An Ab initio study of tautomerism between formhydroxamic acid and formhydroximic acid

Ab initio MO calculations including electron correlation with the 4-31G and 4-31G ** basis sets were performed in order to study the formhydroxamic acid-formhydroximic acid tautomerism. The geometries, relative energies, and activation energy of the tautomer and transition state were determined. Based on total-energy calculations at the MP 4/4-31G **//RHF /4-31G ** plus the scaled zero-point vibration energy level, the energy of formhydroxamic acid is determined to be lower than that of formhydroximic acid by 40.7 kJ/mol. The activation energy of the formhydroxamic acid-formhydroximic acid tautomerism via a 1,3-intramolecular hydrogen shift is 151.4 kJ/mol. © 1992 John Wiley & Sons, Inc.     

A study of the AMO method as applied to the lithium metal. I. Review,results, and discussion

The total electronic energy per atom in the lithium metal has been calculated for three different Fermi surfaces as a function of the internuclear distance. In each case the optimized AMO energy as well as the total energy corresponding to doubly filled molecular orbitals (MO ) has been calculated. For densities around the equilibrium density the spherical Fermi surface yields the lowest energy whereas a cubic Fermi surface is preferred for low densities. For densities around the equilibrium there is no band splitting: the AMO energy coincides with the MO energy. The computations have been carried out within an LCAO approximation with overlap and multicenter-integrals calculated accurately.     

Repulsive double many-body expansion potential energy surface for the reactions N(4S)+H2<-->NH(X3Sigma-)+H from accurate ab initio calculations

A single-sheeted DMBE potential energy surface is reported for the reactions N(4S)+H2<-->NH(X3Sigma-)+H based on a fit to accurate multireference configuration interaction energies. These have been calculated using the aug-cc-pVQZ basis set of Dunning and the full valence complete active space wave function as reference, being semi-empirically corrected by scaling the two-body and three-body dynamical correlation energies. The topographical features of the novel global potential energy surface are examined in detail, including a conical intersection involving the two first 4A' potential energy surfaces which has been transformed into an avoided crossing in the present single-sheeted representation.     

Chromatography in silico, quantitative analysis of retention of aromatic acid derivatives

A quantitative analysis of the retention of aromatic acid derivatives in reversed-phase liquid chromatography (RPLC) is conducted using a molecular mechanics calculation in the CAChe program. The molecular interaction energy value is calculated by subtracting the energy value of the complex from the sum of energy values of a model phase and an analyte. Several model phases are constructed, and the feasibility of applying the method to a variety of compounds is examined based on improving the contact surface area and the capability of computer software and hardware. Interaction energy values are calculated for both molecular and ionic forms. The predicted retention factors of partially ionized acids obtained using a combination of dissociation constants correlated well with the values measured by RPLC with pH-controlled eluents.     

The conformational potential energy surface of IOONO and the isomerization and decomposition processes

The conformational potential energy surface of iodine peroxy nitrite was investigated using high levels of electronic structure theory. Two minimum energy conformers and five energy maxima have been determined. The comparison with other peroxy nitrites shows interesting correlations with the internal rotational barriers of the Cl, Br analogues and with peroxynitrous acid. Distinct transition states for the isomerization to iodine nitrate and the scission of the peroxy bond have been calculated. Finally, the thermochemistry of IOONO and IONO₂ has been reconsidered.     

Electrokinetic Behavior of Fluorite

The electrokinetic behavior of fluorite mineral was studied under various partical sizes and different concentrations of oleic acid at constant pH. The particle size has been reduced with an increase in activation time. The surface energies of milled fluorite minerals were calculated theoretically and experimentally. The zeta potential of the fluorite/water system has shifted to lower side with an increase in particle size. The isoelectric point (iep) of fluorite minerals has been shifted to lower side with increase in oleic acid concentration. This indicates the chemisorbed oleate formation on fluorite. A sharp decrease in zeta potential in the pH range of 6.5–8.4 and the decrease in calculated free energy of adsorption shows the formation of calcium dioleate precipitate on fluorite.     

