bluuebunny/crossref_metadata_2025_split huggingface dataset:
3,6,9,10‐Tetrahalogenphenanthrene. Eine neue Cycloarylierungsreaktion von DDT‐Derivaten
Authors: Weis C. D. 
Published: December 2004

AbstractA simple synthesis of tetrachlorophenanthrene starting from DDT has been realized. 1,1,1,2‐tetrachloro‐2,2‐bis‐(4‐chlorophenyl)‐ethane (I) and its rearranged product 1,1,2,2‐tetrachloro‐1,2‐bis‐(4‐chlorophenyl)‐ethane (V) and other analogs substituted by halogen in the para‐position undergo a cycliarylation yielding 3,6,9,10‐tetrahalogenophenanthrenes. Partial dechlorination of this tetrachlorophenanthrene yields 3,6‐dichlorophenanthrene. Oxidation gives 3,6‐dichloro‐9,10‐phenanthrenequinone, and chlorosulfonation leads to 3,6,9,10‐tetrachloro‐2,7‐bis‐(chlorosulfonyl)‐phenanthrene. The mechanism of this cyclization reaction in presence of LEWIS acids is discussed and compared with the cyclization of DDT derivatives to yield fluorenones.
Multiple aromatische sigmatropische Umlagerung von γ, γ‐Dimethylallyl‐phenyläther
Authors: Scheinmann F. , Barner R. , Schmid H. 
Published: December 2004

AbstractThe rearrangement of γ,γ‐dimethylallyl phenyl ether (1), contrary to previous reports, gives a mixture of 4‐(γ,γ‐dimethylallyl)‐phenol (2), 2‐(α,β‐dimethylallyl)‐phenol (3) and 2,2,3‐trimethylcoumaran (4). The ratio of the reaction products is dependent on the solvent and the reaction temperature. The mechanism for the reaction is discussed in terms of multiple sigmatropic rearrangements.
Über ein neues Glykosidierungsverfahren Synthese von Epipodophyllotoxin‐β‐D‐glucopyranosid. 21. Mitt. Über mitosehemmende Naturstoffe [1]
Authors: Kuhn M. , Von Wartburg A. 
Published: December 2004

AbstractA new method for the synthesis of glycosides is described. Epipodophyllotoxin (4) reacts with 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranose in the presence of BF3‐etherate at low temperature to yield tetra‐O‐acetyl‐epipodophyllotoxin‐β‐D‐glucopyranoside (6). This compound, which is sensitive to acid and base, can be converted into the free glucoside 8 by zinc acetate catalysed methanolysis. Glycosidation of podophyllotoxin (1) occurs under the same conditions but is associated with an inversion at C‐1 of the aglycone moiety, leading also to the acetylated epi‐glucoside 6. It is assumed that the glycosidation proceeds through a common carbonium ion intermediate (12), generated from 1 and 4 respectively by the action of BF3. The intermediate 12 is substituted by the pyranose component from the less hindered side, giving exclusively 1‐epi derivatives (e.g. 6). The glycosidation reaction is also highly stereoselective with respect to the glycosidic linkage. The stereochemistry of this bond is determined by the configuration at C‐1 of the pyranose compound employed for the glycosidation. Further experimental evidence for the proposed mechanism consists in the glycosidation of diphenylmethanol (14) to the corresponding β‐D‐glucoside 15. Scope and limitation of the new glycosidiation method are briefly discussed.
Massenspektrometrische Untersuchung von Pleiocarpamin‐Derivaten. 9. Mitteilung über das massenspektrometrische Verhalten quartärer Stickstoffverbindungen [1]
Authors: Leuzinger F. , Hesse M. , Schmid H. 
Published: December 2004

