Influence of the OH groups of hydroxylated rutile (110) surface on the Lewis acidity: an investigation of CO adsorption by quantum-mechanical simulations

The adsorption of carbon monoxide on a clean and hydroxylated rutile (110) surface has been investigated using a periodic approach at DFT/B3LYP level. The hydroxylated surface was modelled by considering both terminal and bridging OH groups. The variation of the electrophilicity of the Lewis acid site near these groups was evaluated by taking into account the adsorbate–substrate distance, the magnitude of the interaction energy and the blue-shift of the adsorbed CO stretching frequency. The results obtained suggest that the electrophilicity increases in proximity to OH terminal groups, and decreases near the OH bridging groups.     

Gas‐phase studies of copper catalyzed aerobic cross coupling of thiol esters and arylboronic acids

Electrospray ionization/mass spectrometry (ESI‐MS) is used to monitor a Cu‐catalyzed aerobic cross‐coupling reaction between thiol esters and arylboronic acids. The ESI spectra show the formation of Cu‐complexes with the starting thiol ester 1 and the coupling product. The formation of an ionic complex at m/z 305 is observed, most likely occurring upon the elimination of a mixed anhydride from [(1)CuOAc]⁺. An online monitoring of the reaction using ESI‐MS was carried out allowing calculation of rate constants and thermodynamic parameters (ΔH^?, ΔS^?, and ?G^?) for the title reaction.     

A Definitive Example of Aluminum-27 Chemical Shielding Anisotropy

Solid-state²⁷Al NMR spectra have been obtained for a crystalline 1:1 complex of AlCl₃and OPCl₃. Aluminum chloride phosphoryl chloride, AlCl₃· OPCl₃(1), is unusual in that the Al–O–P bond angle is close to 180°. From analysis of the²⁷Al MAS NMR spectra, it was determined that the²⁷Al nuclear quadrupole coupling constant is 6.0(1) MHz, the asymmetry in the electric field gradient (efg) tensor is 0.15(2), and the isotropic chemical shift, δ_iso(²⁷Al), is 88(1) ppm. Solid-state²⁷Al NMR of a stationary sample reveals a line shape affected by a combination of anisotropic chemical shielding and second-order quadrupolar interactions. Analysis of this spectrum yields a chemical shift anisotropy of 60(1) ppm and orientations of the chemical shift and electric field gradient tensors in the molecular frame. Experimental results are compared with those calculated usingab initioHartree–Fock and density functional theory.     

Gas‐phase acidity of bis[(perfluoroalkyl)sulfonyl]imides. Effects of the perfluoroalkyl group on the acidity

The gas‐phase acidity (GA) values were determined for a number of perfluoroalkyl‐substituted sulfonylimides by measuring proton‐transfer equilibria using a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The GA scale below 286.5 kcal mol^?1 for (CF₃SO₂)₂NH was extended and partially revised. The GA value of (C₄F₉SO₂)₂NH which is currently the strongest acid was revised from 284.1 to 278.6 kcal mol^?1. The effect of fluorine atoms on the acidity of perfluoroalkyl‐substituted sulfonylimides was described with the following model where N_(α), N_(β), N_(γ), and N_(δ) are the numbers of fluorine atoms at α, β, γ, and δ position in R_fSO₂ (R_f = perfluoroalkyl group), respectively. This correlation indicates that the electron‐withdrawing ability of the R_fSO₂ group can be described in terms of the number of fluorine atoms in the perfluoroalkyl group corrected by taking into account their positions. Copyright © 2014 John Wiley & Sons, Ltd.     

燃料与自由基的Lewis数对预混气体点火的影响

通过渐近理论分析研究了燃料与自由基的Lewis数对预混气体点火的影响。采用包含自由基的两步化学反应,基于火焰球模型,推导出了描述火焰球半径随点火能以及燃料与自由基的Lewis数而变化的关系式。并在此基础上发现不同参数条件下成功点火的三种情况,研究了燃料与自由基的Lewis数对最小点火能的影响。研究结果表明:随着燃料Lewis数的增大,最小点火能增大;随着自由基Lewis数的增大,最小点火能减小。     

