Identity SN2 Reactions. The Relationship Between Transition State Geometry,Selectivity and the Mechanism of Solvent Action

Reactivity trends in the identity S_N2 reaction (X⁻ + CH₃X → XCH₃ + X⁻) are discussed using the state correlation diagram model. The model projects that the activation process can be defined as a distortion effort to transfer a single electron from the nucleophile to the leaving group across the alkyl group (CH₃). Three domains of reactivity are discussed (a) the geometry of the transition state (looseness and tightness), (b) the intrinsic selectivity of substrates, and (c) the mechanism of solvent action. A link is drawn between these three domains, and a physical insight is provided.     

The Effect of Temperature on Competing Photochemical Hydrogen Abstraction Reactions in the Solid State

Irradiation of 4aα,5,8,8aα-tetrahydronaphthoquin-1-on-4β-o1 (1a) and its 6,7-dimethyl derivative 1b in the solid state leads to two products. The first is formed via intramolecular hydrogen abstraction by carbonyl oxygen followed by radical coupling, and the second is produced through initial hydrogen abstraction by enone carbon and subsequent radical coupling. X-ray crystallography reveals that both processes are topochemically allowed, and the geometric parameters for the hydrogen transfers and the radical coupling reactions are tabulated. In the case of 1b, the photoproduct ratio was found to be temperature dependent with hydrogen atom abstraction by carbon predominating at lower temperatures. From the slope of the linear plot of the natural logarithm of the photoproduct ratio versus the reciprocal of the temperature, an activation energy difference of approximately 4 kcal/mole is calculated. The results are interpreted as being due to competing reactions from (n,π*)³ and (π*)³ excited states, the latter (hydrogen abstraction by carbon) having a lower activation energy than the former (hydrogen abstraction by oxygen).     

The Relationship Between the Microhardness and Glass Transition Temperature of Inorganic Glasses Compared with Polymeric Glasses

ABSTRACT

In this article an attempt is undertaken to verify the approach already successfully applied to polymeric glasses for deriving a simple analytic relationship between the glass transition temperature, T_g , and Vickers microhardness, H_v , (for polymers it is H_v  = 1.57 T_g –571, H_v in MPa, T_g in K). On the basis of previously reported data for H_v and T_g of 12 inorganic glasses (lead-silicate-, alkali-silicate-, alumosilacate, and quartz glasses) a linear relationship in the form H_v  = 5.87 T _g + 1740 (H_v in MPa, T_g in K) is derived. In addition, a critical analysis of the published attempt for theoretical deriving of the relationship between H_v and T_g is also offered.     

Acid–Base Reactions of Transition Metal Oxides in the Solid State

Subsolidus compatibility data exist for a number of ternary oxide systems containing a transition metal oxide. Ternary diagrams, suitable for the present purpose, are limited mainly to those that include FeO, Fe₂O₃, ZnO, or Cr₂O₃, and these are examined in the context of Lewis acid–base interaction by considering the electron densities borne by the oxygen atoms or ions. These electron densities can be expressed on the optical basicity scale, and a significant acid–base difference exists between the reactants when they differ markedly in optical basicity. For many reactions the optical basicity difference between the products is much less, suggesting that acid–base neutralization is a major driving force. This principle has been found previously for nontransition metal oxide ternary systems. However, there are notable exceptions, especially in reactions where FeO or ZnO is the end product. This exceptional behavior is examined.     

On the Temperature Dependence of the Viscosity of Multicomponent Glasses in the Glass Transition Range

The viscosities of eight optical glasses are measured in the vicinity of the glass transition temperature (450–680°C, 10¹¹–10¹² P). It is demonstrated that the Shishkin and Williams–Landell–Ferry equations are applicable in the temperature range under investigation. The parameters of the fluctuation free volume concept are calculated. The physical meaning of these parameters is discussed.     

