bluuebunny/crossref_metadata_2025_split huggingface dataset:
Refined Insight in Stereochemical and Directional Features of the FeI‐Mediated Dehydrogenation of Tetralin
Authors: Seemeyer Katrin , Schwarz Helmut 
Published: December 2004

AbstractExperimental results demonstrate that, in the course of gas‐phase Fe+‐mediated dehydrogenation of tetralin, the metal ion sticks to the same plane of the hydrocarbon surface. The study of 5‐substituted, labeled tetralin analogues reveal the operation of an interesting substituent effect: Steric hindrance imposed by a CH3 group at C(5) deflects the metal to the more easily accessible region of C(1)/C(2); in contrast, a CH3O substituent at C(5) directs the metal ion to the more congested C(3)/C(4) region which clearly points to a coordination of Fe+ to the MeO group in the course of the haptotropic migration.
Synthesen und Untersuchungen von [Oxazolo[2,3‐a]isoindol‐9b(2H)‐yl]phosphonaten und ‐phosphinaten: Eine neue Klasse von Heterocyclen
Authors: Neidlein Richard , Greulich Peter , Kramer Walter 
Published: December 2004

Syntheses and Investigations of [Oxazolo[2,3‐a]isoindol‐9b(2H)‐yl]phosphonates and ‐phosphinates: a New Class of HeterocyclesWe attempted to synthesize diethyl (1‐methyl‐2‐phthalimidoethyl)phosphonate (14a) in a Michaelis‐Becker reaction using diethyl sodiophosphonate (13) and the tosylate 12a of (2‐hydroxypropyl)phthalimide as starting materials. Instead of TsO substitution in 12a by the nucleophile 13, the carbonyl C‐atom of the phthalimido moiety was attacked by 13, followed by an intramolecular nucleophilic substitution at C(2) of the side chain leading to the (oxazolo[2,3‐a]isoindolyl)phosphonate 15a (Scheme 1). Similarly, 12a and N‐(2‐bromoethyl)phthalimide (12b) reacted with butyl (benzene)sodiophosphinate (18) to the (oxazolo[2,3‐a]isoindolyl)(phenyl)phosphinates 20a and 20b, respectively (Scheme 2). The attempt to synthesize enantiomerically pure 2‐substituted (2‐phthalimidoethyl)phosphonates 27 starting from L‐α‐amino‐acids failed, too (Scheme 3): the main products of the reaction of the N,N‐phthaloyl‐O1‐tosyl‐L‐aminoalcohols 25a–d with 13 were the 3‐substituted (oxazolo[2,3‐a]isoindolyl)‐phosphonates 26a–d, the desired 27b and 27c being observed as by‐products in the 31P‐NMR spectrum.
Syntheses of the First Selenium‐Containing Bicyclic β ‐Lactams as Potent Antimicrobial Agents
Authors: Hwu Jih Ru , Lai Long‐Li , Hakimelahi Gholam H. , Davari Hady 
Published: December 2004

AbstractSyntheses of the cis‐configurated isodethiaselenapenam 5 (Scheme 1) as well as the isodethiaselenacephems 29 and 31 (Scheme 2) were accomplished, in which the key step involved addition of Se to the corresponding carbanions of 1, 25, and 27 followed by internal alkylation. β‐Lactams 29 and 31 were found to possess biological activity against several pathogenic microorganisms in vitro. The electronic activation of the lactam moiety in the isodethiaselenacephem 31 and the corresponding isocephem 33 remarkably enhanced their biological activity. Isodethiaselenacephem 31 was more toxic than isocephem 33 in experimental animals.
β‐Peptides: Synthesis by Arndt‐Eistert homologation with concomitant peptide coupling. Structure determination by NMR and CD spectroscopy and by X‐ray crystallography. Helical secondary structure of a β‐hexapeptide in solution and its stability towards pepsin
Authors: Seebach Dieter , Overhand Mark , Kühnle Florian N. M. , Martinoni Bruno , Oberer Lukas , Hommel Ulrich , Widmer Hans 
Published: December 2004

