bluuebunny/crossref_metadata_2025_split huggingface dataset:
Etude par RMN des 2‐2′ ‐Dihalogeno‐diethylethers—II: Effet de Solvant
Authors: Haloui Ezzeddine , Canet Daniel , Granger Pierre 
Published: May 2005

AbstractL'effet de solvant sur les éthers disubstitués de formule (XCH2CH2)2O avec X  Cl, Br, I a été étudié. Les pourcentages des différentes formes stables ont été déterminés pour chaque solvant suivant la méthode de Lin et il est montré que ces trois halogénures évoluent vers les formes gauches quand la constante diélectrique de la solution augmente.De plus, il est montré que les couplages géminés dans le cas du dérivé iodé diminuent algébriquement quand la polarité du solvant augmente. Les auteurs pésentent une tentative de corrélation des variations des couplages géminés avec l'évolution conformationnelle.
Carbon‐13 nuclear magnetic resonance spectroscopy—VII:para‐substituted fluorobenzenes
Authors: Miyajima Goh , Akiyama Hiromichi , Nishimoto Kichisuke 
Published: May 2005

AbstractC‐13 and F‐19 NMR spectra of seventeen para‐substituted fluorobenzenes were measured and the chemical shifts as well as coupling constants with respect to substituents were analysed. The chemical shifts of the fluorine, the C1 and the C2 atoms were found to depend on the total electron densities. In the case of the C3 atom, the chemical shifts seem to depend on π‐electron densities rather than the total electron densities. The present calculations also indicate that the chemical shift of the C4 atom depends mainly on σ‐electron densities due to the inductive effects of substituents. The strongest factor influencing the coupling constant, nJ(CF), is also considered to be the π‐electron densities on the carbon atoms. In the case of the direct couplings, 1J(CF), the π‐bond orders are important.
Proton exchange and protonation of substituted oxadiazoles in trifluoroacetic acid
Authors: Puar Mohindar S. , Cohen Allen I. 
Published: May 2005

AbstractThe rates of NHCOOH proton exchange between 5‐amino‐(1a) and 5‐N‐methylamino‐(1b)3‐[2‐(5′‐nitro‐2′‐furyl)vinyl]‐1,2,4‐oxadiazoles and trifluoroacetic acid (TFA) have been measured by NMR spectroscopy. The values of the first‐order rate constant and thermodynamic parameters for 1a and 1b, respectively, are: kapp (sec−1) = 820 and 40 (50°C), ΔF (kcal/mole) = 14·7 and 16·5, ΔH# (kcal/mole) = 17·3 and 24·3 and ΔS# (e.u.) = 17 and 34. The comparison of rate constants indicates that after correction for proton equivalency proton exchange in 1a is faster than in 1b by a factor of ten. The presence of an NH2 proton resonance (1a) and an N‐methyl doublet (J = 5·0 Hz) between 0 and 30° (1b) suggests that 1a and 1b are present as amines and not as imines in TFA.
13CMR‐Tieftemperatur‐Untersuchungen an Cyclooctan‐Konformeren
Authors: Schneider Hans‐Jörg , Keller Toni , Price Roger 
Published: May 2005

AbstractDie Konformerengleichgewichte verschiedener monosubstituierter Cyclooctane werden durch 13CMR‐Tieftemperatur‐Spektroskopie bestimmt. Aus den 13C‐Verschiebungen kann auf die Geometrie der Konformeren geschlossen werden. Durch Vergleich berechneter und experimenteller Spektren werden für die Konformerenumwandlungen einige ΔG#‐Werte erhalten.
14N, 1H spin couplings in diethylmethylvinylammonium bromide
Authors: Ueyama (nee Ohtsuru) Masako , Tori Kazuo 
Published: May 2005

AbstractThe proton magnetic resonance spectrum of diethylmethylvinylammonium bromide, in which splittings due to 14N, 1H spin couplings are clearly observed as strongly perturbed second‐order patterns, has been analysed and the difference in the substituent effect between a methyl and an ethyl group upon 1H, 1H and 14N, 1H spin couplings are summarised.
Steric effects in 31P NMR spectra: ‘Gamma’ shielding in aliphatic phosphorus compounds
Authors: Quin Louis D. , Breen Joseph J. 
Published: May 2005

