bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the oxidative cleavage of the CC triple bond during the Autoxidation of Acetylenic Hydrocarbons. II. Studies concerning the reaction of ketocarbenes with molecular oxygen
Authors: Rao T. S. S. , Pritzkow W. 
Published: January 2005

Abstractα‐Diazoacetophenone, α‐diazopropiophenone, α‐diazobutyrophenone and α‐diazodesoxybenzoin were thermally and photochemically decomposed in the presence and in the absence of oxygen using benzene, cyclohexane and chlorobenzene as solvents. The products expected from the reaction of the short‐lived intermediate ketocarbenes with oxygen (α‐diketones and lower carboxylic acids, especially benzoic acid) could not be detected. No substantial difference was found between the composition of the reaction mixtures formed in the presence and absence of oxygen. The results show that the oxidative cleavage of the CC triple bond during the autoxidation of acetylenic hydrocarbons does not proceed via the corresponding oxirenes or the valence‐isomeric ketocarbenes.
NMR‐ und UV‐VIS‐Spektroskopische Untersuchungen an Push‐pull‐Butadienen
Authors: Michalik M. , Peseke K. 
Published: January 2005

N.M.R. and U.V.‐VIS Spectroscopic Investigations on Push‐pull Butadienes13C‐n.m.r., d‐n.m.r. and u.v.‐vis spectroscopical data show that the push‐pull character of the investigated butadienes is lowered by substitution at the carbon atom in 3‐position of the butadiene chain.
Oxidation of 2,3‐Bis(hydroxymethyl)indole
Authors: Misztal S. , Mokrosz J. L. , Bielecka Z. 
Published: January 2005

AbstractOxidation of 2,3‐bis(hydroxymethyl)indole (1) with MnO2 yields as intermediate 3‐formyl‐2‐hydroxymethylindole (2) and finally 2,3‐diformylindole (3). The structure of 2 was proved by both chemical methods and 13C n.m.r. spectra. Use of DMSO acetic anhydride mixture as the oxidative agent, however, yields the 3,3′‐diindolylmethane derivative 4, instead of 2 or 3.
Pyryliumverbindungen. 43 [1]. Arylsubstituierte 5‐(2‐Dialkylamino‐thiazol‐5‐yl)‐pentadienone aus 2,4,6‐Triaryl‐pyryliumsalzen und 2‐Dialkylamino‐4‐arylthiazolen
Authors: Zimmermann T. , Fischer G. W. , Teller J. , Dehne H. , Olk B. 
Published: January 2005

Pyrylium Compounds. 43. Arylsubstituted 5‐(2‐Dialkylamino‐thiazol‐5‐yl)‐pentadienones from 2,4,6‐Triarylpyrylium Salts and 2‐Dialkylamino‐4‐aryl‐thiazoles2,4,6‐Triarylpyrylium salts 1 react with 2‐dialkylamino‐4‐aryl‐thiazoles 7 (used in substance or prepared in situ from α‐thiocyanato‐acetophenones 9) in the presence of an appropriate acid‐binding agent (e.g. piperidine acetate or sodium acetate) to give 5‐(2‐dialkylamino‐4‐aryl‐thiazol‐5‐yl)‐1,3,5‐triaryl‐penta‐2,4‐dien‐1‐ones 8. As reaction medium aliphatic alcohols (ethanol, n‐propanol), dipolar aprotic solvents (acetonitrile) or chlorinated hydrocarbons (methylene chloride, chloroform) can be used. On the other hand, under the same conditions 2‐amino‐4‐phenyl‐thiazole (10) reacts with salts of type 1 via pyrylium ring transformation yielding 2,4,6‐triaryl‐1‐(4‐phenyl‐thiazol‐2‐yl)‐pyridinium perchlorates 11.
Site of alkylation in pyrimidine derivatives: Studies on the structure of 1‐Alkyl‐4‐amino‐6‐methylpyrimidinium Iodides
Authors: Zeuner F. , Niclas H.‐J. , Reck G. , Schenk H. 
Published: January 2005

