半经验分子轨道法优化枞酸结构

运用分子轨道理论中的半经验MINDO／3，MNDO与PM3量子化学计算方法分别对松香中的枞酸分子进行几何结构优化，结果表明，3种方法预测枞酸菲环骨架内的键长、键角、两面角结果与文献值基本一致，而菲环外羧基及异丙基的键长、键角和两面角计算值与文献值有较大偏差，这是由于枞酸分子之间氢键作用以及异丙基热运动比较强烈影响的缘故。在不考虑羧基及异丙基相关的键长、键角和两面角之后，发现PM3方法计算的键长、键角与两面角的结果与文献值比较吻合，计算值与文献值的相关系数R^2分别为0．96432、0．91989和0．99912，而MINDO／3和MNDO的计算值与文献值偏差稍为大些。     

Zur Allyl-Cyclopropyl-Isomerie von substituierten Kationen: Eine AMl- und MNDO-Untersuchung

On the Allyl-Cyclopropyl Isomerism of Substituted Cations: An AMl and MNDO Study Three series of cations (2-X-allyl cations ( 1 ), 1-X-cyclopropyl cations ( 2 ) and 1-X-isopropyl cations ( 3 )) were investigated by both the MNDO and AMl quantum chemical methods. For π-electron donators (X = NH₂, OH, NHOH) derivatives 2 are more stable than 1 . The opposite is valid for derivatives with δ-electron acceptors (X = NO₂, CHO, halogens). AMl values are closer to experimental or ab initio heats of formation than MNDO results. Therefore, by means of AMl only, reasonable ringstrain energies were obtained for 2 , while the MNDO method failed in all investigated cases. It has been shown that the unknown 2-hydroxyaminoallyl cation is probably more stable than its cyclopropyl analogue.     

Pyryliumverbindungen,XXV. Quantenchemische Berechnungen zur Valenzisomerisierung von 2-Amino-2H-pyran und -thiopyran

Pyrylium Compounds. XXV. Quantum Chemical Calculations Concerning the Valence Isomerization of 2-Amino-2H-pyran and -thiopyran The equilibrium 2-amino-2H-pyran 6 ⇌ 5-amino-2,4-dien-1-one 7 was investigated using the semi-empirical MINDO/3 and MNDO methods. In accordance with experimental findings for the substituted derivatives 1/2a–d , the introduction of a methyl group into the position 3 of 6 or the exchange of oxygen by sulfur shifts the equilibrium towards the cyclic structures 8 and 10 , respectively. Polar solvents, the influence of which was estimated applying the reaction field approach as well as the solvaton theory, and entropy effects are calculated to favour the ring-open valence isomer 7 . These results also correspond to experimental results.     

Laser Raman spectrum of isotactic polybutene-1 fibres

Detailed polarized laser Raman spectra of isotactic hexagonal polybutene-1 fibres are presented. The use of different scattering geometries enables us to determine unambiguously the symmetry of Raman bonds from 300 to 3000 cm^?1. The comparison between calculated and observed intensities enables us to test the individuality of CH₂ and CH₃ group vibrations and shows that some bands, more particularly those located between 800 and 1200 cm^?1, can only be explained by the coupling of skeleton vibrations with side group vibrations.     

Towards an understanding of stacked base interactions: non-equilibrium phase transitions as a probable model

Summary The distances of stacked bases of DNA in different conformations can-not be calculated by equilibrium potentials, since they exhibit not more than only one minimum. However, a double potential minimum is obtained by considering the most simple semiclassical model of excitons that are coupled adiabatically to lattice vibrations, hence forming polaritons. By use of Danilov's extended Hückel approximation of DNA excitons, stacked base distances can be calculated that agree fairly well with the experimental data. The errors of this approach are small as compared to the differences of the distances in various conformations. Consequently, this model may work as a first base of understanding molecular interactions in DNA.     

AM1, MNDO AND MINDO/3 TREATMENTS OF HÜCKEL TYPE CYCLACENES

Hückel type cyclacenes having R = 3–10 have been subjected to quantum chemical analyses at the level of AM1, MNDO and MINDO/3 (UHF and RHF) type semi-empirical treatments. The structures have been found to be stable but endothermic in nature. No cryptoannulenic effect has been observed when AM1 (UHF) and MNDO (UHF) treatments are used. Whereas MINDO/3 (UHF) and all the RHF type calculations indicated certain degree of cryptoannulenic effect R = 4 through 8 for the heat of formation values. Frontier molecular orbital energies of the systems have also been reported.     

CORROSION INHIBITION AND ADSORPTION BEHAVIOR OF SOME AZO DYE DERIVATIVES ON CARBON STEEL IN ACIDIC MEDIUM: SYNERGISTIC EFFECT OF HALIDE IONS

Corrosion inhibition of carbon steel in HCl by azo dye derivatives (ADD) was investigated using chemical and electrochemical techniques. Results obtained indicate that ADD inhibited the corrosion of carbon steel in the acid medium. Inhibition efficiency increases with increase in ADD concentration and is synergistically enhanced on addition of iodide and bromide ions. By fitting the obtained experimental data with the Langmuir adsorption model and the Arrhenius equation, some thermodynamic and kinetic parameters for the corrosion process were estimated, and the values support the results obtained. Some quantum chemical parameters and the Mulliken charge densities for ADD were calculated by the MNDO semi-empirical method to provide further insight into the mechanism of inhibition of the corrosion process.     

