bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deactivation behaviour of Photoexcited Aryltropylium Ions. IV. Influence of Ion Pair Formation
Authors: Abraham W. , Dreher B. , Kreysig D. , Sadovskij N. A. , Kuzmin M. G. 
Published: January 2005

AbstractAryltropylium salts exhibit an unusually effective self quenching of fluorescence in dependence on their concentration in dichlòromethane. The quenching process is investigated by static and time resolved fluorescence measurements. The observed biexponential fluorescence decay is interpreted by the emissions of ion pairs and free cations. The rate constant of fluorescence quenching by formation ion pair is two orders of magnitude greater than the diffusion constant.
Reversed substituent effect on CO Stretching Vibrations in Maleinimide Derivatives
Authors: Perjéssy Alexander , Augustin Manfred 
Published: January 2005

AbstractThe arithmetic means of wave numbers of symmetric and antisymmetric CO stretching vibrations measured in tetrachloro‐ and trichloromethane of 31 substituted maleinimides were correlated with Taft inductive σ* substituent constants. The series of N‐phenyl and N‐(4‐methylphenyl) derivatives exhibit normal i.e. positive values of slope of vs σ* correlations. In series of substituted N‐methylmaleinimides (and probably also in maleinimides) the negative values of slope of vs σ* correlations indicate a reversed substituent effect on the CO stretching vibration. The mechanism of transmission of substituent effects in maleinimidee system is discussed considering the results of above mentioned observations.
Synthese und Reaktionen von 2‐Arylhydrazono‐N‐phenyl‐succinimiden
Authors: Augustin M. , Jeschke P. 
Published: January 2005

Synthesis and Reaction Behaviour of 2‐Arylhydrazono‐N‐phenyl‐succinimides2‐Arylhydrazono‐N‐phenyl‐succinimides 4a–f are prepared by the heating of 2‐ethoxycarbonyl‐3‐hydroxy‐N‐phenyl‐maleimid 1 with arylhydrazines or ammonium salts 2a–c in acetic acid. The Knoevenagel condensation of the methyleneactive compound 4a with aldehydes in the presence of pyridine forms the corresponding Z‐isomers 5a–e.The succinimides 4a–c are deprotonated to the anions 6a–c, which with heterocumulenes give the new keten‐S,S‐ and keten‐S,N‐acetals 7a–c, 8a–c and (Z/E)‐9a, b. The intramolecular cyclization of 7b and (Z/E)‐9b leads to 1,5‐disubstituted pyrazol‐3,4‐dicarboxylic imides 10a, b. Further derivatives of these heterocyclic series are available by a base promoted opening of the imid ring.
Synthesis of Phosphino Alkane Sulfonates and their corresponding sulfonic acids by reaction of alkalimetal‐phosphides with sultones
Authors: Paetzold Eckhardt , Kinting Annegret , Oehme Günther 
Published: January 2005

AbstractAlkalimetal salts of dialkyl‐ and diphenylphosphino alkane sulfonic acids (1–4, 6, 7) were prepared by reaction of alkalimetalphosphides with sultones at ambient temperature. The sulfonates can be converted into the free sulfonic acids by ion exchange. This method opens an access to water soluble phosphines (8, 9) which can be important as ligands in transition metal complexes for catalytic processes.The use of water soluble tertiary phosphines as ligands in catalytic active transition metal complexes seems to be an achievement of the last ten or twelve years [1]. An important aspect of application is the realization of two phase systems with the catalyst in the water phase acting in the interface. After the catalytic process the catalyst can be separated easily from the product and the recovery of the expensive transition metal is possible.Hydrophilicity of phosphines usually is achieved introducing highly polar hydroxy‐, amino‐, carboxylato‐, ammonium‐, sulfonato‐, and polyether‐groups, respectively, but only tetraalkylammonium‐, polyether‐ and sulfonato‐groups are suitable for a large pH‐range.Sulfonato groups can be introduced into phenylphosphines by sulfonation with sulfur trioxide in sulfuric acid leading to meta sulfonated products. Especially mono‐ and polysulfonation of triphenylphosphine was investigated by AHRLAND, CHATT et al. [2]. Monosulfonation occurs under mild conditions, but the selectivity of a multiple sulfonation is low, and there are some problems with the separation of reaction products [3]. Nevertheless, phenylphosphines with chiral substituents were sulfonated by this method and used as ligands in rhodium complexes for asymmetric syntheses [4]. A way to a triphenylphosphine sulfonated in the para position was given by SCHINDLBAUER [5], but his method seems to be less satisfactory with respect to yield and selectivity.
Studies on alkylheterocycles. I. A convenient Synthesis of Phthalazines
Authors: El‐Bannany A. A. , El‐Assar A. A. , El‐Nagdy M. H. 
Published: January 2005

