bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhomogene Verformungserscheinungen bei Schwingbeanspruchung des Vergütungsstahls 42 CrMo 4
Authors: Eifler D. , Macherauch E. 
Published: May 2005

AbstractDas Wechselverformungsverhalten von normalisiertem 42 CrMo 4 ist für Beanspruchungen σa < ReS durch Ent‐ und Verfestigungsvorgänge gekennzeichnet. Die Wechselentfestigung erfolgt inhomogen und ist mit der Ausbreitung sog. Ermüdungslüdersbänder verbunden, die anschließende Verfestigung erfolgt homogen.Das Wechselverformungsverhalten von vergütetem 42 CrMo 4 ist für Beanspruchungen mit σa < Rp0,2 mit Entfestigungsvorgängen verbunden, die kontinuierlich in die Rißausbreitungsphase übergehen. Die während der Wechselverformung ablaufenden plastischen Deformationsvorgänge sind bis zum Probenbruch extrem inhomogen und auf sog. Ermüdungszonen beschränkt. Eine Erniedrigung der Anlaßtemperatur und der Spannungsamplitude verstärkt die Inhomogenität.
Entwicklung auf dem Gebiet der Lebensdauervorhersage an mehrachsig beanspruchten komplexen Bauteilen
Authors: Ott W. , Nowack H. 
Published: May 2005

AbstractIm Hinblick auf die Erzielung höherer Ausnutzungsgrade technischer Strukturen ist das Vorliegen mehrachsiger Beanspruchungsbedingungen im besonderen Maße zu berücksichtigen. In der vorliegenden Arbeit wird eine Übersicht über im Schrifttum mitgeteilte Vorhersagemethoden für Belastungen in der Nähe der Dauerfestigkeit und im Zeitfestigkeitsbereich gegeben. Die Anwendung der meisten Methoden besonders für den Zeitfestigkeitsbereich ist an das Vorliegen von Beanspruchungsereignissen in Form geschlossener “Schwingspiele” gebunden. Diese Beschränkung wird mit Hilfe eines neuen Schadensberechnungsverfahrens auf der Grundlage der plastischen Arbeit überwunden. Es erfolgt eine kurze Beschreibung dieser auf beliebige dreidimensionale elastisch‐plastische Beanspruchungen anwendbaren Methode, die eine Finite Element Analyse in Verbindung mit dem Werkstoffmodell nach Mróz, weiterhin ein inkrementelles Schadensberechnungskonzept einschließt.
Einfluß der Laminatkomponenten von CFK‐Werkstoffen auf das statische und das dynamische Verhalten
Authors: Baron Ch. , Schulte K. 
Published: May 2005

AbstractDer Einfluß auf das statische und das dynamische Verhalten eines konventionellen und eines modifizierten duktileren Matrixsystems wurde bei Verwendung zweier hochfester Kohlenstoffasertypen mit unterschiedlicher Bruchdehnung untersucht. Mit den jeweiligen Faser‐Matrix‐Kombinationen wurden drei verschiedene Laminate gebildet, ein unidirektionales Laminat [08], ein Kreuzlaminat [ 02, 902, 02, 902]sund ein annähernd quasi‐isotropes Laminat [02, ±45, 02, ±45,90]s. Es zeigt sich, daß die Verwendung eines duktilen Matrixsystems zu einer Verzögerung in der Schadensentwicklung führt. Dies wirkt sich dahingehend aus, daß sowohl die statischen als auch die dynamischen Eigenschaften verbessert werden. Bei der Verwendung des duktilen Matrixsystems zusammen mit der Faser höherer Bruchdehnung führt die Verbesserung der statischen Festigkeit nicht in gleichem Maße zu einer Verbesserung der Ermüdungsfestigkeit.
Einfluß einer Laseroberflächenhärtung auf die Dauerlestigkeit von glatten Proben mit kurzem Riß aus dem Stahl C70W2
Authors: Schädlich St. , Winderlich B. , Brenner B. 
Published: May 2005

