Effects of H/D-isotope substitution and temperature on the volume characteristics of tetra-n-butylammonium bromide dissolved in methanol and its D-isotopomers

Densities of Buⁿ ₄NBr solutions in MeOH, MeOD, and CD₃OH were measured at salt concentrations of up to 1.5 solvomolality units (nearly 2.63·10^–2 mole fraction) at 278.15, 288.15, 298.15, 308.15, and 318.15 K. The limiting partial molar volumes of Buⁿ ₄NBr dissolved in these alcohols were calculated. The isotope effects in the volume characteristics of the stoichiometric mixture of ions, [Buⁿ ₄N⁺ + Br^–], are mainly due to the vibrational changes in the solvent structure upon deuteration of different molecular fragments. Structural transformations in infinitely dilute solution of Buⁿ ₄NBr in methanol are governed by non-specific solvation of the symmetrical Buⁿ ₄N⁺ cation.     

Ionization constants for deuterium oxide in deuterium oxide-organic mixtures

A potentiometric method using a glass electrode has been applied to determination of ionization constants for deuterium oxide (D₂O) in binary mixtures of D₂O with dioxane, tetrahydrofuran, acetone, dimethylsulfoxide, CH₃CH₂OD, and CH₃OD at 25°C. The results are compared with values of ionization constants for H₂O obtained previously in the corresponding H₂O-organic mixtures, and the isotope effect is shown to be small. Further calculations with the D₂O results show that the first five solvents mentioned above are neither appreciably acidic nor basic in D₂O solution, but that CH₃OD shows slightly acidic behavior (pK_a=16.0±0.3).     

19F and 1H NMR spectra of halocarbons

19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed.     

Ligand dynamics and reactivity in trimetallic clusters

The general relationships between trinuclear cluster reactivity and the ligand dynamical processes in these systems are explored. Three specific mechanistic studies are presented: (1) the rate and stereochemistry of ligand addition to ₃-imidoyl complexes, (2) the factors influencing the rate of carbon-hydrogen bond activation in ₃-alkyne complexes, and (3) the origin of anomalously large kinetic deuterium isotope effect in metal to ligand and ligand to metal hydrogen transfer in trinuclear and binuclear complexes. In all three cases, the current state of the mechanistic studies are summarized and the possible rate of specific ligand dynamical processes in controlling the mechanism are put forth.     

High-Temperature Proton Conductors Based on Strontium and Barium Cerates: The Interphase Exchange and Diffusion of Oxygen

Kinetic parameters of interphase exchange of oxygen in high-temperature proton conductors BaCe_0.95Nd_0.05O_3- and SrCe_0.95Y_0.05O_3- are determined using an isotope exchange method in the temperature range 630-820°C at oxygen pressures of 2.7-13.3 gPa and diffusion coefficients for oxygen are calculated. Effective energies of activation of oxygen exchange and diffusion coefficients for oxygen are calculated. Dependence of exchange characteristics and the diffusion coefficients on the oxygen pressure in the gas phase is investigated. The oxygen exchange on the surface of studied oxides is shown to proceed only with the participation of oxygen of the oxides, which causes high rates of interphase exchange of oxygen of studied cerates of barium and strontium. It is shown that the obtained data satisfactorily agree with those found in the relevant literature.     

Mechanistic investigation of the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes

The mechanism for the 2,5-diphenylpyrrolidine-catalyzed enantioselective alpha-chlorination of aldehydes with electrophilic halogenation reagents has been investigated by using experimental and computational methods. These studies have led us to propose a mechanism for the reaction that proceeds through an initial N-chlorination of the chiral catalyst-substrate complex, followed by a 1,3-sigmatropic shift of the chlorine atom to the enamine carbon atom. The suggested reaction course is different from previously proposed mechanisms for organocatalytic enamine reactions, in which the carbon-electrophile bond is formed directly. Furthermore, the rate-determining step in the overall reaction was determined and the presence of nonlinear effects was probed.     

Investigations with the finite element method on the Cyber 205

We are trying to investigate systematically the application of the finite element method (FEM) for solving the Schrödinger equation. The present paper is devoted to the calculation of vibrational transition probabilities for the collinear reactive system A + BC (i.e. H+H₂ and their isotopes). The calculations are fully two-dimensional and the results are compared with earlier FEM calculations and conventional basis set expansion methods using the the R-matrix or S-matrix propagation.We made extensive analysis of FEM on the vector-computer Cyber 205 and developed a vector code for the efficient use in two dimensions, so that in the near future applications even in three dimensions will be possible.For the hydrogen exchange reactions we investigated the following isotope combinations: (a) H + H₂, b) H + DH, D + HD and H + MuH (symmetric reaction), (c) D + HH, H + DD and Mu + DD (asymmetric reaction). We calculated the transition probabilities for up to five open vibrational channels and found excellent agreement with known exact values.     

The kinetics of reaction of 4-nitrophenylnitromethane with N’-Propyl-N,N-dipropylbenzimidamide in aprotic solvents. a steric effect on tunneling

Thermodynamic and kinetic parameters have been established for the reaction between the carbon acid, 4-nitrophenylnitromethane, (4-NPNM), and the base N’-n-propyl-N,N-di-n-propylbenzimidamide, (N’PDPBA), in mesitylene and in chlorobenzene. In some cases deuteron transfer from 4-(D₂)NPNM to the base has also been studied. In addition, some results for the proton transfer reaction in tetrahydrofuran have been collected. Spectrophotometric methods have been employed to monitor the ion-pair product, which is solvatochromic. In general the solvent dependence of the parameters is as expected, but there is some indication of specific solvation. The kinetic isotope effects of 11 and 8 in mesitylene and chlorobenzene, respectively, are larger than those predicted classically. However, as is discussed the n-propyl group on the secondary nitrogen of the base may serve to reduce the extent of tunneling compared to that in an unsubstituted analogue by a steric effect.     

THEiEARLY JINNING JUVENILE CONTINENTAL CRUST TRANSFORMATION TYPE GRANITOIDS FROM SOUTHERN ANHUI PROVINCE, CHINA

It is considered that the early Jinning period granitoids from southern Anhui Province belong to the continental crust transformation (S) type and have their own characteristics which are different from those for general continental crust transformation type granitoids. They were formed at the early stage of the late Proterozoic era when that region was at an island-arc stage of the continental margin environment. By that time the continental crust was just formed and had a nature of juvenile crust. It is this juvenile crust that determined a series of characteristics of that type granitoids and made them a relatively independent rock type. They are the products formed by the continental crust in a certain stage of development.