bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exciplexes of zinc meso‐tetraphenylporphyrin with arenediazonium salts, oxygen and p‐benzoquinone
Authors: Becker H. G. O. , Lehmann T. , Zieba J. 
Published: January 2005

AbstractZinc meso‐tetraphenylporphyrin (ZnTPP) forms triplet exciplexes with different arenediazonium salts (p‐Et2N, p‐MeO, p‐Me, p‐t‐Bu, p‐H, p‐Cl, p‐Br) and p‐benzoquinone, and a singlet exciplex with oxygen (probably formed after energy transfer from excited ZnTPP to 3O2 to yield 1O2).The absorption spectra of these exciplexes are nearly identical and – except of pronounced fine structures – similar to the spectrum of 3(ZnTPP)*.By means of WARE treatment of flash‐photolytically determined rate constants or of quantum yields equilibrium constants, lifetimes and further data of diazonium salt exciplexes are determined. The equilibrium constants and lifetimes are very similar and amount to about 104 M−1 and 20 μs, respectively.The equilibrium constants of the oxygen and p‐benzoquinone exciplexes are determined by competition experiments; they amount also to about 104 M−1.The diazonium salt exciplexes belong to the charge‐shift type. Their equilibrium constants are, therefore, independent of the solvent polarity, as is interestingly also observed for the oxygen exciplex which formally belongs to the charge‐separation type.The p‐benzoquinone exciplex dissociates in acetonitrile as has been found also by other authors.
Tieffarbige Systeme mit Oxalsäurestruktur — eine Strukturkorrektur
Authors: Beckert R. , Bauer W. 
Published: January 2005

Deep Coloured Systems with Oxalic Acid Substructure‐a Structural CorrectionBasing on a recent spectroscopic investigation the structure of earlier described deeply coloured systems derived from oxalic acid imidochlorides and thioacetamide has to be revised. Due to the poor solubility of these systems their spectroscopic characterization led to the misinterpretation as tetramethin‐bridged thiazolines 1. By means of 1H‐NOE‐Difference‐Spectroscopy of newly synthesized derivatives with lipophilic substituents a imidazolin‐thion substructure 4 has been found. Such an arrangement of the heteroatoms clearly reflects a 1,3‐rearrangement with participation of the oxalic acid system.
Synthesis of Mammalian Gonadoliberin Analogs with the N‐terminal glutamine or glutamine or glutamic acid
Authors: Masiukiewicz Elżbieta , Rzeszotarska Barbara , Fortuna Gabriela , Kochman Kazimierz 
Published: January 2005

AbstractSynthesis of two mammalian gonadoliberin analogs, [Gln1]GnRH and [Glu1]GnRH, in solution by the peptide segment coupling of the [(2 + 4) + 4] type has been described.
Cycloadditions‐Eliminierungsreaktionen mit 4‐Aryl‐5‐arylimino‐1,2,4‐dithiazolidin‐3‐onen (Senföloxiden)
Authors: Tittelbach Franz 
Published: January 2005

Cycloaddition Elimination Reactions of 4‐Aryl‐5‐arylimino‐1,2,4‐dithiazolidin‐3‐ones (Mustard Oil Oxides)4‐Aryl‐5‐arylimino‐1,2,4‐dithiazolidin‐3‐ones (1) react with isocyanates, isothiocyanates, and cyanic acid esters by exchange of the COS‐part from 1 affording thiadiazole and dithiazole derivatives 4, 5, 6 or 12. The reaction products are able to give further exchange reactions. Ring opening of 2‐substituted 4‐aryl‐5‐arylimino‐1,2,4‐thiadiazolin‐3‐ones (4) and ‐3‐thiones (6) yields thio‐ and dithiobiurets (7, 8) with aryl substituent in 3‐position. Oxidation of dithiobiurets, generated from 6, affords dithiazolidines 9, which are Dimroth‐isomers of 6.
Reactions of 2‐arylhydrazones of 1,2,3‐triketones with 1,2‐diaminoethane. II. Synthesis of 2,9‐Diarylazo‐3,8‐dimethyl‐1,10‐diphenyl‐4,7‐diaza‐2,8‐decadiene‐1,10‐diones and 6‐Amino‐2‐arylazo‐3‐methyl‐1‐phenyl‐4‐aza‐2‐hexen‐1‐ones
Authors: Opozda Ewa , Śledziewska Ewa 
Published: January 2005

