Excess reactivity, lack

Answer /Af the reaction rate is changing with each neutron generation, we ffdencte this increase or decrease as a change caused by either an I excess or lack of "reactivity " Tnus, the reactivity of a nile refers... 

Canadian Deuterium-Uranium Reactor (CANDU). The CANDU reactor is interesting because it can mn continuously and be fueled online. With a capacity factor near 100%, the CANDU bums plutonium the quickest. Online fueling would also be very useful for putting the entire inventory through one reactor rapidly to self-protect the fuel. Because plutonium provides excess core reactivity, the core could be cooled and moderated with light water instead of heavy water. The large core also allows low power densities. However, this modified CANDU concept could have positive temperature coefficients of reactivity. Lack of experience with this concept is the main reason that it has not been studied further. 

A few results have been reported on the oxidation of cyclohexanol by acidic permanganate In the absence of added fluoride ions the reaction is first-order in both alcohol and oxidant , the apparent first-order rate coefficient (for excess alcohol) at 25 °C following an acidity dependence k = 3.5-1-16.0 [H30 ]sec fcg/A , depends on acidity (3.2 in dilute acid, 2.4 in 1 M acid) and D2o/ H20 is f-74. Addition of fluoride permitted observation of the reaction for longer periods (before precipitation) and under these conditions methanol is attacked at about the same rates as di-isopropyl ether, although dioxan is oxidised over twenty times more slowly. The lack of specificity and the isotope effect indicates that a hydride-ion abstraction mechanism operates under these conditions. (The reactivity of di-isopropyl ether towards two-equivalent oxidants is illustrated by its reaction with Hg(II).) Similar results were obtained with buffered permanganate. 

Attempts to hydrolyze S-b-MM under either acidic or basic conditions were unsuccessful. Reaction of S-b-MM with TsOH under the same conditions described by Brown and White (6) resulted in no reaction as evidenced by comparison of the 1H NMR and IR spectra of the product with that of the starting material. At the molecular weights and MM contents that we were working with, the S-b-MM was insoluble in the reaction medium, which may explain its lack of reactivity. Although the hydrolysis of methyl methacrylate under basic conditions is known to be quite sluggish, we nevertheless subjected S-b-MM to two days of reflux in aqueous THF in the presence of excess KOH. As expected, the product was spectroscopically identical to the starting copolymer. 

Having in hand reasonable quantities of these unique building blocks has allowed for the discovery of new reactions and therefore the synthesis of original compounds. Their lack of reactivity toward transition metal centers is probably due to the excessive steric hindrance about the car-bene center. 

Most metals vaporize as atoms, which are highly reactive as a result of the input of the heat of vaporization and the lack of steric restrictions. The basic strategy in metal atom synthesis is to codeposit the metal atoms with a large excess of reactant, thereby promoting reaction between the metal atom and the substrate and suppressing recombination to the bulk metal. As shown schematically in... 

Reactions 12a and 12b consume dissolved sulfide. This fact fits nicely with the data of White et al. (35), who could not detect free sulfide in their study. Dissolved sulfide is frequently absent in freshwater sediments (e.g., 39 see Urban, Chapter 10, for a discussion). This lack of sulfide is explained by an excess of reactive iron over the total sulfide concentration (19, 40). 

Exercise 22-11 Why do fairly reactive arenes, such as benzene, methyl benzene, and ethylbenzene, react with excess nitric acid in nitromethane solution at a rate that is independent of the concentration of the arene (i.e., zero order in arene concentration) Does this lack of dependence on arene concentration mean that nitration of an equimolar mixture of benzene and methylbenzene would necessarily give an equimolar mixture of nitrobenzene and nitromethy I benzenes Why or why not ... 

Holton claimed in a patent application that (3/ ,45)-A-benzoyl-3-0-EE-(3-lactam 11 (5 equiv), obtained through tedious classical optical resolution of racemic t (. -3-hydroxy-4-phenylazetidin-2-one, could be directly coupled with 7-TES-bac-catin III (8) in the presence of 4-dimethylaminopyridine (DMAP) and pyridine and the subsequent deprotection afforded paclitaxel in ca. 82% yield.54 Although this procedure was proved to work by us and by others, the use of a large excess of (3-lactam is obviously inefficient. Moreover, the Holton procedure did not work at all when /V-f-Boc-(3-lactam 12 was used for our attempted syntheses of docetaxel and its 10-acetyl analogue. This is due to the lack of reactivity of the A-r-Boc-(3-lactam 12 toward the C-13 hydroxyl group of a protected baccatin III under the Holton conditions. The lack of reactivity is ascribed to the substantially weaker... 

At this stage, two major observations still need to be accounted for the lack of reactivity of aliphatic substrates and the need for a five-fold excess of DEAD or DEAD-H2 over CuCl Phen to achieve quantitative oxidations of benzylic and allylic alcohols. 

The tantalum-benzyne complex (130) is much less reactive than other early transition-metal aryne complexes. It shows no reaction with acetone, benzophenone, benzaldehyde, acetonitrile, 3-hexyne, or methanol. The lack of reactivity of 130 was attributed to nonlability of the PMe3 ligand. Indeed, no phosphine exchange was observed when 130 was mixed with an excess of PMe3-d9. Refluxing 129 in a mixture of methanol and toluene (3 10 v/v) leads to clean formation of 131. This presumably results from reaction of a 16-electron benzyne complex with the alcohol. 

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