bluuebunny/crossref_metadata_2025_split huggingface dataset:
Konformative Beweglichkeit Flexibler Ringsysteme–XII Modellrechnungen zur Ringinversion bei Methylsubstituierten Cyclohexanen
Authors: Schmid H. G. , Jaeschke A. , Friebolin H. , Kabuß S. , Mecke R. 
Published: May 2005

AbstractZur Interpretation der experimentell bestimmten Werte der Aktivierungsenergie bzw. der freien Aktivierungsenthalpie der Ringinversion wurden für Cyclohexan, 1,1‐Dimethyl‐, 1,1,3,3‐ und 1,1,4,4‐Tetramethyl‐ sowie 1,1,3,5,5‐Hexamethylcyclohexan Modellberechnungen des ‘relativen’ Energieinhalts von Grund‐, Zwischen‐ und Übergangskonformationen durchgeführt. Dazu wurde das Hendrickson'sche Rechenmodell so erweitert, daß mit molekülinternen Variablen (Bindungsabständen, Valenz‐ und Torsionswinkeln) die Topographie und der ‘relative Energieinhalt’ jeder beliebigen unsymmetrischen Konformation berechnet warden können.Zur optimalen Anpassung der berechneten Daten an die experimentellen Ergebnisse wurden insgesamt 17 verschiedene Kombinationen von Potentialfunktionen für Deformation von Valenzund Torsionswinkeln und HH‐Wechselwirkung verwendet.Bei Anwendung des erweiteren Rechenverfahrens auf die Cyclohexanmolekel ergab sich, daß die halbsesselähnliche Konformation nicht, wie bisher angenommen, einzige Übergangskonformation der Sesselinversion ist, vielmehr gibt es außerdem unendlich viele unsymmetrische Übergangskon‐formationen gleichen Energieinhalts. Die Rechnungen ergaben für die Methylcyclohexane, daß bei Molekülen mit synaxialer Anordnung von Methylgruppen der relative Energieinhalt des Sessels zwar stark angehoben ist, der Sessel ist jedoch in allen Fällen selbst bei den Molekeln des 1,1,3,3,5,5‐Hexamethylcyclohexans die stabilste Konformation. Die günstigsten Twistkonformationen sind um 2,6 bis 6,5 kcal/mol energiereicher. Bei der Berechnung der Aktivierungsenergie wurde gefunden, daß bei synaxialer Stellung von mindestens zwei Methylgruppen der relative Energieinhalt der Übergangskonformation weniger stark angehoben ist als derjenige der Sesselform, wodurch die Aktivierungsenergie im Vergleich zum Cyclohexan erniedrigt wird; bei 1,4‐Stellung der Substituenten wird dagegen der relative Energieinhalt der Übergangskonformation stärker angehoben als der des Grundzustandes, die Aktivierungsenergie wird erhöht.
Determination des taux de deuteriation de molecules organiques par resonance magnetique nucleaire
Authors: Martin Gérard J. , Quemeneur Marie‐Thérèse , Martin Maryvonne L. 
Published: May 2005

AbstractLes précisions de différentes méthodes de détermination du taux de deutériation de molécules organiques par RMN sont évaluées. On compare successivement les méthodes de changement de tube‐échantillon et les méthodes utilisant un étalon interne. Ces méthodes sont ensuite appliquées au dosage du deutérium dans plusieurs molécules et les résultats sont comparés à des mesures de spectrographie de masse.
Substituent effect in aromatic proton NMR spectra—IV Proton NMR spectra of monosubstituted (poly) methylbenzenes
Authors: Nomura Yujiro , Takeuchi Yoshito 
Published: May 2005

AbstractProton NMR spectra of 1‐substituted 2,4‐dimethylbenzenes (2), 1‐substituted 2,6‐dimethylbenzenes (3) and 1‐substituted 2,4,6‐trimethylbenzenes (4) were determined and the SCS values compared with those of monosubstituted benzenes (1). SCS of 1 are assumed to be primarily due to the effects of π‐electron charge density, substituent electric field and substituent diamagnetic anisotropy, and the van der Waals interaction: thus

