Beryllium substitution

Xe of adsorbed xenon 602 Pt of supported catalyst 604 ° T1 of thallium-containing Be of beryllium-substituted V of vanadium-containing catalysts 649 Ga of gallium-containing 656 La of lanthanum-substituted 677... 

Conroy and Perlow [235] have measured the Debye-Waller factor for W in the sodium tungsten bronze Nao.gWOs. They derived a value of/= 0.18 0.01 which corresponds to a zero-point vibrational amplitude of R = 0.044 A. This amplitude is small as compared to that of beryllium atoms in metallic beryllium (0.098 A) or to that of carbon atoms in diamond (0.064 A). The authors conclude that atoms substituting tungsten in bronze may well be expected to have a high recoilless fraction. 

Beryllium(II) is the smallest metal ion, r = 27 pm (2), and as a consequence forms predominantly tetrahedral complexes. Solution NMR (nuclear magnetic resonance) (59-61) and x-ray diffraction studies (62) show [Be(H20)4]2+ to be the solvated species in water. In the solid state, x-ray diffraction studies show [Be(H20)4]2+ to be tetrahedral (63), as do neutron diffraction (64), infrared, and Raman scattering spectroscopic studies (65). Beryllium(II) is the only tetrahedral metal ion for which a significant quantity of both solvent-exchange and ligand-substitution data are available, and accordingly it occupies a... 

The combination of toxic hazard and high price (itself in part due to the extra measures needed in production processes to ensure the workers safety) has been an effective brake on commercial development of beryllium chemistry. Where possible substitute, albeit less effective, materials are often used titanium as an alternate lightweight metal or carbon fiber composites, phosphor-bronzes in place of beryllium alloys, aluminum nitride in place of BeO (1). 

Stability Constants of Some Substituted Malonato and Related Beryllium(II) Complexes ... 

The superior coordinating capacity of phosphonate over carboxylate is illustrated in the 9Be NMR spectra in Fig. 25 (260). The similarity of the spectra obtained by reaction of BeS04 and methylphosphonic acid or phosphonacetic acid indicates that the carboxylate group is not bound to the beryllium under these experimental conditions. It should be noted that substitution of a water molecule by a phosphonate ligand causes the 9Be resonance to move upfield when it co-ordinates, as does the fluoride ion (271), the only other monodenate ligand... 

AlBeMet (beryllium—aluminum), 3 648-649, 649t, 650t Alberger process, 22 805 Alborixin, 20 131, 137 Albumin. See also Egg albumen as blood substitute, 4 111 processes, 12 146 properties of, 12 151t worldwide use of, 12 147-148 Alcalase, 10 252 Alcan multipolar cell, 15 337 Alcogel, 23 56... 

The resulting functional has been evaluated for the initial orbitals of the lithium and beryllium atoms given in Section 4.6. Using the same process of intra- and inter-orbit optimization carried out in Section 4.6, but substituting, in each step, the value for /(r) given by the Fade approximant obtained from Eq. (189), energy values were obtained for the Li and Be atoms that are indistingishable from those previously calculated with the exact values of/(r), namely, when Eq. (40) is solved. 

Beryllium in Plants and Animals. In 1888 F. Sestini found beryllium in land plants grown m soils containing it (92, 93). He found later that, although beryllium may take the place of magnesium as a nutrient for wheat, it is not a complete substitute for magnesium in the production of seed (93). Beryllium is occasionally present m bone (94). 

Sestini, F., "Experiments with wheat on the substitution of beryllium for... 

The amount of amorphous polymer, which is generally produced in small percentage (9-16%) contemporaneously with the non-atactic polymer, is independent of reaction time (see Table II). It is on the contrary closely connected with the nature of the catalytic system employed and changes, for instance, when the triethylaluminum is substituted by other metal alkyls (beryllium alkyls, propylaluminum, isobutylaluminum, etc.) 5,28). It also depends on the purity of the a-titanium trichloride, in particular increasing in the presence of other crystalline modifications of titanium trichloride [i.e. -TiCU (27)] and of titanium compounds obtained by reduction of titanium tetrachloride at low temperature with aluminum alkyls. 

