bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three rotational isomers of se‐methyl N,N‐di‐isopropyldiselenocarbamate and the sulphur analogue found in low temperature 1H NMR spectra
Authors: Takeda Yu‐ichi , Tanaka Toshio 
Published: May 2005

AbstractVariable temperature 1H NMR spectra of Se‐methyl N,N‐di‐isopropyldiselenocarbamate, CH3SeC(Se)N (C3H7‐i)2, in CS2 have indicated that internal rotations around both the carbamate CN and isopropyl–nitrogen bonds are restricted below −40°C; the compound exists as three rotational isomers with respect to the isopropyl‐nitrogen bond with mol ratios of approximately 0·54:0·31 :0·15. The corresponding dithiocarbamate, CH3SC(S)N(C3H7‐i)2, has also been found to exist as three isomers with ratios of about 0·71:0·27:0·02 under similar conditions. Possible conformations of both carbamate esters are proposed, together with the assignments of each proton signal.
Long range 13C1H coupling constants IV—methoxy‐, amino‐ and hydroxypyridines
Authors: Takeuchi Yoshito , Dennis Nicholas 
Published: May 2005

AbstractOne bond and long range 13C1H coupling constants for some methoxy‐, amino‐ and hydroxypyridines are described. An unambiguous assignment of carbon‐13 resonances is carried out based on the analysis of the fine splitting caused by long range couplings. J values for compounds other than 2‐ and 4‐hydroxy‐pyridines are explainable in terms of the values previouly obtained for cyano‐ and methylpyridines. The hydroxypyridine‐pyridone tautomerism affects 2J(Hα), i.e. 2J associated with the α proton. This effect can be used to differentiate pyridones from hydroxypyridines.
Vicinal interproton couplings through two heteroatoms. II—Coupling 3J(HNOH) occurring in m‐Nitrophenylhydroxylamines
Authors: Bouchet Philippe , Coquelet Claude , Elguero José 
Published: May 2005

AbstractThe proton NMR spectra of certain arylhydroxylamines in DMSO‐d6 show a vicinal coupling through nitrogen and oxygen. The assignment of OH and NH signals was made using a 15N labelled derivative.
Conformational Analysis of cyclotrisilazanes by the NMR method
Authors: Lavrukhin B. D. , Andrianov K. A. , Fedin E. I. 
Published: May 2005

Abstract1H NMR spectra of substituted cyclotrisilazanes are discussed in terms of conformational analysis. Experimental spectra are consistent with an equilibrium involving chair conformers, following from simulating the effect of phenyl substituents and the temperature dependence of methyl proton chemical shifts. The barrier to chair‐chair interconversion in hexamethyl‐cyclotrisilazane is estimated. An analysis is carried out of the shielding of non‐equivalent methyl groups in substituted cyclotrisilazanes.
Proton NMR determination of the 2,4–/2,6–isomer ratio in commercial toluene di‐isocyanates
Authors: Platten M. R. 
Published: May 2005

AbstractThe CH3‐proton resonances for the 2,4‐ and 2,6‐isomers of toluene di‐isocyanate separate when hexafluorobenzene is used as a solvent. Integration of these absorptions over an expanded sweep scale gives the isomer ratio with an accuracy of ±0.5% over the range normally encountered with commercial samples.
NMR study of 4‐membered rings. VIII—The sign of the four‐bond couplings in adducts of cyclopentenone with vic‐dichloroethylenes
Authors: Bongini A. , Lamartina L. , Mondelli R. , Tagliabue G. 
Published: May 2005

AbstractThe proton spectra of the four stereoisomers prepared by photocycloaddition of 2‐cyclopentenone to cis and trans dichloroethylene have been analysed using tickling and INDOR techniques in order to obtain the sign of the cross‐ring four‐bond coupling constants in the cyclobutane ring. These parameters are correlated with the relative orientation of the protons involved. The complete NMR analysis of the seven‐spin system of the cycloadduct endo‐7‐phenoxybicyclo[3.2.0]hept‐2‐en‐6‐one has been carried out and all the four‐bond coupling constants have been obtained and discussed. The sign of the cross‐ring coupling in the cyclobutanone ring has been determined.
Etude théorique des déplacements chimiques du phosphore en RMN
Authors: Rajzmann Michel , Simon Jacques‐Claude 
Published: May 2005