Effects of fuel Lewis number on flame spread over solids

Using a detailed two-dimensional numerical model, a systematic investigation has been made to study the effect of fuel Lewis number (Le_F = α/D_F) and mass transfer on flame spread over thin solids. The fuel Lewis number affects the flame spread rates for both concurrent and opposed flames over thin fuels. The dependence of the flame spread rate on Le_F for these two spreading modes is, however, not the same. In opposed flame spreads (zero-gravity, self-propagation, and normal gravity downward propagation), the flame spread rate vs. Le_F curve is non-monotonic with a maximum value occurring at an intermediate value of Le_F = 0.5. In steady, concurrent spread in zero-gravity with low-speed flow and a constant flame length, the flame spread rate decreases with Le_F in a monotonic manner. By using the computational model as a tool, the effects of fuel mass diffusion perpendicular to and parallel with the solid surface are isolated to obtain more physical insight on the two-dimensional aspect of fuel mass transfer on flame spread. In addition, the model has also been used to decouple the solid evaporation process so that the fuel diffusion effect in the gas-phase can be isolated. Both of these theoretical exercises contribute to the understanding of mass transfer effects on the flame spreading phenomena over solids.     

Raman spectroscopic determination of the acidity constants of salicylaldoxime in aqueous solution

A sensitive and efficient method for the determination of acidity constants of salicylaldoxime (SALO) (2‐hydroxybenzaldehyde oxime), using both Raman spectroscopic and potentiometric methods, at 30 °C in 50% (wt/wt) of ethanol–water mixture and at the constant ionic strength I = 0.1 M is proposed. The effect of pH on the Raman spectra has also been studied. The Raman spectroscopic technique allows the identification of compounds in different molecular and molecular ionic structures. The limit of detection (LOD) was determined to be 0.05 mol dm⁻³ for SALO by means of Raman peak area. Copyright © 2010 John Wiley & Sons, Ltd.     

近似程度对强耦合磁极化子平均数特性的影响

本文应用幺正变换和线性组合算符法研究了极性晶体内强耦合磁极化子的平均数^-n与磁场B和温度T之间的依赖关系。讨论了在不同的近似计算程度情况下,磁极化子平均数与磁场和温度的特性。对RbCl晶体所作的数值计算结果表明：当计算的近似程度较低时,磁极化子的平均数随温度的升高而减小,但随磁场的加强而增大;当计算的近似度较高时,磁极化子的平均数随温度的升高而增大,但随磁场的加强而减小。     

A Theory of Evolving Natural Constants Based on the Unification of General Theory of Relativity and Dirac's Large Number Hypothesis

Taking Dirac's large number hypothesis as true, we have shown [Commun. Theor. Phys. (Beijing, China) 42 (2004) 703] the inconsistency of applying Einstein's theory of general relativity with fixed gravitation constant G to cosmology, and a modified theory for varying G is found, which reduces to Einstein's theory outside the gravitating body for phenomena of short duration in small distances, thereby agrees with all the crucial tests formerly supporting Einstein's theory. The modified theory, when applied to the usual homogeneous cosmological model, gives rise to a variable cosmological tensor term determined by the derivatives of G, in place of the cosmological constant term usually introduced ad hoc. Without any free parameter the theoretical Hubble's relation obtained from the modified theory seems not in contradiction to observations, as Dr. Wang's preliminary analysis of the recent data indicates [Commun. Theor. Phys. (Beijing, China) 42 (2004) 703]. As a complement to Commun. Theor. Phys. (Beijing, China) 42 (2004) 703 we shall study in this paper the modification of electromagnetism due to Dirac's large number hypothesis in more detail to show that the approximation of geometric optics still leads to null geodesics for the path of light, and that the general relation between the luminosity distance and the proper geometric distance is still valid in our theory as in Einstein's theory, and give the equations for homogeneous cosmological model involving matter plus electromagnetic radiation. Finally we consider the impact of the modification to quantum mechanics and statistical mechanics, and arrive at a systematic theory of evolving natural constants including Planck's ħ as well as Boltzmann's k_B by finding out their cosmologically combined counterparts with factors of appropriate powers of G that may remain truly constant to cosmologically long time.     