AbstractThe alkylation of 4‐amino‐6‐methylpyrimidines (1a‐f) in DMSO or nitrobenzene at room temperature affords the 1N‐alkylated products 2a‐h. Treatment of 1a‐c with an excess of methyl iodide in the presence of powdered alkali metal hydroxides/DMSO gives the pyrimidinium salts 2g, i, j. Carbon‐13 n.m.r. and X‐ray studies have shown that in the case of compounds 2 the polymethine structure B is preferred.
Physico‐Chemical Studies of the CaO‐Ethylene Glycol System. Determination of free lime in industrial products
Authors: Delimi R. , Ghorab M. F. , Chtcherbakov V. , Messadi D. 
Published: January 2005

AbstractOptimum conditions for a conductometric determination of free lime in industrial products, using alternating current conductometry are elaborated. The analysis of the variation of the conductivity in dependence on concentration in the temperature (°C) range [25–100] allowed the determination of dissociation parameters of calcium glycolate viz. dissociation constant and equivalent conductivity at infinite dilution, which in turn led to the determination of the calcium glycolate concentration from the measured conductivity. The conductometric determination of free lime is only influenced by the presence of SrO. The water content of the solvent (ETG) must not exceed 0.5%.
Synthese und spektroskopische Eigenschaften chiraler 1,3‐Oxazolidine
Authors: Evers R. , Michalik M. 
Published: January 2005

Synthesis and Spectroscopic Properties of Chiral 1,3‐Oxazolidines(1S,2S)‐2‐Amino‐1‐(p‐nitrophenyl)‐propan‐1,3‐diol 2a and the (1R,2R)‐configurated isomer 2b react with N‐substituted dithiocarbimidic acid diesters and ketenedithioacetals, respectively, to give the 2‐substituted chiral 4‐hydroxymethyl‐5‐phenyl‐1,3‐oxazolidines 4 and 7. N‐Carbmethoxy‐dithiocarbimidic acid dimethylester yields under the same conditions the isomeric 1,3‐oxazolidine 5. On treatment of 4 and 7 with isocynantes crystalline urethanes 9 are formed.
Pyryliumverbindungen. 45 [1]. 4‐Aroyl‐fluorene aus 2,4,6‐Triaryl‐pyryliumsalzen und Indan‐1‐on via 2‐(5‐Oxo‐pent‐2‐en‐1‐yliden)‐indan‐1‐one
Authors: Zimmermann T. , Fischer G. W. , Olk B. 
Published: January 2005

Pyrylium Compounds. 45. 4‐Aroyl‐fluorenes from 2,4,6‐Triaryl‐pyrylium Salts and Indan‐1‐one via 2‐(5‐Oxo‐pent‐2‐en‐1‐yliden)‐indan‐1‐ones2,4,6‐Triarylpyrylium salts 1 react with indan‐1‐one in the presence of an appropriate buffer system (e.g. piperidine acetate, triethylamine/acetic acid, triethylamine or sodium acetate) to yield the 2‐(1,3,5‐triaryl‐5‐oxo‐pent‐2‐en‐1‐yliden)‐indan‐1‐ones 2. For the reaction medium aliphatic alcohols (methanol, ethanol), dipolar aprotic solvents (acetonitrile) or chlorinated hydrocarbons (methylene chloride, chloroform, carbon tetrachloride) can be used. On treating 2 with sodium methanolate in methanol, a cyclization reaction occurs giving rise to the 4‐aroyl‐1,3‐diaryl‐fluorenes 3. As by‐products 1,3‐diaryl‐fluorenes 8 (e.g. 1,3‐diphenyl‐fluorene) are formed. ‐ I.r., n.m.r. and u.v. spectroscopic data of the novel compounds 2 and 3 are reported.
Darstellung von Benzo[c]thiophenen nach neueren Varianten der Hinsberg‐Reaktion
Authors: Volz Wolfgang , Voss Jürgen 
Published: January 2005