AbstractDie Laserhärtung als ein lokales Wärmebehandlungsverfahren von Stählen kann zur partiellen Wiederherstellung der Dauerfestigkeit anrißgeschädigter Bauteile eingesetzt werden. Die Untersuchungen werden an Flachproben aus dem Stahl C70W2 mit kurzem Anriß durchgeführt. Die durch die Laserhärtung erzielte Steigerung der Dauerfestigkeit gegenüber dem angerissenen Grundzustand von über 80% wird auf die Anhebung des Schwellwertes für Rißausbreitung infolge der martensitischen Umwandlungshärtung, die Wirkung von Eigenspannungen an der Rißfront und eine eventuelle Rißabstumpfung zurückgeführt.
The effect of temperature on selectivity in capillary SFC
Authors: Jones Brian A. , Shaw Timothy J. , Clark Jody 
Published: May 2005

AbstractRetention indices (RI) for a variety of probe compounds were determined on 50‐μm i. d. columns coated with eight different stationary phases under density programmed SFC conditions at isothermal temperatures of 80 and 150°C. RI values were strongly dependent on temperature for polar probes on the polar phases containing high levels of cyanopropyl or polyethylene glycol (PEG) functionality. A lower apparent polarity was observed for polar columns at higher temperatures. Moderate RI differences were apparent with the same probes on columns with polarizable stationary phases of high phenyl or biphenyl content. Nonpolar alkyl substituted stationary phases showed only a slight temperature dependence on RI for all test compounds. Alkanes of lower molecular weight eluted at lower densities on all columns when the temperature was raised because of the contribution of volatility to elution in SFC. This same effect was observed for the higher alkanes on both nonpolar and PEG columns, but they eluted at similar densities on cyanopropyl columns and at higher densities on columns with polarizable phases when the temperature was raised. Temperature controlled selectivity tuning is a useful tool in optimizing separations in SFC.
On‐line coupled liquid chromatography and capillary supercritical fluid chromatography: Large‐volume injection system for capillary SFC
Authors: Cortes Hernan J. , Campbell Robert M. , Himes R. Paul , Pfeiffer Curt D. 
Published: May 2005

AbstractA sample introduction system for capillary SFC was developed to allow introduction of relatively large sample volumes without significant decrease in chromatographic efficiency and resolution. The system includes a sample inlet capillary which receives the liquid aliquot from the LC, whereupon the solvent is eliminated by passage of nitrogen gas. The inlet capillary is then pressurized with CO2 and the analytes are transferred to an impactor interface where they are deposited. The analytes are then eluted through the impactor interface and the capillary SFC column by pressure programming of the CO2 mobile phase. The system was demonstrated in a multidimensional mode using microcolumn liquid chromatography in the first dimension. Narrow bands were obtained in the final SFC step for C‐36 hydrocarbon and pentaerythritol tetrastearate.
Conformational analysis of biphenyls using 13C NMR spectroscopy
Authors: Roberts R. M. G. 
Published: May 2005

Abstract13C chemical shifts of biphenyl and fluorenyl derivatives have been used to estimate interplanar angles (0) for biphenyls in solution. Values of 0 for biphenyls with no ortho substituents lie in the range 26 +plusmn; 5°, which agree well with estimates using other techniques. The method also gave excellent agreement for ortho‐substituted derivatives. The value of 0 for 2,2′‐dimethylbiphenyl was calculated at 73°, close to values obtained from UV spectroscopy and adsorption studies.
NMR spectra of platinum and rhodium complexes of phenazine and related ligands
Authors: Newmark Richard A. , Siedle Allen R. 
Published: May 2005

AbstractProton and 13C NMR spectra are reported for cis‐(amine)Rh(CO)2Cl and trans‐(amine)PtCl2(C2H4), where amine = tetramethylpyrazine, phenazine, phenazine N‐oxide and quinoxaline. Relative labilities of the amine and ethylene ligands were determined.
Dynamic 13C NMR: A study of aryl‐substituted 1‐phenyl‐3,3‐tetramethylenetriazenes
Authors: Foster N. , Pestel B. 
Published: May 2005