AbstractThe β‐hexapeptide (H‐β‐HVal‐β‐HAla‐β‐HLeu)2‐OH (2) was prepared from the component L‐β‐amino acids by conventional peptide synthesis, including fragment coupling. A cyclo‐β‐tri‐ and a cyclo‐β‐hexapeptide were also prepared. The β‐amino acids were obtained from α‐amino acids by Arndt‐Eistert homologation. All reactions leading to the β‐peptides occur smoothly and in high yields. The β‐peptides were characterized by their CD and NMR spectra (COSY, ROESY, TOCSY, and NOE‐restricted modelling), and by an X‐ray crystal‐structure analysis. β‐Sheet‐type structures (in the solid state) and a compact, left‐handed or (M) 31 helix of 5‐Å pitch (in solution) were discovered. Comparison with the analogous secondary structures of α‐peptides shows fundamental differences, the most surprising one at this point being the greater stability of β‐peptide helices. There are structural relationships of β‐peptides with oligomers of β‐hydroxyalkanoic acids, and dissimilarities between the two classes of compounds are a demonstration of the power of H‐bonding. The β‐hexapeptide 2 is stable to cleavage by pepsin at pH 2 in H2O for at least 60 h at 37°, while the corresponding α‐peptide H‐(Val‐Ala‐Leu)2‐OH is cleaved instantaneously under these conditions. The implication of the described results are discussed.
Lipase‐Catalysed Regioselective Deacetylation of androstane derivatives
Authors: Baldessari Alicia , Bruttomesso Andrea C. , Gros Eduardo G. 
Published: December 2004

AbstractA series of acetoxy derivatives of androstane was deacetylated in organic solvents by several lipases. The most satisfactory results were obtained with lipase from Candida cylindracea (CCL) and Candida antarctica (CAL). In some derivatives, CCL and CAL showed an overwhelming regioselectivity towards the removal of the 3β‐ or the 17β‐acetyl group (see Table 2). Three new steroid derivatives were obtained through this approach. A hypothetical rationale for the behaviour of these enzymes is given.
Synthesis and Characterization of the (5′ → 5″)‐Ester of Adenosine 5′‐diphosphate with α‐D‐ribofuranose cyclic 1″,2″‐phosphate: A NAD derivative produced during tRNA splicing
Authors: Hall Jonathan , Genschik Pascal , Filipowicz Witold 
Published: December 2004

AbstractThe synthesis and spectroscopic properties of the (5′ → 5″)‐ester of adenosine 5′‐diphosphate with ribofuranose cyclic 1″, 2″‐phosphate 3, a recently discovered metabolite produced during tRNA splicing, are reported.
Nucleotides. Part XLVIII. Synthesis of 2′‐amino‐2′‐deoxyarabinonucleoside phosphoramidite building blocks
Authors: Walcher Gunter , Pfleiderer Wolfgang 
Published: December 2004

AbstractChemical syntheses of 2′‐amino‐2′‐deoxyarabinonucleosides of uracil, thymine, cytosine, adenine, and guanine and their conversion into suitably protected 3′‐phosphoramidite building blocks 24–28 for oligonucleotide synthesis are described. The 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) group was used for protection of the aglycon and the 2′‐amino functions.
Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination
Authors: Lutz Andreas , Ward Thomas R. 
Published: December 2004

AbstractThe synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
Synthesis of a Ketorolac Model via Aromatic Carbenoid Insertion
Authors: Müller Paul , Polleux Philippe 
Published: December 2004

AbstractThe decomposition of diazo ester 2b with chiral RhII catalysts proceeded via intramolecular aromatic carbenoid insertion to the racemic pyrrole derivative 5b in 72% yield. In contrast, the benzoylated precursor 16 afforded no ketorolac 1b when exposed to RhII. Methyl 2‐diazo‐4‐phenylbutyrate (19), in turn, reacted, by 1,2‐hydrogen migration rather than by aromatic substitution, to 20.
Etudes sur les matières végétales volatiles XXXVI. Présence d'époxylinalol dans les huiles essentielles
Authors: Naves Y. R. 
Published: December 2004

AbstractL'époxylinalol libre ou estérifié existe dans l'essence de lavandin, libre dans l'essence de shiu. L'acétate d'époxylinalyle est séparé quantitativement des esters acétiques des alcools satellites au moyen de son complexe hexacyanoferrique(II).
Zur Krystallstruktur des p,p′‐Dichlordiphenyl‐trichlor‐äthan
Authors: Wild H. , Brandenberger E. 
Published: December 2004

Abstract1. p,p′‐Dichlordiphenyl‐trichlor‐äthan krystallisiert in der orthorhombisch‐hemimorphen Klasse C2v und zwar mit C—Pbc als wahrscheinlichem Raumsystem.
Recherches sur l'électrolyse avec le courant ondulé. IV. Observations sur le comportement des anodes de platine poli dans l'électrolyse de solutions utilisées en vue de la préparation du perborate
Authors: Briner E. , Löwy E. 
Published: December 2004

