Constant Valence Research Articles

Some mechanisms of catalytic direct and oxidative chlorination of propylene

1. The order of activity of the catalysts was found: CuCl2 > FeCl3> CoCl3 > CrCl3, which is in agreement with the similar dependence of their activity on the M-C1 binding energies for the reactions of direct and oxidative chlorination of propylene. 2. Differences were established in the character of the effect of inhibitors on the rate of the reactions of direct and oxidative chlorination of propylene on metal chlorides of constant and variable valence. 3. The kinetic parameters of the reactions of direct and oxidative chlorination of propylene on metal chlorides were found. The kinetic equations for the processes on Lid are identical to the reaction of free radical chlorination of propylene. For CuCl2, a radical mechanism with a small chain length is most probable.

High temperature behaviour of the mixed valence compounds EuCu 2Si 2, YbCu 2Si 2 and the reference compounds CaCu 2Si 2 and GdCu 2Si 2

Some physical properties (thermal expansions, magnetic susceptibilities and heat contents) of EuCu 2Si 2, YbCu 2Si 2 and reference compounds CaCu 2Si 2 and GdCu 2Si 2 have been measured in the temperature range 300–1000 K. The results obtained together with previous findings show that the valence of EuCu 2Si 2 is strongly dependent on T (valency, 2.9 at 100 K to 2.3 at 1000 K) while YbCu 2Si 2 maintains an almost constant valence value of 2.85, at least from 300 to 1000 K. For EuCu 2Si 2 an approximate determination of the energy required in the electronic process involved is also presented.

On the chemistry and mineralogy of boron in pure and in mixed systems: A review

Abstract Boron (B) is the third member of the third periodic group. It is a nonmetal with an atomic number of five and a constant valence of 3+. Boric acid [B(OH)3]and H2Bo3 − are the most common geologic forms of B, with boric acid the predominant form of B in agricultural soils. Boron occurs mainly in silicate minerals. The 10 μg/g B concentration of the earth's crust is distributed among common rock types. Less than five percent of total soil B is available for crop uptake. This helps to explain the occurrence of B deficiency in 41 of the 50 states. The availability of soil B depends on soil texture, pH, and soil moisture content. A number of soil components have shown an affinity for B. These include Al‐ and Fe‐ hydroxy compounds, ferromagnesian minerals found in sand and silt separates, Al‐ and Fe‐ oxides, and organic matter. Studies have shown B adsorption to increase with increasing pH. Boric acid predominates at pH values less than 7.0 and borate ions predominate in solutions of higher pH. Boron a...

An Investigation of Charge Effects on NMR. Coupling Constants. The Charge Induced Variation of s‐Densities at the Nucleus

AbstractThe dependence of the ns‐density at the nucleus, | ψ ns (0) | 2, on atomic number and charge is examined for the elements helium to radon. The validity of the widely used assumption of a constant valence s‐density at the nucleus, as well as the statement that metal‐phosphorus NMR. coupling constants, 1J (M,P), are strongly influenced by contraction of the phosphorus 3 s orbital is critisized. A possible explanation by rehybridisation within an MO‐framework is offered instead.

Force constant calculations—III

Abstract Forms of the Urey-Bradley-Simanouti force field and a four constant valence field have been investigated for phosphorous trimethyl which for this purpose has been regarded as R3P where R has mass 15. A computer programme has been used to converge on best values of force constants for selected values of the rcRPR interbond angle in the range 100° to 109° 28′. For angles in the range 100–106° converged values of the constants are obtained from reasonable initial guesses. The values are surprisingly sensitive to the interbond angle chosen. For angles of 108° and above oscillation and not convergence is obtained. It is shown that these oscillations arise from the absence of real solutions in the neighbourhood of the initial guesses. A more detailed examination of the force fields for the various interbond angles shows: (i) that for 109° 28′ there are two sets of real solutions for the force constants in other regions which can be reached by the computer programme if the initial guesses are appropriate but these are physically unacceptable, (ii) that for angles 100°–106° there are regions where no convergence will be obtained if the intitial guesses are inappropriate and (iii) that for angles 100°–106° a second set of real solutions can be obtained which is no less appropriate than the first.