AbstractAn examination of published 31P NMR spectral data for aliphatic phosphorus compounds has revealed that chain lengthening and branching effects on the chemical shift can be interpreted in terms similar to those used for 13C and 15N shifts. For six families of phosphorus compounds, a β‐carbon substituent was shown to deshield phosphorus, while a γ‐carbon caused shielding. The effects are additive, and good agreement was obtained between 31P shifts calculated with the appropriate constants and the experimental values. Shielding by γ‐carbon is indicative of the operation of a steric influence on 31P chemical shifts, not heretofore articulated. The γ‐effect is also useful in explaining the unusually large shielding found in six‐membered cyclic phosphines.
Lanthanide‐induced shifts in proton NMR spectra of cyclohexanones
Authors: Shapiro B. L. , Johnston M. D. , Shapiro M. J. 
Published: May 2005

AbstractThe lanthanide‐induced shifts (LIS) of the lanthanide shift reagent (LSR) Eu(FOD)3 are reported for a large number of cyclohexanones, especially those which are highly substituted. The following compounds were synthesized and characterized: 3‐(aryl)‐3,5,5‐trimethylcyclohexanones, in which aryl = 1‐naphthyl, phenyl, o‐anisyl, m‐anisyl, p‐anisyl and p‐chlorophenyl. Some analogous compounds were also studied: 3,5,5‐trimethylcyclohexanone, 4‐tert‐butyl‐cyclohexanone, 3,3,5,5‐tetramethylcyclohexanone 3‐(1‐naphthyl)5,5‐dimethylcyclohexanone and para‐tert‐butyl‐anisole. A method for the regression analysis of the concentration dependence of the LIS of these substrates is developed and reported, and used to derive the limiting incremental LIS (Δ2) for the LS2 complex and to evaluate the proton chemical shifts (δ0) in the absence of LSR. An ‘incremental dilution’ technique was found to be most appropriate to insure constant substrate concentrations, needed to extract both Δ2 and δ0. The conformations of the 3‐(aryl)‐type systems and analogous compounds were studied via LIS and found to conform to:—(i) an axially disposed aryl substituent in the 3,3,5,5‐tetra‐substituted cyclohexanones and (ii) a flattened chair form of the cyclohexanone ring with distortions in this chair form being an increase in the syn‐diaxial (C‐3, C‐5) substituent distance (C‐3 and C‐5 substituents still eclipsed). The LIS were fully compatible with these structural assumptions.
Détermination des Axes Propres et des Valeurs Principales du Tenseur ḡ dans deux Radicaux Libres Nitroxydes par Étude de Monocristaux
Authors: Bordeaux D. , Lajzerowicz‐Bonneteau J. , Briere R. , Lemaire H. , Rassat A. 
Published: May 2005

AbstractLa structure de la phase basse température du radical nitroxyde tétraméthyl‐2,2,6,6 pipéridine oxyle‐1 (Tanane) a été déterminée. Ce radical libre est isomorphe du tétraméthyl‐2,2,6,6 pipéridinol‐4 oxyle‐1 (Tanol). Une étude en résonance paramagnétique électronique de monocristaux a permis de déterminer les valeurs principales et l'orientation des axes propres du tenseur ḡ pour ces deux radicaux. Pour le Tanane, la liaison NO est une direction propre du tenseur ḡ. Pour le Tanol, il existe un angle de 8° ± 2° entre cette direction propre et la liaison NO. Il est vraisemblable que, dans le cas du Tanol, la liaison hydrogène intermoléculaire est responsable de la déviation observée pour les axes propres situés dans le plan miroir , ainsi que des plus faibles valeurs mesurées pour gxx, gyy et gzz.
Conformations of highly hindered aryl ethers—VIII Interannular HF coupling in diphenyl ethers
Authors: Lehmann F. Pedro A. , Johnson LeRoy F. 
Published: May 2005