AbstractEthyl‐2‐arylhydrazono‐2,3‐dioxobutyrate 1a, b reacted with ethylcyanoacetate to yield the pyridazino derivatives 2a, b. Similarly, the pyridazine 2c was obtained via reaction of 3‐arylhydrazonopentan‐2,3,4‐trione with the same reagent. The phthalazines 6 were obtained upon reaction of 2a–c with ylidenemalonitrile 3a, b. The styrene derivatives 7a–d were isolated from the reaction of 2a–c with the appropriate aromatic aldehyde. Compounds 7a–d were subsequently utilized for the synthesis of 6a, d–f respectively via reaction with malononitrile. On the other hand, the phthalazine derivative 8 was formed upon reaction of 2a with either ethylcyanoacetate or malononitrile.
An improved and efficient Synthesis of Quinoxalinecarboxamide 1,4‐Dioxides from benzofuroxan and acetoacetamides in the presence of calcium salts
Authors: Stumm G. , Niclas H.‐J. 
Published: January 2005

AbstractAn improved and efficient method for the preparation of the title compounds 3 is described. Thus, quinoxalinecarboxamide 1,4‐dioxides 3 are synthesized in high yields by reaction of benzofuroxan 1 with acetoacetamides 2 in the presence of catalytic amounts of calcium salts and ethanolamine. The reaction is assumed to involve a chelate mechanism with 4 as intermediate. Side reactions are studied by means of HPLC and TLC.
A novel method for the Amination of 4,6‐Dinitrobenzofuroxan via meisenheimer complexes
Authors: Göuhrmann B. , Niclas H.‐J. 
Published: January 2005

AbstractThe reaction of 4,6‐dinitrobenzofuroxan 1 with alkali metal salts of succinimide, phthalimide, and formamides affords σ‐N–C bonded Meisenheimer complexes 3. The adducts 3a–c may be directly oxidized to the in 7‐position aminated dinitrobenzofuroxan derivatives 6a–c by treatment with aqueous nitric acid. In the case of 6a the oxidation of 3a proceeds with loss of carbon monoxide. For the preparation of 6d–g the alkali metal salts 3d–g must be transformed to the corresponding silver salts 4d–g before oxidation.
Struktur‐Aktivitäts/Selektivitäts‐Beziehungen von Oxidationskatalysatoren
Authors: Kripylo Peter , Koppe Jürgen 
Published: January 2005