AbstractFaisant suite aux recherches précédentes sur la production de l'ozone par électrolyse de solutions d'acide sulfurique avec du courant ondulé, on a étudié — toujours en utilisant des électrodes de platine poli — la formation d'oxygène actif dans des solutions alcalines de composition propre à la préparation de perborate.
Über eine neue l‐Aminosäure‐oxydase (Ophio‐l‐aminosäure‐oxydase). 2. Mitteilung
Authors: Zeller E. A. , Maritz A. 
Published: December 2004

Abstract1. Auf verschiedene Weise konnte gezeigt werden, dass in den Giften von Naja, Bothrops atrox, Vipera aspis, Vipera latastei und Vipera libetina das in der ersten Mitteilung als Ophio‐l‐aminosäure‐oxydase (Ophio‐oxydase) bezeichnete Ferment auftritt. Geringe Unterschiede gehen nicht über die auch sonst bei Fermenten bekannten artspezifischen Eigentümlichkeiten hinaus.
Zur percutanen Resorption lipoidlöslicher Substanzen aus organischen Lösungsmitteln
Authors: Stadlin Walter 
Published: December 2004

Abstract1. In Aceton und Wasser aa gelöstes Oestron bewirkt bei Auftropfen auf die Nackenhaut des Meerschweinchens eine erhebliche Vergrösserung der Zitzen.
Über Vinylchlorid und seine Polymerisationsprodukte. I. Zur Kenntnis von Polyvinylchlorid
Authors: Fierz‐Davie H. E. , Zollinger Hch. 
Published: December 2004

Abstract1. Der direkte oxydative Abbau von Polyvinylchlorid liefert keine zur Konstitutionsbestimmung brauchbaren Resultate.
Über den Aufbau von Viskosefasern mit Mantelbildung
Authors: Wuhrmann K. 
Published: December 2004

AbstractDie quantitative optische Untersuchung von Viskosefasern mit Mantelbildung ergibt, dass in Übereinstimmung mit früheren qualitativen Beobachtungen die Mantelzonen bedeutend höhere Doppelbrechungswerte aufweisen als die Faserkerne.
Hydrogen bonding in simple π‐electron systems I. Pyridinium–pyridine
Authors: Sabin John R. 
Published: December 2004

AbstractIn this work, the application of the Pariser–Parr–Pople scheme to hydrogen‐bonded systems containing π electrons has been examined. The potential energy curves for the movement of the hydrogen atom in the bond have been calculated, and the reliability of the results obtained from this method, applied in this manner, have been discussed.
The ground state of atomic two‐electron systems in the independent particle model
Authors: Hoor Marten J. Ten 
Published: December 2004

AbstractScaled variational functions of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \phi _{\alpha k} = e^{ - (Z - 1 + e^{ - \alpha kr})kr} $\end{document}, where Z is the nuclear charge and α is a parameter, and \documentclass{article}\pagestyle{empty}\begin{document}$ \phi _{\beta \alpha k} = e^{ - (\beta + e^{ - \alpha kr})kr} $\end{document}, where both α and β are parameters, are used for the description of the ground state of atomic two‐electron systems in the independent particle model. The scale factor k has been introduced in order to satisfy the virial theorem.Apart from the energy, a number of one‐electron expectation values have been calculated and the results are compared with those obtained from other variational functions.The function ϕαk yields already a good approximation to the Hartree–Fock solution whereas with the function ϕβαk the Hartree–Fock results are practically reproduced.
On the formulation of spin‐free quantum chemistry
Authors: Heldmann G. 
Published: December 2004

AbstractA set of spin‐free functions ϕi(r),i = 1 …︁ f, is obtained which form the basis of spin‐free quantum chemistry. The ϕi(r) show a one‐to‐one correspondence to antisymmetric space‐spin functions Ψi(r, σ) with spin functions constructed according to Löwdin's projector operator method.
Vibronic absorption spectrum of the ethylene dimer
Authors: Sadlej Andrzej J. 
Published: December 2004

AbstractVibronic coupling theory is used to construct the vibronic absorption spectrum of the ethylene dimer. It is shown that in this case an extended four‐parameter form of the vibronic Hamiltonian should be considered. In addition to the commonly used three vibronic parameters, the difference between the ground and excited state force constants of the monomer is taken into account.Numerical calculations were performed for the dimer geometry resembling that of norbornadiene. Some comments on the interpretation of the absorption spectrum of norbornadiene are made.
Free‐electron model for electronic spectra of benzene
Authors: Sen Purnendranath , Basu Sadhan 
Published: December 2004

