NMR investigation on the conformational properties of N-[2-pyridyl-N-oxide]-amino derivatives

The proton NMR spectra of N-[2-pyridyl-N-oxide]-derivatives of primary and secondary ethylamines, containing a substituent R on the C atom bearing the amino function, have been completely analysed in terms of the fundamental NMR parameters. The preferred conformations of the compounds investigated were established by the indications from NOE experiments as well as: (1) the long range coupling across the five bond between the aminic hydrogen and the proton in 4-position of the pyridine-N-oxide ring (⁵J_m^H,NH ～ 0·5 c/s), (2) the value of the vicinal coupling constant in the fragment CHNH (³J_NHCH ～ 7–9 c/s), (3) the large deshielding (Δτ ～ 1–1·5 ppm) observed for the resonance position of the proton on the asymmetric C atom in secondary amine derivatives with respect to the corresponding primary ones, and (4) the diamagnetic shielding produced on protons in position 3 and 4 of the pyridine-N-oxide ring by different aromatic groups introduced in the R substituent.The NMR data confirmed the preferred rotamers previously suggested on the basis of ORD and CD measurements.     

Thermodynamic properties of two metal-rich tantalum sulfides: Ta2S and Ta6S

The incongruent vaporization reactions of Ta₂S and Ta₆S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of P_S(obs) to equilibrium the enthalpies of the reactions $\text{3}\text{2}\text{Ta}{}_2\text{S(s)}\text{=}\text{1}\text{2}\text{Ta}{}_6\text{S(s) + S(g)}$ and Ta₆S = 6 Ta(s) + S(g) were found to be $\text{ΔH}{}^0{}_{298}\text{R}\text{= 53.0(0.3) · 10}{}^3\text{K}$ and $\text{ΔH}{}^0{}_{298}\text{R}\text{= 58.1(0.4) · 10}{}^3\text{K}$, respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation.     

Intensities of wagging and rocking bands of water in MnCl2 · 2H2O and CoCl2 · 2H2O

IR relative integrated intensities and half-widths of rocking (R) and wagging (W) bands of water in MnCl₂ · 2H₂O and CoCl₂ · 2H₂O are presented at 300 K and 120 K. Departure of observed intensity into D_W/D_R from those predicted by the fixed dipole model is attributed to anisotropic dynamic changes in dipole during these oscillations. A quantity representing the variation of this anisotropy between W and R oscillations is computed and its origin is discussed. An increase by 20% to 50% in both D_W and D_R on lowering the temperature has also been discussed.     

The stoichiometric hydrogenation of 9-methylidenefluorene and related compounds with hydridocobalt tetracarbonyl

9-Methylideneflourene (IIa) reacts rapidly with HCo(CO)₄ at -67° C to give a quantitative yield of 9-methylfluorene (IIIa); k₂  (13.4 ± 0.5) × 10^-2 l mol^-1_S^-1. Although the internal olefin, 9-ethylidenefluorene (IIb) reacts more slowly than IIa, it is hydrogenated about 2.5 times as fast as the terminal olefin, 1,1-diphenylethylene (I). Measurement of the rate of the reaction of IIb with DCo(CO)₄ and comparison with HCo(CO)₄ shows a very large inverse isotope effect k_H/k_D of 0.43.     

Flash photolysis resonance fluorescence study of the reaction Cl + O3 → ClO + O2 over the temperature range 213–298 K

Rate constants for the removal of Cl atoms in the reaction Cl + O₃ → ClO + O₂ were measured by the flash photolysis resonance fluorescence technique over the temperature range 213–298 K. The rate constant is given by the Arrhenius expression (2.94 ± 0.49) × 10^?11 exp[?(298 ± 39)/T] in units of cm³ molecule^?1 s^?1. Comparison with recent results from other laboratories are presented.     