AbstractLa méthode des perturbations est appliquée aux fonctions d'onde CNDO/S pour calculer les déplacements chimiques du phosphore de quelques phosphines, phosphites, phosphonates et phosphates. Nous montrons la nécessité d'introduire les orbitales 3d du phosphore et de considérer Zeff3d comme un paramètre à déterminer pour chaque famille de composés. Les valeurs calculées sont alors en bon accord avecl' expérience.
Stereochemical aspects of proton chemical shifts. III—Configurational assignments in pentacyclic systems without recourse to a karplus equation
Authors: Anteunis Marc , Danneels Dirk 
Published: May 2005

AbstractIt is shown that in contrast to the use of coupling constants, chemical shift criteria may lead to unambiguous structural elucidations in pseudorotational frameworks (pentacycles, heptacycles, etc.).
Long range HH couplings and bond fixation in 2‐pyrones
Authors: Sardella D. J. , Holak T. , Vogel G. 
Published: May 2005

AbstractWe have determined the magnitudes of all possible four‐, five‐ and six‐bond HH couplings in four 2‐pyrone derivatives. Substituents exert a negligible effect on the couplings. The allylic couplings are position‐specific (J34 = 1·2; J45 ≤ 0·2; J56 = 0.8) and the observed pattern of alternating magnitudes is indicative of π‐bond fixation. The allylic couplings can be translated into π‐bond orders which agree well with results of recently published SCF‐MO calculations on 2‐pyrone. Finally, comparison of long range coupling constant data for 4,6‐dimethyl‐2‐pyrone with those for related cyclic anhydrides and trans‐1,3‐pentadiene further supports the picture of 2‐pyrone as a slightly perturbed butadiene, in agreement with extensive chemical and physical evidence.
Exemple d'une transposition dyotropique à l'état solide Mise en evidence par RMN haute résolution
Authors: Grenier‐Loustalot M. F. , Lectard A. , Metras F. 
Published: May 2005

AbstractL'analyse des spectres RMN à 250 MHz de tribromo‐2,3,6 méthyl‐4 cyclohexanones a permis de déterminer avec précision les constantes de couplage J(HH) de ces composés. La validité des attributions a été contrôlé en reconstituant les spectres par calcul électronique. Les résultats observés ont été interprétés en terme de déformation géométrique.
Influence de la substitution sur la structure de la benzophenone. X.—Etude conformationnelle de benzaldehydes, acetophénones et benzophénones substitués par complexation avec les lanthanides
Authors: Grimaud Marcel , Pfister‐Guillouzo Geneviève 
Published: May 2005

AbstractLa résonance magnétique nucléaire du proton à basse température s'est révélée peu fructueuse dans l'étude conformationnelle des benzophénones substituées. Cependant, l'analyse des déplacements induits par les lanthanides nous a permis de recouper de façon très satisfaisante les résultats obtenus par diffusion Rayleigh dépolarisée et dipolemétrie pour les benzophénones meta et ortho substituées. L'existence en solution d'un équilibre conformationnel pour ces composés est confirmée.
An NMR study of some N‐arylaminopropenylylidenearylammonium salts
Authors: Richards C. P. , Webb G. A. 
Published: May 2005

AbstractThe preparation, characterisation and 1H NMR spectra of some N‐arylaminopropenylylidenearylammonium salts are reported. The NMR data show that in DMSO the cations exist as conjugated amino–imines, generally as the ‘all‐trans’ geometrical isomer. An exception is found in the case of the 4‐nitrophenyl derivative which produces a mixture of the ‘all‐trans’ and ‘cis‐trans’ isomers with slow exchange between them at room temperature. The relative stability of the ‘all‐trans’ isomer increases as the salt becomes more ionic. By varying the temperature, pH and nature of the anion it is found that exchange of the NH protons on the cation controls the appearance of spin‐spin coupling between the NH and 1,3‐propene protons.
Determination of relative signs of 13C13C coupling constants in doubly labelled compounds
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractAnalysis of the noise decoupled 13C spectra of doubly 13C labelled compounds where the two labelled carbons are identical, makes the determination of reltive signs of 13C13C coupling constants possible in a very simple way. The involved carbon form AA'X or AA'B spin systems.
13C NMR: Stereochemical dependence of the one‐bond coupling constant 1J13CH in α‐halogenoketones
Authors: Cantacuzene J. , Jantzen R. , Tordeux M. , Chachaty C. 
Published: May 2005