气体引射器型红外抑制器的结构及性能研究

通过介绍红外抑制器的工作原理，用实验和数值方法分析了由不同的抑制器结构引起的不同红外抑制效果。通过对多组参数的数值计算和实验测量，得出了有关结构参数对红外抑制装置工作性能的影响规律，为以后抑制器的设计提出了最佳的组合方案和取值范围。实验结果表明，装置有较好的红外抑制效果。     

Relationship Between the Low Temperature Thermolysis and Detonation Temperature of Carbocyclic Nitroaromatic Compounds

In this paper, a new relationship between the activation energies (E_a) of the low temperature thermolysis and detonation temperature for different carbocyclic nitroaromatic compounds is introduced. Two structural parameters are needed to obtain a relatively good correlation for E_a. The resulting R² value of the new correlation is 0.942. The new equation assumes that the calculated detonation temperature can be applied to predict E_a of carbocyclic nitroaromatic compounds with the general formula C_aH_bN_cO_d and any complicated molecular structure. The proposed new method was also used to predict E_a of some technologically attractive high thermostable polynitro arenes with complex molecular structure, e.g., 2,2′,2″,2′′′,4,4′,4″,4′′′,6,6′,6″,6′′′‐dodecanitro‐[1,3′,1′,1″] quaterphenyl (DODECA).     

Relationship Between Structure and Glass Transition Temperature in Low-silica Calcium Aluminosilicate Glasses: the Origin of the Anomaly at Low Silica Content

The anomalous behavior of the glass transition temperature ( T _g) in low silica calcium aluminosilicate glasses has been related to the structural modifications observed by neutron and X-ray diffraction. The diffraction data indicate that Al and Si are in tetrahedral sites and that Ca atoms are in distorted octahedral sites. By subtracting the correlation functions for glasses at constant SiO₂ or constant Al₂O₃ content, we have shown that Si and Al atoms are introduced in a different way within the glass structure. Si is present in various Q ⁿ sites, while Al resides in Q³ and Q⁴ sites for glasses with high CaO content and enters fully polymerized Q⁴ sites with increasing SiO₂ or Al₂O₃ content. The higher proportion of Al in Q³ positions at high CaO content yields a depolymerization of the network. The lower connectivity will contribute to a decrease of the viscosity, which may be at the origin of the decrease of T _g for glasses at low silica content.     

Temperature Dependence of Excited-State Proton Transfer and Geminate Recombination Processes in Water and in Glycerol-Doped Ice

The reversible proton dissociation and geminate recombination of photoacids was studied as a function of temperature in neat water, binary water mixture containing 0.6 mol% glycerol, and doped ice containing 0.6 mol% glycerol. The deuterium isotope effect on both condensed phases was also studied. 8-hydroxypyrene-1,3,6 trisulfonate trisodium salt was used as the electronically-excited-state proton emitter. The experimental data are analyzed by the Debye–Smoluchowski equation solved numerically with boundary conditions to account for the reversibility of the reaction. We propose a qualitative model to describe the unusual temperature dependence of the proton transfer rate in the liquid phase. We also propose a model for proton transfer in solid ice based on L-defects transport as proton acceptors. While in the liquid phase at t > 10°C the proton dissociation rate constant is almost temperature independent, in glycerol-doped ice we find a large temperature dependence.     

碱土替换铝硅酸盐玻璃硬度和玻璃转变温度反向演化的结构起源

为探究过铝区碱土铝硅酸盐玻璃随碱土离子替换硬度(HV)和玻璃转变温度(Tg)的演化规律及结构起源,采用激光加热气动悬浮技术,制备了摩尔组成为xRO·(49–x)Al2O3·51SiO2(x=0～16;R=Mg,Ca,Sr,Ba)的系列碱土铝硅酸盐玻璃样品.采用显微维氏硬度仪、差示扫描量热法(DSC)分别对样品的维氏硬度...     

