Phosphorous-centered studies

Harger has studied the rearrangement of A-substituted N-phosphinoylhydroxylamines in the presence of base . He proposed a concerted mechanism based on the observed retention of the configuration at the phosphorous center during the transposition , and on studies with 0-labelled compounds . Similar cyclic transition states 572 were proposed in the base-induced rearrangement of A,0-bis(diphenylphosphinoyl)hydroxylamines (571) (equation 254). However, in the rearrangement of O-benzoyl-A-(diphenylphosphino-thiol)hydroxylamine where a transposition of O and S atoms occurs, the proposed cyclic transition state has sulfur participation . 

The (TMS)3SiH mediated addition of phosphorus-centered radicals to a number of alkenes has been investigated in some detail. Reaction (73) is an example of phosphorous-carbon bond formation using four structurally different phenylseleno derivatives with 3 equiv of (TMSlsSiH and AIBN in refluxing benzene for 2h. Comparative studies on the reaction of the four phosphorus-centered radicals have been obtained. Although the reaction with 1-methylene cyclohexane is efficient with all four derivatives, different selectivity is observed with electron-rich or electron-poor alkenes. 

The most important mineral example is natural scheelite. ScheeUte emits a bright blue emission in a broad band centered at 425 nm (Fig. 4.9) with a decay time of several ps. Calcium tungstate CaW04 has long been known as a practical phosphor, and has been carefully studied. The intrinsic blue luminescence center is the complex ion in which the central W metal ion is... 

Starting from the optimized configuration of hydrogenated nanocrystals (described in Section 3.1.1), the self-consistent electronic response to an impurity atom has been studied. The screening has been studied introducing a substitutional phosphorous ion (P+) at the nanocrystal center. The electron density induced by the impurity, into a nanocrystal with n Si and m H atoms, is calculated as [123,124]... 

Abstract Transition metal carbides and phosphides have shown tremendons potential as highly active catalysts. At a microscopic level, it is not well understood how these new catalysts work. Their high activity is usually attributed to ligand or/and ensemble effects. Here, we review recent studies that examine the chemical activity of metal carbides and phosphides as a function of size, from clusters to extended surfaces, and metal/carbon or metal/phosphorous ratio. These studies reveal that the C and P sites in these compounds cannot be considered as simple spectators. They moderate the reactivity of the metal centers and provide bonding sites for adsorbates. 

To study the interaction of functional groups in close proximity zn-cyclopha-nes [59] are good model systems. The C-H group in 95 directs to the center of the aromatic ring leading to a proton NMR shift of 6 = -4.03. Heteroatoms, such as silicon or phosphorous [60], were also incorporated to study their interaction with the 7r-system. 

Almost all the published work on R-activated KCl deals with Eu activators, and very little was done on other KC1 R phosphors. Balraj and Veeresham (1992) describe the optical absorption and the TL of KChPr (1062 ppm). The glow curve of RT X-irradiated crystals exhibited TL peaks at 358, 393 and 453 K (heating rate 30Kmin ). These peaks were also observed in pure KCl and so they are not related to Pr. It seems from the results that the Pr enhances the TL, an effect that has to be confirmed by additional measurements. The TL of KCl Gd + was studied by Vijayan and Murti (1989). It showed peaks at 381, 407 and 478 K and an emission band at 2.61 eV with a shoulder at 2.76 eV All the TL peaks were found to be related to Z centers. 

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