AbstractMass spectrometric analysis of quaternary nitrogen compounds has shown that three principal thermal processes occur, namely dealkylation, Hofmann degradation and substitution. Only in the cases of dealkylation and the Hofmann degradation has direct chemical evidence been previously obtained. The first part of this paper presents mass spectrometrical and chemical evidence for the pyrolytic formation of a substitution product, e. g. 5.By means of different deuterated derivatives the mechanisms of fragmentation of the mavacurine derivative ϵ2‐dihydromavacurine methochloride (8) and of the corresponding Hofmann base (14) have been formulated.
Zusammensetzung der Neutrallipide und deren Fettsäuren aus Walhirnen. III. Hirne von Grindwalen (Globicephala melaena)
Authors: Lesch Peter , Neuhaus‐Meier Sylvia , Bernhard Karl 
Published: December 2004

AbstractThe lipids from the brain of six pilot whales were extracted and separated into different fractions. The grey matter contains 8% cerebrosides, 6% sphingomyelines, 21% ethanolamine cephalines, 26% lecithines and 22% cholesterol; the white matter 22, 8, 17, 12 and 25%, respectively. We analysed the fatty acid composition of each fraction.In comparison to the human brain, the brain of the pilot whale contains more glycerophos‐phatides and less sphingolipids, in comparison to the fin whale, more cerebrosides.
Herstellung von Iminen durch Gasphasen‐Pyrolyse: N‐Methyl‐äthylidenimin
Authors: Meier J. , Akermann F. , Günthard Hs. H. 
Published: December 2004

AbstractN‐methyl‐ethylidenimine (CH3CHNCH3) was obtained by pyrolysis of 2‐methylaziridine in a gas phase flow system, using quartz as a catalyst. Pyrolysis of aziridine gave mainly N‐methyl‐methylenimine (CH2NCH3). Under the conditions used in this work, pyrolysis of both compounds surprisingly showed cleavage of the CC‐bond in the three‐membered ring. No monomeric ethylidenimine (CH3CHNH) could be isolated by pyrolysis of trimeric ethylidenimine (2,4,6‐trimethyl‐hexahydro‐1,3,5‐triazine), whereas N‐vinyl‐ethylidenimine (CH3CHNCHCH2) could be identified as one of the pyrolysis products. NMR. data for N‐methyl‐ethylidenimine and N‐vinyl‐ethylidenimine are given for identification purposes.
Tricyclische CuII‐ und NiII‐Chelate aus 2,2‐Bis‐(2‐hydroxyarylazo)‐biphenyl bzw. ‐diphenylsulfid
Authors: Schetty G. , Eder M. 
Published: December 2004

AbstractTricyclic CuII and NiII chelates are produced from some 2,2′‐bis‐(2‐hydroxyaryl‐azo)‐biphenyls and ‐diphenyl sulphides. From their electron spectra it is concluded that in the Ni complexes of the azo‐biphenyl dyestuffs the central atom is coordinated in a different way (probably planar) from that in the corresponding Cu complexes. On the other hand, the valences of both metals in the azo‐diphenyl sulphide complexes seem to have the same steric arrangement. This arrangement is probably the same as that of the CuII ion in the azobiphenyl dyestuffs, which could be tetrahedral.
Menschliches Calcitonin. III. Struktur von Calcitonin M und D
Authors: Neher R. , Riniker B. , Rittel W. , Zuber H. 
Published: December 2004

AbstractHuman calcitonin M and its dimer calcitonin D, two highly active peptides isolated from C cell tumours, were subjected to sequence studies using chemical and enzymatic methods. For calcitonin M, containing 32 amino acid residues, the following structure was derived: magnified image
Though the disulphide bridge between position 1 and 7, and the C‐terminal proline amide of human calcitonin M are the same as in porcine α‐thyrocalcitonin, many amino acid residues ‐ 18 in all ‐ are different throughout the molecule. Arginine and tryptophan are absent; on the other hand, lysine and isoleucine are to be found at position 18 and 27 respectively. Methionine changes its place from position 25 to 8 adjacent to the disulphide bridge. Experimental evidence indicates that calcitonin D represents the antiparallel dimeer of calcitonin M.
Die Struktur der Hydrate von Co3[Co(CN)6]2 und Cd3[Co(CN)6]2
Authors: Ludi A. , Güdel H. U. 
Published: December 2004