AbstractUsing a three dimensional free‐electron model for the π‐electron system the energies of the various singly and doubly excited configurations of benzene have been calculated. It has been found that the energies of the various singly excited configurations are in good agreement with the values obtained by Craig; whereas the energies of the doubly excited configurations are higher than those obtained by Craig. Therefore the configurational mixing for the doubly excited configurations is not necessary in this kind of model.
The hydrogen atom in a cubic field of electric dipoles
Authors: Blokker Esko 
Published: December 2004

AbstractThe full rotational symmetry of the hydrogen atom is lowered to that of the double group of Oh. This is done by a cubic field of electric dipoles. Symmetry‐adapted spin orbitals have been calculated and with them the energies of the lowest states as functions of the distance from the dipoles to the atom, the dipole moment, and the size of the atoms forming the dipoles. The Hamiltonian used is obtained by starting with the Dirac equations and then making some simplifications and approximations.
High orders corrections to the Van der Waals–London forces. II. Interaction of two molecules with isotropic polarizabilities
Authors: Malrieu J. P. 
Published: December 2004

AbstractThe infinite summation of intermolecular ring diagrams is extended to any pair of interacting molecules with isotropic polarizabilities. The calculation no longer requires the use of a minimal basis set. The polarizabilities α,α′ may be factorized at all orders, and an expression is derived, which gives modified Van der Waals energies. For heavy atoms the series converges if αα′/R6 is smaller than 1, R being the interatomic distance. This inequality is easily satisfied for the Van der Waals distances, and in practice the correction due to the high orders of the perturbation expansion remains weak. The role of the EPV diagrams and the connection with a configuration interaction treatment are discussed.
On the Mavroyannis–Stephen relativistic long‐range interaction energy term between optically active molecules
Authors: Chang Tai Yup 
Published: December 2004

AbstractThe relativistic long‐range intermolecular interaction energy term of Mavroyannis and Stephen is estimated for some amino acids by using optical rotatory dispersion data and for hexahelicene by using theoretical values of excitation energies and rotational strengths. The result shows that the interaction energy may be significant for the interaction between some essentially dissymmetric chromophores such as hexahelicene, but that it is unimportant for other cases.
Studies on Rydberg orbitals. IV. Basic formulas for the one‐electron perturbation calculation of molecular Rydberg excited states
Authors: Hosoya Haruo 
Published: December 2004

AbstractGeneral expressions are obtained for the energies of complex and real forms of any hydrogenic orbital (n, l, m) in a cluster of point charges of any geometry. This is a perturbation calculation of hydrogenic Rydberg orbitals in a one‐electron hard core approximation. A model calculation of 3d‐electrons of carbene, ethylene and benzene with varying charge distribution is given.
Quasi‐relativistic approximation in the SCF‐MO‐LCAO method
Authors: Bersuker I. B. , Budnikov S. S. , Leizerov B. A. 
Published: December 2004

AbstractA quasi‐relativistic approach to the MO‐LCAO method is formulated taking into account the relativistic effects with an accuracy up to (v/c)2 terms, the relativistic part of the electronic interaction in the Hamiltonian being neglected. In the framework of this approximation a set of SCF equations of the Roothaan form is derived; here only the relativistic analogue to the closed shell systems with one‐determinant wave functions is considered. In so doing three types of relativistic corrections arise which are quite similar to those of the Pauli equation for one‐electron atoms. The new matrix elements appearing due to these corrections can be reduced to some common integrals, which have to be calculated with relativistic radial atomic functions. The method allows a semi‐empirical approach to the problem and does not require the Dirac four‐component atomic functions (unknown in the most cases), thus making possible approximate quasi‐relativistic electronic structure calculations of heavy‐atom compounds.
Analysis of reduced density matrices in the co‐ordinate representation. III. Electron density and correlation in the ground states of H2 and the H6 ring system within some approximations of the simple LCAO type
Authors: Sperber Gunnar 
Published: December 2004

AbstractThe electron density and spatial correlation as given by the MO, VB and AMO methods for H2 and H6 are studied by means of diagrams. For comparison, diagrams representing accurate wave functions for H2 are also given. The study of model functions representing localized bonds leads to results concerning the nature of localized electron pairs in agreement with those of Lennard‐Jones.
Theoretical calculations on σ‐systems. III. Alkyl halides and alkanes
Authors: Bhattacharyya Subirnath , Bhaumik Amiyansu 
Published: December 2004