Preparation of Benzo[c]thiophenes Using a Modified Hinsberg‐ReactionWhereas the tetrahydrobenzo[c]thiophenes 3 and 6 are easily obtained from 1 and 2 or 4 their dehydrogenation (i. e. aromatization) is difficult and the yields are low. However, the method allows to prepare hitherto unknown benzo[c]thiophenes with special substituents in the 1,3‐positions.
Elektrochemische Synthese von (E)‐Thiokohlensäure‐S‐ethenyl‐O‐ethyl‐diestern
Authors: Hess U. , Schulze M. 
Published: January 2005

Electrosynthesis of (E)‐Ethenyl‐O‐ethyl‐thiocarbonatesElectrochemical reductions of 4‐aryl‐ and 4,5‐diaryl‐1,2,3‐thiadiazols (1–5) in acetonitrile/0,1 M tetraalkylammonium‐supporting‐electrolyte at Hg‐cathodes in the presence of ethylchloroformiate (CAE) yield (E)‐S‐(2‐aryl) ethenyl‐ and S‐(1,2‐diaryl)ethenyl‐O‐ethyl‐thiocarbonates (1a–5a). The S‐carboxylation proceeds via preformation of cyclic‐voltammetric‐ and 1H‐nmr‐provable CAE‐complexes, ring‐opening and N2‐elimination in a two‐electron reduction. The synthesis including a rearrangement of a N‐tos‐S‐CAE‐complex is discussed in context with CNDO/2 quantum chemical calculation. Thermochemical synthesis of this new class of thiocarbonates proved unsuccessful.
Alternative derivation of perturbation expansions in the projection operator formalism
Authors: Timoneda J. Juanós I 
Published: January 2005

AbstractThe perturbation‐theoretic expansions obtained from Löwdin's projection operator formalism are derived in a new way, using Kato's formulation of perturbation theory. Kato's approach provides a convenient alternative to diagrammatic techniques for obtaining eigenvalues and eigenvectors. Different normalization criteria imposable on the wave function are easily visualized in terms of the operator that yields the perturbed state vector when it acts upon the unperturbed wave function.
Water‐Chain intervention in the ketonization of vinyl alcohol. An ab initio study
Authors: Lledós A. , Bertrán J. , Ventura Oscar N. 
Published: January 2005

AbstractThe ketonization of vinyl alcohol in aqueous solution has been studied by means of ab initio calculations, using the STO‐3G basis set. The intervention of a chain of two water molecules reduces dramatically the potential barrier. This result agrees with experimental facts.
Spin and charge densities from Hiller–Sucher–Feinberg identities. Test calculations for He, B, C, N, O, and F atoms and H2O, N2, and CH3 molecules
Authors: Ishida Kazuhiro 
Published: January 2005

AbstractSpin and charge densities for several atoms and molecules can be calculated by the use of the Hiller–Sucher–Feinberg identities in the Hartree–Fock (HF) or the unrestricted Hartree–Fock (UHF) level with Gaussian basis sets. Previously presented formulas for the necessary integrals are improved for rapid computations when the d‐type Gaussian functions are added to the basis set. For charge density, a reliable description is obtained even for the HF or the UHF wave function, despite the use of the noncusp basis functions. The lack of the cusp in the Gaussian functions can be overcome also for spin density.
Accurate SCF computations on hydrogen bonds: Role of polarization functions on the bridge hydrogen atom
Authors: Seel M. , Del Re G. 
Published: January 2005

AbstractFor Hartree–Fock calculations, the limited basis 6–31G(*), with p functions on the bridge proton as the only polarization functions, is shown to be better balanced than the larger 6–31G* basis with d polarization functions on the heavy atoms and is therefore, a more suitable basis for the Hartree–Fock description of hydrogen bonds in large systems.
Theoretical study of lithium‐fluoride and lithium‐chloride ion pairs in aqueous solution. An SCF‐CNDO/2 approach including continuum solvent effects
Authors: Gómez‐jeria J. S. , Contreras Renato R. 
Published: January 2005

