bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoaddition of Ethyl 2,2‐Dimethyl‐5‐oxo‐5,6‐dihydro‐2H‐pyridine‐1‐carboxylate to 2,3‐dimethylbut‐2‐ene
Authors: Jeandon Christophe , Constien Ralf , Sinnwell Volker , Margaretha Paul 
Published: December 2004

AbstractOn irradiation (350 nm) in the presence of excess 2,3‐dimethylbut‐2‐ene, the newly synthesized title compound 5 affords as main products the unexpected cyclopropylpyrrolidine 10 (50%) and the spiro‐oxetane 9 (25%).
Influence of Lewis Acids on the [4 + 2] Cycloaddition of N,N′‐Fumaroylbis[(2R)‐bornane‐10,2‐sultam] to Cyclopentadiene and application to various dienes
Authors: Bauer Tomasz , Chapuis Christian , Kucharska Anna , Rzepecki Piotr , Jurczak Janusz 
Published: December 2004

AbstractAmong seventeen different Lewis acids, TiCl4 was found to be the best catalyst for the [4 + 2] cycloaddition of cyclopentadiene to N,N′‐fumaroylbis[(2R)‐bornane‐10,2‐sultam] ((−)‐1). Independently of the TiCl4 molar concentration, almost constant and complete (98–89% d.e.) diastereofacial π‐selection was achieved in the Diels‐Alder addition of (−)‐1 to cyclopentadiene, cyclohexadiene, isoprene, and 2,3‐dimethylbuta‐1,3‐diene.
Observations sur la photolyse de l'oxyde biazotique (protoxyde d'azote) à l'état comprimé
Authors: Briner E. , Karbassi H. 
Published: December 2004

AbstractEn nous servant de la lampe à vapeur de mercure comme source de rayons ultraviolets, nous avons étudié la photolyse de l'oxyde biazotique (protoxyde d'azote) comprimé à des pressions allant de 5 à 40 atm.
Viskosität und Ladung des Albuminions
Authors: Pauli Wolfgang 
Published: December 2004

Abstract1. Das mit steigendem HCl‐Zusatz zu hochgereinigtem Seralbumin unter starkem Anstieg der Viskosität gebildete positive Proteinion besitzt im Optimum von η eine Ladungszahl Lz ∼ 80 je Teilchen und diente den Versuchen zum Studium seiner Feldwirkung.
Zur Dehydrierung der Hexahydro‐benzoesäure im Tierkörper
Authors: Bernhard Karl , Caflisch‐Weill Henriette 
Published: December 2004

AbstractFrühere Befunde über die Umwandlung der Hexahydro‐benzoesäure zu Benzoesäure im Tierkörper erfuhren eine Erweiterung. Da der Mensch und z. B. das Kaninchen in wechselnden Mengen Benzoe‐ bzw. Hippursäure als normales Stoffwechselprodukt ausscheiden, ist ein vermehrtes Auftreten derselben nach Gaben von Cyclohexan‐carbonsäure kein sicherer Beweis für stattfindende Dehydrierung. Mit Hilfe von Deuterium als Indikator, d. h. durch Herstellung und Verabreichung d‐haltiger Hexahydro‐benzoesäure konnte gezeigt werden, daß Mensch, Hund und Kaninchen zu dieser Dehydrierung befähigt sind. Die Aromatisierung des Cyclohexanringes ist im Tierkörper in vielen Fällen leicht möglich.
Untersuchungen über die Sulfierung des Naphthalins
Authors: Fierz‐David Hans Eduard , Richter Carl 
Published: December 2004

Abstract1. Das Isomerenverhältnis ist bei direkter Sulfierung ein kompliziertes. Bei 130° konnten, von Naphthalin ausgehend, alle nach der Armstrong'schen Regel möglichen Disulfosäuren nebeneinander nachgewiesen werden, so auch die 1,5‐ neben der 2,6‐Säure.
Etudes sur les matières végétales volatiles XXXIII. Sur l'évaluation des alcools tertiaires dans les huiles essentielles
Authors: Naves Y. R. 
Published: December 2004

AbstractLa méthode imaginée par Schryver en vue du titrage des phénols, fondée sur le dégagement d'ammoniac au contact de l'amidure de sodium n'est pas applicable à l'évaluation des alcools. En dehors de l'hydroxyle, d'autres éléments de la molécule régissent et les valeurs obtenues sont, de ce fait, excessives. Par contre, la méthode de Tschugaeff‐Zerewitinow, selon la technique de Soltys, permet le titrage satisfaisant des alcools, dans l'espace de trente minutes.
Hydrogen bonding in simple π‐electron systems II. Pyridine–pyrrol
Authors: Sabin John R. 
Published: December 2004