AbstractA novel type of interannular coupling (6JH,F = 1.0 to 1.3 Hz) has been observed in some fluorodinitrodiphenyl ethers between the fluorine(s) on one ring ortho to the ether linkage and a proton ortho to it on the other ring. 1H and 19F chemical shift and coupling constant data support the previous conclusion that these ethers preferentially adopt a twist (propeller) conformation. On account of the geometrical disposition of the six bonds between the interacting nuclei and the latter's spatial proximity in this conformation, direct coupling through‐space is indicated. Concerted libration around the ether bonds brings about magnetic equivalence of the o‐fluoro substituents on one ring and causes equal coupling to be observed to the o‐proton on the other ring. The possiblity that the coupling is mediated by an intervening π‐cloud is suggested as an alternate mechanism for indirect coupling. The observed interannular transmission of spin information provides evidence in favor of a recent proposal made concerning the mode of action of the thyroid hormones.
NMR long‐range coupling and shift effects in the assignment of stereochemistry to 3‐substituted 5,6‐dehydroisoquinuclidines
Authors: Krow Grant , Rodebaugh Ronald 
Published: May 2005

AbstractThe complementary NMR techniques of long‐range W‐plan coupling and substituent shift effects on nearby olefinic hydrogens have been used to assign the stereochemistry of 3‐phenyl‐ and 3‐acetyl‐dehydroisoquinuclidines (2 to 5).
Magnetic nonequivalence in NMR spectroscopy—II. The role of hydrogen bonding in 2,2,4‐trimethylpentane‐1,3‐diol and its monoisobutyrates
Authors: Fantazier Richard M. 
Published: May 2005

AbstractThe methylene protons in 2,2,4‐trimethylpentane‐1,3‐diol (1), its 1‐isobutyrate (2) and 3‐isobutyrate (3) monoesters, are magnetically nonequivalent with respect to chemical shift. Under the same experimental conditions, the chemical shift differences are 14·4 Hz, 46·2 Hz and 18·2 Hz for 1, 2 and 3, respectively. These nonequivalences were examined as a function of temperature and concentration. The large nonequivalence in 2 is attributed to a highly restricted conformation resulting from intramolecular hydrogen bonding. Less favorable steric interactions result in a substantially smaller contribution of intramolecular hydrogen bonding in 3, while in 1 intermolecular hydrogen bonding occurs exclusively. Infrared data were obtained in support of these conclusions.
Correlation of molecular orbital indices of reactivity and proton chemical shifts: Acenaphtho[1,2‐b]‐ and ‐[1,2‐c]thiophens
Authors: Bartle K. D. 
Published: May 2005

AbstractNuclear magnetic resonance proton chemical shifts may be correlated with free valence, a representative reactivity index, for fluoranthene and two novel sulphur heterocyclic analogues, acenaphtho[1,2‐b]‐ and ‐[1,2‐c]thiophens. Such correlations arise fortuitously, however, and an attempt to explain them in terms of intrinsic properties of the Hückel‐McWeeny theory of proton shielding is proved to be fallacious.
The sign of four‐bond couplings in cyclobutanes: NMR spectra ofvic‐dihalo‐2,3‐oxazabicyclo[3.2.0]hept‐3‐enes
Authors: Mondelli R. , Gamba A. 
Published: May 2005

AbstractThe spectra ofvic‐dihalo‐2,3‐oxazabicyclo[3.2.0]‐hept‐3‐enes were analysed and the sign of all the coupling constants determined by tickling experiments. Stereochemical assignments, and three and four‐bond coupling are discussed in particular.
Etude de nitrophénylhydrazones α‐carbonylées—I. RMN des molécules modèles acycliques
Authors: Venien Frédéric , Lefeuvre Mme M. 
Published: May 2005