AbstractThe temperature‐dependent 13C NMR spectra of a series of para‐substituted 1‐phenyl‐3,3‐tetramethylenetriazenes have been analyzed by the band width method. Electron‐donating substituents clearly accelerate the rate of rotation about the N‐2N‐3 bond in the triazenes; electron withdrawers retard that motion. The exchange averaging process observed in the carbon spectra obeys a linear free energy relationship when Hammett σ* parameters are used in the correlation. These results corroborate those already obtained by analysis of 1H NMR spectra of similar triazenes, regarding the likely contribution of a 1,3‐dipolar resonance form to the ground state of the molecule.
1H NMR analysis of the methoxy group conformation in methoxychromones
Authors: Kövér Katalim E. , Borbély J. 
Published: May 2005

AbstractThe methoxy group conformation of chromone derivatives was studied by 1H NMR methods. For the qualitative determination of the conformational preferences of the model compounds, proton relaxation rates, spin‐spin decoupling difference spectroscopy and 2D COSY experiments were applied. NOE data were used in the calculations of conforrmer population ratios in these six‐spin (ABCX3) systems.
13C NMR Study of 3,9‐di(alkylphenoxy) ‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro[5.5]undecanes
Authors: Pätoprstý V. , Malík Ľ. , Goljer I. , Göghová M. , Karvaš M. , Durmis J. 
Published: May 2005

Abstract13C NMR chemical shifts and 13C‐31P coupling constants of fourteen derivatives from 3,9‐di(alkylphenoxy)‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro[5.5]undecane and of eight derivatives of the 3,9‐dioxo type are reported. All investigated compounds possess a chair conformation with the lone pair or the phosphoryl oxygen in the equatorial position. The alkylphenoxy groups are in a cis position with respect to the lone pair or the phosphoryl oxygen. Conformational changes about the arylO bond can be monitored via 31POC13C couplings and their angular dependence was found to be non‐symmetric.
Carbon‐13 NMR study of some new macrocycles. 13C chemical shifts of nactin antibiotic models
Authors: El Malouli Bibout M. , Samat A. , Faure R. , Elguero J. 
Published: May 2005

AbstractThirty two‐linked macrocycle models of natural ionophorus nactin antibiotics were studied by 13C NMR spectroscopy and their chemical shifts are reported.
Applications of 15N NMR to a study of tautomerism in some monocyclic azoles
Authors: Bojarska‐Olejnik E. , Stefaniak L. , Witanowski M. , Hamdi B. T. , Webb G. A. 
Published: May 2005

Abstract15N NMR shielding measurements reveal that thiolo‐imidazole and ‐tetrazole exist almost entirely as the thione form. Quantitative estimates of the position of tautomerism in 1,2,3‐triazole and tetrazole are obtained. The reported assignments are supported by means of INDO/S‐SOS shielding calculations.
Two‐dimensional NMR studies of polyene systems. II. β‐carotene
Authors: Wernly Jacques , Lauterwein JÜRgen 
Published: May 2005

AbstractTwo‐dimensional NMR results are presented for β‐carotene in chloroform. J‐resolved 1H NMR spectroscopy allows the accurate determination of the chemical shifts and coupling constants for the olefinic protons. In order to obtain sufficient signal intensity in the projection spectrum for the HC‐7, HC‐10 and HC‐14 protons, spin decoupling of the long‐range coupled methyl and methylene protons was necessary. 1H,13C chemical shift‐correlated NMR spectroscopy gave a relationship between the directly bonded olefinic CH pairs. Cross‐sections through each 13C chemical shift allowed the assignment of the carbon resonances. Simulation of the cross‐sections was possible when the 180° carbon pulse was removed in the standard pulse sequence. It is shown that, under these conditions, the cross‐sections correspond to partial 13CH satellite spectra.
Carbon‐13 NMR lanthanide induced shifts and T1 studies of the conformation of friedelin
Authors: Wazeer Mohammed I. M. 
Published: May 2005