Structure‐Activity/Selectivity Correlation of Oxidation CatalystsVarious reactive forms of oxygen are active in the selective oxygen functionalization of olefins and aromatic compounds.These forms are different on different crystal faces of transition metal oxides as shown by their different cation‐oxygen bond lengths. Therefore, face specifity of transition metal oxides as catalysts can be expected for the selective oxidation of hydrocarbons.Furthermore, the reactivity of the framework oxygen in the transition metal oxides for selective oxygen functionalization of hydrocarbons is dependent on the nature of the catalytic cycle (one‐ or two‐electron‐processes).Therefore, structure sensitivity of oxidation catalysts on the selectivity of transition metal oxides as oxidation catalysts is possible. Starting from this concept the following phenomena of the activity/selectivity relations are discussed for the most important industrial oxidation catalysts:
—ensemble effects on the selectivity of supported Ag catalysts for the oxidation of ethylene to ethylenoxide.
—face specifity of multicomponent Bi/Mo‐oxide catalysts in the selective oxidation of propylene to acrolein and in the ammoxidation of propylene.
—structure sensitivity of V2O5‐containing catalysts in the oxidation of aromatic compounds.
Study on the Reactions of 3‐Benzoyl‐2,4,5‐pyrrolidinetrione with aliphatic diamines, phenylhydrazine, semicarbazide and guanidine derivatives
Authors: Żankowska‐Jasińska Wanda , Ostrowska Katarzyna 
Published: January 2005

Abstract3‐Benzoyl‐2,4,5‐pyrrolidinetrione (1a,b) with aliphatic diamines, phenylhydrazine, semicarbazide, and guanidine derivatives yields mono and binary salts (4, 7, 10, 11‐14), enamines (2, 3), imine (5), pyrrolo[3,4‐c]pyrazole (6) and pyrrolo [3,4‐e][1,4]diazepine (8), respectively. The influence of the reagents basicity on the route of cyclocondensation is studied.
Synthesis and characterization of substituted 2‐diazo‐1 ‐oxo‐1,2‐dihydzonaphthalenes and their products of photolysis and thermolysis
Authors: Baumbach B. , Bendig J. , Nagel T. , Lubsky B. 
Published: January 2005

AbstractSeveral 2‐diazo‐1‐oxo‐1,2‐dihydronaphthalene{ (1, 2) have been synthesized by reaction of selected hydroxy compounds and 2‐diazo‐1‐oxo‐1,2‐dihydzonaphthalene‐5‐ and ‐4‐sulfonylchloride, respectively.Photolysis as well as thermolysis of 1 and 2 leads to final products, the nature of which depends on the position of substitution. So, reactions of 5‐substituted derivatives (1) yield the corresponding indene‐3‐carboxylic acids 3 and their esters 5, respectively. In contrast, reactions of 4‐substituted derivatives (2) lead to the formation of the 1‐sulfo‐indene‐3‐carboxylic acid derivatives 4 and 6. Prepared compounds have been characterized by means of mass, ultraviolet, infrared, 1H‐n.m.r. ind 13C‐n.m.r. {pectroscopy.
Pyryliumverbindungen. 46. 4‐Aroyl‐fluoren‐9‐one durch Ringtransformation von 2,4,6‐Triaryl‐pyryliumsalzen mit Indan‐1,3‐dion
Authors: Zimmermann T. , Fischer G. W. , Olk B. 
Published: January 2005

Pyrylium Compounds. 46. 4‐Aroyl‐fluoren‐9‐ones by Ring Transformation of 2,4,6‐Triarylpyrylium Salts with Indan‐1,3‐dioneThe ring transformation of 2,4,6‐triarylpyrylium salts 1 with indan‐1,3‐dione in the presence of a condensing agent such as piperidine acetate, triethylamine/acetic acid, triethylamine or sodium acetate leads to 4‐aroyl‐1,3‐diaryl‐fluoren‐9‐ones 6. As reaction medium aliphatic alcohols (methanol, ethanol), dipolar aprotic solvents (acetonitrile, dimethylformamide) or chlorinated hydrocarbons (methylene chloride, chloroform) can be used. The structure of the novel compounds 6 was confirmed by spectroscopic methods as well as by independent synthesis of the fluorenone 6a.
Dielectric Relaxation and Short Range Order of a Liquid Crystalline Benzoate
Authors: Kresse H. , Haas S. , Heinemann S. , Kremer F. 
Published: January 2005