AbstractL'étude par RMN des nitrophénylhydrazones α‐carbonylées nécessite une bonne connaissance du groupe hydrazono et des effets qu'il provoque, comparativement au carbonyle, sur les protons de la chaîne carbonée. L'étude RMN de cétones aliphatiques et aromatiques et de leurs arylhydrazones (ortho,para et dinitrés) permet d'atteindre cet objectif. Les valeurs de déplacement chimique des protons de la cétone servent de référence à partir desquelles les influences suivantes sont mises en évidence: l'identité du proton étudié (méthyle, méthylène ou méthyne); la position de ce proton par rapport au groupe hydrazono (en α, β ou γ); la configuration syn ou anti du reste hydrazono; la substitution de ce groupe.L'anisotropie du groupe nitrophényl hydrazono ainsi mise en évidence semble principalement attachée à la paire libre de l'azote doublement lié et secondairement au groupe nitro et à sa polarisation.Les effets provoqués par les chaînes carbonée et azotée l'une sur l'autre, laissent prévoir que l'azote porteur de l'hydrogène doit posséder une hybridation proche de sp2.Enfin, le déplacement chimique du proton lié à l'azote est trés sensible aux diverses substitutions de la molécule, ce qui laisse présager un rôle ‘antenne’ dans les hydrazones α‐carbonylées.
Chemische Verschiebungen von Methylprotonen in 1H‐NMR‐Spektren von Alkylcyclohexanen
Authors: Werner H. , Köhler H. J. , Mühlstädt M. , Zschunke A. , Mann G. 
Published: May 2005

AbstractDie chemischen Verschiebungen der Alkylprotonen von 51 methyl‐ und tert‐butyl‐substituierten Cyclohexanen wurden bestimmt. Der Resonanzbereich axialer Methyl‐gruppen erstreckt sich von δ = 0,63 bis 0,98 ppm, der von äquatorialen von δ = 0,81 bis 1,02 ppm. Die chemischen Verschiebungen axialer Methylgruppen werden durch Nachbargruppen stärker beeinflusst als die der äquatorialen Methylgruppen. Die Shifteffekte von Alkylgruppen auf Methylprotonen werden mit denen auf Ringprotonen verglichen.
An NMR study of cis‐2‐butene partially oriented in a nematic phase
Authors: Burnell E. E. , Diehl P. 
Published: May 2005

AbstractThe NMR spectrum of cis‐2‐butene partially oriented in a nematic phase has been analysed, and information about the geometry and the indirect spin‐spin coupling constants has been obtained. Assuming the barrier of rotation of the methyl groups and other geometrical information from microwave studies, we obtained = 126 ± 2° and = 116.8 ± 0·6°. The angle that the CH3 rotation axis makes with the double bond was calculated to be 127·5 ± 0.4°; this value is closely linked with the assumed value of = 109°28′.
An abnormal spin‐spin coupling of vinylic‐allylic protons generated by a constraint of configuration
Authors: Chow Y. L. , Streith J. , Taurand G. 
Published: May 2005

AbstractIn a system where a rigid or frozen conformation constrains an allylic proton to orient nearly perpendicular to the plane of the olefinic bond, the allylic spin coupling may become comparable to, or greater than, the vicinal spin coupling. This anomalous situation is demonstrated in three series of compounds: the adducts of diazoalkanes to 1,2‐diazepines, 4‐piperidinocycloalk‐2‐en‐1‐one oximes and heterobicyclo[3,2,0]hept‐3,6‐dienes, where the NMR spectra have been well established by decoupling experiments.
Position specificity of 13C31P coupling constants for methyl substituents in phospholes and 2—Phospholenes
Authors: Quin L. D. , Borleske S. G. , Stocks R. C. 
Published: May 2005

AbstractThe 13C—31P coupling constant is much larger for a 2‐methyl substituent (about 20 Hz) than for a 3‐methyl substituent (about 5 Hz) in phospholes and 2‐phospholenes, and appears useful for assigning structures in these compounds.
Self‐association of thiols. The baggy fit problem in weak complexes
Authors: Hu Siung J. , Miller Sidney I. 
Published: May 2005