Corrosion inhibition of carbon steel in hydrochloric acid by furan derivatives

The efficiency of three furan derivatives (2-methylfuran, furfuryl alcohol and furfurylamine), as corrosion inhibitors for carbon steel in 1 M HCl, has been determined by gravimetric and electrochemical measurements. These compounds inhibit corrosion even at very low concentrations, and furfuryl alcohol is the best inhibitor. Polarization curves indicate that all compounds are mixed inhibitors, affecting both cathodic and anodic corrosion currents. Adsorption of furan derivatives on the carbon steel surface is in agreement with the Langmuir adsorption isotherm model, and the calculated Gibbs free energy values confirm the chemical nature of the adsorption. The structural and electronic properties of these inhibitors, obtained using AM1, PM3, MNDO and MINDO/3 semi-empirical self-consistence field methods, are correlated with their experimental efficiencies.     

Quantenchemische Berechnungen zur Addition von CH3–XFX (X = 0,…,3) an Ethen. I. Semiempirische Untersuchungen mit der AM1-Methode

Quantum Chemical Calculations on the Addition of CH₃–_XF_X (X = 0,…,3) to Ethene. I. Semiempirical Investigations by Means of the AM1 Method AM1 calculations are reported for the homolytical addition of CH_3–XF_X (X = 0,…,3) to ethene. The structures of the reactants, the products and the transition states, as well as the reaction enthalpies are described reasonably. The calculated activation barriers are significantly different from the experimental activation energies, probably because the parametrisation is not well suited for the energetics of radical species, especially radical transition states. MNDO gives similar results, MINDO/3 fails completely.     

铝硅酸盐矿物的Raman振动特征解析

分别测定了蓝晶石、红柱石和夕线石3种铝硅酸盐天然矿物晶体的Raman光谱,并利用Materials Studio3.0软件计算3种矿物的Raman振动频率,分析其简正振动模式,确定了三种矿物特征谱峰的归属,解析了铝对铝硅酸盐Raman光谱振动特征的影响.结果表明:随着四配位铝的增加(从蓝晶石、红柱石到夕线石),800～1 200 cm-1波数区间内谱峰频率降低,该区间的谱峰归属于Si-Onb间非桥氧对称伸缩振动;700～800 cm-1区间内出现的谱峰归属于Al-Onb间非桥氧的对称伸缩振动.当铝全部为六配位时,会引起800～1 200 cm-1区间内的谱峰向高频方向迁移.这为进一步利用Raman光谱来研究硅酸盐玻璃和熔体结构中铝的作用提供了重要依据.     

Generalized susceptibility of dislocation in ferroelectrics

Bending vibrations of dislocations in ferroelectric crystals are investigated. Vibration spectrum is shown to consist of two branches: “quasi-acoustic” (ω → 0 at q → 0, where ω, q - are frequency and wave vector, respectively) and “quasi-optical” (ω ≠ 0 at q = 0). Generalized susceptibility of dislocation is calculated. It is shown that energy dissipation at crystal polarization vibrations, accompanying dislocation vibrations, has a noticeable influence on dislocational vibrations damping.     

Effect of Electronic Charge on Oxygen Atom of Oxygen-Containing Oxidizers on Characteristics of Reactive Rocket Fuels

Abstract

The calculations of typical oxygen-containing oxidizers of rocket fuels OF₂, O₂, ClO₃F, H₂O₂, N_{2O 4}, HNO₃, were carried out by quantum chemical semi-empirical MNDO method in Dewar and Teel parameterization with minimization of total energy of molecular system by Davidon-Fletcher-Powell method. The optimized electronic and geometric structure of these oxidizers was obtained. We established correlative dependencies between some parameters of the following reactive fuels (H₂, N₂H₄, N₂ H₂(cH₃)₂ ～CH₂～, Al H₃, B₅H₉, Be H₂): and minimum electronic charge on oxygen atom qo_min of oxygencontaining oxidizers. The latter being calculated by the MNDO method.     

Thermal Expansion of Vitreous Silica

The thermal expansion of vitreous silica is negative at low temperatures. This negative expansion can be explained as being caused by the transverse vibrations of the oxygen atoms. The frequency of such vibrations, because of the structure of vitreous silica, decreases as the structure shrinks, and this decrease results in negative thermal expansion.     