When, however, the substituent is sterically hindered, then:

where cπ∼V may be constants predictable from the theories associated with each component. By estimating SCSπ∼V or cπ∼V, a quantitative separation of SCS into their components was attempted. It is shown, however, that the data available, as well as the nature of this approach, cannot necessarily be sufficient for this purpose.Various effects which might also contribute to the proton NMR chemical shifts of sterically hindered molecules are also discussed.
The NMR spectrum of pentafluorothiophenol
Authors: Lustig E. , Hansen E. A. , Ragelis E. P. 
Published: May 2005

AbstractHigh‐precision line measurements and tickling were shown to yield information, often not accessible, on the assignment and signs of spin coupling constants. For pentafluorothiophenol‐d, this information was obtained for the three meta‐JFF's. Relative to C6F5SH, the 19F resonances in C6F5SD experienced an upfield ‘isotope’ shift.
NMR studies of complex formation between N‐methyl morpholine and sulphur dioxide
Authors: Harris R. K. , Spragg R. A. 
Published: May 2005

AbstractProton magnetic resonance spectra of methylene dichloride solutions containing N‐methyl morpholine and sulphur dioxide have been studied as a function of temperature. Complex formation reduces the rate of interchange of magnetic sites via inversion at nitrogen but increases the rate of ring inversion. The conformational preference of the complex is discussed. It is suggested that interaction with SO2 may be a useful general method of studying nitrogen inversion.
Application des relation de Mislow et Raban a la determination de configuration (mesothreo) par resonance magnetique nucleaire
Authors: Le Goaller Raymond , Pierre Jean‐Louis , Arnaud Paul 
Published: May 2005

AbstractLa configuration meso ou thréo de molécules diastéréoisomères est déterminée à partir des spectres RMN respectifs xde chaque isomère. Les relations de symétrie (Raban et Mislow), qui existent entre protons ou groupes de ces molécules sont différentes par chaque diastéréoisomère d'un couple donné et ces différences se traduisent dans les déplacements chimiques et constantes de couplage mis en jeu. Des attributions de configuration sont ainsi rendues possibles.
Multipolar complexes–II The self association of ‐NO2 ‐CN and ‐COCN polar groups
Authors: Uschold R. E. , Taft R. W. 
Published: May 2005

AbstractFluorine nuclear magnetic resonance (F‐NMR) has been used to determine dissociation constants for multipolar complexes formed by several p‐substituted fluorobenzenes in CCl4 and cyclohexane at 25°. Data in CCl4 were also obtained at −20°. The results are interpreted in simplified terms as dipole‐dipole interactions which lead to a complex of net zero dipole moment. Although the dissociation constants are not of high accuracy, the values obtained do indicate that both polarity and steric effects are important in the presumed multipolar complexes.
NMR spectrum of phenylacetylene oriented in the nematic phase
Authors: Diehl P. , Khetrapal C. L. 
Published: May 2005

AbstractThe NMR spectrum of phenylacetylene has been studied in the nematic phase of a mixture of 50% 4‐methoxy benzylidene 4‐amino‐α‐methyl cinnamic acid‐n‐propyl ester and 50% anisole‐p‐azophenyl‐n‐capronate at 30°C. Ratios of interproton distances have been derived.
NMR spectra of some alkyl(oxinato)tin(IV) complexes
Authors: Kawasaki Yoshikane 
Published: May 2005

AbstractProton magnetic resonance spectra of a series of alkyl(oxinato)tin(IV) complexes, alkyl(oxinato)thallium(III), dimethylbis(oxinato)lead(IV), 8‐methoxyquinoline, 2‐methyl‐8‐hydroxyquinoline and 8‐hydroxyquinoline were studied. The indirect spin‐spin coupling constants J23, J34 and J24 of the oxinato ligand in the alkyl(oxinato)tin(IV) complexes and of 8‐methoxyquinoline were found to be 4.4 ± 0.2, 8.3 ± 0.2 and 1.7 ± 0.2 Hz, respectively. When the interaction between tin and nitrogen in the oxinato ligand is not strong as in trialkyl(oxinato)tin(IV), the resonance of the 2‐proton of the ligand shifts to high magnetic field relative to that of 8‐methoxyquinoline, but in the case of the strong interaction, as in dimethyl(oxinato)halogenotin(IV), the resonance is shifted to low magnetic field. The 4‐proton signals, however, shift monotonously to low magnetic field with increasing interaction. The behaviour of the 2‐proton signals was explained by a paramagnetic anisotropic effect of a nitrogen lone pair of the oxinato ligand and an intramolecular electric field effect and that of the 4‐proton by the latter effect. By comparing the change of the δ‐values of the 2‐, 3‐ and 4‐protons of the alkyl(oxinato)tin(IV) complexes and those of 8‐hydroxyquinoline by altering the solvents, from methylene chloride to benzene, it was found that the electron density around the 2‐carbon is reduced in the complexes compared with that of 8‐hydroxyquinoline.
The NMR spectra and conformations of cyclic compounds—IV: The conformation of 3,4‐cyclopropyl‐proline
Authors: Abraham R. J. , Gatti G. 
Published: May 2005