AbstractThe crystal structures of Co3[Co(CN)6]2, 12 H2O (a, = 10.210 ± 0.005 Å) and Cd3[Co(CN)6]2, 12 H2O (a = 10.590 ± 0.005 Å) have been determined by X‐ray powder methods. According to the measured density the unit cell contains 1 1/3 formula units with 4 Co2+ (Cd2+) in 4a, 2 2/3 Co3+ in 4b, 16 C and 16 N in 24e, 8 H2OI near 24e, (96k) and 8 H2OII near 8 c (192 l). Structure factor calculations based on the space group Oh5 ‐ F m 3 m lead to the following final values of the reliability index R: 0.038 (Co3[Co(CN)6]2, 12 H2O) and 0.037 (Cd3[Co(CN)6]2, 12 H2O). The interatomic distances for the cobaltous compound (in parentheses for the cadmium compound) are: Co3+‐C: 1.88 Å (1.89); C‐N: 1.15 Å (1.17); Co2+‐N: 2.08 Å (2.24); Co2+‐OI: 2.10 Å (2.27); shortest OI‐H‐OII‐bonds: 2.89 Å (2.82). Co3+ is octahedrally coordinated by six carbon atoms, the divalent metal ion by four nitrogen atoms and two water molecules. The two different metal ions are connected by M2+‐N‐C‐Co3‐bonds to a threedimensional network. The infrared and electronic spectra are shown to be in agreement with the results of the structure analyses of these compounds. The observed positions of the OH‐stretching vibrations lead to a hydrogenbond‐length of 2.8–2.95 Å.
Un nouveau mécanisme réactionnel en série aromatique: Addition ‐ substitution
Authors: Aubort J.‐D. 
Published: December 2004

AbstractReactions of three disubstituted sodium phenolsulfonates with bromine are examined in various conditions. In aqueous medium, two reactions may occur: bromodesulfonation (an electrophilic substitution) or/and formation of corresponding p‐benzoquinones. In methanol, only bromodesulfonation is observed. Formation of p‐benzoquinones is explained by a solvolytic displacement on the quinoloid product of bromine addition on phenolsulfonate.A reaction scheme is proposed, which explains the observed effects of substrate structure and reaction medium.
Umbellamin, ein neues «dimeres» Indolalkaloid 130. Mitteilung über Alkaloide [1]
Authors: Morita Y. , Hesse M. , Schmid H. 
Published: December 2004

AbstractUmbellamine (f; C41H48N4O4), a «dimeric» indole‐indoline alkaloid, was isolated from the root bark of Hunteria umbellata (K. SCHUM.) HALL. F.; it is probably identical with the alkaloid hunterine (structure unknown) of NeUSS & CONE [14]. Thermolysis yielded (+)‐eburnamenine (II), whereas a detailed mass spectrometric study of I, of its O‐methyl and O‐acetyl derivatives, and also of the derived diol V revealed the presence of a phenolic hydroxy‐pseudoakuammigine group as second part, the benzene nucleus of the latter being linked to the C‐14 atom of the eburnamenine component (present in the dihydrom form).The n.m.r. study of umbellamine and of its derivatives showed that the phenolic hydroxy group is either at C‐10′ or C‐11′ and that the dihydroeburnamenyl residue is connected to C‐11′ or C‐10′ of the pseudoakuammigine residue. A choice between these alternatives was possible by investigation of the hydroxylated base IX arising from the latter component, and obtained in small quantities by treatment of umbellamine with zinc or tin in acid. Its constitution, deduced by uv., n.m.r. and mass spectrometry, suggested that the hydroxy group is fixed at C‐11′. If this is correct, the dihydrocburnatnenyl residue is linked to C‐10′ of the pseudoakuarnmigine residue. Thus we propose formula I for umbellamine.
Umwandlung von 3‐Oxo‐17‐äthylendioxy‐19‐mesyloxy‐δ1,4‐androstadien in dreifach ungesättigte A‐homo‐19‐norsteroide Über Steroide, 215. Mitteilung
Authors: Wieland P. , Anner G. 
Published: December 2004

