Effect of Aging on the Physico Chemical Properties of Glass Fiber under Different Environmental Conditions

Glass fibers were characterized for physical and chemical changes before and after subjecting to aging under different environmental conditions. The conditions selected were: low temperature, outdoor atmosphere, indoor atmosphere, chemical environment, 95% humidity & water soaking treatment. The results show that glass fiber is a good candidate to resist sunlight, corrosive atmosphere, low temperature and shady atmosphere. The influence of prolonged time exposure to water caused a detrimental effect on the properties of the glass fiber. Hence, prolonged exposure to water should be avoided for the integrity of the glass fiber under study.     

Quantum Chemical Study of Spatial Structure and Stereoelectronic Properties of Iminodihydrofuran Ensembles

A quantum chemical study of structural peculiarities of iminodihydrofuran ensembles (from dimers to tetramers with individual calculations for penta- and hexamers) associated with their rotation isomerism was carried out. Three basic spatial packings of the iminodihydrofuran chains were distinguished with increasing the number of ensemble elements. The spiral and linear packings are equally probable from the standpoint of their thermodynamic stability. The third packing, exhibiting the curvature radius, is inferior to the former two, as judged from the relative stability. It was shown that ensembles in the alternating linear-spiral form are fundamentally possible to exist. Data was obtained testifying to a possibility for the intramolecular hydrogen bond forming between the imine and amine moieties in the tetramer spiral structures; activation barriers of intramolecular prototropic rearrangement were determined.     

A Theoretical Study of the Structure and Thermochemical Properties of Alkali Metal Fluoroplumbates MPbF3

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Molecular Structure and Properties of N,N'-Disulfinyl-1,2-diaminobenzene

According to X-ray diffraction data, N,N'-disulfinyl-1,2-diaminobenzene in crystal exists as a planar Z,Z isomer. On heating or under the action of catalytic amounts of water, as well as in reactions with LiN(SiMe₃)₂ or PCl₅ in 1:1 or 1:2 molar ratios it quantitatively converts into 2,1,3-benzothiadiazole. According to ^{1 5}N NMR data, this transformation is accompanied by deshielding of the nitrogen atoms by 18 ppm.     

Ge@C82结构及性质的理论研究

采用密度泛函理论方法,对Ge@C82的结构及性质进行计算研究.结果表明,由于包合Ge,C82碳笼平均键长增长,碳笼增大,而且Ge原子略微偏离碳笼中心.三重态的C2Ge@C82为能量最低结构.自然布居分析表明,C2C82与Ge之间未发生电子转移,可以用C2Ge@C82来表示它的结构.C2C82和C2Ge@C82的红外光谱计算结果显示,二者的主要区别为C2Ge@C82在1100～1200 cm-1区间的吸收峰变得更尖锐.     

Cyclobutene-1,2-diones. A Theoretical and Spectroscopic Study

The properties of substituted cyclobutene-1,2-diones 1 are examined by the use of (17)O NMR spectroscopy and theoretical calculations and compared to those of cyclopropenones 2 and other models. Cyclobutene-1,2-diones have less negative charge per oxygen compared to cyclopropenones, and electron donation by substituents enhances the negative charge on oxygen. Calculated (17)O chemical shifts reproduce the measured trends. The dianions of squaric and deltic acids are highly stabilized by negative charge delocalization to the oxygens.     

Theoretical Study of the Substituent Effect on the Electronic Structure and Spectral Properties of Six Salicylaldehyde Schiff Bases

Russian Journal of Physical Chemistry A - In the present work, the ground- and excited-state geometries for a series of salicylaldehyde hydrazones (SHs) were optimized including SH-Ph, Naph-SH-Ph,...     

Synthesis,Crystal Structure and Spectroscopic Properties of 1,2-Benzothiazine Derivatives:An Experimental and DFT Study

1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide(1) and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide(2) were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared(IR) spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory(DFT) at the 6-31G+(d) basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential(IP), Electron Affinities(EA) and coefficients of the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of com- pounds 1 and 2 were simulated for the first time.     