AbstractBy measuring the shifts of the 13C NMR signals of 29 carbons of friedelin, induced by the lanthanide shift reagent Pr(fod)3, and using a computer program, it is shown that friedelin exists in a chair‐chair‐chair‐twist boat‐boat conformation in solution. Lanthanide metal binds exclusively to one site on the carbonyl group of friedelin, away from the nearest methyl group. 13C T1 data are consistent with the suggested conformation of friedelin.
Conformational analysis and 13C NMR spectra of some 2,6‐diarylpiperidin‐4‐ones
Authors: Hasan Misbah Ul , Arab Mohammad , Pandia Rajan K. , Sekar R. , Marko Dale 
Published: May 2005

AbstractThe 13C NMR spectra of several methyl substituted 2,6‐diaryl‐4‐piperidones (aryl = phenyl, o‐chlorophenyl) have been measured. Substituent parameters for methyl and chloro groups have also been derived and are discussed in terms of their steric and electronic interactions. Both the methyl substitution at C‐3 and chlorine substitution in the ortho position of the phenyl ring cause significant changes in the 13C chemical shifts, which can be satisfactorily explained on the basis of steric interactions taking place in the preferred conformations of these molecules. In compounds with o‐chloro groups, the aryl ring is oriented such that the chlorine is syn to the axial hydrogen on the aryl‐bearing carbon. The shielding effect of the carbonyl group is found to be more pronounced on an adjacent equatorial methyl than on an adjacent axial methyl group.
Proton deshielding by spatial proximity: An experimental and theoretical study for ortho‐substituted anisoles
Authors: Contreras R. H. , Ferraro M. B. , de Kowalewski D. G. , Díaz L. 
Published: May 2005

AbstractA quantitative estimation of the proton deshielding effect produced by a sterically crowded environment was obtained experimentally, based on departures from the chemical shift additivity rule of protons ortho to OCH3 and NO2 groups in benzene derivatives, where a conformational change from these side‐chain groups is expected. The influences of these conformational changes were also analysed from a theoretical point of view. Calculations of the magnetic shielding tensor were carried out at the INDO approximation with gauge invariant atomic orbitals, together with the uncoupled Hartree‐Fock approach. Theoretical results for these proton deshielding effects are in very good agreement with those determined experimentally.
Investigation of Benzimidazoles. 6—transmission of substituent effects in dianion radicals of 2‐substituted 5(6)‐nitrobenzimidazoles studied by ESR spectroscopy
Authors: Lopyrev V. A. , Larina L. I. , Vakul'skaya T. I. , Shibanova E. F. , Titova I. A. , Voronkov M. G. 
Published: May 2005

AbstractThe substituent effects in dianion radicals of fourteen 2‐substituted 5(6)‐nitrobenzimidazoles, electrochemically generated in acetonitrile, were studied by ESR. It was found that the substituent influence on the nitro group is transmitted with approximately equal contributions from the inductive and resonance components, independently of the pairs of the σIσR, σIσRo,σIσR+ and ℱℛ substituent constants used. The radical stabilization constant σ contributes much to the correlation of the hyperfine splitting constants of H‐6 and the heterocyclic nitrogen atoms. The transmission through the benzimidazole ring in dianion radicals of nitrobenzimidazoles is half that of the benzene ring in anion radicals of para‐substituted nitrobenzenes.
Structure at the anomeric centre in 2‐alkoxytetrahydropyrans and their radicals, studied by 13C coupling in NMR and ESR spectra
Authors: McKelvey Ronald D. , Sugawara Tadashi , Iwamura Hiizu 
Published: May 2005

AbstractSeveral 2‐alkoxytetrahydropyrans labelled with 13C in the 2‐position were prepared by hydroboration‐carbonylation (with 13CO) of the protected but‐3‐en‐1‐ol derivatives. The ESR spectra were measured for the corresponding 2‐alkoxytetrahydropyran‐2‐yl radicals produced by the reaction with the tert‐butoxy radical. The hyperfine coupling constant to carbon was 99±0.5 G. The deviation from planarity for these radicals was estimated to be approximately 11°, with sigma bond angles of 116°. The s character of the singly occupied orbital was approximately 8.1%. Anomeric, one‐bond 13CH NMR coupling constants were also determined. Axial hydrogens had coupling constants of approximately 155 Hz, while equatorial hydrogen coupling constants were ca 164 Hz. These values were interpreted in terms of greater s character in the equatorial CH bonds. This could be caused by greater ring CO double bond character when the alkoxy group is axial, through no‐bond resonance to the exocyclic alkoxy group.
On the Chemistry of Pyrrole Pigments. 60—Natural isotopic abundance 15N NMR spectra of verdinoid bile pigments and their partial structures
Authors: Falk Heinz , Müller Norbert 
Published: May 2005