光折变晶体KTa0.5Nb0.5O3光学特性的第一性原理研究

用全电势线性缀加平面波法(FLAPW)计算了KTa0.5Nb0.5O3四方相和立方相 的光学特性，即介电函数虚部ε２(ω)、光学吸收系数I(ω)和反射率R(ω). 在四方相，介电虚部沿a，b轴，在3，7和23eV附近，分别有三个介电峰.沿c轴的三个介电峰分别位于4，8和23eV.其中4eV附近的介电峰非常尖锐而且高.从8至18eV，沿a，b ，c轴三个方向都有许多低的介电峰.通过对两相光学特性的对比分析发现铁电相KTa0.5Nb0.5O3具有更强的各向异性. 关键词： 平面波法计算 光学常量和参数 铁电体     

Influence of the Substitution Degree on the Dilute Solution Properties of Cellulose Acetate

Modification of intrinsic viscosity, coil size, and preferential adsorption coefficients of cellulose acetate with various substitution degrees in single and mixed solvents was investigated at different temperatures. Miscibility is attained by specific competitive interactions between the solvent-solvent and solvent-polymer systems, which induce modification in the composition of solvent mixtures both inside and outside the polymer coil. The conformational properties in solutions were correlated with the preferential adsorption coefficients, known as depending on the interaction parameters of the polymer/solvent/solvent systems. The intermolecular interactions observed in the cellulose acetate solutions assure the main properties necessary for obtaining membranes with different applications.     

Hg绿谱线超精细结构分析及相互作用常数计算

比较了Hg的546.1 nm绿谱线超精细结构的理论计算值和实验值,定出了原子超精细结构磁偶极矩相互作用常数Am和电四极矩相互作用常数Be.     

超分子屏蔽效应对富勒烯自由基C59N·稳定性的影响及其诱导的(C59N)2中键接碳笼C-C键的转移重构

富勒烯自由基通常是在空气中短暂存在或不稳定的短寿命物种,超分子屏蔽是近年来被发展用于稳定富勒烯自由基稳定的一种有效策略.本文将共价桥联碳质π电子共轭双嵌N分子碗作为客体C₅₉N·富勒烯自由基的理想宿主体,通过密度泛函理论计算研究了二者之间的主客体相互作用、热力学、自旋电子密度等性质.结果发现C₅₉N·富勒烯自由基嵌螯在该钳形双分子碗的凹穴内而被屏蔽,从而有效避免单电子结构的暴露和C₅₉N·自由基之间的化学二聚,即显著增强其动力学稳定性和寿命,这种策略对富勒烯自由基在自旋电子学、超分子电子器件或光电转换器件等领域的应用具有潜在指导价值.此外,本研究还发现通过超分子屏蔽策略,理论上可以实现对(C₅₉N)₂二聚体分子中键连两个碳笼的C-C进行重构,这也为富勒烯相关体系中C-C键构建的提供了一种新的思路与途径.     

First-principles study of the structural,mechanical and electronic properties of ZnX2O4（X=Al,Cr and Ga）

This paper performs first-principles calculations to study the structural,mechanical and electronic properties of the spinels ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 ,using density functional theory with the plane-wave pseudopotential method. Our calculations are in good agreement with previous theoretical calculations and the available experimental data. The studies in this paper focus on the evolution of the mechanical properties of ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 under hydrostatic pressure. The results show that the cubic phases of ZnAl2O4 ,ZnGa2O4 and ZnCr2O4 become unstable at about 50 GPa,40 GPa and 25 GPa,respectively. From analysis of the band structure of the three compounds at equilibrium volume,it obtains a direct band gap of 4.35 eV for ZnAl2O4 and 0.89 eV for ZnCr2O4 ,while ZnGa2O4 has an indirect band gap of 2.73 eV.     

Solid-state NMR strategies for the structural characterization of paramagnetic NO adducts of Frustrated Lewis Pairs (FLPs)

By N,N addition of NO to the norbonane annulated borane-phosphane Frustrated Lewis pair (FLP) 1 a five-membered heterocyclic persistent aminoxyl radical 2 and its diamagnetic hydroxylamine reduction product 3 are prepared, and the comprehensive multinuclear solid state NMR characterization (¹H, ¹¹B, ¹⁹F, ³¹P) of these FLP adducts is reported. Signal quantification experiments using a standard addition method reveal that the ¹¹B and ³¹P NMR signals observed in 2 actually arise from molecular impurities of 3 embedded in the paramagnetic crystal. In contrast analogous quantification experiments reveal that the ¹H and ¹⁹F MAS-NMR spectra originate from spin-carrying molecules. Peak assignments are based on DFT-calculated Mulliken spin densities, which lead to the surprising result that the largest paramagnetic shift affecting a proton NMR resonance in 2 originates from intermolecular interactions. For the ¹⁹F nuclei, experiments and calculations indicate that paramagnetic shift effects are very small. In this case, assignments are based on DFT chemical shift calculations carried out on diamagnetic 3 and ¹⁹F(¹¹B) Rotational Echo Adiabatic Passage DOuble Resonance (REAPDOR) experiments. The set of experiments described here defines an efficient strategy for the structural analysis of paramagnetic FLP adducts.     