Ab initio vibration and ro-vibrational spectrum of the 1A1 state of He2Si2+

The low-lying ro-vibrational states for the ground electronic state (1A1) of HeSi2+ have been calculated using an ab initio variational solution of the nuclear Schr?dinger equation. A 96 point CCSD(T)/cc-pCVQZ potential energy surface (PES) has been calculated and a Ogilvie-Padé (3,6) potential energy function has been generated. This force field was embedded in the Eckart-Watson Hamiltonian from which the vibrational and ro-vibrational eigenfunctions and eigenenergies have been variationally calculated. A 70 point QCISD/aug-cc-pCVTZ discrete dipole moment surface (DMS) was calculated and a 5th order power series expansion (in terms of the two bond lengths and the included bond angle) has been generated. Absolute line intensities have been calculated and are presented for some of the most intense transitions between the vibrational ground state and the low-lying ro-vibrational states of this ion.     

Exact quantum calculations on the collinear hydrogen atom transfer reaction I. Study on oscillations of the reaction probabilities of Cl + HCl

1-D quantum calculations of reaction probabilities have been carried out for the collinear reaction Cl + HCl (v≤3)→ClH (v′≤3) + Cl using hyperspherical coordinates. An LEPS potential energy surface with a shallow well depth of ?3.22 KJ/mol has been used in the calculations. The state-to-state reaction probabilities have been calculated. According to the results obtained we found that the diagonal (v=v′) reaction probabilities dominate over the off-diagonal (v≠v′) reaction probabilities and the largest off-diagonal reaction probabilities are smaller than 0.1. The reaction probabilities show oscillation as a function of energy. Dynamic resonances strengthen for the potential energy surface with a well.     

Quasi-Classical Trajectory Study of the Chemical Reaction Ca+CH3I

The Ca＋CH3I→CaI＋CH3 reaction system has been studied with the quasi-classical trajectory method on the extended Lond-Eyring-Polanyi-Sato（LEPS） potential energy surface. At collision energy Ecol=10.78 kJ/mol, the calculated results show that the CaI vibrational population peaks are located at v=2. The calculated cross section decreases slowly with the collision energy increasing. The angle product distributions tend toward backward scattering. The calculated （P2（J^1·K）） values deviate slightly from-0.5 and decrease with increasing collision energy. The Quasiclassical trajectory calculation（QCT） results are in reasonable agreement with experimental data. Moreover, the dynamics of the reaction has been discussed.     

Transcrystallization of PTFE fiber/PP composites. II. Effect of transcrystallinity on the interfacial strength

It has been found that transcrystallinity of polypropylene (PP) develops easily on the polytetrafluoroethylene (PTFE) fiber surface in spite of the low surface energy of the fiber. Effect of the transcrystallinity on the interfacial strength has been extensively investigated using a single-fiber pull-out test. By controlling the crystallization temperature, range 25–130°C, the thickness of the transcrystalline layer varied from 0 to 175 μm for thick specimens, ca. 1 mm thick. Measurements of the adhesive fracture energy, the interfacial shear strength and the frictional stress were carried out for specimens with different embedded fiber lengths. Results show that interfacial strength and fracture energy are independent of the transcrystalline thickness. The calculated value of interfacial shear strength is 3.6 MPa, and the fracture energy for debonding is 2.1 J/m². The presence of transcrystallinity does not promote the level of adhesion in PTFE/PP composites. However, the frictional stresses at the debonded fiber/matrix interface increase with transcrystalline thickness. It is attributed to the residual stresses which arise from shrinkage when specimens are cooled from crystallization temperature to room temperature. © 1996 John Wiley & Sons, Inc.     