AbstractThe 1H magnetic resonance spectrum of the title compound has been completely analysed, using 60, 100 and 220 MHz spectrometers. The values of the chemical shifts and coupling constants obtained confirm the proposed structure and also provide information on the conformation. The molecule is slightly boat‐shaped.
Etude de la Protonation du Groupe Amide par Resonance Magnetique Nucleaire. Comportement des Anilides Substitues en Milieu Acide Concentre
Authors: de Lockerente Serge Rysman , Nagy Otto B. , Bruylants Albert 
Published: May 2005

AbstractEn étudiant par RMN cinq anilides de formule générale magnified image en milieu acide, les auteurs ont mis en évidence la protonation de l'atome d'azote de l'ion amidonium formé.
Semidiones—X. Radical anions derived from 1,1,2,2‐bis(1,3‐diketo‐2,2‐bindanylidene)ethane and 1,1,4,4‐bis(1,3‐diketo‐2,2‐bindanylidene)butene‐2
Authors: Neugebauer Franz. A. , Russell Glen A. 
Published: May 2005

AbstractThe 1,1,2,2‐bis(1,3‐diketo‐2,2‐bindanylidene)ethane radical anion (13) and 1,1,4,4‐bis (1,3‐diketo‐2,2‐binanylidene)butene‐2 radical anion (14)We employ herein nomenclature wherein the term ‘radical anion’ means the gain of one electron of the named substrate.
representing 1,6‐ and 1,8‐conjugated semidiones have been prepared by reduction. Electron spin resonance hyperfine splitting constants have been assigned on the basis of Hückel and McLachlan calculations.
PMR studies of N‐substituted‐2,5‐dimethyl‐4‐piperidones
Authors: Hassan M. M. A. , Casy A. F. 
Published: May 2005

AbstractPMR characteristics of some isomeric 1‐substituted‐2,5‐dimethyl‐4‐piperidones are reported and major isomers shown to have a trans 2,5‐dimethyl configuration. Differences between benzylic methylene signals of isomeric 1‐benzyl analogs provide evidence of the preferred conformation of the cis derivative. Evidence of the D/H exchange of α‐protons in 1,2,5‐trimethyl‐4‐piperidone base and of addition of D2O to the carbonyl group of the corresponding hydrochloride and methiodide salts is also demonstrated. The effect of a 2‐methyl substituent upon the chemical shifts of N‐methyl groups in some piperidine methiodides is discussed.
FF coupling constants in dichlorotetrafluorocyclopropanes
Authors: Cavalli Luciano 
Published: May 2005

AbstractThe 19F NMR spectra of the cis‐ (1) and the trans‐isomer (2) of the 1,2‐dichlorotetrafluorocyclopropane and that of the 1,1‐dichlorotetrafluorocyclopropane (3) have been investigated at different temperatures and in several solvents. magnified image From chemical shift calculations the two geminal fluorines in the cis‐isomer (1) could be assigned and on this basis the two vicinal coupling constants of 1, Jtrans (ca. 140°) and Jcis (ca. 0°), were unequivocally distinguished. By frequency sweep double resonance Jtrans has been shown to be of opposite sign to Jgem, whereas for Jcis the situation has been found to be reversed. Therefore Jtrans is presumably negative and Jcis positive. Only the N(Jcis + Jtrans) value could be extracted from the vicinal coupling constant in the fragment CFClCFCl could be evaluated. It has been noted that Jcis is more sensitive to changes in temperature than is Jtrans. The variations of Jcis and Jtrans induced by solvents are, on the contrary, small and irregular and no correlation with the dielectric constant of the medium has been noted. The different temperature dependence of Jcis and Jtrans can be useful for assigning the vicinal FF coupling constants in cyclopropane derivatives and also for defining their signs. This method was applied to the coupling constants extracted from the 13C satellite spectrum of isomer 3. The coupling constants results were compared with some literature data already known, and some rationalisation and correlations from the trends was attempted.
A new method for structure determination of trifluoroacetyl steroids by 19F‐NMR
Authors: Voelter Wolfgang , Breitmaier Eberhard , Jung Günther , Bayer Ernst 
Published: May 2005