Influence of salts of 1,1,2,2-tetrachloroethane on the acidity function of the solutions of methanesulfonic acid

The influence of salts CH₃SO₃Na and/or CH₃SO₃Bu₄N on the acidity function H ₀ of methanesulfonic acid (MSA) and its solutions in water, N,N-dimethylformamide (DMF) in mixtures of methanesulfonic acid-N,N-dimethylformamide MSA-DMF ≤ 1 and ethyl acetate (EA) in a mixture of methanesulfonic acid-ethyl acetate MSA/EA (1: 1) and 1,1,2,2-tetrachloroethane (TCE) on H ₀ of methanesulfonic acid (MSA) and its mixtures with N,N-dimethylformamide (DMF), 2-pyrrolidine (Pyr) and ethyl acetate (EA) with the ratios of MSA: DMF equal to 1: 1 and 2: 1, MSA: Pyr (2: 1) and MSA: EA, equal to 2: 1, 1: 1, and 1: 2 is investigated by the indicator method at 25°C. It is revealed that a change in the acidity of the solutions of MSA in the aprotic solvents can occur as a result of the influence of salts both on the equilibrium composition of the nascent complexes and on their ionizing ability (both of these factors change acidity on addition of salts to the mixture of MSA-EA (1: 1)). An explanation is proposed why CH₃SO₃Na and CH₃SO₃Bu₄N influence differently on the acidity of aqueous solutions of MSA. It is established that in the solutions of (TCE) the ionizing ability of MSA and its complexes with DMF, Pyr and EA, which have different degree of the proton transfer ($ K_{T_i } $ K_{T_i } ), depends on the concentration ratio of MSA: TCE and ($ K_{T_i } $ K_{T_i } ): TCE.     

Study of the structure and refractive parameters of diethylamine and triethylamine

The refractive index (n) and thermal coefficient of the refractive index (dn/dt) are measured at four wavelengths for the diethylamine and triethylamine. The measurements are carried out using the Bellingham+Stanley model 60/ED high-accuracy Abbe refractometer. The optical permittivity (ε) and its variation with temperature are calculated. Applying the Cauchy equation, the following refractive properties are obtained: the optical dispersion dn/dλ, the dielectric dispersion dε/dλ, the variation of -dn/dT, dε/dT, as a function of wavelength (λ), and Cauchy's constants against temperature. Additionally, molar refractivity versus temperature and wavelength are determined.     

First-principle calculation for the phonon structure on iron-based superconductors

We perform first-principle phonon calculations for three typical iron-based superconductors, i.e., LaFeAsO,BaFe₂As₂, and FeSe. Though those crystals have different structures, we find that the optical modes associated with Fe vibration have almost similar characters. Moreover, we examine the pressure effect on phonons in FeSe. By increasing the external pressure, the phonon mode frequency related to Fe vibration effectively rises up and the electronic density of states at Fermi level also increases. These results may correlate to the critical temperature enhancement under high pressure.     

Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV–Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative pK_a values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated pK_a values provides solid support for the acid–base reactions proposed in this work.     

A simple theoretical treatment of quadrupolar effects on magic-angle-spinning solid-state NMR spectra of spin-1/2 nuclei in the limit of large quadrupole coupling constants

A simple approach is discussed for studying the effect of quadrupolar nuclei on the magic-angle-spinning solid-state NMR lines of spin-1/2 nuclei in the limit of large quadrupole coupling constants. Equations are derived both for the isotropic shifts and the Pake-like powder patterns for any quadrupolar spin and for arbitrary orientations of the internuclear vector with respect to the unique axis of an axially symmetric quadrupole tensor. First-order effects due to a small Zeeman perturbation on these lines are explored, as well as deviations from axial symmetry in the electric field gradient when S = 3/2 quadrupolar nuclei are involved. Spectral parameters likely to be observed in the case of coupling between ³¹P and ²⁰¹Hg are also discussed.