AbstractDielectric investigations on 4‐nitrobenzyl 2,5‐bis‐(4‐n‐hexyloxybenzoyloxy)‐benzoate A (10Hz – 100MHz) and a mixture of A and rodlike benzoates B (10Hz – 100kHz) reveal for A two main relaxation mechanisms in the liquid crystalline phases. The low frequency one connected with the reorientation around the short molecular axis shows in mixtures an anormal increase of the intensity with temperature. The unexpected behaviour of the static dielectric constants of A as well as the systematic change of the dielectric data in the mixture with B are interpreted by a systematic change of the antiparallel correlation of A in the short range.
Konformationsanalyse freier und komplexierter Kronenether in Lösung
Authors: Kleinpeter E. 
Published: January 2005

Conformational Analysis of Free and Complexed Crown Ethers in SolutionThe conformational analysis of the crown ether family by means of n.m.r. spectroscopy is reviewed here. Conclusions about preferred conformations are drawn from dipolar (NOE) and scalar couplings (nJH,H),13C chemical shifts and their temperature dependences as well. Information about the flexibility are available from dynamic n.m.r. spectroscopy and the spin‐lattice relaxation times T1 Also conformational variations as result of the complexation of cations or other guest molecules, flexibility variations and the stoichiometry of the complexes obtained can be readily studied by the same n.m.r.‐parameters. Special remarks are referenced to the respective possibilities of CP‐MAS‐13C‐ n.m.r. spectroscopy in the solid state as well as other alternative methods of conformational analysis in solution as are dipole moment measurements and the RAMAN vibrational spectroscopy. The conformational peculiarities of the crown ether family are summarized.
Energies of optical excitations and ionization potentials for hydrocarbons with multiple bonds according to results of the DVM‐Xα calculations
Authors: Gutsev G. L. , Boldyrev A. I. , Ovchinnikov A. A. 
Published: January 2005

AbstractThe electronic structure of the C2H2, C2H4, and trans‐C4H6 molecules is calculated using the discrete variational Xα‐method (DVM‐Xα). The calculated energies of optical excitations and ionization potentials are compared with both experimental data and results of other nonempirical methods. We conclude that DVM‐Xα is a reliable method for investigating the electronic structure of polyenes.
The electronic structure of all‐trans‐polyenes C2nH2n+2, n = 3–7
Authors: Gutsev G. L. , Boldyrev A. I. , Ovchinnikov A. A. 
Published: January 2005

AbstractThe electronic structure of the C2nH2n+2 trans‐polyenes, n = 3–7, is calculated by the Discrete Variational Xα method (DVM‐Xα). The valence ionization potentials (IP) calculated using the Clementi double zeta basis agree with the known experimental data within several tenths an electron volt. However, the DVM energies of the π → π* optical excitations are systematically underestimated by 0.8–1.0 eV. For polyenes with equal C—C bond lengths, the computed energies of the first optical transitions are smaller than those of polyenes with alternating C—C bond lengths. The charge distribution in polyenes is analyzed in the framework of a Mulliken scheme. The composition of the frontier molecular orbitals (MO) is analyzed.
Discrete spatial symmetries in energy derivatives
Authors: Banerjee Ajit , Jensen James O. 
Published: January 2005

AbstractBased upon the invariance of N‐particle systems under discrete operations of reflection, inversion, and rotation by 2π/n, a method for obtaining complete sets of relations among energy derivatives of all orders has been presented. The method is based on the criterion that, for a discrete symmetry operation such as reflection across a plane; the change in energy due to simultaneous arbitrary displacements of each particle is equal to another set of “conjugate” displacements of all particles. Applications of the above relations for particular molecular systems possessing a combination of symmetry operations is also presented. Here, via the row echelon analysis, the number of independent derivatives are found, and simple symmetry relations that allow determination of the remaining derivatives are presented. For example, for a homonuclear diatomic molecule with D2h symmetry only 1 of the 6 first derivatives and 1 of the 21 second derivatives need to be independently calculated.
The formation of highly excited H in the reaction H2+(v) + H2 → H + H
Authors: Schatz George C. , Badenhoop Jay K. , Eaker Charles W. 
Published: January 2005