AbstractPrevious work in this laboratory concerning the properties of hydrogen bonds in the base pairs of DNA [1–6] has led to considerable interest in the properties of hydrogen bonds in π‐electron systems. The first paper in this series [7] has investigated the usefulness of the LCAO–MO–SCF method and the Pariser–Parr–Pople approximation as applied to this problem, by calculation on the ideal pyridine–pyridinium complex. In this paper, a relation with experiment will be established by comparison of the results obtained from this method of calculation with the properties of the experimentally observable pyridine–pyrrol system.
Might the difference between Schrödinger and Ruedenberg's local contributions to the kinetic energy represent elastic deformations of the electron?
Authors: Jørgensen Chr. Klixbüll 
Published: December 2004

AbstractIn Schrödinger's equation, the local contribution to the kinetic energy is sometimes negative, but it allows a conservative potential in contrast to an alternative, never negative, energy proposed by Ruedenberg. The total kinetic energy evaluated in certain characteristic volumes, and in all of space, is identical in the two cases. Dirac's suggestion in 1962 of a bubble‐surface representing the electron is applied in a far‐reaching, but incomplete, attempt to identify external kinetic energy with a first‐order relativistic effect and the internal energy constituting the difference between Schrödinger and Ruedenberg's proposals is related to oscillations of the surface.
On the calculation of London–Van der Waals interactions in a monopole‐bond polarizability approximation with application to interaction between purine and pyrimidine bases
Authors: Rein Robert , Claverie Pierre , Pollak Michael 
Published: December 2004

AbstractMethods for calculating intermolecular interaction energies are evaluated in a specific application to double‐stranded DNA‐like configurations between bases. The total interaction is decomposed in such a way, that existing methods can be hybridized so that each method can be utilized to its best advantage. In addition, a new method is suggested for the computation of the dispersion interaction between the σ‐electron system of one molecule and the π‐electron system of the other. Results of various approaches applied to base pairs and double‐stranded dimers are summarized and compared in a number of tables.
Wellenmechanische Untersuchungen an der Wasserstoffbrücke zwischen zwei Berylliumatomen
Authors: Janoschek R. , Diercksen G. , Preuss H. 
Published: December 2004

AbstractThe systems Be2H+ and Be2H− have been investigated for different nuclear positions, the H atom being situated between the Be atoms, taking all electrons into account, using the Allgemeines Programmsystem/SCF–MO–LC(LCGO) Verfahren. For Be2H+ there results a minimum total energy of −29.3824 a.u. in the linear symmetric configuration with a bond distance of 1.609 Å. The ionization energy was estimated to be 12.37 eV. The formation of Be2H+ can be interpreted as an addition of Be to BeH+ with an exotherm heat of reaction of 7.0 kcal/mole. The electron affinity of BeH+ (ionization energy of BeH) was estimated to be approximately 7.24 eV. All force constants of Be2H+ and BeH+ have been computed. Using SCF results, the Be2H− was found to be unstable.
Molecular‐orbital calculations on electrophilic substitution and relative basicities in pyrrole, indole, furan, and benzofuran
Authors: Hermann Robert B. 
Published: December 2004

AbstractTwo molecular‐orbital methods—extended Hückel theory and CNDO/2—have been used to estimate the relative electrophilic reactivities of the alpha and beta positions in the nonalternant heterocyclic compounds pyrrole, indole, furan, and benzofuran by comparing total transition‐state energies. The order of basicities of three positions of indole and pyrrole are predicted. Charge densities are also calculated and evaluated in the light of n.m.r. chemical shift data.
Convergence studies in configuration interaction calculations
Authors: Pipano A. , Shavitt I. 
Published: December 2004