Molecular orbital studies of the thermal decomposition mechanism of dimethylnitramine

The electronic structures of dimethylnitramine (DMNA) were calculated using ab initio Gaussian 80 program at the Hartree-Fock level with STO-3G and STO-4-21G basis set, respectively. The Mulliken bond order of the N NO₂ bond is the least one in comparision with those of the other bonds in the DMNA molecule. Two potential energy curves along the N N bond splitting pathway (R_{N N}) were obtained using MINDO/3 and MNDO methods, respectively. These curves have the same trend and are qualitatively consistent with the results obtained from the thermolysis of nitromethane (CH₃NO₂). It was found that the frontier MO levels and the net charges of groups are changed with R_{N N} distance. The products of thermal decomposition and the energy changes were calculated by MINDO/3 method and are discussed in this paper.     

Molecular modeling of reduction reactions of dicyandiamide on zinc: a theoretical study of epoxy adhesive/galvanized steel adhesion

Molecular orbital calculations have been used to model the interfacial reactions that occur during bond formation of epoxy adhesives to galvanized steel. The theoretical calculations were applied to interfacial reactions of generic dicyandiamide-crosslinked epoxy adhesives on zinc surfaces. Semi-empirical MNDO molecular orbital calculations were used to model the reduction reactions. The calculations were used to predict the most stable tautomer of dicyandiamide as well as to suggest the structure of the most likely zinc-dicyandiamide reduction products. The results of the calculations are consistent with infrared spectroscopic studies of dicyandiamide reduction on zinc surfaces that suggest the formation of carbon-nitrogen multiply bonded moieties. An MNDO geometry optimization of dicyandiamide suggests that one tautomeric form of dicyandiamide, the diamino form, is the most stable structure by about 9.3 kcal/mol. The optimized geometry of the diamino form of dicyandiamide is nearly planar, suggesting that the molecule has a π-system largely isoelectronic with butadiene. The symmetry and magnitude of the coefficients for the atomic orbitals of the lowest unoccupied molecular orbital (LUMO) of the diamino form of dicyandiamide are consistent with the formation of a radical anion reduction product which would afford a carbodiimide intermediate on the zinc surface.     

Temperature broadening of vibrational lines in glasses

The shape of vibrational lines and the temperature dependences of their width for structures with short-range and medium-range orders in oxide glasses have been studied. The relationship describing the contour of the line associated with internal vibrations of glass-forming polyhedra is derived in the framework of the model for deformation broadening of the vibrational spectra of two-level systems. It is found that the line within the width is represented by a Lorentzian contour, and the line wings decay as (ω − ω₀)⁻⁴. It is demonstrated that a similar contour is observed for the lines corresponding to the intrinsic vibrations of clusters with hinged bonds, which form the boson peak. The shape of the line at 806 cm⁻ for vitreous boron oxide, which is calculated in the framework of the proposed model, is in complete agreement with the experimental data in the temperature range 80–1900 K.     

Temperature broadening of vibrational lines in glasses

The shape of vibrational lines and the temperature dependences of their width for structures with short-range and medium-range orders in oxide glasses have been studied. The relationship describing the contour of the line associated with internal vibrations of glass-forming polyhedra is derived in the framework of the model for deformation broadening of the vibrational spectra of two-level systems. It is found that the line within the width is represented by a Lorentzian contour, and the line wings decay as (ω − ω₀)⁻⁴. It is demonstrated that a similar contour is observed for the lines corresponding to the intrinsic vibrations of clusters with hinged bonds, which form the boson peak. The shape of the line at 806 cm⁻ for vitreous boron oxide, which is calculated in the framework of the proposed model, is in complete agreement with the experimental data in the temperature range 80–1900 K.     

Extinction of Combustible Forest Materials by Constant and Varying Actions of an Inert Gas Flow in the Combustion Zone

It is found that an inert flow around elements of combustible forest materials (CFM) with a rate exceeding certain values leads to flame extinction. Theoretically, this can be explained by cooling of the gas in the combustion zone. It is shown that calculated values of the combustion temperature agree well with experimental data. The effect of vibrations of CFM elements on the extinction of gasphase combustion is considered for the first time.     

Thermal Transport in Off-Stoichiometric Uranium Dioxide by Atomic Level Simulation

The thermal conductivity of hypo- and hyperstoichiometric UO₂ is calculated as a function of defect concentration and temperature using the direct method in molecular dynamics simulations. Anion defects, the dominant defects in UO₂, are shown to significantly influence the thermal conductivity. Lattice dynamics calculations show how this reduction arises from changes in the nature of the lattice vibrations, as characterized by the polarization vectors and participation ratios. In addition, ²³⁵U isotopic defects are shown to have a negligible influence on the thermal conductivity.     

Mathematical model for the initiation of intense acoustic vibrations in a ramjet ejector combustor and their suppression by resonators

A mathematical model is constructed to describe the mechanism of intense acoustic vibrations in a ramjet ejector combustor based on the instability of natural acoustic vibrations in the combustor due to jet exhaust. The feedback necessary for the onset of instability of acoustic waves is taken to be their interaction with the unsteady gas motion induced by the vortex sheet from the trailing edges of the combustor. An algorithm for suppressing intense acoustic vibrations in the combustor using resonators is developed. The obtained theoretical results are compared with the results of experimental studies.