AbstractSCF‐CNDO/2 calculations, including solvent effects via an extended version of the Generalized Born Formula (GBF), have been performed for LiX(H2O) species (n = 1,2; X = F, Cl). Several minima in the free energy surface, representing intimate and solvent‐separated ion pair structures, have been analyzed. Qualitative results show a preferential stabilization of the intimate forms with respect to the solvent‐separated ones. The results are discussed on the basis of a convenient partition of the total solute‐solvent free energy. The interaction of the ionic species with the bulk solvent neglected in previous studies appears to be responsible for the preferential stability of the intimate forms.
Bohr orbit theory revisited. II. Energies for 1S, 2P, 3D, and 4F states of helium
Authors: Harcourt Richard D. 
Published: January 2005

AbstractA modified Bohr orbit procedure is used to calculate the energies for the 1S ground state and the 2P, 3D, and 4F excited states of the helium atom. The energies are calculated from \documentclass{article}\pagestyle{empty}\begin{document}$ {{\int\limits_0^\pi {E\left(\Phi \right)P\left(\Phi \right)d\Phi } } \mathord{\left/ {\vphantom {{\int\limits_0^\pi {E\left(\Phi \right)P\left(\Phi \right)d\Phi }} {\int\limits_0^\pi {P\left(\Phi \right)d\Phi } }}} \right. \kern-\nulldelimiterspace} {\int\limits_0^\pi {P\left(\Phi \right)d\Phi } }} $\end{document}, in which E(ϕ) is the Bohr orbit energy for angle ϕ between the position vectors \documentclass{article}\pagestyle{empty}\begin{document}$ \vec r_1 $\end{document}
r1 and \documentclass{article}\pagestyle{empty}\begin{document}$ \vec r_2 $\end{document}
r2, and P(ϕ) is a probability function for this angle. Numerical procedures are used to evaluate the integrals. Energies that range between −2.9082 and −2.9054 au are calculated for the 1S state (cf. −2.9037 au, exact). The Bohr energies for the excited states are −2.1318, −2.1240, −2.0562, −2.0555, −2.0314, and −2.0312 au, which are generally close to the exact energies of −2.1332, −2.1239, −2.0557, −2.0557, −2.0313, and −2.0313 au for the 23P, 21P, 33D, 31D, 43F and 41F states. Some relationships that exist between the Bohr theory and the Schrödinger local energies are discussed. Approximate Bohr orbit estimates for the energies of the 2P states of He, Li+,…,Ne8+ are reported.The invariance of the two‐electron Bohr hamiltonian with respect to the interchange of the electron coordinates leads to two classical probability functions when the orbit quantum numbers for the two electrons differ.
A simple introduction to colored symmetry
Authors: Coxeter H. S. M. 
Published: January 2005

AbstractThe problem of systematically coloring periodic patterns has interested textile designers, artists, and crystallographers since 1935. The classification of possible procedures has been seen to depend on space groups and their subgroups and factor groups. Crystallographers naturally worked in Euclidean three‐space before generalizing to two, and then four, dimensions. The present treatment deals with the one‐dimensional case in a manner that can easily be extended. Avoiding the crystallographers' customary emphasis on translations, among the various kinds of symmetry operations, allows the classification to be readily adapted to non‐Euclidean geometries.
Integral processing in beyond‐Hartree‐Fock calculations
Authors: Taylor Peter R. 
Published: January 2005

AbstractThe increasing rate at which improvements in processing capacity outstrip improvements in input/output performance of large computers has led to recent attempts to bypass generation of a disk‐based integral file. The “direct” SCF method of Almlöf and co‐workers represents a very successful implementation of this approach. The present work is concerned with the extension of this general approach to CI and MCSCF calculations. After a discussion of the particular types of MO integrals for which — at least for most current generation machines — disk‐based storage seems unavoidable, it is shown how all the necessary integrals can be obtained as matrix elements of Coulomb and exchange operators that can be calculated using a direct approach. Computational implementations of such a scheme are discussed.
Implementation of the complex coordinate method for resonances and photoionization cross sections by means of matrix element extrapolation
Authors: Froelich Piotr , Sangfelt Erland , Weiner Brian 
Published: January 2005

