Inter-ring rotational potential of biphenyl and its effect on poly(p-phenylene)

Detailed ab initio studies have been done on the inter-ring torsional states of the biphenyl molecule using self-consistent field molecular orbital method. The potential goes through a minimum at an angle of 38°. The height of the potential barrier for the coplanar state is 2.01 kcal/mol. When the phenyl rings are perpendicular to each other, this height increases to 2.37 kcal/mol. The role of correlation and polarization is found to be important. The shape of the potential suggests that polyparaphenylene may possibly exist as a super helix.     

Extraction spectrophotometric determination of cobalt and nickel using ethylthioxanthate

A spectrophotometric method for the determination of cobalt and nickel using a new reagent sodium ethylthioxanthate has been described. The yellow-colored cobalt complex and red-colored nickel complex have been extracted quantitatively using carbon tetrachloride in the pH ranges 4.0–11 and 4.0–6.7, respectively. The colors of these complexes are stable and absorbances have been measured at 389 nm for cobalt and 495 nm for the nickel complexes. Few ions interfere but the method has been applied successfully for the determination of these metal ions in various complex materials.     

Phthalocyanines as oxidation-reduction indicators

Summary Copper phthalocyanine tetrasulphonic acid has been found to work satisfactorily as an inside indicator in the cerimetric titration of hydro-quinone and metol. It has the advantage that the indicator correction in titrations with 0.01 N solutions of ceric sulphate is much less than with the ferroin indicator, amounting to only 0.02 ml for two drops of the indicator solution.Part II: See Z. analyt. Chem. 163, 1 (1958).     

1,3,4-oxadiazolin-2-ones from carbo-t-butoxyhydrazones

5-Substituted-1,3,4-oxadiazolin-2-ones 2 were synthesized by the oxidation of carbo-t-butoxyhydrazones 1 of aromatic aldehydes with lead tetraacetate or, preferably, iodosobenzene diacetate. In some instances 5-acetoxy-1,3,4-oxadiazoles 3 were obtained along with 2 . The oxidation of carboethoxyhydrazones 4 gave 2-ethoxy-1,3,4-oxadiazoles 5 .     

A Note on the Indirect Controls for a Coupled System of Wave Equations

By a procedure of successive projections, the authors decompose a coupled system of wave equations into a sequence of sub-systems. Then, they can clarify the indirect controls and the total number of controls. Moreover, the authors give a uniqueness theorem of solution to the system of wave equations under Kalman’s rank condition.     

Influence of crystallite size on acetone hydrogenation over copper catalysts

Acetone hydrogenation was studied over a family of Cu/SiO2 catalysts as well as UHP Cu powder and a Cu chromite catalyst. Oxygen chemisorption via dissociative N2O adsorption was used to count surface Cu atoms and calculate crystallite sizes, and a microwave absorption technique was used to measure the electrical conductivity of these Cu particles. Under differential reaction conditions at 423 K and 1 atm, all catalysts exhibited deactivation on stream and activities were typically 10-20% of their initial values after 3-4 h on stream. However, initial turnover frequencies (TOFs) varied from 0.056 s(-1) on the most highly dispersed Cu catalyst to 0.50 s(-1) on Cu powder, with the highest TOF of 2.4 s(-1) occurring on 110 nm crystallites. A similar trend with a broader (80-fold) variation was observed in the "steady-state" TOF values. Apparent activation energies varied between 11 and 14 kcal/mol. These initial TOF values are in good agreement with previous results, and a correlation exists between TOF and Cu crystallite size in this reaction, which appears to be structure sensitive. In addition, the electrical conductivity of these dispersed Cu nanoparticles, which was always less than that of bulk Cu, also increased with increasing Cu crystallite size; consequently, the change in this parameter may offer a possible explanation for the increase in TOF.     

Spectrophotometric determination of ziram (dithiocarbamate fungicide) by thiocyanate and rhodamine 6G method

A sensitive spectrophotometric method has been developed for the determination of ziram in water, vegetables and grains. The method is based on the dissociation of dithiocarbamate complex of zinc with thiocyanate and rhodamine 6G at pH 4 to form a pink coloured complex that is stabilized by gelatin. The method is simple and Beer's law is obeyed over the concentration range of 0.05-1 ppm of ziram. The method is free from interference of similar dithiocarbamate fungicides containing Mn(2+) and Fe(3+) ions.     

Magnetic properties of amorphous Mn x B100−x alloys

Magnetic properties of amorphous Mn _x B_100–x alloys ranging fromx = 30 to 70 under high magnetic fields and low ac magnetic fields in the temperature range from 4.2 K to room temperature have been investigated. Samples which have Mn concentrations of aboutx = 40–60 show spin-glass-like properties in the low-temperature region. This spin-glass characteristics result from a frustration in the spin system which is caused by the competition of ferromagnetic and antiferromagnetic interactions between randomly distributed Mn atoms. Both magnetization at 4.2 K and paramagnetic momentP _eff as a function of Mn concentration show a peak aroundx 44 which drops rapidly towards both sides of the Mn content.     

Nonresonant third-order susceptibility measurements in the nematic liquid crystal K18

We have observed a large nonresonant third-order nonlinear susceptibility, X ⁽³⁾ (-; , 0, 0) in the isotropic phase of a nematic liquid crystal 4-n-hexyl-4-cyanobiphenyl (K18). The highest value of X ⁽³⁾ obtained at 632.8 nm is 1.16274×10^-18 m²V^-2 corresponding to a temperature 29.3°C. The observed second-order pretransitional temperature T ^* from our measurements is 1.2°C below the first-order nematic to isotropic transition temperature. The dependence of the Kerr constant on (T-T ^*)^-1 is found to be in good agreement with the predictions of the Landau-de Gennes model.