AbstractA quasiclassical trajectory surface hopping method has been used to study H(v) + H2 → H + H for v = 0, 3, 7, 10, 13, and 17 with an emphasis on determining the H internal energy and angular momentum distributions for high v. For v = 13 and 17, significant cross sections are found for producing H at energies above its dissociation energy. An average metastable H lifetime of 11.5 ps for v = 13 and 4.7 ps for v = 17 is found, but there is also a much longer lived component to the lifetime distributions that is more important for v = 13 than for v = 17. Some of the longer lived metastables correspond to high angular momentum orbiting states of H, but other sources of metastability are also present.
Matrix elements for the Morse potential using ladder operators
Authors: Berrondo M. , Palma A. , López‐Bonilla J.L. 
Published: January 2005

AbstractThe algebra of the two‐dimensional harmonic oscillator is exploited to obtain matrix elements between eigenstates of the Morse potential. This follows after mapping the latter into the radial equation of the former problem by means of a change of variable and the use of the angular variable as a dummy variable.
Exact wave functions for few‐particle systems: The choice of expansion for coulomb potentials
Authors: McIsaac K. , Maslen E. N. 
Published: January 2005

AbstractFor exact few‐particle wave functions the choice of expansion has a strong influence on the ease with which the coefficients may be determined. Some expansions, such as those involving hyperspherical coordinates, require complicated expressions for Coulomb interaction potentials. The choice of expansion provides a possible means for minimizing algebraic problems in determining the exact wave function. The complexity due to the nonseparable terms in the potential occurs at different stages of the solution of the Schrödinger equation when the expansion is transformed. When solving recurrence relations to determine the wave function, it is necessary to understand the relationship between degrees of freedom in the solution and the boundary conditions. The degrees of freedom in the solution must be chosen to ensure that the wave function is continuous and normalizable and that the derivatives are bounded everywhere.
Analysis of inter‐ring coupling effects in N‐heterobicyclic π‐systems using a structural definition of aromaticity
Authors: Gready Jill E. 
Published: January 2005

AbstractA purely structural definition of aromaticity based on the average ring bond length and ‐bond order is proposed. The definition is illustrated for N‐heterocycles by reference to theoretical STO‐3G and 3‐21G geometries and charges for some pteridine derivatives. The treatment focuses on the gross structural changes (i.e., ring size, overall degree of π‐electron delocalization, and net ring charges), accompanying chemical changes, such as substitution, tautomerization, ring reduction, and deazination, as well as the structural interdependence of the two rings in a bicyclic ring system.
Hole localization and broken symmetry: A theoretical study of core electron ionization in the Li2 molecule
Authors: Bacskay George B. , Bryant Glenn , Hush Noel S. 
Published: January 2005

AbstractAb initio SCF, CI, CEPA, and MCSCF techniques are compared and contrasted in a theoretical study of the 1s core ionized Li2 molecule from the point of view of core hole localization. In agreement with earlier studies of symmetric core ionized molecules, SCF theory is found to give a physically reasonable description of core ionization only when symmetry breaking is allowed. This results in a dramatic lowering of the energy of the core ionized state and hence of the ionization potential. By extension, CI wave functions that are developed in terms of a broken symmetry SCF reference plus its single and double excitations are found to perform significantly better than those constructed from symmetry adapted SCF orbitals. Alternatively, if the full point group symmetry is to be retained, a multiconfigurational treatment is called for and, in agreement with the conclusions of an analogous study on O2 [H. Ågren, P.S. Bagus, and B.O. Roos, Chem. Phys. Letters 82, 505(1981)], it is found that a modestly sized MCSCF wave function is capable of accounting for the energetic effects of symmetry breaking. Potential energy curves for Li2 and several states of core ionized Li2 have been calculated, allowing predictions of the adiabatic ionization potential and vibrational, satellite, and Auger structures in the photoelectron spectrum of Li2 to be made.
Bases for the irreducible representations of O(3) symmetry adapted to a crystallographic point group
Authors: Gould M. D. , Chandler G. S. 
Published: January 2005