Abstract4‐oximino‐17‐ethylenedioxy‐A‐homo‐δ1(10),2,4a‐19‐nor‐androstatriene is formed by treatment of 3‐oximino‐17‐ethylenedioxy‐19‐mesyloxy‐δ1,4‐androstadiene with sodium hydroxide. An analogous reaction occurs with the corresponding semicarbazone, but under the same conditions 3‐hydrazino‐17‐ethylenedioxy‐19‐mesyloxy‐δ1,4‐androstadiene leads to 17‐ethylenedioxy‐A‐homo‐δ2,4,5(10)‐19‐norandrostatriene.
Über eine neue Ringschlussreaktion mit 3‐Dimethylaminopropyl‐carbinolen zu Oxolanen. Mitteilung über Grignard‐Reaktionen mit Halogenalkylaminen [1]
Authors: Marxer A. 
Published: December 2004

AbstractA new ring‐closure reaction is described, consisting in the treatment of basic carbinols of types 2, 8, 13, 16, with sodamide or sodium hydride, and adding to the sodium salts formed an alkyl halide. Oxolanes of types 5, 9, 14, 17, 20, are formed.
Photochemische Umwandlungen. XXVII [1]. Ein «stabiles» Benzoloxid Vorläufige Mitteilung
Authors: Prinzbach H. , Vogel P. 
Published: December 2004

AbstractBy thermal isomerization of the 3‐oxa‐6.7‐diphenyl‐tetracyclo [3.2.0.02, 7. 04, 6]‐heptane‐1. 5‐dicarbomethoxylate (4) besides the oxanorbornadiene 3 and the hydroxy‐fulvene 7, the ‘stable’ benzeneoxide 7‐oxa‐2.5‐diphenyl‐bicyclo [4.1.0] hepta‐2.4‐diene‐3.4‐dicarbomethoxylate (5) has been isolated. In the temperature range −50 to 170°C no equilibration with the monocyclic oxepine 6 has been detected.
Free‐electron model and triplet‐state lifetime of benzene
Authors: Sen Purnendranath , Basu Sadhan 
Published: December 2004

AbstractUsing the free‐electron model the triplet‐state lifetime of benzene for the 330 mμ band has been estimated to be about 36 sec, which compares favourably with the corrected experimental value of 30 sec. It has also been established that the perturbing singlet must be a π‐σ singlet rather than a π‐π singlet.
Localized impurity states in the Hartree‐Fock, LCAO approximation. I.
Authors: Martino F. 
Published: December 2004

AbstractOne‐electron energies and wave functions for deep trap impurity electrons in a crystal are calculated by the Hartree‐Fock, single determinant method. The interactions arising from a many‐electron single determinant crystal wave function, with automatic inclusion of exchange effects, are those which determine the one‐electron functions and energies. The crystal plus impurity system has no translational symmetry and hence the Bloch theorem is not applicable for the solution of the essentially infinite Hartree‐Fock eigenvalue matrix. Thus we develop a technique in which the Hamiltonian and overlap matrices are written in terms of bordered matrices, with the interaction of the impurity functions with the rest of the crystal environment contained in the bordering rows and columns. The resulting secular equation explicitly includes the effects of orthogonalization of the entire basis set, including the impurity functions. This technique could be used in an iterative calculation of the electronic structure of a small number of electrons, assuming that the rest of the electrons in the environment are fixed according to an initial estimate.
Inelastic molecular collisions with an orientation‐averaged interaction energy
Authors: Shin Hyung Kyu 
Published: December 2004