Correlation between the Width of the Glass Transition Region and the Temperature Dependence of the Viscosity of High-Tg Glasses

A correlation exists between the width of the glass transition region measured using DTA or DSC during heating and the activation enthalpy Δ H _η^* for the shear viscosity of high-Tginorganic glasses. This is demonstrated by the constancy of a dimensionless parameter C = (Δ H _η^*/ R )(1/Tg – 1/Tg'), where Tg and Tg' are temperatures marking the extrapolated onset and finish of the transition region on the DTA or DSC trace. The logarithm of the shear viscosity at Tg, log η (Tg), is also approximately constant for high-Tg glasses. Using the universal values of C and log η (Tg), fairly reliable estimates of shear viscosities from the transition range through the working range can be made from the Tg and Tg' values obtained using DTA or DSC.     

中空玻璃凹凸与温度变化关系的探讨

影响中空玻璃反射影像质量的因素有多种多样,如环境温度、气压、钢化加工、中空加工方式等等。本文仅通过模拟环境温度变化的实验,测试和分析不同尺寸和结构的中空玻璃在不同温度条件下发生变形的程度,通过中空玻璃凹凸变形与温度、气压变化的关系进行探讨,有助于玻璃深加工企业更好地控制中空玻璃的平整度。     

西安市冬季天然气用气负荷与气温关系分析

城市天然气用气负荷受当地气象因素、居民生活习惯、节假日和当地消费水平等多种因素共同影响,其中气温对城市天然气负荷变化的影响最为显著.本文根据西安市天然气负荷量和气温的历史数据,通过相关性分析和回归分析等方法,找出天然气日均负荷变化与日均气温之间的关系,为天然气负荷预测和调度提供参考.     

Effect of Dual Impeller‐Sparger Geometry on the Hydrodynamics and Mass Transfer in Stirred Vessels

The understanding of the effect of impeller‐sparger configurations on gas dispersion and mass transfer is very important to improve the performance of gas/liquid contactor systems. The influence of the impeller positions, the upper turbine diameter, the sparger ring diameter and its location in regard to the lower impeller on the power consumption, the volumetric mass‐transfer coefficient and the overall oxygen transfer efficiency were studied in a nonstandard curved bottomed reactor with an agitated system with dual disk style turbines. In the range of the gas flow rates studied, the most efficient impeller‐sparger arrangement for the oxygen transfer is the impeller system with turbines of different diameters located at C = 0.25 and IC = 0.5, and with the sparger of smaller diameter than the lower impeller settled below the impeller. A new model to estimate the k_La with an average relative error of 8 %, which takes the reactor operation conditions and the influence of the impeller‐sparger geometry into account, was also proposed.     

Equibiaxial Stress Effect on Fracture Strength of Indented Soda-Lime Glass in Water Environment: An Examination for Dependence on Crack-Tip Blunting

Equibiaxial stress effects were observed in constant stressing rate tests of indented soda-lime glass in a water environment. To discuss whether the equibiaxial stress effects on fracture strenght in a water environment were caused by the blunting of crack tips by chemical reaction between the glass and moisture, the specimens with controlled surface flaws soaked in hot water to make the crack tip blunt were fractured under both uniaxial and equibiaxial tensile stresses under both vacuum and air environments. The biaxial strengthening observed under restricted subcritical crack growth indicates that equibiaxial stress effects in a water environment are caused by the rounding of the initial crack tip.     

Temperature Dependence of Interfacial Bonding and Configuration Transition in Graphene/Hexagonal Boron Nitride Containing Grain Boundaries and Functional Groups

