition as it passes into the engine for combustion ie, there should be no excess air or excess fuel. The main purpose is to permit the TWC catalyst to operate effectively to control HC, CO, and NO emissions. The oxygen sensor is located in the exhaust system ahead of the catalyst so that it is exposed to the exhaust of aU cylinders (see Fig. 4). The sensor analyzes the combustion event after it happens. Therefore, the system is sometimes caUed a closed loop feedback system. There is an inherent time delay in such a system and thus the system is constandy correcting the air/fuel mixture cycles around the stoichiometric control point rather than maintaining a desired air/fuel mixture. 

There is a reasonably good stoichiometric control observed in these aminolysis reactions. Therefore, in principle, the extent of chlorine replacement can be regulated by the ratio of the reactants. If mixtures of products are formed, these are generally amenable to separation by column chromatography. Separation of individual stereoisomers is often accomplished by procedures such as fractional crystallization. 

Redistribution reactions between 28 and 29 to form mixed-imido compounds were not detected. On the other hand, oxo-imido interchange reactions readily take place between MeRe03 and 29. As a consequence, new compounds are formed, MeReO(NR)2, 30, and MeRe02NR, 31. The product obtained is largely under stoichiometric control, as represented by these equations (62) ... 

There are two gereral routes to mikto-arm star polymers. The first method makes use of the stepwise addition of living polymers to multifunctional chloro-silane compounds [59-62], The Athens group uses the sequential addition of living polymers to multifunctional chlorosilane compounds under tight stoichiometric control [63, 64],... 

MOLECULAR WEIGHT CONTROL IN LINEAR POLYMERIZATION 2-6a Need for Stoichiometric Control... 

Experimentally, a few series of oligo(l,l-silole)s have been prepared as models of poly(l, 1 -silolejs and their structures and photophysical properties have been studied in detail59,61,62. We have prepared a series of oligo( 1,1 -silolejs 57 having 3,4-diphenyl-2,5-dimethylsilole as a monomer unit. The stoichiometrically controlled reduction of 1,1-dichlorosilole with sodium followed by treatment with 1-methyl-1-chlorosilole affords tersilole57a and quater-silole 57b, as shown in Scheme 1059. Kira and coworkers have reported the synthesis of... 

The mechanistic significance of Eq. 3.1, despite its great utility in mineral solubility studies, is, on the other hand, almost nil. No implication of reaction pathways, other than the postulate of stoichiometric control of aqueous-phase products, can be made on the basis of an overall reaction alone, since it features only enough species to satisfy minimal equilibrium criteria. Any number of additional kinetic species can intervene to govern the reaction pathways, which may be parallel, sequential, or a combination of these two, and the detailed interactions of the solid phase with the aqueous phase are often unlikely to be represented accurately by a spontaneous decomposition reaction like Eq. 3.1. As a case in point, the dissolution reaction of calcite (the forward reaction in Eq. 3.14) may be considered. Given the existence of protons and carbonate species in the aqueous-solution phase, at least three overall reactions more specific than Eq. 3.14 can be postulated to epitomize the detailed interactions of calcite with aqueous species 7,33,34... 

The reaction of two acyclic olefins to produce a mix of new products is finding use in organic synthesis. The reaction under many circumstances produces the statistical mixture of products. High yields of the cross product can sometimes be obtained by either stoichiometric control or by the use of functional groups. When unfunctionalized olefins are used in the reaction, all the products are of similar stability and reactivity. Under these conditions, a 1 2 1 mixture of olefins will lead to only a 50% yield of the cross product. However, as shown below, if an excess of one of the olefins is used, the percentage yield based on the minor olefin may be much higher (Eq. 6.14) [1]. 

In the absence of alcohol the reduction may be halted at the dihydro stage, but with difficulty. Stoichiometric control (3 equiv. of metal) gives reasonable results, but it seems to be most effective to use 5 equiv. of lithium with added iron(III) chloride. Thus, from the reduction of (112), quenching with ammonium chloride gives either the 1,2- or 1,4-dihydro products (114) and (115), respectively, while reaction with methyl iodide affords excellent yields of the 2-methyl-1,2-dihydro derivatives (113 Scheme 20). 

Nomura, N., Tsurugi, K., Okada, M. Mechanistic rationale of a palladium-catalyzed allylic substitution polymerization-carbon-carbon bondforming polycondensation out of stoichiometric control by cascade bidirectional allylation. Angew. Chem., Int. Ed. Engl. 2001,40, 1932-1935. 

Stoichiometric control is sometimes important, e.g., when trinuclear complexes with linear Pds units are formed ... 

To form metal-metal bonds from mononuclear complexes, bulky ligands that could inhibit the approach of the two metal centers must be avoided. Addition of halogens to [(RNQaRh] for most alkyl and aryl groups, except for the bulky t-butyl group, proceeds under stoichiometric control to give bl- or trinuclear products that are linked... 

Greater stoichiometric control. The use of molecular precursors sol-gel processing allows precise amounts of starting materials to be mixed together in solution with control of the exact stoichiometry and thus the desired final properties upon calcination. This aspect of the technique is particularly important for the production of complex oxides such as the materials used for high-Tc superconductors. 

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