AbstractThe one‐bond coupling constant 1J 13CH for the halogenated carbon in α‐halogenocyclohexanones is more important when the CH bond is in the equatorial then in the axial position. When a conformational equilibrium is present, the resulting coupling is a linear function of the equilibrium constant.
Solvent effects upon the proton NMR linewidth in dimethylformamide
Authors: Herres W. , Ziessow D. 
Published: May 2005

AbstractThe NMR linewidth of the formyl proton in dimethylformamide has been studied in the neat liquid and twelve organic solvents. It varies by more than one order of magnitude which is referred to solvent viscosity changes and to the protonation of dimethylformamide. The data do not allow the distinction between N‐ and O‐protonation without further knowledge of the solvent dependence of either the nitrogen‐14 spin lattice relaxation time or the spin‐spin coupling 2J(NH).
Etude par RMN protonique d'heterocycles voisins de l'oxazaphospholane‐1,3,2. II—Le diméthylamino‐2 méthyl‐3 oxazaarsolane‐1,3,2
Authors: Devillers Jean , Cornus Martin , Navech Jacques , Wolf Jean‐Gérard 
Published: May 2005

AbstractLe spectre de résonance magnétique protonique du diméthylamino‐2 méthyl‐3 oxazaarsolane‐1,3,2 est très sensible à la température et à la nature du solvant. L'analyse complète du spectre protonique à −48 °C dans le toluène deutérié montre que la molécule est dans une conformation privilégiée au niveau C‐4C‐5. Dans le nitrobenzène à +31 °C, le spectre de type A2X2 indique un mouvement de libration autour de cette liaison. A température plus élevée un nouveau phénomène de coalescence peut être expliqué par l'inversion de l'atome d'arsenic.
Study of rotation barriers in N,N‐dimethylnicotinamide and quaternary salt derivatives by proton NMR. A correlation of rotation barriers of N,N‐dimethylamides with carbon‐13 chemical shifts
Authors: Lepoivre J. A. , Dommisse R. A. , Alderweireldt F. C. 
Published: May 2005

AbstractThe rotational barrier in the N,N‐dimethylamide group is studied by proton NMR for N,N‐dimethylnicotinamide and two quaternary salts in aqueous solution. The carbon‐13 NMR spectra of a number of aromatic N,N‐dimethylamides are discussed. A roughly linear correlation is found between the ΔG≠ values of the rotation barriers and the chemical shifts of the carbon atom substituted by the amide group.
13C‐NMR‐Spektren von Monoterpenen
Authors: Bohlmann F. , Zeisberg R. , Klein E. 
Published: May 2005

AbstractDie 13C‐NMR‐Spektren von fast 100 Monoterpenen zeigen, daß sie zur Charakterisierung derartiger Verbindungen sehr brauchbar sind. Besonders wertvoll ist diese Methode zur Klärung stereochemischer Probleme. Bis auf wenige Fälle folgen die beobachteten chemischen Verschiebungen den allgemeinen Regeln. Die Probleme der Messungen mit Verschiebungsreagenzien werden diskutiert.
Structure and protonation study of the imidazo [1,2‐a]‐pyrimidine system in 1H nuclear magnetic resonance
Authors: Marchetti Leonardo , Pentimalli Luciano , Lazzeretti Paolo , Schenetti Luisa , Taddei Ferdinando 
Published: May 2005