AbstractThe importance of molecular orientations for vibrational‐translational energy transfers between diatomic molecules has been investigated. An angle‐dependent potential function is assumed, and it is averaged over the orientations and vibrations of colliding molecules. For I2I2 and Cl2Cl2, it is found that the calculated average vibrational transition probability for a colinear collision is over‐estimated by large factors (1/γ) compared to that obtained when all possible molecular orientations are considered. At 3000K, 1/γ = 34.4 for I2I2 and 17.6 for Cl2Cl2, while it is 6.8 and 5.9 for N2N2 and O22, respectively. It is also shown that 1/γ decreases rapidly as temperature increases. At 20000K, 1/γ ≈︂ 3 for I2I2, Cl2Cl2, and N2N2, while it is ≈︂ 2.5 for O2O2. In general, when the molecules are large, and when strong attractive forces act between them, 1/γ is very large at low temperatures (<10000K).
Electronic structures and spectra of halogenated purines and pyrimidines II.π‐Electronic structure of 2‐chloropurine and its related derivatives
Authors: Song Pill‐Soon 
Published: December 2004

AbstractElectronic structures and spectra of “non‐alternant” heterocyclic 2‐chloropurine and its analogs have been computed with different MO techniques, namely, HMO, ω‐SCF‐HMO (ω = 1.4 and 0.5), and PPP semiempirical SCF‐ASMO‐CI. Triplet‐state energies have been calculated by the last method. In general, it is found that at least semiquantitatively consistent results on the ground‐state properties of the molecules are obtained from the different MO methods. As expected, excited states of the molecules are not satisfactorily treated by the HMO and σ techniques. However, an excellent agreement between the observed and calculated π‐π* transition energies has been obtained with the PPP method. In view of the semiquantitative consistency of the ground‐state properties, the use of simple methods such as HMO and ω(=0.5)‐SCF techniques is justifiable for limited application to molecular biology.Results on the molecular geometry, dipole moments, ionization potentials, xanthine oxidase reactivity and spectra have been discussed with regard to the halogen substitutions in the purine base. The significance of these results with reference to the biological uses of substituted purines is briefly described.
Exposé d'une méthode de détermination des orbitales virtuelles pour les interactions de configurations. Application à l'etat fondamental de l'atome de béryllium
Authors: Leclercq J. ‐M. 
Published: December 2004

AbstractA method for the determination of the virtual orbitals for configuration interaction is described. This method is a generalization of the one used by Watson in 1960 for the ground state of the beryllium atom. The important point in the method is to complete the set of functions used successively. As an illustration the method is applied to the ground state of the beryllium atom. The method seems to be efficient.
Configuration interaction study of H2 and H3 systems
Authors: Gianinetti E. , Majorino G. F. , Rusconi E. , Simonetta M. 
Published: December 2004

AbstractThe configuration interaction method has been applied to the H2 and H3 systems. The effect of increasing the size of the atomic Slater‐type orbital basis has been studied. A minimization procedure with respect to orbital exponents has been carried out.
Zur konstruktion von energiehyperflächen
Authors: Preuss H. 
Published: December 2004

AbstractAn analytical approximation for the hypersurface ℰ (pr‐approximation) is given using the two‐ and three‐center‐functions pλμ and r, which is valid for any number N of atoms and is invariant with respect to the number of centers in its analytical structure (rule of construction). This is valid too if N is reduced either by the association of atoms or by transitions to infinity. pλμ can be fixed by two‐center‐systems. But r is still free except for the fulfilling of some simple requirements. The rule of construction proposed for ℰ is an example for using so‐called analytical computers.
Group theory and reaction mechanisms: Permutation theoretic prediction and computational support for pseudorotation modes in C2H and C5H rearrangements
Authors: Bouman Thomas D. , Duncan Charles D. , Trindle Carl 
Published: December 2004