AbstractThe reaction of 2‐arylhydrazones of 1‐phenyl‐1,2,3‐butanetrione with 1,2‐diaminoethane yields 2,9‐diarylazo‐3,8‐dimethyl‐1,10‐diphenyl‐4,7‐diaza‐2,8‐decadiene‐1,10‐dione (2a‐d) (Schiff base type A) and monocondensation products ‐ 6‐amino‐2‐arylazo‐3‐methyl‐1‐phenyl‐4‐aza‐2‐hexen‐1‐ones (3a‐e) (“half” units ‐ Schiff bases type B). The structure of both types of compounds characterized on the basis of spectroscopic data (m.s., i.r., 1H‐n.m.r.).
Strukturanalytische Untersuchungen an Folgeprodukten aus Sulfonamiden. VIII. Zur Struktur der Reaktionsprodukte aus 1,1,3‐trisubst. Thioharnstoffen und N‐Tosyl‐iminothiokohlensäuremethylester‐chlorid
Authors: Hans M. , Schöffmann T. , Dehne H. , Matos E. N. 
Published: January 2005

Structure‐Analytical Investigations of Consecutive Products of Sulphonamides. VIII. About the Structure of Reaction Products from 1,1,3‐Trisubst. Thioureas and N‐Tosyl‐iminothiocarbonic Acid Methylester ChloridesThe structure of a variety of reaction products from 1,1,3‐trisubstituted thioureas (1 a–e) and N‐tosyl‐iminothiocarbonic acid methylester chlorides (2) is investigatigated with respect to whether a sequence SO2NCSC (structure I) or SO2NCNC (structure I) is form ed. The problem is solved by means of m.s. and i.r. spectra as well as the Feigl test. The results of these investigations show that structure I is formed.
Synthese von 6‐(pyrid‐4‐yl)‐substituierten Pyrido[: 3‐d]pyrimidinen und 1,8‐Naphthyridinen
Authors: Haber H. , Hagen V. , Schlender M. 
Published: January 2005

Synthesis of 6‐(4‐pyridinyI)‐substituted Pyrido[2,3‐d]pyrimidines and 1,8‐NaphthyridinmsA series of new 6‐(4‐pyridinyl)‐substituted pyrido‐[2,3‐d]pyrimidines 2–4and 1,8‐naphthyridines 6, respectively, is described. Cyclisation of 2‐amino‐5‐(4‐pyridinyl)‐pyridinm‐3‐carboxamide 1a with diethyl oxalate gives the pyrido‐[2,3‐d]pyrimidinm 2a. Alkylation of(2a) yields the 3‐ethylaminoxyrido[2,3‐d]pyrimidine derivative 2b. Saponification of 2a,b gives the corresponding carboxylic acids 3a,b, which are decarboxylated by heating above the melting point to give 4a, b. The 2‐amino‐5‐(4‐pyridinyl)‐pyridinm carboxylic acid derivatives 1 b–e react with ethylmalonylchloridm and diethyl malonate to afford the 1,8‐naphthyridines 6b–e. The 1‐oxide 7 in a similar reaction gives 8 and the oxdiazole(9) which is converted by ring transformation to the 1,8‐naphthyridine 10.
Neue Möglichkeiten zur Verwendung von 2‐Furaldehyd: Synthese von Oxaundecan‐1,2,10,11‐tetraol
Authors: Marzec K. 
Published: January 2005

New Possibilities of Application of 2‐Furancarboxaldehyde: Synthesis of 6‐Oxaundecane‐1,2,10,11‐tetraolStarting from 2‐furancarboxaldehyde (1), a method for the synthesis of 6‐oxaundecane‐1,2,10,11‐tetraol (8) is presented and the possibilities of applying this compound for the preparation of polyurethane resins are discussed. In addition, a method for the preparation of new di(pent‐4‐enyl)ether (7) is described.
Zur Molekülverknüpfung mit Schwefelchloriden. X. Bis(arylamino‐chloralkyl)‐sulfane aus N‐β‐Methallyl‐N‐tosyl‐anilinen und Schwefeldichlorid
Authors: Hollmann K. , Ecke M. , Mühlstädt M. 
Published: January 2005