Synthesis and Hydrogenation of 1,2-1,4-1,2-Stereotriblock Polybutadienes and the Study of Their Properties

The effects of various polar modifiers, their concentration, and the polymerization temperature on the microstructure of poly-butadiene obtained during anionic polymerization using lithium α-methyl naphthalene as the bifunctional initiator were studied. 1,2-1,4-1,2-Stereotriblock polybutadiene was synthesized by polymerization in cyclohexane to a certain conversion and polymerization was completed in the presence of diethylene glycol dimethyl ether. The microstructure of the stereotriblock copolymer was characterized by IR and ¹H-NMR. GPC showed that the stereo-block polybutadiene has a narrow MWD. Two T_g's of the copolymer with higher molecular weight exist, as shown by dynamic mechanical test. The stereotriblock copolymer was hydrogenated using cobalt 2-ethyl hexanoate and triisobutyl aluminum as the catalyst. The hydrogenated product was shown to be a (butene-1-ethylene-butene-1) triblock copolymer which consists of more than 30% crystallinity and exhibits the behavior of a thermoplastic elastomer. The relationship between stress-strain properties arid the contents of the blocks was also studied.     

层状复合氧化物La4BaCu5-xMxO13(M=Mn, Co)的物化性质和结构中活性氧的研究

合成了一系列结构为层状ＡＢＯ３的复合氧化物Ｌａ４ＢａＣｕ５－ｘＭｘＯ１３（Ｍ＝Ｍｎ，Ｃｏ），并利用ＸＲＤ、Ｘ射线能谱、氧程序升温脱附和化学分析方法对它们的结构和活性氧种进行了研究。ＸＲＤ分析结果表明：它们的结构为五层的ＡＢＯ３结构。活性氧种的研究表明Ｌａ４ＢａＣｕ５Ｏ１３中掺杂Ｍｎ或Ｃｏ之后，样品中明显存在的ＭＣｕ（Ｍ＝Ｍｎ，Ｃｏ）之间的协同作用，并且ＣｕＭｎ之间协同作用明显比ＣｕＣｏ的强。     

同晶置换改性FAU分子筛结构及吸附性能的密度泛函理论研究

采用密度泛函理论(DFT)方法,考察了八面沸石(FAU)型分子筛β笼孔道结构内含氧化合物(甲醇、二甲醚、丙醛)的吸附,并进一步计算研究了Zn,Ca同晶置换改性的作用机理.研究结果表明,β笼孔道结构内,Al原子为甲醇、二甲醚和丙醛的吸附活性位,Si原子无吸附活性.Zn,Ca掺杂的β笼结构内,正2价的Zn和Ca掺杂替换正3价的Al,导致邻近的Si原子位置形成缺电子空穴,增强了甲醇、二甲醚和丙醛的吸附,而杂原子Zn和Ca本身并没有吸附活性.     

Influence of the Chemical Structure of Oligodienourethanoepoxide on Its Rheological Properties

Rheological properties of urethane-containing oligomers as influenced by intermolecular interactions in them were studied.     

A Quantum Chemical Study of the Acidity of Acetylene and 1,2-Dihydrobuckminsterfullerene Derivatives

DFT PBE0/cc-pVDZ method and the polarizable continuum model were used to determine pK _a values for buckminsterfullerene-acetylene hybrids C₆₀HCCH, C₆₀HCN, tert-butylacetylene, and propyne relative to tert-BuC₆₀H in a vacuum, carbon disulfide, tetrahydrofuran, and dimethyl sulfoxide. The energies of the СH-acid molecule and the carbanion (fulleride- or acetylide anion) were calculated using the same number of Gaussian orbitals. The surfaces of cavities formed by molecules and anions in a solvent are composed of spheres encompassing both atomic nuclei and lone electron pairs. An additional sphere excludes the solvent from the inner cavity of the fullerene.     

可紫外光固化聚酰亚胺的设计制备及性能研究

以含酚羟基的2,2-双(3-氨基-4-羟基苯基)六氟丙烷(6FAP)作为接枝光敏单元的载体,以刚性苯并咪唑单元赋予材料良好的力学性能,设计合成了一种具有紫外光固化能力的可溶性聚酰亚胺.系统探究了光源距离、光源电流通量、光引发剂种类和含量、活性稀释剂种类等对固化成型过程的影响,确定了光固化聚酰亚胺的组成配方及工艺条件(光源距离为10 cm、电流通量为100%、双(2,4,6-三甲基苯甲酰基)-苯基氧化膦(Irgacure 819)含量为3 wt%、活性稀释剂1-乙烯基-2-吡咯烷酮(NVP)为20 wt%),并对光固化薄膜的基本性能进行了分析.光固化薄膜的拉伸强度达到123 MPa,固化树脂在5%(Td5)和10%(Td10)热失重时的温度分别为410和487℃,且具有较低的润湿性和吸水性.研究结果可为开发新型光敏性聚酰亚胺提供研究基础.     

