Catalysts altered

Various metal complexes catalyze the addition of catecholborane and pinacolbo-rane to aliphatic terminal alkenes (Table 1-2). Neither the borane reagents nor the catalysts alter the high terminal selectivity, but a titanium catalyst does (entry 3). Although Cp2TiMe2 [30] exhibits high terminal selectivity for vinylarenes, aliphatic alkenes afford appreciable amounts of internal products, whereas an analogous Cp 2Sm(THF) [31] allows selective addition of catecholborane to the terminal car-... 

Though a catalyst alters the mechanism of a reaction, the reaction s position of equilibrium is unaltered, meaning its chemical yield remains the same. 

Additions of water during the polymerization of THF increased the polydispersity of the product polymer (Table 14). Even four percent of water (based on the catalyst) altered the molecular weight distribution of the equilibrium polymer due to the appearance of a considerable amount of low molecular weight fractions. At higher concentrations, the polydispersity was even greater. 

The importance of acyl cations in acetylation is indicated in several studies (Gore, 1955). Friedel-Crafts catalysts alter the rate of acylation but do not modify the selectivity of the reaction. For example, the antimony pentachloride-catalyzed benzoylation of toluene proceeds 1.3 x 103 more rapidly than the aluminum chloride-catalyzed reaction. 

Fluorination of this catalyst altered the pore structure in the following way. The sample pore volume increased from 0.78 to 1.42 cc. per gram, and the median pore radius increased to 154 A. However, the BET surface area of the sample remained close to 228 sq. meters per gram. The total calculated pore area changed only from 226 to 216 sq. meters per gram. The surface area had probably de-... 

The irradiation of surface catalysts alters the properties of these catalysts through defect production on their surface. These defects have been observed to enhance and inhibit catalytic activity in specific cases. For example, the irradiation of silica gel enhances the rate of H2-D2 exchange on it. 

In the lab, concentrations of catalysts are usually small compared to the concentration of the reactants and products. In such cases, increasing the concentration of the catalyst increases the rate of the reaction. If the concentration of the catalyst is large compared to the reactants and products, the rate changes little or not at all with the catalyst concentration. Since catalysts alter reaction mechanisms, reactions with catalysts require separate rate constants. Remember, a catalyst doesn t prevent the original reaction from proceeding, so the total rate is given by the sum of the rates for both reactions. For instance, a first order uncatalyzed reaction may follow the rate law ... 

Analysis of the published results has led us to a conclusion that the base catalysts alter the mechanism of coverage. Namely, in the presence of organic bases alkylchlorosilanes react with silica by island-like, while non-catalyzed reaction follows random mechanism. 

A catalyst alters the free energy of activation AG and not the standard free energy A G° of the reaction. 

A catalyst is a substance that alters the rate of a reaction without appearing in any of the products of that reaction it may speed up or slow down a reaction. For a reversible reaction, a catalyst alters the rate at which equilibrium is attained it does not alter the position of equilibrium. 

The most effective method of altering the rate of a reaction is by using a catalyst. Catalysts alter the rates of individual reactions, or whole mechanisms, in ways that can be nothing short of startling. Reactions that do not proceed at measurable rates in the absence of a catalyst can be made rapid and selective by the introduction of minor amounts of a non-consumable material, the catalyst. 

Reflect and Apply Does the presence of a catalyst alter the standard free energy change of a chemical reaction ... 

Explain, in terms of collision theory, why changes in temperature and in pressure and the addition of a catalyst alter the rate of a gas phase reaction. 

Among various species of Gu(III) in alkaline medium, monoperiodatocuprate(III) is considered to be the active species for the title reaction. The active species of osmium(VIII) is understood to be as [OsO COH) ]. The activation parameters evaluated for the catalyzed and uncatalyzed reactions explain the catalytic effect on the reaction. The Os(VIII) catalyst alters the reaction path by lowering the energy of activation. 

The vapour will start to flow over the hot catalyst. Move the Bunsen flame back to the catalyst and continue to heat it strongly. In this way, move between the Vaseline and catalyst, altering the Bunsen flame accordingly. When Vaseline vapour passes on to the hot catalyst this will start... 

Silylalumination of Alkynes and Alkenes. The reagent adds to 1-alkynes in a regio- and stereoselective (cis addition) manner. Transition metal catalysts alter the regioselectivity (eq 1). ... 

Cases where addition of a copper catalyst alters the product composition offer a clue to the reaction type. When benzenedi-azonium fluoborate is decomposed in nitrobenzene, the product is 3-nitrobiphenyI, presumably formed in an ionic reaction. If a copper catalyst is added, the product is a mixture of 2- and 4-nitrobiphenyl. 

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