Abstract15N NMR spectra, at natural isotopic abundance, of synthetic bilatrienes‐abc and 2,3‐dihydrobilatrienes‐abc and also those of partial structures are presented. The implications of the 15N chemical shifts on structural features, especially tautomerism, are discussed and compared with results obtained by x‐ray photoelectron spectroscopy.
NMR studies in the heterocyclic series. 27—Carbon‐13 NMR determination of the protonation site of aminopyrazoles in trifluoroacetic acid
Authors: Bruix Marta , De Mendoza Javier , Claramunt Rosa Maria , Elguero José 
Published: May 2005

AbstractThe 13C NMR data for 3‐aminoindazole and 14 aminopyrazoles were obtained in neutral and acidic media (trifluoroacetic acid) and compared with those for a series of pyrazoles, aminothiophenes and anilines as models for protonation. From the chemical shifts and coupling constants it is possible to conclude that all 3‐aminopyrazoles, 3‐aminoindazole and 5‐aminopyrazoles protonate on the heterocyclic ring nitrogen atom. This first protonation strongly deactivates the exocyclic nitrogen atom, so that no double protonation is observed, even in sulphuric acid. On the other hand, 4‐aminopyrazoles are stronger bases, which are protonated first at the amino group and then on both nitrogen atoms.
13C NMR Spectroscopy of lignan and neolignan derivatives
Authors: Agrawal P. K. , Thakur R. S. 
Published: May 2005

Abstract13C NMR shielding data for about 300 compounds are tabulated, and critical spectral features are discussed as a guide to the use of the technique in structure elucidation and stereochemical allocations of lignan, neolignan and their derivatives. Unanalysed reported data have been analysed and, wherever necessary, 13C signal assignments have been revised on the basis of more recent evidence and, to obtain consistency throughout the series.
Quaternization of pyrido[2,3‐b]pyrazines: 1H and 13C NMR Study
Authors: Chupakhin O. N. , Charushin V. N. , Chernyshev A. I. , Esipov S. E. 
Published: May 2005

AbstractThe structure of N‐methylpyrido[2,3‐b]pyrazinium salts has been examined by 1H and 13C NMR. 6‐Dimethylamino‐ and 6‐morpholino‐pyrido[2,3‐b]pyrazines were shown to undergo quaternization by methyl iodide at N‐4 of the pyrazine ring, whereas the pyridine ring N‐5 was the N‐alkylation site in the reaction of unsubstituted pyrido[2,3‐b]pyrazine with methyl iodide under the same conditions. The effects of quaternization on the 1H and 13C chemical shifts and the nJ(CH) values are discussed.
Rotational Dynamics by NMR to Probe Solvation of 2‐Pyridone in Hydroxylic Solvents
Authors: Tiffon Bernard , Guillerez Jean , Ancian Bernard 
Published: May 2005

AbstractThe dynamics of the molecular rotation of 2(1H)‐pyridone and 1‐methyl‐2(1H)‐pyridone in toluene, carbon tetrachloride, methanol and water have been investigated at 305 K by13C and2H NMR. Both chemical shifts and relaxation times show that 2‐pyridonc forms stable hydrogen‐bonded complexes in methanol and in water, reorienting as a complete unit and taking with it two solvent molecules. These solvated species are stable within the liquid‐state temperature range, and reorient according to the hydrodynamic law as indicated by the14N line width measurements. It follows that the lifetimes of these complexes are always greater by at least an order of magnitude than the rotational correlation time scale. Analysis of the14N quadrupole coupling constants and the rotational anisotropy support the structure and stability of these complexes.
Observation of long‐range 1H‐1H coupling correlation by the two‐dimensional SUPERCOSY technique as an aid in resonance assignment
Authors: Mayor S. , Hosur R. V. 
Published: May 2005

