RELATIONSHIPS BETWEEN X—H STRETCHING OVERTONE FREQUENCIES AND BOND LENGTHS/BOND ANGLES

A relationship between the X-H (X = N, O, C, and so on) equilibrium bond length in a Morse oscillator and the X-H stretching overtone frequency shifts is obtained theoretically. We use the equation to discuss the empirical linear relationships that have been proposed for heterocyclics, alkanes and fluorinated benzenes. On the other hand, a unified relationship between the X-H bond angles and the experimental quantities (ω(?) and the coupling strength λ) is also presented for XH2, XH, and XH4 molecules or molecular fragments. Calculations of X-H bond angles for a number of molecules show that the results from our equations are in excellent agreement with the experimental values. Also we can extract the information of relative magnitude of bond coupling force field.     

Melt‐state polymer chain dimensions as a function of temperature

The unperturbed chain dimensions (〈R²〉_o/M) of cis/trans‐1,4‐polyisoprene, a near‐atactic poly(methyl methacrylate), and atactic polyolefins were measured as a function of temperature in the melt state via small‐angle neutron scattering (SANS). The polyolefinic materials were derived from polydienes or polystyrene via hydrogenation or deuteration and represent structures not encountered commercially. The parent polymers were prepared via lithium‐based anionic polymerizations in cyclohexane with, in some cases, a polymer microstructure modifier present. The polyolefins retained the near‐monodisperse molecular weight distributions exhibited by the precursor materials. The melt SANS‐based chain dimension data allowed the evaluation of the temperature coefficients [dln 〈R²〉_o/dT(κ)] for these polymers. The evaluated polymers obeyed the packing length (p)‐based expressions of the plateau modulus, G = kT/np³ (MPa), and the entanglement molecular weight, M_e = ρN_anp³ (g mol^?1), where n_t denotes the number (～21) of entanglement strands in a cube with the dimensions of the reptation tube diameter (d_t) and ρ is the chain density. The product np³ is the displaced volume (V_e) of an entanglement that is also expressible as pd or kT/G. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1768–1776, 2002     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part VII: Cyclodextrins with an inverse substitution pattern – synthesis and enantioselectivity

Transferring the site of specific substitution of dipentylated cyclodextrins with methyl or acyl residues from the secondary 3-hydroxyl group to the primary 6-hydroxyl group was expected to provide new information on the mechanism of chiral recognition. The 3-position points towards and the 6-position points away from the cyclodextrin cavity which via inclusion complex formation is supposed to play a major role in chiral separation. The “inverse” 6-O-acyl-2,3-di-O-pentyl-cyclodextrins displayed almost no enantioselectivity but the corresponding 6-O-methyl derivatives are a versatile supplement to the chiral capillary GC phases nowadays available. Among the compounds that could be enantiomerically resolved are alcohols, amino acids, alkyl halides, bicyclic ethers, acetals, olefins, other hydrocarbons and chiral pharmaceuticals.     

Correlation analysis of quantum chemical data and the polarizability effect in H-complexes

The study is concerned with analysis of the energies of formation (E), frequency shifts (Δν) in IR spectra, ionization potentials (IP) of H-complexes, hydrogen bond lengths (r), and spin densities (sd) in H-complexes involving radical cations, obtained from quantum chemical calculations for 20 series of H-complexes. It was for the first time established that the E, IP, r, and sd values and the changes in enthalpy (δH) depend not only on the inductive and resonance effects but also on the polarizability effect of the substituents bound to the donor and acceptor centers in the H-complexes. Interrelations between the polarizability effect and the molecular structure of H-complexes are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 602–608, April, 2006.     