AbstractA new implementation of the complex coordinate method for calculation of molecular resonances and photoionization cross sections is presented. The method originates from the idea of analytic continuation of stabilization graphs, but instead all matrix elements are numerically continued. Exterior scaling is invoked in conjunction with the use of dilationally adapted basis sets. It is operationally equivalent to the bivariational method in the Feshbach‐partitioned manifold of complex basis functions, but no complex integrals are calculated. Instead, the complex eigenvalue problem arises from the analytical continuation of the realvalued matrix elements pertinent to any atomic or molecular structure code in its standard (real) form. That includes the possibility of using numerical basis sets. Since the method does not require modification of existing numerical codes, it can serve as a complement to any large scale CI or MCSCF molecular structure calculation.
The peri effect in aromatic hydrocarbon carcinogenesis: An empirical force field examination
Authors: Seybold Paul G. , Lipkowitz Kenny B. 
Published: January 2005

AbstractMethyl substitutents located peri to bay‐region benzo rings of polycyclic aromatic hydrocarbons generally reduce or eliminate carcinogenic activity, most likely because such substituents force the hydroxyl groups of dihydrodiol intermediates to adopt preferentially pseudodiaxial, rather than pseudodiequatorial, conformations. Empirical force field calculations have been employed to examine the influences of peri and other positional substituents on hydroxyl conformation, taking naphthalene, anthracene, and phenanthrene as model compounds. For the unsubstituted naphthalene and anthracene dihydrodiols, the pseudodiequatorial conformation is preferred. This preference is reduced by adjacent methyl substitution and reversed by peri methyl substitution. Because of steric crowding the phenanthrene bay‐region dihydrodiol preferentially adopts a pseudodiaxial conformation. The results are discussed in relation to recent experimental evidence.
Spectroscopic studies on some phenylethylamine drugs: Molecular orbital calculations
Authors: Abu‐Eittah R. H. , Hamed M. M. , Abdou M. M. 
Published: January 2005

AbstractThe electronic absorption spectra of some phenylethylamine drugs, namely, d‐pseudoepherine, l‐pseudoephedrine, l‐ephedrine, dl‐ephedrine dl‐norephedrine, phenylethylamine, methoxyphenamine, and l‐noradrenaline were investigated in polar and nonpolar solvents. The observed transitions were interpreted, and the role of σ‐π interaction was explored. Molecular orbital calculations were performed on representatives of the above group of compounds, namely, d‐pseudoephedrine, l‐ephedrine, and l‐noradrenaline using the INDO procedures and adopting the best conformer of the molecule. The transition energy, band intensity, and dipole moments were calculated and corresponded satisfactorily with the experimental values.
Cellular spin resonance inversion by ion‐induced dipoles
Authors: Pollock J. Kent , Pohl Douglas G. , Pohl Herbert A. 
Published: January 2005

AbstractCellular spin resonance (CSR) or electrorotation is the spinning of cells or other particulate matter in rotating electric fields. The spin rate of the (bio)particle varies markedly with the applied frequency and often is seen to have rather sharp maxima as the frequency is varied. In certain frequency ranges, living cells often are observed to undergo a striking inversion of their spin rate and then spin counter‐clockwise (CCW) while the direction of rotation of the applied electric field is clockwise (CW).The CSR spectra are presumably due to dipolar interactions with the applied field, as are the spectra obtained by straightforward dielectrophoresis (DEP) techniques. The two spectra, however, differ radically in the low frequency ranges (below about 1 MHz). It is our objective to explain this apparently anomalous behavior.We believe that the anomaly appears primarily because one is comparing rotational with translational force responses. In the DEP techniques, the simpler translational force arising from the comparative polarizability of cell versus medium (water) gives a straightforward measure of the differential polarizability owing to volume and surface effects pro forma. In the CSR techniques the spin rate reflects the torque on the cells and hence emphasizes polarization at the outer periphery of the cells rather than that of the average overall polarizability.The problem is considered in terms of a living or dead cell rotating with an angular velocity Ω in a fluid medium of viscosity η when it is subject to an electric field rotating at angular frequency ω. It is observed in many experiments that Ω ≪ ω, and also that the sign of Ω for the same cell can change from CW to CCW and back to CW as the applied frequency ω of the CW electric field is increased. Moreover, the sign and magnitude of the CSR spectra differ for living and dead cells. All of these experimental results can be explained quantitatively by using Maxwell's equations and the dielectric properties of a lossy dielectric sphere in an ionically conductive dielectric fluid.
Direct calculation of the Hartree–Fock interaction energy via exchange–perturbation expansion. The He …︁ He interaction
Authors: Jeziorska Małgorzata , Jeziorski Bogumił , Čížek Jiří 
Published: January 2005