Proton sponge and fatty acid interactions at the air-water interface. Thermodynamic, spectroscopic, and microscopic study

Mixed Langmuir and Langmuir-Blodgett (LB) films of a proton sponge, namely, diphenyl bis(octadecylamino)phosphonium bromide, and a fatty acid, docosanoic acid, with different molar ratios have been fabricated. Surface pressure versus area per molecule isotherms were registered, and the excess areas and excess Gibbs energy of mixing were calculated. Strong interactions between the proton sponge and the fatty acid take place at the air-water interface. The existence of a stoichiometric 1:1 acid-base reaction between the two components forming a complex on the water surface at high surface pressures has been demonstrated. Furthermore, the reaction had an efficiency close to 100% at the air-water interface; meanwhile, it hardly takes place in organic solvents such as chloroform or even a mixture of chloroform and dimethyl sulfoxide. The floating films were transferred to solid supports and characterized by means of several techniques including IR spectroscopy, X-ray diffraction, and atomic force microscopy, revealing the presence of highly ordered alkyl chains and a constant architecture along the different layers as well as the presence of different domains in the LB films, except those having a 1:1 proton sponge-fatty acid ratio that are homogeneous. Such domains have been interpreted as the presence of two different phases, the 1:1 complex plus the excess component in the mixture.     

Relative energy of organic compounds II. Halides, nitrogen, and sulfur compounds

The energies of the following types of compounds are characterized by their calculated relative enthalpies: alkyl, alkenyl, and aryl halides; carboxylic acid halides; carbonyl halides; amines; carboxylic acid amides; hydrazine derivatives; nitriles; heteroaromatic compounds; nitro-compounds; organic nitrites and nitrates; organic sulfides; thiols; disulfides; sulfoxides; sulfones; organic sulfites and sulfates; and selected inorganic compounds. Stabilization energy of pyrrol and thiophene has been estimated.     

Crystal Structure and Quantum Chemical Ab Initio Calculations of Ibotenic Acid,an Excitatory Amino Acid Receptor Agonist

Ibotenic acid, a constituent of Amanita muscaria, is a potent NMDA receptor agonist. The structure of the ibotenic acid zwitterion monohydrate in the crystalline state has been determined by X-ray crystallography. The crystal structure has two ibotenic acid monohydrate formula units in the asymmetric unit and features an extensive hydrogen bond network. The ibotenic acid zwitter-ions in the crystalline state are compared to the in vacuo structure calculated by quantum chemical ab initio calculations at the HF/6-31+G* level and the effects of the hydrogen bond network on the structures in the solid state are discussed. The calculated potential energy curve with respect to side-chain orientation displays a single energy minimum. The conformations corresponding to the solid-state conformations are calculated to be ca. 2 kcal/mol higher in energy than the minimum-energy conformation in vacuo.     

Spin-probe studies. II. Applications to polymer characterization

The spin-probe technique has been employed to study interactions between several small organic nitroxides and host polymers in which they are dissolved. By this method one is able to study the mobility of the dissolved molecule in its microscopic environment using electron spin resonance spectroscopy. The behavior of one nitroxide has been examined in twelve different polymers and copolymers. An ESR line shape parameter has been correlated with T_m and T_g. In addition, energy barriers for the rotation of the dissolved nitroxides in the polymers have been calculated. They range from 7.8 to 18 kcal/mole, depending on the structure of the nitroxide and the polymer. Similar experiments in a hydrocarbon solvent afford a rotational energy barrier of 3.8 kcal/mole.     

磺酸树脂在樟脑肟贝克曼裂解反应中的催化作用

我们发现以磺酸树脂作为固体酸催化樟脑肟贝克曼裂解反应可以生成α-龙脑烯腈.考察了溶剂、催化剂用量、反应温度和反应时间等对反应的影响.在优化条件下樟脑肟可以完全转化,α-龙脑烯腈选择性高达90.5%.动力学研究表明,樟脑肟在磺酸树脂催化下的贝克曼裂解反应服从准一级动力学模型,经过最小二乘法求得反应的表观活化能为64.6kJ/mol.     