AbstractA series of CI calculations for the ground state of BH3 in which various levels of excitation from the ground state are included are compared with each other and with the full‐CI(196 configurations) result. The comparisons cover calculations in terms of two different molecular orbital bases—the canonical SCF basis and a simple, arbitrarily chosen, symmetry orbital basis. As expected, single and, to a lesser extent, triple excitations are of little importance in the SCF case but cannot be ignored for the arbitrary basis. However, as soon as all excitations ≦4 are included, there is practically no difference in the results for the two bases, both giving energies quite close to the full‐CI value. In fact, the energies for the two bases are in close agreement also in the (0 + 1 + 2 + 3)‐excitation calculation and in qualitative agreement in the (0 + 1 + 2) case.Two methods are tested for the selection of the important higher‐excitation configurations, and it is found that results very close to full CI can be obtained with substantially fewer functions. Particularly promising is the application of the “unlinked cluster” approach, based on the ideas developed by Sinanoğlu and others, to the prediction of the coefficients of evenly excited configurations from those of the doubly‐excited functions in a limited‐CI calculation.
An application of perturbation theory ideas in configuration interaction calculations
Authors: Gershgorn Z. , Shavitt I. 
Published: December 2004

AbstractConfiguration interaction calculations of electronic wave functions for atoms and molecules have generally been limited to relatively small basis sets because of the exponential increase in the number of configurations as basis functions are added. While higher than quadruply excited configurations are of negligible importance in CI wave functions, it is shown that the effect of triple and quadruple excitation configurations can be substantially included even when the matrix elements between such configurations are neglected, leaving only their diagonal elements and the elements connecting them with the single and double excitations. This approximation is seen to be formally practically equivalent to a first‐order perturbation expression for the wave function (second‐order for the energy) based on an optimum linear combination of the zero, single, and double excitation configurations as the zero‐order function. If suitable procedures are used, the amount of computational effort involved in such a calculation is roughly proportional to the fourth power of the number of basis functions employed, thus preventing the CI stage of the calculation from increasing in magnitude much faster than the stages involving the calculation and manipulation of the elementary integrals.
Upper and lower bounds to polarizabilities and van der Waals forces I. General theory
Authors: Goscinski Osvaldo 
Published: December 2004

AbstractUpper and lower bounds to polarizabilities, and long‐range interactions of atoms and molecules are derived using operator inequalities.The formulae for the dispersion and the three‐body non‐additive forces are given in terms of the S(k), related by sum rules to properties of the separated systems.Some known approximations are obtained but with additional information about their nature, as well as several new inequalities. Their interest is that they give explicit and rigorous bounds involving quantities available from experimental data.
Numerical studies for a theoretical analysis of semiempirical LCAO–CI methods
Authors: Carpentieri M. , Porro L. , Del Re G. 
Published: December 2004

AbstractA numerical investigation of Del Re and Parr's formulas [1] for the treatment of π systems has been preformed in the case of five‐membered rings, using two different expressions for the core Hamiltonian and different values for the effective charges. The results obtained are discussed by analysing the three stages of the calculation: (a) a non‐iterative LCAO–MO calculation; (b) the same calculation with corrections for exchange and repulsion terms arising from fluctuations of the orbital populations; (c) configuration interaction. The calculations are interesting also because they do not involve the zero differential overlap approximation; a calculation without inclusion of overlap hse been carried out for pyrrole and the results have been compared with those including S.The main conclusions hold also for σ electrons, and can serve to assess better the validity of simple σ calculations.
The electronic structure of tetrahedral III–V compounds: The ground state of boron nitride
Authors: Coulson C. A. , Doggett G. 
Published: December 2004

AbstractThe bond‐orbital theory of III–V compounds, previously described by Coulson, Redei and Stocker, is used to calculate the effective atomic charges and the binding energy per bond in boron nitride. The theory is reformulated in a manner which is convenient for performing both ab initio and semiempirical calculations. Two different choices for the atomic‐orbital exponents are considered and, in both cases, the results obtained from the ab initio method are at variance with the earlier calculations in predicting an electronic charge displacement from nitrogen to boron. The magnitude of the effective charges is found to vary according to the method of partitioning the overlap charge between the nitrogen and boron atoms. The use of orthogonalized Slater 2s functions is also examined.The semiempirical calculations are performed with an explicit inclusion of the Madelung energy from the outset. The ionicity in the bond is shown to be determined by the competition between the difference in orbital electronegativities and the difference in Madelung potential across the ends of the bond. Unfortunately, the semiempirical theory breaks down because the energy per bond passes through a maximum at the optimum value of the polarity parameter. The reasons for this behaviour are examined and discussed.
Self‐consistent‐field method including correlation effect for atomic systems. Three‐ and four‐electron atomic systems
Authors: Modrak P. 
Published: December 2004