AbstractA useful method for the assignment of hydroxyl groups in steroids is described in which hydroxy‐steroids are reacted with trifluoroacetic anhydride. The δ‐values of the CF3 signals from the resulting trifluoroacetates characterize the positions of the trifluoroacetylated hydroxyl groups.
Protonenresonanz‐Untersuchungen an N,N‐Dialkylaminoboranen. Substituentenabhängigkeit der Rotationsbarriere um die NB‐Bindung 1,2
Authors: Imbery D. , Jaeschke A. , Friebolin H. 
Published: May 2005

AbstractAn einer Anzahl von N,N‐Dialkylaminoboranen wurde die Substituentenabhängigkeit der Rotationsbarriere um die NB‐Bindung mit Protonenresonanzen studiert. Dabei konnte (1) eine deutliche Abhängigkeit der Barriere von der Größe der Substituenten festgestellt werden, die auf eine ‘sterische Behinderung der Mesomerie’ zurückgeführt wird, und (2) eine z.T. außerordentlich große Erleichterung der Rotation, wenn Alkylgruppen am Bor durch ein Chlor bzw. eine zweite Aminogruppe substituiert werden. Die Erniedrigung der Rotationsbarriere um ca. 10 kcal/Mol in Bis‐aminoverbindungen verglichen mit den entsprechenden Monoaminoverbindungen wird durch eine Verminderung des Doppelbindungsgrades jeder NB‐Bindung infolge Beteiligung zweier N‐Atome an der Mesomerie des Grundzustandes erklärt. Dieser Effekt ist bei der Aminogruppe weit größer als bei einem Chloratom.
The solvent effect on polar compounds containing acidic hydrogens
Authors: NG Soon 
Published: May 2005

AbstractThe effect of aromatic and non‐aromatic solvents on the proton chemical shifts of 23 polar compounds has been determined. The protons which are activated by electron‐withdrawing groups show large highfield shifts in benzene (relative to the isotropic solvents). Based on evidence provided by infrared data, the highfield shifts of the acidic protons in benzene solution are interpreted in terms of a model involving CHπ hydrogen bonding. This model successfully interprets the data reported previously for steroidal ketones. The same model can be extended to benzene solutions of other polar compounds containing strongly electron‐deficient sites to which alkyl groups are attached. It is observed that the use of CCl4 as a reference solvent in studies of benzene induced shifts may have greater significance, since these two solvents have similar dielectric constants.
Concentration dependent chemical shifts in the NMR spectrum of 3,5‐dimethyl‐5‐nitro‐tetrahydro‐1,3‐oxazine
Authors: Crabb T. A. , Judd S. I. 
Published: May 2005

AbstractThe marked concentration dependence of the chemical shifts of the C2, C4 and C6 protons in 3,5‐dimethyl‐5‐nitro‐tetrahydro‐1,3‐oxazine is described.
Molecular structure of pyrimidine by NMR in the nematic phase
Authors: Khetrapal C. L. , Patankar A. V. , Diehl P. 
Published: May 2005

AbstractThe NMR spectrum of pyrimidine has been studied in the nematic phase of 4‐methoxy benzylidene‐4‐amino‐α‐methyl cinnamic acid‐n‐propyl ester at room temperature. The ratios of all the interproton distances are determined and found to differ significantly from those obtained from microwave data. The molecule, like other aromatics, is shown to orient preferentially with its plane in the direction of the magnetic field.
Recherches par resonance magnetique nucleaire sur les rotations empechees—IV: Determination des parametres d'activation associes a l'interconversion des isomeres de rotation autour de la liaison CC dans la serie des composes carbonyles vinyliques β‐amines
Authors: Filleux‐Blanchard Marie‐Louise , Durand Henri , Martin Gérard Jean 
Published: May 2005