AbstractThe 1H NMR spectra of imidazo [1,2‐a]pyrimidine derivatives have been analysed to study the aromatic character and protonation behaviour of this system. By employing the ‘ring currentn’ model and calculations based on the coupled Hartree‐Fock method it can be deduced that a large π‐electron delocalisation exists in this heterocyclic system and affects the screening constant of the protons. Charge density schemes obtained by SCF techniques agree with the reactivity behaviour of these molecules.A detailed study of protonation carried out by following the 1H NMR spectra both in trifluoroacetic acid and in aqueous hydrochloric acid shows that the most probable site of protonation is N‐1, but leaves open the possibility of a rapid exchange of one proton between N‐1 and N‐8.
Substituent effects on 13C13C coupling constants and chemical shifts in 13C labelled polycyclic aromatic hydroxy compounds
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractThe effects of an hydroxy substituent on 13C13C coupling constants and 13C chemical shifts have been measured in 1‐hydroxynaphthalene‐2‐13C and 1‐hydroxypyrene‐1‐13C. The changes observed in the 13C13C couplings show the effect of a substituent attached directly to the labelled carbon or to a carbon ortho to this. In both situations the effect is a decrease in the numerical magnitude of most of the long range 13C13C coupling constants.
Application des mesures de couplages 15NH à la détermination de configurations d'oximes
Authors: Crépaux Danielle , Lehn Jean‐Marie 
Published: May 2005

AbstractPlusieurs oximes, enrichies en 15N, d'aldéhydes hétérocycliques ont été préparées dans les formes syn et anti. La forme la moins stable peut être obtenue par irradiation UV de l'autre. Le couplage géminal 15NH dans le fragment RCH15NOH permet une attribution non ambiguë de la configuration; il est de 13 à 16 Hz et de 2 à 3 Hz pour les formes anti et syn, respectivement. Les oximes 1 à 4 sont préférentiellement anti, alors que la forme stable des oximes des aldéhydes de N‐méthyl pyridinium (8 à 11) est syn et non pas anti comme cela avait été admis. Cette réattribution présente un intérêt spécial puisque 2‐PAM (8), qui est un excellent antidote réactivant l'acétylcholinestérase inhibée par phosphorylation, a été utilisée pour étudier la géometrie du site actif de l'enzyme.
Evaluation of limiting‐induced shifts of disubstituted adamantane derivatives on the basis of shift additivity
Authors: Hájek M. , Vodička L. , Hlavatý J. 
Published: May 2005

AbstractA quantitative interpretation of 1H NMR spectra of symmetrically disubstituted adamantane derivatives (2,4‐adamantanedione, 2,6‐adamantanedione and 2,4‐adamantanetdiol) with shift reagents is reported. Assumptions are made of shift additivity and an average coordination of one molecule of the shift reagent to both functional groups. A much better fit between the experimental and the calculated set of limiting‐induced shifts was obtained for calculations based on shift additivity.
1H and 13C NMR study of the enol–enolic tautomerism of some cyclic β‐ketoaldehydes
Authors: Shapet'ko N. N. , Radushnova I. L. , Bogachev Yu. S. , Berestova S. S. , Potapov V. M. , Kiryuschkina G. V. , Talebarovskaya I. K. 
Published: May 2005

AbstractAldehyde (δCH) and enolic (δOH) proton chemical shifts, the corresponding spin–spin coupling constants (JCH,OH) and the 13C chemical shifts (δC) have been measured for three cyclic β‐ketoaldehydes as a function of temperature. A tautomeric equilibrium has been shown to exist between the aldo–enol (A) and hydroxymethylene ketone (B) forms. The chemical shifts δCH δOH and δC for the two pure tautomeric forms A and B have been calculated. The enthalpy changes ΔH in the tautomeric process A⇄B and the percentages of the tautomeric forms have been determined.
Détermination de la forme la plus stable de l'ortho‐dichlorofluorure de benzyle par RMN en phase nématique
Authors: Gout E. , Béguin C. , Canet D. , Marchal J. P. 
Published: May 2005

AbstractLa valeur des couplages directs dans l'ortho‐dichlorofluorure de benzyle, obtenus par RMN en phase nématique, permet d'affirmer que la position la plus stable du CH2F est telle que le fluor se trouve dans un plan perpendiculaire au cycle benzénique. L'interprétation complète de ces couplages en fonction de la géométrie de la molécule laisse cependant supposer une modification de l'orientation intervenant en même temps que la rotation du groupement CH2F.
3J(PCNH) in phosphorus substituted thioformamides as a configurational probe
Authors: Dahl Otto , Laursen Svend Aage 
Published: May 2005