AbstractThe Hartree‐Fock (HF) equations for the (He)2 system are solved using a suitable exchange perturbation technique. The HF interaction energy is then obtained directly from a rapidly convergent iteration procedure. The method remains convergent for short interatomic distances, where the interaction energy surpasses the energy of intraatomic excitations. The fast convergence of the method is a result of the proper treatment of the exchange‐deformation effects. In the region of the van der Waals minimum, these effects account for 50% of the HF deformation energy.
“Non‐muffin tin” corrections of the SCF Xα‐SW Method. I
Authors: Rubin I. R. , Lobatch V. A. , Shulgin B. V. 
Published: January 2005

AbstractThe recently developed crystalline cluster method within the framework of the Johnson multiple scattering technique was successfully used in calculations of ionic cubic crystals and the defects with a cubic symmetry. In this paper a simple way of extension of the method to noncubic systems by a partial elimination of “muffin‐tin” approximation (MTA) is proposed.The procedure suggested does reduce the intermediate integrals to the one‐dimensional ones, and they are calculated analytically. It is supposed that an approach of taking into account the nonspherical shape of the potential inside the “muffin‐tin” (MT) spheres will be effective in crystals with an ionic type of chemical bond.
Development and parametrization of sindo1 for second‐row elements
Authors: Jug Karl , Iffert Rüdiger , Schulz Joachim 
Published: January 2005

AbstractThe semiempirical MO method SINDO1 is extended to second‐row atoms from sodium to chlorine. The basis set has a provision to include d orbitals. To retain rotational invariance in a d orbital set, a number of hybrid integrals has to be included that invalidate the zero differential overlap (ZDO) assumption even in a symmetrically orthogonalized basis set. The inclusion of d orbitals rendered the set‐up of integral calculation of the original INDO method impractical. Instead of one subroutine for each integral, all explicitly calculated integrals (overlap, core, electronic repulsion) are now contained in a single subroutine under unifying aspects. The parametrization scheme includes pseudopotentials and adjusts the total energy under inclusion of zero point energies to experimental heats of formation of ground states. The vibrational frequencies for the calculation of zero point energies are obtained from calculated force constants and G matrix elements by a scaling procedure. The results for geometries, energies, and dipole moments are compared with MNDO data.
Exchange perturbation theories
Authors: Klein D. J. 
Published: January 2005

AbstractVarious earlier‐proposed perturbative approaches to the description of weakly interacting species are considered. It is argued that most of these perturbative approaches, including many of the so‐called exchange perturbation theories, exhibit a number of difficulties and limitations, which have not previously been emphasized. From these criticisms positive suggestions as to the nature of a general exchange perturbation‐like theory are made. Finally, a candidate for such a theory is outlined.
Method of local‐scaling transformations and density functional theory in quantum chemistry. II. The procedure for reproducing a many‐electron wave function from x‐ray diffraction data on one‐electron density
Authors: Kryachko Eugene S. , Petkov Ivan Zh. , Stoitsov Mario V. 
Published: January 2005

AbstractThe computational procedure for reconstructing a many‐electron wave function on the basis of x‐ray diffraction data of one‐electron density is proposed within the method of local‐scaling transformations.