Strontium has four naturally occurring isotopes (Table 4.2). It is a member of the alkaline earths (Group 2A) along with beryllium, magnesium, calcium, barium, and radium (Fig. 2.4). Strontium substitutes for calcium and is abundant in minerals such as plagioclase, apatite, and calcium carbonate. 

Complexes of related species such as keto acids, keto esters, and acetoacetanilides are known, particularly for beryllium.93 270 285 286,287 Bromination and nitration studies have been carried out on a wide range of -substituted N-acetoacetamides of beryllium and show introduction of bromo and nitro groups at the 3-position.285,286... 

Chemical Composition. Diamond is nominally pure carbon with a 12C 13C ratio of about 99 1. Although other elements are often reported in analyses, most are considered to be present in oxide, silicate, and sulfide phases as inclusions in the diamond. Only boron, nitrogen, and possibly beryllium are considered to be truly substitutional in the lattice. Hydrogen and oxygen, possibly as OH, may also be important structural contaminants though they may also be present as second-phase gases along with CO, C02, H20, CH4, and other species (20). 

In the above examples, the nucleophilic role of the metal complex only comes after the formation of a suitable complex as a consequence of the electron-withdrawing effect of the metal. Perhaps the most impressive series of examples of nucleophilic behaviour of complexes is demonstrated by the p-diketone metal complexes. Such complexes undergo many reactions typical of the electrophilic substitution reactions of aromatic compounds. As a result of the lability of these complexes towards acids, care is required when selecting reaction conditions. Despite this restriction, a wide variety of reactions has been shown to occur with numerous p-diketone complexes, especially of chromium(III), cobalt(III) and rhodium(III), but also in certain cases with complexes of beryllium(II), copper(II), iron(III), aluminum(III) and europium(III). Most work has been carried out by Collman and his coworkers and the results have been reviewed.4-29 A brief summary of results is relevant here and the essential reaction is shown in equation (13). It has been clearly demonstrated that reaction does not involve any dissociation, by bromination of the chromium(III) complex in the presence of radioactive acetylacetone. Furthermore, reactions of optically active... 

Cohall is added as a lower-cost substitute for beryllium. 

In all of, these cases substitution of the second alkyl can then occur to yield the dialkoxide or diphenoxide. This allowed the isolation of the monomeric beryllium phenoxide Be(OAr )2 (OAr = 2,6-di-t-butylphenoxide).98 The alkyls of the Group IV metals, MR (M = Ti, Zr, Hf), undergo rapid reactions with common alcohols and phenols yielding eventually the corresponding tetra-alkoxides or -phenoxides and four equivalents of alkane.97,100 With very bulky substituted alcohols or phenols the reactivity can be very sluggish, in some cases leading to only partial substitution (equation 28). 66,100... 

Some of the alternative TOF instrument designs involve replacing the beryllium filter with either a crystal or a mechanical chopper to monochromate the incident beam. With this change, the spectrometer can be used with a higher incident neutron energy (typically E 50 meV) so that a smaller momentum transfer Q is possible for 5 the same energy transfer (21,22). With a monochromatic incident beam, a beryllium filter is sometimes substituted for the chopper after the sample in order to increase the scattered intensity but with a sacrifice in the,minimum Q attainable. Energy transfers up to 100 meV (800 cm" ) can be achieved with TOF spectrometers at steady state reactors before the incident neutron flux is limited by the thermal spectrum of the reactor. (With hot moderators such as at the Institut Laue-... 

Aliphatic Substitution and the Walden Inversion. The rate of substitution of radioactive iodine into sec-octyl iodide in acetone was found to be the same as the rate of racemization of d-sec-octyl iodide by sodium iodide. The radioactive iodine was produced by bombardment with neutrons from 150 millicuries of radon mixed with beryllium and embedded in paraffin. 

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