AbstractCoupling between P and (N)H has been observed in the 1H{14N}NMR spectra of a series of phosphorus substituted thioformamides, R12/P(X)C(S)NHR2. For R2 = H one of the two couplings constants 3J(PCNH) is much larger than the other. The larger constant is assumed to be 3J(PCNH) (trans) and the magnitude of 3J(PCNH) for several compounds with R2 = Me or Ph is used to assign the configuration about the C(S)N bond.
Amines α et β acétyléniques. Couplages J(15NH), J(15N13C) et hybridation de l'azote
Authors: Bottin‐Strzalko T. , Pouet M. J. , Simonnin M. P. 
Published: May 2005

AbstractLes trois amines 15N‐méthylaniline, 15N‐méthylphénylpropargylamine et 15N‐méthylphénylpropynylamine ont été étudiées par RMN du 1H et 13C. Les grandeurs des couplages 1J(15N13C) et 1J(15N13C) indiquent que l'hybridation de l'azote est intermédiaire entre sp3 et sp2 dans le 15N‐méthylaniline et la 15N‐méthylphénylpropargylamine mais est sp2 dans l'amine α‐acétylénique. La valeur du couplage 1J(15N13Csp), calculée à l'aide de la relation de Binsch, est plus faible que la valeur expérimentale, ce qui suggère que les mécanismes orbitalaire et dipolaire apportent une contribution non négligeable à ce couplage.
Dynamic NMR: A new intensity ratio for evaluation of lifetime in paripartite A ⇌ B systems
Authors: Dimitrov Valentin S. 
Published: May 2005

AbstractA simple formula for evaluation of rates of exchange in paripartite A ⇌ B systems is introduced. It is concerned only with the intensity ratio in a two‐site system in much the same way as that of Rogers and Woodbrey, but the new formula is also applicable above the coalescence point of the spectrum. The formula has been applied to the classical case of N,N‐dimethyltrichloroacetamide. An error analysis demonstrates that the approximations inherent in the derivation of the new formula lead to smaller errors than do those of Rogers and Woodbrey.
NMR‐Untersuchungen über inter‐ und intramolekulare Wechselwirkungen in substituierten Trifluormethylphenylisocyanaten, Fluorphenylisocyanaten, in Fluoranilin und Fluornitrobenzol
Authors: Kosfeld R. , Henke L. 
Published: May 2005

AbstractDie chemischen Verschiebungen der Fluor‐ und Protonensignale substituierter Trifluormethylphenylisocyanate, Fluorphenylisocyanate, des Fluoranilins und des Fluornitrobenzols werden in Abhängigkeit von der Probentemperatur und der Konzentration des Lösungsmittels Tetrachlorkohlenstoff ermittelt. Der Temperatureinfluß auf die chemischen Verschiebungen der Fluorsingale ortho‐substituierter Trifluormethylphenylisocyanate wird von der intramolekularen Wechselwirkung zwischen den Trifluormethylgruppen und den ortho‐Substituenten bestimmt, die zu einem Anstieg der chemischen Verschiebungen mit zunehmender Temperatur führt.Die Temperaturabhängigkeit der Elektronenverteilung innerhalb meta‐ und para‐substituierter Trifluormethylphenylisocyanate ist hauptsächlich auf intermolekulare Wechselwirkungen zurück‐zuführen, die eine Abnahme der chemischen Verschiebungen der Fluorsignale mit steigender Probentemperatur verursachen.Da sich die Protonen der untersuchten Substanzen an der ‘molekularen Oberfläche’ befinden, ist der van der Waals‐Effekt für die Temperaturabhängigkeit der chemischen Verschiebungen der Protonensignale bestimmend. Das Lösungsmittel Tetrachlorkohlenstoff verursacht mit zunehmender Konzentration infolge einer Schwächung des Anisotropie‐Effektes einen Anstieg der chemischen Verschiebungen der Fluor‐ und Protonensignale aller untersuchten Substanzen.
Diazanaphthalenes: A 13C NMR investigation on the site of protonation and pKa values
Authors: van de Weijer Peter , Thijsse Hans , van der Meer Douwe 
Published: May 2005