AbstractWe construct bases for the irreducible representations of the rotation group O(3) which are symmetry adapted to a Crystallographic point group. We obtain explicit expressions for the cubic groups, which are valid for arbitrary values of the angular momentum quantum number l. Our method yields an efficient algorithm for both analytical and numerical work. An explicit formula for the multiplicities of an irreducible representation for the cubic groups in an arbitrary angular momentum term l is also derived.
Unitary transformation on the model space. Comparison of Brandow's and Kirtman's versions of quasidegenerate many body perturbation theory
Authors: Svrček Michal , Hubač Ivan 
Published: January 2005

AbstractIn this paper we study the unitary transformations on the model space in quasidegenerate many body perturbation theory (QDMBPT). From this point of view we compare Brandow's and Kirtman's versions of QDMBPT up to the fifth order of perturbation expansion. We show that, starting from Brandow's QDMBPT, we can derive various versions of effective Hamiltonians order by order, of which the Kirtman's version is the simplest one. The operator of unitary transformation we express through the correlation operator.
Shape resonances in electron–molecule scattering. A proposed model in terms of S matrix poles and associated generalized quantum numbers
Authors: Krylstedt Peter , Elander Nils , Brändas Erkki 
Published: January 2005

AbstractAs an extension of the recent atomic work of Krylstedt et al. [1, 2], we propose the synthesis of the static exchange plus polarization model within the multiple scattering Xα formalism and the exterior complex rotation method for the study of shape resonances occurring in molecular collisional systems. The bound state multiple scattering Xα method is reviewed with special attention to the form of the various wave functions for the different molecular regions. In connection with the inclusion of continuum electron exchange into the scattering model, we analyze a possible solution to the problem of asymptotical behavior caused by the local density‐based free electron gas approximation used in this case. We also propose a method to fix the cutoff parameter, inherent in the polarization potential, for symmetry‐related molecular participants in the scattering process, thereby obtaining a possible predictive power for the one‐parameter scattering model.Titchmarsh–Weyl's theory is used to formally connect the above formulation to scattering theory. The theoretical difficulties in obtaining a unique meromorphic continuation of the S matrix are investigated in connection with the requirements on the actual potential to be exterior dilation analytic. Furthermore, the occurrence of asymptotic quantum numbers is noted and discussed in conjunction with muffin tin‐like approximations and related exterior complex rotated schemes.It is found that the electron exchange part of the nonstatic one‐body potential exhibits a functional form that is not exterior dilation analytic, albeit the general electron and nuclear many‐body problem involving Coulomb forces are dilation analytic. Although the immediate consequences indicate a rotation angle (θ) dependence on the S matrix continuation, a uniquely defined assignment of the cutoff parameter r0 = r0(θ) makes the present nonstatic model “exterior dilation analytic” in the sense that it mimics the dilation analytic structure of the full many‐body problem at the same time obeying “asymptotic” spherical symmetry via the associated constant of evolution. However, in the static exchange approximation the above difficulties are shown to be circumvented via a certain reformulation, leading to a regular analytic asymptotic form for the interaction potential.
Inclusion of relativistic effects into ZDO methods. I. A quasi‐relativistic CNDO/1
Authors: Boča Roman 
Published: January 2005

AbstractA version of the CNDO/1 method has been outlined that includes dominant relativistic effects. The method utilizes a nonempirical parametrization based on atomic Dirac–Fock calculations. The goal of this QR‐CNDO/1 method lies in its applicability to molecules consisting of arbitrary atoms (z = 1–118). Applications to molecular geometries and ionization potentials for 50 molecules are presented.