AbstractThe PMR technique has been used to obtain thermodynamic data for hydrogen bonding of alkanethiols (RSH) in 1:1 dimers in carbon tetrachloride. At ca. 303°K these are (R, 104K(M−1), −ΔH°(kcal/mole), −ΔS°(eu)): n‐C3H7, 51 ± 5, 0.9 ± 0.15, 13 ± 1; i‐C3H7, 50 ± 10, 0.8 ± 0.3, 13 ± 1; n‐C4H9, 35 ± 2, 0.8 ± 0.15, 14 ± 1; t‐C4H9, 14 ± 4, 1.1 ± 0.7, 16 ± 2; C6H11, 1.3 ± 2, 0.7 ± 0.3, 15 ± 1. Alkanethiol self‐association is weak, and although an exact expression [Eqn. (5)] reproduces spectral data precisely, the fit is sufficiently ‘loose’ or ‘baggy’ so that values of K, ΔH° and ΔS° are uncertain. The methodology of the treatment of self‐association data and their errors is examined and Deranleau's useful approach is extended. The impossibility of obtaining reliable data for very weak (< 10 %) or very strong (> 90 %) associations by techniques equivalent to ours is emphasized. The possibility of cyclic thiol dimers is discussed. It is suggested that the PMR method cannot give trustworthy self‐association data for aryl or arylalkylthiols because of the relatively large anisotropy effects introduced into the dilution shift.
Interactions Intramolécularies—XVII Calcul des constantes de couplage en RMN du cyclohexane et de cyclohexanes substitués. Comparaison des méthodes de Pople et Santry et des perturbations finies
Authors: Pouzard Guy , Rajzmann Michel , Bodot Hubert , Pujol Louis 
Published: May 2005

AbstractLes constantes de couplage RMN 3J, 4J et 5J entre protons ont été calculées par les deux méthodes citées, pour le cyclohexane et pour les conformères de ses dérivés monosubstitués (substituants: Li, CH3, OH, F). La comparaison des deux méthodes sur la base de la théorie des groupes met en évidence la nécessité d'utiliser la méthode des perturbations finies dont les résultats sont confrontés avec les données expérimentales de la littérature.
Déplacements Chimiques Induits par Complexation à l'Europium en Série Δ1‐Pyrazoline
Authors: Franck‐Neumann Michel , Sedrati Madjid 
Published: May 2005

AbstractLe complexe Eu (FOD)3 constitue un bon réactif de déplacement en spectroscopie de RMN de Δ1‐pyrazolines. Les 5 exemples décrits ici ont été choisis en série polycyclique pour mettre en évidence l'utilité de cette technique en vue de l'attribution des stéréochimies.
Proton magnetic resonance studies of actinomycin‐related peptides containing N‐methyl groups
Authors: Mauger A. B. , Rzeszotarski W. J. , Ford R. A. 
Published: May 2005

AbstractThe PMR spectra of several cyclic and acyclic dipeptide derivatives representing portions of the actinomycin structure have been studied. In the spectra of the acyclic compounds temperature‐dependent duplicity resulted from the equilibration of conformers possessing cis and trans peptide bonds. The lanthanide shift reagent Eu(FOD)3 was utilized to distinguish N‐methyl groups in the two conformations and observations were made on the steric dependence of the observed shifts. The origin of the wide variation in chemical shift of N‐methylvalyl α‐protons is discussed in relation to the conformation of actinomycin.
Long‐range 4J coupling constants and conformation of the four‐membered heterocycles
Authors: Fomichov A. A. , Zon I. A. , Gella I. M. , Kostyanovsky R. G. , Saprin A. N. , Markov V. I. 
Published: May 2005

AbstractThe correlation between the puckering angle of the four‐membered cycle and 4J has been obtained from analysis of the PMR spectra of some 2‐substituted azetidines and oxetanes. The absolute values of 4Jcis and 4Jtrans were found to decrease with decreasing of the puckering angle.
The use of DSS as an internal standard in PMR studies of nucleic acid interactions
Authors: Live David. H. , Chan Sunney I. 
Published: May 2005

AbstractTwo commonly used PMR internal reference compounds, 3‐(trimethyl silyl) propane sulfonic acid sodium salt (DSS) and 3‐(trimethyl silyl) sodium propionate (TSP), have been shown to interact with purine in aqueous solution, causing significant shifts in the resonance position of their reference protons. Tetramethyl ammonium chloride (TMACl) appears to be a more suitable reference compound for such studies.
NMR stereotopic induced shifts in epimeric mixtures
Authors: Enríquez R. , Taboada J. , Salazar I. , Díaz E. 
Published: May 2005