AbstractL'effet de la nature du substituant R sur l'équilibre conformationnel s‐cis‐s‐trans est examiné dans la série (CH3)2NCHCHCOR. L'utilisation d'un programme de calcul des courbes théoriques de l'échange permet la détermination des paramètres d'activation ΔH* et ΔS*.
NMR‐untersuchungen an dialkylsubstituierten piperidinen—II: 2.5‐, 2.6‐ und 3.5‐ dimethylpiperidine
Authors: Wendisch Detlef , Naegele Walter , Feltkamp Herbert 
Published: May 2005

AbstractDie Gemische der stereoisomeren 2.5‐ und 2.6‐ Dimethylpiperidine wurden durch katalytische Hydrierung der entsprechenden Lutidine hergestellt und die einzelnen Isomeren durch fraktionierte Destillation getrennt; die beiden isomeren 3.5‐Dimethylpiperidine wurden nach einem speziellen Verfahren hergestellt. Die Konfigurationszuordnung erfolgt durch Analyse der 220 MHz (in einem Fall 100 MHz) Spektren. Alle Protonen des Piperidinringes können weitgehend zugeordnet werden. Ausserdem wird über die 13C‐Spektren der beiden isomeren 3.5‐Dimethylpiperidine berichtet. Die Protonenspektren aller 12 möglichen Dimethylpiperidine werden eingehend, speziell im Hinblick auf die abschirmende Wirkung der Methylgruppen auf benachbarte Ringprotonen, diskutiert.
Natural abundance 13C NMR studies of perezone and derivatives
Authors: Joseph‐Nathan P. , González Ma. P. , Johnson LeRoy F. , Shoolery James N. 
Published: May 2005

AbstractAssignment of all 13C chemical shifts of perezone (1) and some derivatives was possible using time averaged 25·15 MHz spectra with the aid of proton noise modulated and CW decoupling. Rapid interconversion of tautomeric forms of 2,5‐dihydroxy‐1,4‐benzoquinones is deduced from the 13C spectra.
NMR studies of fluorocarbon diphosphines and oxy‐ and thio‐bisphosphines
Authors: Kang Dae‐Ki , Servis Kenneth L. , Burg Anton B. 
Published: May 2005

AbstractBoth the diphosphine CH3CF3PPCH3CF3 and the thio‐bisphosphine CH3CF3PSPCH3CF3 show 19F and 31P NMR spectra indicative of diastereomeric mixtures of d,l and meso isomers. The temperature‐dependent reversible interconversions of the isomers have been attributed to the inversion at the phosphorus atom. The equilibrium constants for the isomerization reactions have been measured at various temperatures. The fluorine NMR spectra of the meso and d,l isomers of CD3CF3PSPCD3CF3 have been analyzed as M3XX′M3′ spin systems. Good agreement is found between the observed and calculated spectra. The five‐bond fluorine‐fluorine coupling constant of the low‐field isomer is larger than that of the high‐field isomer. The 19F NMR spectra of (CF3)2PP(CF3)2, (CF3)2POP(CF3)2, (CF3)2PSP(CF3)2, CH3CF3PPCH3CF3 and CH3CF3PSPCH3CF3 have been examined over a wide range of temperatures in an attempt to correlate the data to the geometries of these compounds.
Charge density and NMR parameters. Aliphatic derivatives
Authors: Lazzeretti P. , Taddei F. 
Published: May 2005

AbstractThe charge distribution in several substituted aliphatic derivatives was determined by a parametric MOLCAO method. The charges were successfully employed to interpret NMR parameters, namely proton and carbon chemical shift and vicinal proton‐proton coupling constants in ethyl derivatives and carbon‐proton coupling constants.The linear correlations found between NMR parameters and charge densities are restricted to substituents of the same row of the periodic system. The decay along the aliphatic chain of the perturbation induced by substituents on proton chemical shift is also reproduced by charge distribution. Some results also seem to indicate that the substituents affect the hybridization of the attached carbon atom.
Studies of the substituent effect in aromatic systems by 35 Cl‐NQR. Chloroacetanilides ClxC6H5−x NHCOCH3−y Cly
Authors: Pies W. , Rager H. , Weiss Alarich 
Published: May 2005