AbstractThe correlation effect for three‐ and foru‐electron atomic systems has been taken into account by modifying the potentials of the electron interactions appearing in the Hartree–Fock equations. The correlation energies obtained for Li, Be+, B2+, Li−, Be and B+ differ by less than 25 percent from the exact values.
Theory of intermolecular interactions: The long range terms in the dipole–dipole, monopoles–dipole, and monopoles–bond polarizabilities approximations
Authors: Claverie Pierre , Rein Robert 
Published: December 2004

AbstractThe problem of evaluating the long range terms (electrostatic, polarization, dispersion) of the interaction energy between molecules at intermediate distances (i.e. distances of the order of magnitude of the molecular dimensions) is considered. Instead of being approximated by its dipole part, the exact interaction Hamiltonian is treated as proposed by Longuet‐Higgins [11], i.e. the matrix elements are interpreted as electrostatic interactions between state and transition charge distributions. These charge distributions are approximated in a systematic way by sets of point charges (localized on the atoms) or sets of dipoles (localized on the bonds). The various contributions to the energy may then be expressed in terms of atomic net charges and bond polarizabilities. More refined approximations of the charge distributions could be used and correspondingly improved formulae could be derived: as an example, a formula for the σ‐π dispersion energy is derived, where the σ charge distributions are approximated by bond transition dipoles (leading to σ bond polarizabilities in the final formula) while the π charge distributions are approximated by atomic charges.
On the choice and definition of atomic orbital‐bases. II. Promoted Slater orbitals and best‐atom hydrogen‐like orbitals
Authors: Rastelli Augusto , Del Re Giuseppe 
Published: December 2004

AbstractSingle‐exponential functions of the forms 1s̄ = 1s, 2s̄ = N1(2s + b1s + a3s), 2p̄ = N2(2p + c3p) are introduced as an alternative to the Slater orbitals 1s, 2s, 2p for the atoms of the first period. The orbitals are intended for molecular calculations and the parameters a and c should be chosen in order to make the basis consistent with a given preliminary description of the molecule: see Part I, G. Del Re, Intern. J. Quantum Chem. 1, 293 (1967), but, first of all, a study of their behavior in atomic systems is necessary. Therefore orbital exponents and total atomic energies are determined by optimization: the promotion coefficients a and c are zero for best‐atoms and the functions become strictly hydrogen‐like orbitals. Comparisons are allowed with Slater's, Roothaan's, Ransil's and SCF orbitals.Given promoted 2s̄ and 2p̄ orbitals on carbon atoms in a carbon‐carbon sigma bond, we fix the coefficient a and c in order to obtain one center sp orbitals orthogonal to one another. These are discussed, mapped and compared with the two center hybrids obtained by the Löwdin orthogonalization.
Quadratically convergent iteration procedure for geminal determinations
Authors: Loter Joe , Christoffersen Ralph E. 
Published: December 2004

AbstractA general formalism is presented for the determination of the optimum natural orbitals within the various strongly orthogonal geminals of a wavefunction describing a 2N‐electron closed‐shell molecule or atom. The relationship to Hartree–Fock–Roothaan theory is established; the algorithm that is developed is quadratically convergent to the desired result, and does not ignore off diagonal Lagrangian multipliers, or require an infinite series of 2 × 2 orthogonal transformations of the original basis.
On the theoretical foundation of Walsh's rules of molecular geometry in terms of the Hellmann–Feynman theorem
Authors: Coulson C. A. , Deb B. M. 
Published: December 2004

AbstractA new interpretation of the ordinate in a Walsh diagram for a polyatomic molecule is suggested in terms of the Hellmann–Feynman theorem. This makes use of the fact that in a single‐configurational MO wave function the total one‐electron density is the sum of individual densities in the occupied orbitals. Walsh‐type diagrams have been constructed for three different molecules, water, ammonia and hydrogen peroxide.In H2O and NH3 calculation of the force, and thus of the energy, in terms of the valence angle, is made on the assumption that the central (heavy) atom is kept fixed while each of the lighter atoms moves in a plane containing the principal symmetry axis and the relevant bond, in a totally symmetric fashion; for H2O2 the two oxygen atoms are kept fixed.The angular correlation diagrams obtained reproduce the general features of those obtained by plotting Hartree–Fock MO energies as functions of the valence angles. The conclusion emerges that the force formulation provides a satisfactory pictorial basis for understanding molecular geometry in terms of the balance between the electron–nucleus attractive forces resulting from the charge densities in the occupied MO'S, and the nuclear repulsive forces. However, in the absence of highly accurate charge distributions such an approach is unsuitable for the quantitative prediction of molecular quantities such as valence angles, force constants or energy barriers.
Valence‐Bond calculations and matrix elements between two tableau functions of non‐orthogonal orbitals
Authors: Gallup G. A. 
Published: December 2004