Molecule Linkage by Sulfur Chlorides. X. Bis(arylamino‐chloroalkyl)‐sulfanes from N‐β‐Methallyl‐N‐tosyl‐anilines and Sulfur DichlorideReactions of differently substituted N‐β‐methallyl‐N‐tosyl‐anilines 1 with sulfur dichloride yield bis(arylamino‐chloroalkyl)‐sulfanes 2 and 3 and dihydrobenzo‐1,4‐thiazines 4. The structural assignment of the products 2 and 3 was carried out by mass spectroscopy and 1H‐n.m.r.‐spectroscopy.
2,2‐Disubstituted Cyclopentane‐1,3‐diones. Part 5. Simple Procedures for the Preparation of Racemic (1RS,5RS)‐5‐Methyl‐2‐oxabicyclo[3.3.0]octane‐3,6‐dione Starting from 2,2‐Disubstituted Cyclopentane‐l,3‐diones
Authors: Schick H. , Ballschuh S. , Welzel H.‐P. , Schwarz S. 
Published: January 2005

Abstract2‐Methyl‐2‐(prop‐2‐enyl)cyclopentane‐1,3‐dione (15) can be transformed on two different routes into the racemate (1RS,5RS)‐5‐methyl‐2‐oxabicyclo[3.3.0]octane‐3,6‐dione (rac‐13), a key intermediate for the synthesis of 8‐methylprostaglandins. Both routes are characterized by a non‐selective reduction of a 2,2‐disubstituted cyclopentane‐l,3‐dione to the corresponding cyclopentane‐l,3‐diol, followed by lactonization and oxidation of the remaining hydroxy group.
Eine neue Gruppe vom Nereistoxin abgeleiteter Verbindungen ‐ Synthese von Bis‐dimethylamino‐tris‐disulfanen
Authors: Mühlstädt M. , Heinicke J. , Schubert H. 
Published: January 2005

A New Group of Compounds Derived from Nereistoxin ‐ Synthesis of Bis‐dimethylamino‐tris‐disulfanesThe reaction of organo‐thiosulfates, BUNTE‐salts, with mercaptans is a convenient synthesis of disulfanes. Similarly bis‐BUNTE‐salt 7 and tert. butyl mercaptan give bis‐disulfane 5c [9]. By treating 7 with several aliphatic mercaptans we found the formation of the tris‐disulfanes 8a–d in preparative amounts in addition to the bis‐disulfanes 5a–d expected. This reaction was investigated. The preparation of the compounds 8 is described and a proposal is given for a mechanism of the formation of 8 as a thiol‐disulfide‐interchange.
Synthese und Eigenschaften von 2‐Methoxycarbonylmethylen‐ und 2‐ (Formyl‐methoxycarbonylmethylen)‐2H‐Thiopyran‐3‐carbonsäureme‐thylester
Authors: Greif D. , Pulst M. , Weissenfels M. , Scheinmann Feodor 
Published: January 2005

Synthesis and Properties of Methyl‐2‐methoxycarbonylmethylene‐ and ‐2‐(formyl‐ methoxycarbonylmethylene)‐2H‐thiopyran‐3‐carboxylatesDimethyl‐2‐chloro‐propene‐l,3‐dicarboxylate is a easily available reactive C2‐building block for the synthesis of 2H‐thiopyran derivatives la — n in good yields via [C3S + C2]‐cyclisation reactions using β‐thioxoaldehydes and their derivatives as C3S‐synthons. The structure of the stable red products with Z‐configuration (side chain in position 2 of the ring) is elucidated by means of several analytical and spectroscopic methods including X‐ray analysis of compounds 1h and lk.Treating of 1 with Vilsmeier reagent yields title compounds 2 with a remarkable less reactive formyl group at the exo‐methylene group. There is obviously a shielding effect of the carboxylate groups.
Novel Meisenheimer Complexes by the Reaction of 4,6‐Dinitrobenzofuroxan with Pyridinium Ylides
Authors: Niclas H.‐J. , Kind J. , Ramm M. 
Published: January 2005