Theoretical and Experimental Investigation of the 2-Hydroxyquinoxaline Structure: Study of the Tautomerization Equilibrium System and Analysis of the Electronic Properties

All reasonable tautomers of 2-hydroxyquinoxaline (2HQ) are investigated by the DFT B3LYP/6-311G(d) method. The optimized geometries corresponding to the minimum energy show that the keto form QX2 is the most stable form. The geometry optimization parameters (bond lengths, bond angles) are compared to the X-ray values. Calculated FTIR, UV, and NMR spectra of QX2 are compared to the experimental data to achieve a synergetic computational and spectroscopic approach for the structure analysis of 2HQ. The electronic properties, frontier molecular orbitals, and Mulliken atomic charges are calculated.     

Theoretical Study on Thermodynamic Properties and Stabilities of n-Silanes

Abstract

First-principle computations were performed on the n-silane series (Si_nH_2n+2, n = 1–10). The heat of formation (Δ_fH), Gibbs free energy of formation (Δ_fG), bond length, and bond dissociation energy (BDE) for both the Si?Si and Si?H bonds were predicted. The values of Δ_fH and Δ_fG from the accurate high level G3 method for lower silanes (n ≤ 5) were compared with experimental values and used as benchmarks. Thermodynamic properties derived from the G3 method in combination with the permutation reaction are in better agreement with experiments than those with the atomization reaction. The increments of the Δ_fH and Δ_fG values with an increasing SiH₂-unit for n-silanes are 40.39 and 58.93 kJ/mol on average, respectively. The length of Si?Si bond increases slightly on average as the series number increases and then tends to be a constant for higher silanes. The BDEs for both the Si?Si and Si?H bonds initially decrease for lower silanes, and then approach a constant for higher silanes. The BDEs of the Si?Si bonds are smaller than those of Si?H bonds. The higher silanes are more unstable than the lower silanes. The average BDE of Si?Si bond at the MP2 level is ca. 302 kJ/mol, which is only half the experimental BDE value of the C?C bond (618 kJ/mol).

GRAPHICAL ABSTRACT      

Theoretical Study on the Structural and Electronic Properties of Thiocarbamide Hydrochloride

In the present paper, the electronic band structure, density of states （DOS）, and projected density of states （PDOS） analysis of thiocarbamide hydrochloride are reported. Calculations of the electronic properties have been carried out on the basis of fully self-consistent pseudopotential method using DFT. The results show that near the Fermi level, more prominent densities of states are seen between -8 eV and -6 eV in the valence band mainly due to the Cl-3p, N-2p and S-3p orbitals.     

Theoretical Study on the Structures and Properties of Phenobarbital Imprinted Polymers

Recently, the investigation of novel molecularly imprinted polymers（MIPs） has attracted a lot of interest and becomes a fascinating field. The phenobarbital（PHN） was taken as an imprinted molecule and the 2-vinyl-4,6-diamino-1,3,5-triazine（VDAT） was considered as a functional monomer in this study. The geometry optimization, natural bond orbital（NBO） charge, and molecular electrostatic potential（MEP） of PHN and VDAT were studied at the M062 X level belonging to one of the hybrid density functional theories. Furthermore, we discussed the bonding conditions of PHN molecular imprinted polymers（PHN-MIPs） via the hydrogen bond length and atoms in molecules（AIM） theory. The rebinding property of PHN-MIPs was also researched. The results of MEP and NBO charge analysis were coincident. The stability property was excellent when the ratio of PHN and VDAT was 1：4. Except the classic hydrogen bonds, non-classical hydrogen bonds also existed in the imprinted polymers. By simulating the rebinding energies between the pentobarbital（PNT）, barbital（BAR）, and PHN-MIPs after the elution of PHN, the rebinding property of PHN-MIPs to PHN was excellent when PNT and BAR existed all at once. This research can provide theoretical reference for the synthesis and characterization of novel PHN-MIPs.     

ChemInform Abstract: Structure,Properties, and Theoretical Electronic Structure of UCuOP and NpCuOP.

The title compounds are prepared by solid state reaction of U or Np, Cu and/or CuO, and P at 1073—1273 K (evacuated silica tube, 96 h).