AbstractThe proton NMR spectra of epimeric mixtures of menthone (1), carvomenthone (2), carquejone (3), 2,5‐dimethyl‐1,4‐cyclohexanedione (4) and piqueridione (5) were studied using the chemical shift reagent Eu(DPM)3. The results allow quantifications of the epimers and some conformational assignments to be made.
Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXIII: Deformation of the piperidine ring in some bicyclic compounds possessing a bridgehead amide nitrogen atom
Authors: Cahill R. , Crabb T. A. 
Published: May 2005

AbstractSome bridgehead nitrogen compounds possessing the CH(Me)‐bridgehead NC(O) system have been synthesised and their configurations assigned. The chemical shifts of the proton geminal to the methyl group provides evidence for the existence of a deformed chair conformation for the methyl substituted ring.
CIDNP of 13C and 1H nuclei in the reactions of cyclohexadienone carbenes
Authors: Nikiforov G. A. , Markaryan Sh. A. , Plekhanova L. G. , Sviridov B. D. , Rykov S. V. , Ershov V. V. , Buchachenko A. L. , Pehk T. , Saluvere T. , Lippmaa E. 
Published: May 2005

AbstractThermal decomposition of 4‐diazo‐2,6‐di‐tert‐butyl‐2, 5‐cyclohexadien‐1‐one in perhalogenated solvents has been investigated. The decomposition reaction proceeds via a carbene intermediate first to a singlet and then to an effectively triplet free encounter radical pair formed in a halogen abstraction reaction. The polarisation of the stable reaction product is determined by competing processes in the primary cage, intersystem crossing and escape from the cage.
Tris‐(4,4,4‐trifluoro‐1‐(‐2‐thienyl)‐1,3‐butandiono)‐europium(III) als NMR‐Verschiebungsreagens
Authors: Beyer Klaus 
Published: May 2005

AbstractDie Eigenschaften von Europium thenoytrifluoroacetonat als Verschiebungsreagens werden an verschiedenen Substraten untersucht. Auf Grund seiner guten Löslichkeit ist der Komplex bei schwach komplexierenden Substraten dem Eu(DPM)3überlegen.—Im13C‐NMR–Spektrum von D(+)‐Campher werden die Signale von C9und C10zugeordnet.
Identification of 4,5‐asymmetrically substituted 1‐(N‐isoimido)‐1,2,3‐triazoles by benzene induced shifts in NMR spectra—VII
Authors: Alexandrou N. E. , Rodios N. A. , Hadjiantoniou‐Louizou C. P. 
Published: May 2005

AbstractProton chemical shifts, as well as solvent shifts induced by benzene, can be used for the structure determination of 4,5‐asymmetrically substituted 1‐(N‐isoimido)‐1,2,3‐triazoles, derived from the oxidation of α‐diketone bisaroylhydrazones. The geometry of the postulated ‘collision complex’ is discussed and an attempt is made to estimate theoretically the induced shifts of some of the protons.
Etude comparative des méthyl‐borazines par RMN
Authors: Beaumelou G. , Pasdeloup M. , Laurent J.‐P. 
Published: May 2005

AbstractUne étude comparée du borazine (0) et de six méthyl‐borazines (1 à 6) a été effectuée par RMN. Il apparaǐt nettement que le déplacement chimique des protons NCH3 varie peu entre les mono‐, di‐ et triméthyl‐N borazines alors que ce měme paramètre subit une modification importante (au total 0,21 ppm vers les champs forts) quand on passe du triméthyl‐N borazine (HBNCH3)3 à l'hexaméthylborazine (CH3BNCH3)3 par substitution progressive sur les trois atomes de bore (cycles 3,4, 5 et 6). En outre, une variation systématique du paramètre δ a pu ětre décelée entre les composés 3, 4 et 5 pour les protons qui conservent strictement le měme environnement immédiat. Une interprétation qualitative de ce résultat expérimental est proposée en termes d'effets électroniques généralisés au cycle hexagonal plan bore–azote qui caractérise ces molécules.