AbstractThe reaction of 4,6‐dinitrobenzofuroxan 1 with pyridinium ylides 2 affords σ‐CC bonded Meisenheimer complexes 3. The structure of these adducts is studied by n. m. r. spectroscopy and X‐ray structure analysis.
Untersuchung zur Regio‐ und Stereoselektivität der Reaktion von 7,8‐Dimethoxy‐1‐phenyl‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepin mit Phenyloxiranen
Authors: Mondeshka Diana M. , Angelova Ivanka G. , Ivanov Tschavdar B. , Tomov Emil 
Published: January 2005

Reaction of Benzazepines with PhenyloxiranesThe reaction between the 7,8‐dimethoxy‐1‐phenyl‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepines ( ± )‐1, (1S)‐(−)− 1 und (1R)−( + )− 1 and racemic or optically active phenyloxiranes 2a–d leads to a mixture of the regioisomcric carbinoles 3a–d and 4a–d, respectively. In all cases the reaction is not stereospecific, but regiospecific with regard to the p‐phenyl substituted phenyloxiranes 2b–d. The ratio of the isomers was determined by HPLC and the structures of the regioisomers 3a and 4a were deduced from the 1H‐n.m.r. spectra. The newly synthesized carbinols proved to be strong re‐uptake in hibitors of the monoamines dopamine (DA), norepinephrine (NE) and serotonine (5‐HT).
A HAM/3 study of substituted benzenes
Authors: Takahata Y. 
Published: January 2005

AbstractThe semiempirical HAM/3 method is used to study ionization potentials, electron affinities, heats of formation, stabilization energies, dipole moments, and charge of mono‐ and disubstituted benzenes. Ionization potentials and electron affinities are calculated with good accuracy. The ground state properties are generally not well calculated by HAM/3. Errors in heats of formation and dipole moments are up to 50 kcal/mol and 2.4 D.
Vibronic interaction in one‐dimensional polymer
Authors: Tachibana Akitomo , Inoue Takayuki , Yamabe Tokio , Hori Kenzi 
Published: January 2005

AbstractAsymptotic properties of the “attractive” vibronic coupling in a one‐dimensional polymer are analyzed. The strength of the vibronic coupling grows linearly with the size of polymer, which may relate to the softening mechanism of Coulombic repulsive interaction between a Cooper pair of superconducting electrons.
The variational alternant molecular orbital method for 3‐D and 2‐D hydrogen molecule
Authors: de Andrada E Silva E. A. , da Cunha Lima I. C. , da Silva A. Ferreira 
Published: January 2005

AbstractThe Variational alternant molecular orbital method (VAMO) is described and applied to the case of three‐dimensional and two‐dimensional hydrogen molecules. The energies of the electron system are obtained, together with the equilibrium distances of the molecules. The intergrals equivelent to the Slater's integrals of the nonvariational method are described. Applications of this method to realizable systems are described.
Degeneracy lifting in graphite and boron nitride: A perturbational approach
Authors: Lafemina John P. , Lowe John P. 
Published: January 2005

AbstractThe degeneracy lifting in the pi bands, near the Fermi energy, for two‐ and three‐dimensional graphites and boron nitride are qualitatively determined, without calculation, using first‐order perturbation theory and the concept of transferability. The relationships between the band diagrams for several three‐dimensional modifications of graphite and boron nitride are presented in a simple orbital context.
Dynamical analysis of correlated wavefunctions
Authors: Moscardó Federico , San‐Fabián Emilio 
Published: January 2005

AbstractA comparative dynamical analysis of several quasi‐exact wavefunctions for helium has been carried out by computing their corresponding correlation coefficients. The aim is to use the resulting information to study the correlation included in approximate wavefunctions within the factor correlation model. Information about the possibility of making simplifications in the approximate wavefunctions and about the flexibility of the quasi‐exact wavefunctions is also obtained.
On the quenching of Li(2p) by HCl: Nonadiabatic effects
Authors: Yarkony David R. 
Published: January 2005