AbstractThe 35Cl‐NQR spectra of 45 chlorosubsitituted acetanilides, ClxC6H5−xNHCOCH3−yCly, were investigated and the temperature dependence of some spectra, especially of monochloroacetic acid derivatives, was measured. A preliminary assignment of the NQR frequencies is given. A correlation between NQR frequencies and substituent parameters permits the study of the substituent effect of the acetamido group, NHCOCH3−yCly. The chloro‐substitution in the side chain of the acetanilides seems to have no noticeable influence on the 35Cl‐NQR frequencies of the chlorine atoms at the benzene ring. The NQR frequencies of the chlorine atoms in the chloroacetamido group are, on the other hand, insensitive to substitutions at the benzene nucleus. The possibility of steric influences on the NQR spectrum of ortho‐chloro‐substituted acetanilides is discussed. The investigation further confirms that a crystal field effect of about ±500 kHz must be considered in the interpretation of NQR spectra of chlorobenzene derivatives.
Barrières de Rotation Autour des Liaisons CN dans la Série des Urées. Influence du Remplacement de CO par CS
Authors: Filleux‐Blanchard M. L. , Durand A. 
Published: May 2005

AbstractUne barrière de rotation de faible valeur autour de la liaison NCO est mise en évidence dans les urées de formule CH3NHCONHR (R  H, CH3). Les thiourées correspondantes sont examinées afin d'étendre l'étude comparative des systèmes carbonyle‐thiocarbonyle. Les paramètres RMN et les grandeurs thermodynamiques liées au processus d'isomérisation sont discutés.
Long‐range proton‐proton interactions through epoxides
Authors: Joseph‐Nathan P. , Díaz E. 
Published: May 2005

AbstractDouble and triple nuclear magnetic resonance experiments performed at 100 MHz demonstrate the existence of long range 1H—1H couplings through epoxides. In a series of epoxycontaining sesquiterpenoids, interactions between protons separated by up to six sigma bonds were detected. These interactions may have origins similar to the well‐known allylic and homoallylic couplings found in carbon‐carbon double bonded compounds, although they are much smaller in the epoxy systems. We propose to name them as ‘epoallylic’ and ‘epohomoallylic’ interactions. Some couplings are observed directly, whereas in other cases only an improvement in resolution is seen during multiple irradiation experiments. Even in these latter cases the areas of the observed peak do not change upon multiple irradiation which demonstrates the absence of nuclear Overhauser effects. The stereochemistry of some asymmetric centers of the compounds studied is deduced from the spectra.
Solvent effects in nuclear magnetic resonance spectra of some pyrazines, pyrimidines and their N‐oxides
Authors: Paudler William W. , Humphrey Sharon A. 
Published: May 2005

AbstractThe benzene‐induced solvent effects upon the proton chemical shifts of various pyrazines, pyrimidines and their N‐oxides are described. Larger chemical shift effects, implying closer benzeneheterocycle association, are noted in the N‐oxides as compared to the non‐oxidized heterocycles.The solvent‐induced chemical shift changes can be used to establish the site of N‐oxidation in those instances where different isomers can be formed.
Protonenresonanz‐Spektroskopie ungesättigter Ringsysteme—XVI 7,7‐Difluor‐benzo‐cyclopropen
Authors: Günther Harald , Pawliczek Josef Bernd 
Published: May 2005

AbstractDas NMR‐Spektrum von 7,7‐Difluor‐benzo‐cyclopropen (2) wurde zur Bestimmung der chemischen Verschiebungen und Spin, Spin‐Kopplungskonstanten analysiert: δAA′ = 7,6026, δBB′ = 7,4834, ppm; JAB = 6,86, JAA′ = 7,45, JAB′ = 0,34 und JBB′ = 1,89 Hz. Mit Hilfe heteronuklearer Doppelrresonanz‐Experimente wurde ein positives Vorzeichen für 4J(HF) (3,64 Hz) und ein negatives Vorzeichen für 5J(HF) (−0,33Hz) in diesem Molekül sichergestellt. Die Ergebnisse werden im Hinblick auf die Struktur von 2 und die NMR‐Daten, die für Benzo‐cyclopropen gefunden wurden, diskutiert.