AbstractLong‐range four‐ and five‐bond 1H‐1H coupling correlations have been observed in the dipeptide L‐Lys‐L‐Phe by using the two‐dimensional SUPERCOSY technique. Complete resonance assignments of all the non‐exchangeable protons in the dipeptide have been obtained.
Applicability of vicinal heteronuclear (13C‐1H, 15N‐1H, 13C‐15N) coupling constants for conformational analysis of amino acids: Phenylalanine, α‐aminobutyric acid and β‐alanine
Authors: Mikhova Bozhana P. , Simeonov Mario F. , Spassov Stefan L. 
Published: May 2005

AbstractThe vicinal 13C1H, 15N1H and 13C15N spin coupling constants were obtained from the 1H and 13C NMR spectra of various ionic forms of the amino acids phenylalanine, α‐aminobutyric acid and β‐alanine, and also from their 15N isotopomers. It is concluded that the 13C1H and 15N1H coupling constants are reliable parameters for conformational studies of amino acids, whereas the practical applicability of the 13C15N constants for the same purpose is doubtful.
Carbon‐13 nuclear magnetic resonance spectra of the hydrate, keto and enol forms of oxalacetic acid
Authors: Buldain Graciela , Santos Carlos De Los , Frydman Benjamín 
Published: May 2005

AbstractThe 13C resonances of the hydrate, keto and enol forms of oxaloacetic acid in aqueous solutions at low pH, at pH 4.3 and at pH 7.3 were assigned on the basis of the J(CH) values and the chemical shifts of reference compounds. At low pH the hydrate form predominated, while only small amounts of the keto and enol forms were detected. At pH 4.3 and 7.3 the keto form was the major form. In anhydrous dimethyl sulphoxide solution only the keto and enol forms were detected, whereas on addition of water the hydrate form became predominant. On prolonged recording of the spectra at the probe temperature (30°C) citroylformic acid was formed either at low pH or at pH 7–12, whereas only traces of pyruvic acid were detected. The aldol condensation product of oxalacetic acid was detected when the spectra were recorded at 7°C before its decarboxylation to citroylformic acid. In the spectra recorded at pH 3–7 pyruvic acid and its aldol condensation product, 4‐hydroxy‐4‐methyl‐2‐ketoglutaric acid, were detected together with citroylformic acid. A complete assignment of the 13C resonances of these derivatives was made.
Molecular conformation of N,N′‐diarylthioureas: An assessment by 1H NMR and infrared spectroscopy
Authors: Sudha L. V. , Manogaran S. , Sathyanarayana D. N. 
Published: May 2005

AbstractSeveral N,N′‐dipyridyl‐ and N‐phenyl‐N′‐pyridyl‐thioureas were examined in different solvents at various temperatures by 1H NMR in order to study their conformational properties. The influence of concentration and the methyl substituent in the pyridine ring on the chemical shifts of the NH and pyridine groups was investigated. The observed chemical shifts are analysed in terms of the conformational properties of the molecules. Free energy barriers to the internal rotation about the CN bonds have been determined. Infrared spectra have been measured to supplement the NMR studies. Intramolecular hydrogen bonding played a major role in the preferred conformation of pyridylthioureas. The data further revealed an interesting dynamic exchange phenomenon occurring in symmetric N,N′‐dipyridylthioureas between two intramolecularly hydrogen bonded conformers.
13C NMR signal assignment of friedelin and 3α‐hydroxyfriedelan‐2‐one
Authors: Gottlieb Hugo E. , Ramaiah Parimi A. , Lavie David 
Published: May 2005

AbstractThe 13C NMR spectrum of the pentacyclic triterpene friedelin was fully assigned, taking into account signal multiplicities, correlations of the carbon lines with known proton resonances and Eu‐induced shifts. This work clarifies the situation prevalent in the literature, in which three separate groups have published contradictory information. In addition, the carbon and proton spectra of the naturally occurring 3α‐hydroxyfriedelan‐2‐one and its synthetic acetate were analysed. The different preferred conformations of the D/E rings for friedelin (boat‐boat) and polpunonic acid (chair‐chair) are rationalized.