AbstractThe electronic structure aspects of the quenching reaction Li(2P) + HCl → LiCl + H were studied using ab initio state averaged multiconfiguration self consistent field/configuration interaction methods. This reaction proceeds through an avoided crossing of the 1, 2 2A' potential energy surfaces. A region of strong electronic nonadiabaticity was located and (first derivative) nonadiabatic coupling strengths computed. This region of strong electronic nonadiabaticity occurs near a (local) minimum on the 2 2A' potential energy surface which is exoergic relative to its reactant asymptote, Li(2P) + HCl.
Excitation energies, oscillator strengths, and frequency dependent polarizabilities of Be: Comparison of TDHF, EOM (second order), and MCTDHF
Authors: Graham Richard L. , Yeager Danny L. 
Published: January 2005

AbstractLow‐lying excitation energies from the ground state of Be were calculated using a basis set of 61 Cartesian Gaussian functions. Three approximations were employed: the time‐dependent Hartree–Fock (TDHF), second‐order equations‐of‐motion (EOM), and multiconfigurational time‐dependent Hartree–Fock (MCTDHF). The TDHF excitation energies are 0.5–1.1 eV lower than experiment, and the EOM values are 0.3–1.2 eV lower than experiment, whereas the MCTDHF excitation energies deviate on the absolute average from experiment by only 0.03 eV. We found that in an MCTDHF calculation, any proper MCSCF stationary point is a good reference (i.e., initial) state, not just the ground state. Experimental values for oscillator strength are accurately known only for the 2s2X1S → 2s2p1P0 transition. The TDHF value and the MCTDHF value agree with experiment, but the EOM value does not. The agreement of the TDHF value with experiment seems to be coincidental, because for higher lying transitions the TDHF values differ by approximately a factor of two or more from the more accurate MCTDHF. Frequency independent polarizabilities, α(0), were also calculated with the TDHF, HRPA, and MCTDHF and frequency dependent polarizabilities, β(ω), were calculated with the MCTDHF. No experimental data for Be polarizabilities exist, but we expect the MCTDHF values to be among the most accurate calculations available.
Free energy and dispersion forces via response functions
Authors: Obcemea Ceferino H. 
Published: January 2005

AbstractIn a recent paper [5], Ford, Lewis, and O'Connell proposed a remarkable formula for the change in the free energy in terms of the susceptibility alone. This formula came out of their treatment of a quantum oscillator interacting (via dipole coupling) with a blackbody radiation field at finite temperature T. As a result, they found a modification to the Planck formula due to finite line width and a positive energy shift which is of quantum electrodynamical origin.I shall show in this paper that the above result is a general one, not specific to the problem considered, and whose essence can already be traced to the early works of van Kampen and Liftshitz on the theory of van der Waals forces, Maradudin et al. on point defects in lattices, and Mahanty and others on dispersion forces. The above formula can be deduced directly using the argument theorem in theory of contour integration.
Rotational decoupling of vibrational modes due to rotational excitation: Application to a model of the HDO stretching motions
Authors: Shirts Randall B. 
Published: January 2005

AbstractRotational motion can have a significant effect on intramolecular vibrational dynamics. In this paper, we explore the recently discovered phenomenon of rotational decoupling through both quantum mechanical and classical methods. It is found in a model system for the stretching motions of HDO, that rotational motion about the c axis can decouple the stretches. This fact can be understood as a cancellation between kinetic and centrifugal coupling as illuminated using classical resonance analysis and quantum matrix element calculations. The significance of this phenomenon is discussed in infrared multiple photon absorption experiments with specific application to isotope separation in HDO.
Crossed‐Molecular beam studies of the state‐to‐state reaction dynamics of charge transfer at low and intermediate energy
Authors: Futrell Jean H. 
Published: January 2005