Spinel, YbFe2O4, and Yb2Fe3O7 types of structures for compounds in the In2O3 and Sc2O3---A2O3---BO systems [A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, Cu, or Zn] at temperatures over 1000°C

In the Sc₂O₃---Ga₂O₃---CuO, Sc₂O₃---Ga₂O₃---ZnO, and Sc₂O₃---Al₂O₃---CuO systems, ScGaCuO₄, ScGaZnO₄, and ScAlCuO₄ with the YbFe₂O₄-type structure and Sc₂Ga₂CuO₇ with the Yb₂Fe₃O₇-type structure were obtained. In the In₂O₃---A₂O₃---BO systems (A: Fe, Ga, or Al; B: Mg, Mn, Fe, Ni, or Zn), InGaFeO₄, InGaNiO₄, and InFe³⁺MgO₄ with the spinel structure, InGaZnO₄, InGaMgO₄, and InAlCuO₄ with the YbFe₂O₄-type structure, and In₂Ga₂MnO₇ and In₂Ga₂ZnO₇ with the Yb₂Fe₃O₇-type structure were obtained. InGaMnO₄ and InFe₂O₄ had both the YbFe₂O₄-type and spinel-type structures. The revised classification for the crystal structures of AB₂O₄ compounds is presented, based upon the coordination numbers of constituent A and B cations.     

The predissociations of water ions

Experimental relative abundances of D₂O⁺, OD⁺ and D⁺ ions are given as functions of the initial energy of D₂O⁺ ions in the B?²B₂ state. The D⁺ ions are more abundant than expected on the basis of a recent theoretical model. Less kinetic energy is released in D⁺ formation than in OD⁺ formation, for the same excess energy available. It is suggested that OD⁺ formation should be modelled as a statistical reaction, whereas D⁺ formation is more specific. No detailed model can be suggested on present evidence, but it is pointed out that H₂O⁺ (B?²B₂) can be predissociated to OH⁺ by the X? state to H⁺ by the à state, as well as by repulsive states.     

Interaction of chloroform with aniline, o-toluidine and N,N-dimethyl aniline

Heats of mixing aniline, o-toluidine, and N,N-dimethyl aniline with chloroform have been determined by an adiabatic calorimeter. The results have been examined for molecular interactions between them, and they indicate that aniline and o-toluidine are associated through hydrogen bonds. Enthalpy of bond formation in a 1:1 complex has also been determined.     

Phosphorescence of thermally oxidised poly(butadiene) and model enones: temperature dependence

The temperature dependence of phosphorescence of model enone compounds in poly (methyl methacrylate) matrix and glassy methylcyclohexane/isopentane solution and of enones formed from thermal oxidation of poly (butadiene) has been studied over the temperature range 77–220°K. The single discontinuity in the plot for the model enone-glassy solvent is due to the freezing of a (solvent perturbed) barrier to rotation in the enone, and an analogous transition is also observed in the model enone poly (methyl methacrylate) samples and in thermally oxidised poly (butadiene). In the polymer matrices, a second transition corresponding to the γ-transition in poly (methyl methacrylate) and the glass transition temperature T_g in poly (butadiene) are also revealed in the Arrhenius plots. The results demonstrate that care must be taken in ascribing such discontinuities solely to polymer properties since intrinsic properties of the luminescence probe itself may exhibit similar features.     

Neutron diffraction study of the electrochemical passivation of nickel powder

With the aid of the Yamaoka mechanism and a.c. polarographic observables, rate constants for the homogeneous reduction of Co(III)pentammine complexes by Eu(II) are measured. Where comparison is possible, rate parameters obtained by this electrochemical procedure are found to be in good agreement with previous measurements by stopped-flow and pulse radiolysis procedures, with one exception. The order of reactivity for the halopentammineCo(III) complexes is found to follow the sequence RF²⁺>RCl²⁺>RBr²⁺>RI²⁺, where R=Co(III)(NH₃)₅³⁺. This and a pH dependence noted for the RF²⁺ case are suggestive of a predominantly inner sphere reaction pathway.