AbstractVarious aspects of Del Re's method, its extension and correlation with important properties such as nuclear quadrupole coupling constants and spin‐spin coupling constants are discussed. The Del Re parameters for the C–I bond have been evaluated and those for the C–F bond modified. The bond energies and the heats of formation for several σ‐systems have been calculated; the energies of a “bond‐orbital” for several alkanes have been found to be related with their ionization potentials.
Vibrational matrix elements of the quadrupole moment functions of H2, N2 and CO
Authors: Truhlar Donald G. 
Published: December 2004

AbstractThe quadrupole moment functions (molecular quadrupole moment versus internuclear distance) have been determined by quantum mechanical calculations for H2 (by Kolos and Wolniewicz), N2 (by Wahl and Nesbet), and CO (by Nesbet). These functions are used with numerical vibrational wave functions to compute matrix elements which are useful for calculations of scattering cross sections, energy transfer rates and excitation probabilities, and infrared intensities of forbidden bands.
Gauge invariant gaussian orbitals and the ab initio calculation of diamagnetic susceptibility for molecules
Authors: Hall G. G. 
Published: December 2004

AbstractIt is shown that gauge terms can be introduced into the Gaussian functions used as the basis functions for an ab initio calculation of the energy of a molecule in the presence of a uniform magnetic field so that all the integrals become independent of the origin of the vector potential. The perturbation treatment of the diamagnetic susceptibility is considered in the molecular orbital approximation. The results show that the susceptibility can be calculated using only the unperturbed orbitals and their first‐order corrections. All the integrals that arise can be expressed in terms of known functions.
Theorie des Orbitals Moleculaires: Recherche d'une Base STO Homogene pour les Atomes Alcalins et Leur Serie Isoelectronique
Authors: Marinelli Francis 
Published: December 2004

AbstractA method of direct treatment of valence electrons is proposed for the various 2S, 2P,2D, 2F states of the lithium, sodium, and potassium atoms and the corresponding isoelectronic ions. The function describing the outer electron, which is orthogonal to the wave functions of the electrons in the core, is given as a linear combination of generalized Laguerre functions, with effective charges Q = 1, 2 …︁ equal to the charges of the core.A simpler analytical STO function, with non‐integer principal quantum number n is then proposed.
Importance sampling in local energy calculations on H2
Authors: Ehrenson S. , Harp G. D. 
Published: December 2004

AbstractThe importance sampling method of point selection has been used in the local energy framework to obtain least‐squares solutions of the Schrödinger equation for a variety of H2 functions. It is shown that good results are obtainable with relatively small samples, and that the method is rather insensitive within broad limits to the nature of the weighting function employed. Expectation values for a number of operators besides the energy are examined. The energy variances are likewise scrutinized and attempts are made to rationalize their behavior in terms of how and to what extent sample points are chosen.
The use of irreducible operators for determining the complete set of linearly independent crystal field parameters
Authors: Soliverez Carlos E. 
Published: December 2004

AbstractA general method is given for finding the complete set of linearly independent crystal field parameters from symmetry arguments. No recourse is made to expansions of the crystal field in terms of spherical harmonics. The core of the method lies in an extension of the known zero‐trace property of tensor operators, to the case of irreducible operators.
Selected valence electron split‐shell molecular orbital calculations on the diatomic interhalogen molecules
Authors: Sannigrahi A. B. , Mohammad S. Noor 
Published: December 2004

AbstractSelected valence electron split‐shell molecular orbital calculations have been performed on the diatomic interhalogen molecules in order to obtain their binding energies, equilibrium internuclear distances, vibrational force constants, dipole moments and nuclear quadrupole coupling constants. The results are compared with the corresponding closedshell values and with those of some previous semiempirical and nonempirical all valence electron calculations. It is observed that the selected valence electron split‐shell molecular orbital method which involves the least amount of computations yields results in better agreement with experiment than other methods.
A technique for orbital exponent optimization in ab initio HFSCFLCAOMO calculations
Authors: Loubriel G. M. , Selsby R. G. 
Published: December 2004

AbstractA technique for Slater orbital exponent optimization in an HFSCFLCAOMO calculation is proposed in which orbital exponent variation is incorporated into the SCF scheme. This is accomplished by rewriting Slater's rules so that the shielding terms depend on the molecular charge distribution through the elements of the population matrix. The SCF scheme then includes a calculation of a new set of orbital exponents from the coefficients of self‐consistent molecular orbitals obtained from the previous set of exponents. The process is iterated until the energy attains its lowest value.The technique is illustrated by minimal basis calculations on LiH, BH, and HF. Near optimization is obtained with considerably less effort than is necessary for other reported techniques. Aside from interesting properties, the technique can be important for extended basis calculations where exponent optimization is a difficult task.