Effect of temperature on the surface free energy of amorphous carbon films

Diamond-like carbon (DLC) and tetrahedral amorphous carbon (ta-C) have attracted much attention recently for biomedical and antifouling applications due to their excellent biocompatibility and inherent nonstick properties. It has been demonstrated that the solid surface free energy is a dominant factor in cellular or fouling adhesion. However, few data for the surface free energy of DLC and ta-C coatings at temperatures in the range 37-95 degrees C are available. In this study DLC and ta-C coatings on stainless steel 304 sheets were prepared using an unbalanced magnetron sputtering system and a filtered cathodic vacuum arc system, respectively. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces at temperatures in the range 20-95 degrees C were measured using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (e.g., dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the total surface free energy and dispersive surface free energy of the ta-C coatings, DLC coatings, stainless steel 304 and titanium decreased with increasing surface temperature, while the acid-base SFE component increased with increasing temperature.     

Ester decomposition as a two-center synchronous reaction

Experimental data on the molecular decomposition of esters with various structures into an olefin and the corresponding acid in the gas phase are analyzed in terms of the intersecting parabolas method. Enthalpies and kinetic parameters characterizing this decomposition have been calculated for 33 reactions. Ester decomposition is a concerted two-center reaction characterized by a very high classical potential barrier of thermoneutral reaction (148–206 kJ/mol). The totality of reactions examined is divided into eight classes. Activation energies and rate constants have been calculated for 38 reactions using the kinetic parameters obtained. The activation energies and rate constants of the reverse bimolecular reaction of acid addition to olefins have been calculated by the intersecting parabolas method. Factors in the activation energy of ester decomposition and formation reactions are discussed.     

The vibrational spectra, molecular structure and conformation of organic azides : Part IV. An ab initio study of hydrazoic acid, azidomethane, azidoethane, azidoethene and azidomethanal

Fully optimized geometries have been calculated for the title compounds at the Hartree—Fock SCF level and compared with existing experimental data. A basis set of double zeta quality has been employed. For hydrazoic acid, a calculation with a larger basis set, expected to give results near the Hartree—Fock limit, has also been performed. All of the calculations show the azide group to be slightly bent with a trans configuration around the central NN bond. Azidoethane is predicted to exist in two conformations, gauche (71°) and anti, with a negligible energy difference of 0.26 kJ mol⁻¹ between them. Azidoethene and azidomethanal both prefer the syn orientation of the azide group with respect to the C---C or C---O bonds, the computed energy difference between the anti and syn conformations being 3.31 and 30.3 kJ mol⁻¹ respectively.

The barrier to rotation around the C---N bond has been calculated to be 3.75 kJ mol⁻¹ in azidomethane while in azidoethane it was 3.30 and 9.40 kJ mol⁻¹ in the eclipsed anti-clinal (120°) and syn positions, respectively.

Complete harmonic force fields and dipole moment derivatives have been calculated for hydrazoic acid, azidomethane and for the two stable conformations of azidoethane. For azidoethane and azidomethanal only the azide part of the harmonic force field has been calculated. The theoretical harmonic force fields have been modified through scaling by a least squares refinement to the observed wavenumbers of hydrazoic acid, azidomethane and azidoethane (anti and gauche). Infrared vapour phase intensities have been calculated and theoretical spectra are presented for azidomethane and azidoethane.     

Atomistic simulation studies of magnetite surface structures and adsorption behavior in the presence of molecular and dissociated water and formic acid

Static energy minimization techniques have been used to elucidate the surface structures of magnetite crystals in pure and hydroxylated forms. Adsorption energy values in the presence of molecular water, dissociate water and simple carboxylic group molecule (formic acid) are calculated and we found that the carboxylic group do not adsorb strongly in most of the pure and hydroxylated surfaces in comparison to water. Since the associated calcium minerals are floated from magnetite using fatty acid collector, our calculations corroborate the flotation practice of removing these impurity minerals from magnetite.