AbstractAn integral formula is derived involving a new type of determinantal function which reproduces the effect of the Young operator θNPN. This result is used to calculate matrix elements between tableau functions of non‐orthogonal orbitals. Matrices which transform this representation into the traditional valence‐bond scheme are also given.
Use of molecular symmetry in SCF calculations
Authors: Elder M. 
Published: December 2004

AbstractA method is described whereby molecular symmetry properties may be used to reduce the numbers of one‐ and two‐electron integrals that need to be calculated and stored in the course of a molecular SCF calculation. The method is a generalization of a previously reported procedure, extending the earlier work to cover those molecules belonging to point groups which have complex representations. The practical application of the method is discussed and an illustrative example given. The quite extensive tables of molecular symmetry properties which the method uses may be computer generated in a straightforward manner. A procedure for doing this using a minimum amount of input data is presented.
Projection between basis sets: A means of defining the electronic structure of functional subunits
Authors: Fink William H. 
Published: December 2004

AbstractThe general problem of the transfer of the representation of a set of orthonormal functions from one basis to a different, nonequivalent one is considered and specialized to a matrix formulation convenient for use in molecular electronic structure calculations. A procedure is suggested for treating problems where the transfer of representation breaks into a subset of most interest and one of less interest as for example the occupied and virtual orbitals of a Hartree‐Fock SCF calculation. These techniques are then applied to obtain a representation of a methyl group from an SCF wave function for methane.
Spin‐free quantum chemistry. XIII. Spin waves
Authors: Matsen F. A. , Suger J. E. , Picone J. M. 
Published: December 2004

AbstractWe have obtained the Bloch spin wave dispersion formula using the methods of spin‐free quantum chemistry. The spin‐free eigenvectors are waves in spin‐free space. This development makes the point that Bloch spin waves are dynamically spin‐free. The neutron diffraction transition moment for spin waves is calculated employing the antisymmetrized projections of vector products of spin‐free eigenkets and spin kets and is found to be agreement with results of Moorhouse.
Spin‐free quantum chemistry. XIV. The infinite interaction range model for ferromagnetism
Authors: Matsen F. A. , Cosgrove J. G. , Picone J. M. 
Published: December 2004

AbstractThe infinite interaction range model (IIRM) for ferromagnetic systems is presented in its spin‐free formulation. In this formulation the states are labelled by partitions which provide a natural variable for thermodynamic computation. We have extended the calculations of Kittel and Shore by computing to a practical thermodynamic limit (N ∼ 100,000). The heat capacity, magnetic susceptibility and the magnetization of the first two functions exhibit a critical temperature while the magnetization is zero at zero field for all temperatures. Spontaneous magnetization is obtained by linear extrapolation from high field or equivalently by a polarized partition function. Relationships are explored among IIRM, the Heisenberg model and the mean field model. Application to IIRM of the Yang‐Lee condition for a phase transition yields a critical temperature identical to that obtained by the direct calculation.
Brillouin‐Wigner perturbation theory and the generalized eigenvalue equation
Authors: Laughlin C. , Woodward M. R. , Amos A. T. 
Published: December 2004

AbstractA Brillouin‐Wigner perturbation expansion is derived for the generalized eigenvalue equation (F0 + F1)Ψ = μAΨ. The theory is applied through second order to calculate the ground‐state energies of the helium atom and the hydrogen molecular ion. The results are compared with the corresponding Rayleigh‐Schrödinger expansion. For the examples we consider, the Brillouin‐Wigner results through second order are generally superior to the Rayleigh‐Schrödinger ones.
SCF equations for pure spin states with many‐particle interactions
Authors: Lim T. K. 
Published: December 2004

AbstractSCF equations for any pure spin state are given for a spin‐free system with many‐particle interactions. The equations are very simple and explicit. Due to the use of different antisymmetric requirement our equations are different from some of the other methods. In our method, the abstract group theory formalism is converted into some explicit and straightforward equations which makes the many‐particle interaction problem easier to handle.