The quasi-three-dimensional effect induced by functional groups (FGo) and the in-plane stress and structural deformation induced by grain boundaries (GBs) may produce more novel physical effects. These physical effects are particularly significant in high-temperature environments and are different from the behavior in bulk materials, so its physical mechanism is worth exploring. Considering the external field (strain and temperature field), the internal field (FGo and GBs) and the effect of distance between FGs and GBs on the bonding energy, configuration transition, and stress distribution of graphene/h-BN with FGo and GBs (GrO-BN-GBs) in the interface region were studied by molecular dynamics (MD). The results show that the regions linked by hydroxyl + epoxy groups gradually change from honeycomb to diamond-like structures as a result of a hybridization transition from sp² to sp³. The built-in distortion stress field generated by the coupling effect of temperature and tension loading induces the local geometric buckling of two-dimensional materials, according the von Mises stresses and deflection theory. In addition, the internal (FGo and GBs) and external field (strain and temperature field) have a negative chain reaction on the mechanical properties of GrO-BN-GBs, and the negative chain reaction increases gradually with the increase in the distance between FGo and GBs. These physical effects are particularly obvious in high-temperature environments, and the behavior of physical effects in two-dimensional materials is different from that in bulk materials, so its physical mechanism is worth exploring.     

Characterization of the Rate-Limiting Steps in the Dark-To-Light Transitions of Closed Photosystem II: Temperature Dependence and Invariance of Waiting Times during Multiple Light Reactions

Rate-limiting steps in the dark-to-light transition of Photosystem II (PSII) were discovered by measuring the variable chlorophyll-a fluorescence transients elicited by single-turnover saturating flashes (STSFs). It was shown that in diuron-treated samples: (i) the first STSF, despite fully reducing the Q_A quinone acceptor molecule, generated only an F₁(<F_m) fluorescence level; (ii) to produce the maximum (F_m) level, additional excitations were required, which, however, (iii) were effective only with sufficiently long Δτ waiting times between consecutive STSFs. Detailed studies revealed the gradual formation of the light-adapted charge-separated state, PSII_L. The data presented here substantiate this assignment: (i) the Δτ_1/2 half-increment rise (or half-waiting) times of the diuron-treated isolated PSII core complexes (CCs) of Thermostichus vulcanus and spinach thylakoid membranes displayed similar temperature dependences between 5 and –80 °C, with substantially increased values at low temperatures; (ii) the Δτ_1/2 values in PSII CC were essentially invariant on the F_k−to-F_k+1 (k = 1–4) increments both at 5 and at −80 °C, indicating the involvement of the same physical mechanism during the light-adaptation process of PSII_L. These data are in harmony with the earlier proposed role of dielectric relaxation processes in the formation of the light-adapted charge-separated state and in the variable chlorophyll-a fluorescence of PSII.     

聚氨酯软泡叔胺用量与料温的关系

通过对软质聚氨酯泡沫塑料发泡反应中发生的化学反应机理的探讨,运用化学动力学理论,结合实际生产配方数值,推导得不同原料温度下所需叔胺催化剂配方用量的定量计算公式。此公式对不同温度条件下的实用生产配方的拟订有很好的指导作用。     

The Effect of Nanosized Layered Materials on the Structure-Property Relationship of Poly(aniline)s: An FTIR Kinetic Study

Aniline (ANI) was chemically polymerized in the presence of two different nanosized layered materials, zirconylphosphate (ZP) and molyptic acid (MA) under different experimental conditions with nitrogen purging at 45°C. The effect of nanosized layered materials on the rate of polymerization (R_p) and Fourier transform infra red-relative intensities (FTIR-RI) of benzenoid and quinonoid forms of poly(aniline) (PANI) were tested. The thermal stability and electrical conductivity values were boosted with the help of nanosized materials. High resolution transmission electron microscope (HRTEM) determined the size of nano material and its uniform distribution on the PANI matrix. For the sake of comparison, o-toluidine (OT) was polymerized under the same experimental conditions and its structure-property relationship in the presence of nano materials were also tested and critically compared with PANI systems.     

Effect of Temperature Gradient on the Intensity of Light Scattering in Phosphate Glasses in the Glass Transition Range

A correlation between the peak of the intensity of light scattering and the temperature gradient arising across the sample after temperature jumps in the glass transition range is revealed from experimental data. Analysis of the experimental results shows that the peak of the intensity of light scattering is a quadratic function of the temperature gradient. The result obtained is in agreement with the predictions made from the theoretical analysis of the regularities observed in light scattering by nonuniformly heated liquids.