Zur kenntnis ‚Kationen-reicher’︁ Tantalate und Niobate Über Na5TaO5 und Na5NbO5

On Tantalates and Niobates ‘rich in Cations’. On Na₅TaO₅ and Na₅NbO₅ Colourless, transparent single crystals of Na₅TaO₅ [annealed mixtures of Na₂O, Li₂O, and Ta₂O₅, Na : Li : Ta = 6.6 : 1.1 : 1, Ni-cylinder, 1000°C, 75 d] as well as Na₅NbO₅ [annealed mixtures of Na₂O, Li₂O, and Nb₂O₅, Na : Li : Nb = 6.6 : 1.1 : 1, Ni-cylinder, 1000°C, 75 d] have been prepared. Single crystal data show that both isotypic oxides represent a deformed variant of the NaCl-type of structure [Na₅TaO₅: 1154 from 1250 I₀ (hkl), four-cycle diffractometer Philips PW 1100, ω2-θ scan, Ag? Kα , R = 4.88%, space group c2/c with a = 629.3(1) pm, b = 1025.4(2) pm, c = 1004.6(2) pm, b? 106.80(2)°, z = 4 and Na₅NbO₅: 998 from 1247 I₀(hkl), four-cycle diffractometer Philips PW 1100, ω-2θ scan, Ag? Kα , R = 8.58% and R_w = 7.67%, space group C2/2 with a = 629.1(1) pm, b = 1024.4(2) pm, c = 1004.2(2) pm, b? = 106.80(2)°, Z = 4]. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, the latter derived from Mean Effective Fictive Ionic Radii, MEFIR, as well as Charge Distribution, CHARDI, are calculated.     

连接基团链长度对季铵盐二聚表面活性剂C12-s-C12·2Br在水溶液中胶团化行为的影响

用电导法、稳态荧光法和粘度法研究了二聚表面活性剂C12-s-C12*2Br分子中的连接基团链长度(s=2, 3, 4, 6)对其在水溶液中聚集行为的影响. 实验发现, C12-s-C12*2Br的胶团生成能力远比其单体C12TABr强得多, 前者cmc值较后者降低一个数量级. 胶团聚集数N随表面活性剂浓度c的增大而增大, 其中当s=2时的N值在c=7.7 mmol/L后开始急剧增大. 计算结果表明, 此时胶团形状发生了明显变化, 形成了椭球形的胶团. 粘度测定结果也证实了这一点.     

Dissipative structures formed in the course of drying the colloidal crystals of silica spheres on a cover glass

Macroscopic and microscopic dissipative structural patterns formed in the course of drying the deionized aqueous colloidal crystal suspensions of silica spheres (diameter: 103 nm) on a cover glass have been observed. Spoke-like and ring-like patterns are formed in the macroscopic scale; the former is the crack in the sphere film and the latter is the hill accumulated with spheres formed around the outside edge. The neighbored inter-spoke angle, thickness of the film, and other morphological parameters have been discussed as a function of sphere concentration, concentration of sodium chloride, and the inclined angle of the cover glass. Fractal patterns of the mud cracks are observed in the microscopic scale. Capillary forces between spheres at the air-liquid surface and the relative rates between the water flow at the drying front and the convection flow of spheres are important for the pattern formation. Electronic Publication     

N6H6结构和性质的理论研究

采用密度泛函理论的b3lyp方法在6-311＋＋G**基组上对15种分子式为N₆H₆的氮氢化合物进行了理论计算, 并且应用了自然键轨道理论(Nature Bond Orbital, NBO)和分子中的原子理论(Atoms In Molecules, AIM)分析了这些化合物的成键特征和相对稳定性. NBO分析表明N原子孤对电子到相邻的氮氮键的超共轭作用是影响氮氮键长变化的主要因素, AIM计算的氮氮键的键临界点电荷密度与键长呈反比关系. 而且, NBO的立体和超共轭分析表明立体交换排斥能和超共轭作用对这些分子的相对稳定性起了重要作用. G3MP2计算结果表明氮氢化合物的生成热均为正, 并且环状分子的能量和生成热都高于链状分子.     

Study of Densities, Viscosities and Ultrasonic Speeds of Binary Mixtures Containing 1,2-Dimethoxyethane and an Alkan-l-ol at 298.15 K

The viscosity deviation (Δη), the excess molar volume (V ^E) and the ultrasonic speed (u) have been investigated from viscosity (η) and density (ρ ) measurements of binary liquid mixtures of 1,2-dimethyoxyethane with methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, hexan-1-ol or octan-1-ol over the entire range of composition at 298.15 K. The excess volumes are negative over the entire range of composition for all of the mixtures with the exception of hexan-1-ol and octan-1-ol. The excess isentropic compressibilities (K _S ^E) and viscosity deviations are negative for all of the mixtures. The magnitudes of the negative values of V ^E decrease with the number of carbon atoms of the alkan-1-ol. The trend of increasing K _S ^E values with the chain length of the alkanol is similar to that observed in the case of V ^E. Graphs of V ^E, Δ η, K _S ^E, Δ u, L _f ^E and Z ^E against composition are presented as a basis for a qualitative discussion of the results.     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.