Interactions direct

Between the limits of small and large r, the pair distribution function g(r) of a monatomic fluid is detemrined by the direct interaction between the two particles, and by the indirect interaction between the same two particles tlirough other particles. At low densities, it is only the direct interaction that operates through the Boltzmaim distribution and... 

The concept of the potential of mean force can be extended to mixtures and solutions. Consider two ions in a sea of water molecules at fixed temperature T and solvent density p. The potential of mean force w r) is the direct interaction between the ions u.j r) = plus the interaction between the ions tln-ough water... 

Because the neutron has a magnetic moment, it has a similar interaction with the clouds of impaired d or f electrons in magnetic ions and this interaction is important in studies of magnetic materials. The magnetic analogue of the atomic scattering factor is also tabulated in the International Tables [3]. Neutrons also have direct interactions with atomic nuclei, whose mass is concentrated in a volume whose radius is of the order of... 

Niehus H, Spitzl R, Besocke Kand Comsa G 1991 N-induced (2 x 3) reconstruction of Cu(110) evidence for long-range, highly directional interaction between Cu-N-Cu bonds Phys. Rev. B 43 12 619-25... 

Ethyl a-bromopropionate. This preparation illustrates the facile bromination of an acid chloride (propionyl chloride) in the presence of red phosphorus, and the subsequent conversion of the bromoacid chloride into the ethyl ester by direct interaction with ethanol. 

Turning the argument around reactions that do not involve proton transfer steps will only experience a significant effect of the Lewis acids if a direct interaction exists between catalyst and reactant. The conventional Diels-Alder reaction is a representative of this class of reactions. As long as monodentate reactants are used, the effects of Lewis acids on this reaction do not exceed the magnitude expected for simple salt effects, i.e. there are no indications for a direct interaction between Lewis-acid and substrate. 

We conclude that, when employirg hard Lewis-acids in aqueous solution, the term Lewis-acid catalysis should be used with caution, and only after evidence for a direct interaction between Lewis-acid and substrate has been obtained. 

In Chapter 6 we survey what has been accomplished and indicate directions for future research. Furthermore, we critically review the influence of water on Lewis acid - Lewis base interactions. This influence has severe implications for catalysis, in particular when hard Lewis acids and bases are involved. We conclude that claims of Lewis-acid catalysis should be accompanied by evidence for a direct interaction between catalyst and substrate. 

The real value of direct interaction between a lecturer and his audience is in the interest he can aronse by presenting the topic in a challenging and perhaps personal way as well as in the give-and-take interaction of direct exchange and participation. I have always tried in my lectnres to give my stndents not only a presentation of facts and concepts, but, based on my own experience and involvement, to convey to them the fascination of exploring the intrigning world of chemistry. 

There are three advantages to study molecular recognition on surfaces and interfaces (monolayers, films, membranes or soHds) (175) (/) rigid receptor sites can be designed (2) the synthetic chemistry may be simplified (J) the surface can be attached to transducers which makes analysis easier and may transform the molecular recognition interface to a chemical sensor. And, which is also a typical fact, this kind of molecular recognition involves outside directed interaction sites, ie, exo-receptor function (9) (see Fig. 5b). 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

Rhenium hexafluoride is readily prepared by the direct interaction of purified elemental fluorine over hydrogen-reduced, 300 mesh (ca 48 pm) rhenium powder at 120°C. The reaction is exothermic and temperature rises rapidly. Failure to control the temperature may result in the formation of rhenium heptafluoride. The latter could be reduced to rhenium hexafluoride by heating with rhenium metal at 400°C. 

Rhenium heptafluoride [17029-21 -9], ReF, is obtained by the direct interaction of elemental fluorine with hydrogen-reduced rhenium powder at 400°C and slightly over atmospheric pressure of fluorine. It is a pale yeUow soHd, mol wt 319.19 mp, 48.3°C and bp, 73.7°C. 

A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

Chlorides. Anhydrous ThCl [10026-08-1] has usually been prepared by direct interaction of thorium metal, hydride, or carbide with chlorine. 

Bromides and Iodides. The red-brown tribromide, UBr [13470-19-4], and the black tniodide, Ul [13775-18-3], may both be prepared by direct interaction of the elements, ie, uranium metal with X2 (X = Br, I). The tribromide has also been prepared by interaction of UH and HBr, producing H2 as a reaction product. The tribromide and tniodide complexes are both polymeric soflds with a local bicapped trigonal prismatic coordination geometry. The tribromide is soluble in H2O and decomposes in alcohols. 

The presence of metal salts, particularly those containing alkaline-earth cations and/or haUdes, cause some shifts in the polyborate equiUbria. This may result from direct interaction with the boron—oxygen species, or from changes in the activity of the solvent water (63). 

Fig. 13. The stmctures of closo metallaboranes where O represents BH , CH (a) [< /(9j 0-( q -C H )Ni(B22H22)] (b) closo-l]l-[v[-Q ]) -l]l-53i] pri Closo metallaboranes can also be formed by the direct interaction of polyborane and metal carbonyl clusters. For example.

In general, esters having equilibrium constants below unity are not prepared by direct interaction of alcohol and acid in these cases, the acid anhydrides or acid chlorides are used, since the equiUbrium favors the ester product. 

Pd(II) was shown to be separated from Ni(II), Cr(III) and Co(III) by ACs completely, and only up to 3 % of Cu(II) and Fe(II) evaluate from solution together with Pd(II), this way practically pure palladium may be obtained by it s sorption from multi-component solutions. The selectivity of Pd(II) evaluation by ACs was explained by soi ption mechanism, the main part of which consists in direct interaction of Pd(II) with 7t-conjugate electron system of carbon matrix and electrons transfer from carbon to Pd(II), last one can be reduced right up to Pd in dependence on reducing capability of AC. 

Deposits cause corrosion both directly and indirectly. If deposits contain corrosive substances, attack is direct interaction with the aggressive deposit causes wastage. Shielding of surfaces below deposits produces indirect attack corrosion occurs as a consequence of surface shielding provided by the deposit. Both direct and indirect attack may involve concentration cell corrosion, but indirect attack almost always involves this form of corrosion. 

Underdeposit corrosion is not so much a single corrosion mechanism as it is a generic description of wastage beneath deposits. Attack may appear much the same beneath silt, precipitates, metal oxides, and debris. Differential oxygen concentration cell corrosion may appear much the same beneath all kinds of deposits. However, when deposits tend to directly interact with metal surfaces, attack is easier to recognize. 

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