AbstractThe microscopic, state‐to‐state reaction dynamics of charge transfer reactions are reviewed for the two system N(N2, N2)N and Ar+(N2, Ar)N. The crossed molecular beam method demonstrates that the symmetric, molecular case proceeds by two mechanisms at low collision energy (< 0.7 eV). One of these involves an orbiting complex in which the total available energy is redistributed, essentially statistically. The second mechanism is a direct mechanism which involves nearly rectilinear trajectories and corresponds to exactly resonant charge transfer at low energy (0.7 eV) and charge transfer accompanied by vibrational excitation at higher energy (> 10 eV). The orbiting mechanism is dominant at low energies and disappears entirely with increasing collision energy. The unsymmetric, nearly resonant charge transfer reaction is direct at all energies. At very low collision energy (0.6 eV) and moderate collision energy (> 1.5 eV) the dominant reaction channel is the generation of N2+(X2 g, v = 1) with little rotational excitation. At 0.6 eV substantial angular scattering (including back‐scattering) is observed; above 1.5 eV the trajectories are essentially rectilinear. At intermediate energies (0.8 < E < 1.3 eV) a very different mechanism is observed. All the energetically accessible vibrational states of N are formed, each with a preferred scattering angle at a given energy. Related experiments and theoretical models which rationalize some, but not all, of these results are described. The most intriguing puzzle is the “energy window” in which quantum‐state specific, angular‐specific reactive scattering is observed.
Cation binding effect on imidazole tautomerism
Authors: Basch H. , Krauss M. , Stevens W. J. 
Published: January 2005

AbstractBinding of Zn2+ to imidazole (Im) and methyl imidazole (MeIm) is studied by ab initio methods as a model for the effect of cation binding on tautomeric energies. Gradient energy optimized conformations were obtained for all neutral and ionic structures, including the deprotonated molecules and the ylides. The N3H tautomer of MeIm is calculated to be more stable than N1H by about 1 kcal/mole. However, binding of a Zn2+ cation to the available nitrogen site is found to reverse the order of binding, leaving N1H more stable by 1 kcal/mole. Binding of Zn2+ produces a significant perturbation in the electronic structure, a smaller shift in the equilibrium conformation of the imidazole ring, and only a small absolute shift in the relative tautomer energies. Methyl substitution at C5 has a small effect on both conformation and energetics.A high‐energy ylide tautomer is produced by moving the proton bound to C2 to the N1 atom. The binding of Zn2+ to the C2 site is substantially stronger than to the N1 site, yielding nearly isoenergetic ZnIm2+ conformations for binding to either N or C atoms. For the deprotonated salts the lowest energy conformation has the C2N3 bond bridged by Zn2+.
Configuration selection and extrapolation in multireference configuration interaction calculations: The (H2)2 van der waals complex as a benchmark example
Authors: Shavitt Isaiah , Brown Franklin B. , Burton Peter G. 
Published: January 2005

AbstractMultireference configuration interaction (MR‐CI) calculations using energy‐selected and complete‐active‐space reference configurations are compared for a large‐basis‐set treatment of the (H2)2 van der Waals complex in a T geometry. Procedures for estimating truncation errors arising from energy threshold selection of configuration state functions and for extrapolating to the full CI limit are tested by comparisons with untruncated calculations and with the full CI energy. The results of these tests show that great care is required in the use of the correction and extrapolation formulas. Optimization of the orbitals of the reference wave function (compared to the use of SCF orbitals) is found to produce order‐of‐magnitude improvement in the results.
A computational study of some isomerization equilibria and their possible relation to vinyl chloride carcinogenicity
Authors: Murray Jane S. , Politzer Peter 
Published: January 2005

AbstractThere is considerable evidence indicating that the primary in vivo DNA alkylation product of vinyl chloride, believed to be responsible for its carcinogenicity, is the 7‐N‐(2‐oxoethyl) derivative of guanine. Using a representative keto‐enol system, we have studied computationally two possible equilibria involving this adduct. The first is between the 2‐oxoethyl derivatives of the keto and enol forms of the representative system, whereas the second is between the 2‐oxoethyl derivative of the keto form and the corresponding hemiacetal. In the case of the analogous guanine derivatives, such equilibria could lead to disruption of the hydrogen bonding between guanine and cytosine in DNA and could cause miscoding and replicational and transcriptional errors. An ab initio self‐consistent field molecular orbital study has been carried out using the GAUSSIAN 82 system of programs. Optimized structures and energies have been calculated at the 2‐21G level for the representative keto‐enol system and its 2‐oxoethyl and hemiacetal forms. The formation of the 2‐oxoethyl adduct was found to have no significant effect upon this keto‐enol equilibrium, which strongly favors the keto form. Our calculations further show hemiacetal formation to be an unlikely possibility for this system. On the basis of these results and recent data on guanine tautomers, we speculate about the analogous equilibria involving the guanine derivatives.