AbstractThe McIver–Stanton rules concerning the symmetry of transition states have a counterpart in rules concerning the permutation symmetry of single steps in degenerate rearrangements, derivable with the aid of Longuet–Higgins group theory. The generalized rules are illustrated by the widely studied PX5 polytopal rearrangements. The analysis leads to prediction of hitherto unexplored “pseudorotation” pathways for rearrangements in ethyl and homotetrahedryl cations. CNDO computations of system energies, gradients, and curvatures at critical points on the C2H and C5H surfaces indicate that symmetry‐breaking in keeping with the permutation‐theoretic predictions is a key feature of the low‐energy rearrangements of these systems. In particular, computation indicates that the C2v “classical” homotetrahedral cation corresponds to an energy maximum rather than an energy minimum, or a transition state.
Matrix elements and their selection rules from ladder operator considerations
Authors: Hadinger G. , Bessis N. , Bessis G. 
Published: December 2004

AbstractWithin the Schrödinger–Infeld–Hull factorization framework it is shown that, by introducing a parameter ε in the quantization condition, that is, ε(j–|m|)=integer ≥ 0, and, thus, considering “symmetrized” ladder operators, one can use the same formulas to handle both class I (ε = +1) and class II (ε = −1) problems. Starting from this unified point of view, after building up the associated angular momentum operators and their ε‐dependent eigenfunctions, one unique closed‐form expression of the coupling coefficients is obtained. This expression embodies many sparse and known previous results, without being more intricate than any of them. The basic material, allowing the application of a Wignera–Eckart theorem to matrix elements of an operator on the basis of eigenfunctions of factorizable equations, and a quick determination of the associated selection rules are given. Some examples are treated as an illustration.
Determination of excitation energies and transition moments in a second order polarization propagator approach. Application to the Be atom and the CH+ molecule
Authors: Oddershede Jens , Jørgensen Poul , Beebe Nelson H. F. 
Published: December 2004

AbstractExcitation energies and transition moments have been determined from a second order polarization propagator and the effect of including energy shifted denominators has been investigated. Results for Be and CH+ show a change of 2–5% for the transition moments and of 0–20% for the singlet excitation energies in a second order approach compared to a first order (time‐dependent Hartree‐Fock) approximation. Both Be and CH+ are triplet unstable in the time‐dependent Hartree‐Fock approximation. The triplet instability is removed for Be but not for CH+ in a second order polarization propagator approach.
The physics of the born–oppenheimer approximation
Authors: Essén H. 
Published: December 2004

AbstractA new derivation of the Born–Oppenheimer separation of electronic and nuclear motion is presented. The arguments used differ from those in earlier works in not being specially designed for molecules. Instead they aim at an intuitive understanding of the qualitative behavior of the low energy bound states of any, real or hypothetical, Coulomb interacting system of particles. The virial theorem is the starting point of the discussion. After a brief explanation of how it can be used to understand atomic structure it is applied to molecules. It is found that coordinates of collective and individual motion are natural coordinates for the approximate separation, rather than nuclear and electronic. It is also shown that it is the form of the interaction between the particles that is responsible for the separation; the smallness of met/MNu is irrelevant.
Problems of the calculation of intermolecular interactions on complexes with strong delocalized π‐bonds within the PCILO framework
Authors: Lochmann R. 
Published: December 2004

AbstractStrong delocalized π‐bonds must be approximated by localized π‐bonds within the PCILO framework. From this approximation some difficulties result in the calculation of intermolecular interactions. If only one subsystem involves delocalized π‐bonds the difficulties seem to be not very important. But if both subsystems involve such bonds, the PCILO results are not reasonable in some cases.
Calculation of molecular crystals within the PCILOCC framework
Authors: Lochmann R. 
Published: December 2004

AbstractStabilization energies and equilibrium distances of one‐dimensional (HF)n and (H2O)n chains have been calculated by means of the PCILO method for finite chain length and by the PCILOCC method for infinite chain length. Both types of calculation are compared with corresponding CNDO/2‐MO and CNDO/2‐CO calculations. Further we have performed an analysis of the individual contributions of the stabilization energies per monomer of the PCILO and PCILOCC calculations.The results show that the PCILOCC method is well suited for the calculation of molecular associations with translational symmetry.