AbstractThe pH dependence of the 13C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the pKa values have been determined using the Henderson‐Hasselbach equation. The change in 13C chemical shifts under the influence of nitrogen protonation (Δδ) has been predicted using the Δδ values of quinoline and isoquinoline. The correlation between observed and expected Δδ values of the symmetric diazanaphthalenes is very good. Assuming these changes in chemical shifts to be of general validity, the site of protonation in the asymmetric diazanaphthalenes has been determined by comparison of the expected Δδ values for α‐ and β‐nitrogen protonation with the observed ones. The site of protonation for 1,6‐ and 1,7‐naphthyridine is the β‐nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount.
13C NMR spectral studies of arecoline, hordenine, strychnine and brucine
Authors: Srinivasan P. R. , Lichter R. L. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of arecoline, hordenine, strychnine, brucine and their salts were determined and the chemical shifts reported previously for arecoline have been verified by single frequency proton decoupling techniques. Effects of protonation on the carbon resonances in aiding unambiguous assignments in strychnine and brucine are discussed. The quaternary N‐methiodide of brucine was also studied to confirm the assignments made for carbon atoms adjacent to the basic N atom.
Modification d'une sonde de spectromètre C60 HL pour des ètudes de photo CIDNP
Authors: Caplain S. , Vermeersch G. 
Published: May 2005

AbstractLa photo CIDNP est une technique nouvelle permettant d'élucider le mécanisme de réactions photochimiques. Dans la majorité des cas, le problème principal pour sa mise en oeuvre est d'amener suffisamment d'énergie lumineuse au niveau de la sonde de détection.Nous relations ici les modifications que nous avons apporté à la sonde d'un spectromètre JEOL C 60 HL de façon à pouvoir étudier les réactions photochimiques de l'acridine dans les alcools et les éthers.
NMR‐Untersuchungen an Dicyclopentadienderivaten: II.—13C‐NMR: γ‐gauche‐Effekt in Abhängigkeit von der exo/endo‐Isomerie an Dicyclopentadien diolen
Authors: Kleinpeter E. , Kühn H. , Mühlstädt M. 
Published: May 2005

AbstractDie 13C‐FT‐NMR‐Spektren einer Reihe von exo‐ bzw. endo‐Dihydro‐ und Tetrahydrodicyclopentadien‐9, 10‐diolen (exo/exo bzw. endo/endo) werden aufgezeigt und die einzelnen chemischen Verschiebungen unter Verwendung von Eu(fod)3‐ Verschiebungsversuchen bzw. additiver Inkrementberechnung zugeordnet. Dabei werden besonders für die C‐Atome 4, 5, 7, 9. 10 und 1, 3 in Abhängigkeit von der exo/endo‐Stellung des angeknüpften 5‐Ringes bzw. der OH‐Gruppen am Norbornangerüst relativ starke γ‐Effekte bis 12,8 ppm beobachtet, die einen interessanten Einblick in die Geometrie dieser Norboran‐Systeme geben.
1H n.m.r. studies on intramolecular hydrogen bonding in anilides of 6‐methylpicolinic acid N‐oxide
Authors: Brzezinski Bogumil 
Published: May 2005

AbstractThe 1H n.m.r. spectra of eleven anilides of 6‐methyl‐picolinic acid N‐oxide in chloroform were obtained. The influence of temperature, concentration and substituents on the chemical shifts of the NH protons was investigated. The structure of the anilides is discussed.
13C n.m.r. spectra of cyclopropenes
Authors: Günther Harald , Seel Horst 
Published: May 2005

Abstract13C n.m.r. chemical shifts and one bond 13C, 1H coupling constants for cyclopropene and its 1‐ and 3‐methyl derivatives as well as for methyl cyclopropane have been measured. The data for cyclopropene are 108·9 ppm and 228·2 Hz, 2·3 ppm and 167·0 Hz in the olefinic and allylic position, respectively. Substituent effects for the methyl group are discussed.