bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 n.m.r. spectra of 2,3‐dimethylenebicyclo[2.2.1]heptanes and 2,3‐dimethylene‐7‐oxabicyclo[2.2.1]heptanes
Authors: Quarroz Daniel , Sonney Jean‐Marie , Chollet André , Florey André , Vogel Pierre 
Published: May 2005

AbstractThe 13C n.m.r. spectra of 11 derivatives of 2,3‐dimethylenenorbornane, 1–11, of 5 derivatives of 2,3‐dimethylene‐7‐oxanorbornane, 12–16, and of 2,3,5,6‐tetramethylene‐7‐oxanorbornane (17) have been measured and the chemical shifts have been assigned. The effects of 1‐methyl, 5‐hydroxy, 5‐acetoxy, 5‐para‐bromobenzenesulphonyloxy and 5‐keto substituents on the olefinic carbons of the s‐cis‐butadiene group are compared with the same substituent effects reported for model compounds. Apparent linear correlations between the reciprocals of the V←N transition energies of the butadiene chromophores and the differences of the chemical shifts ΔδC between the quaternary and methylene olefinic carbons are found for the dienes 1–3, 12–14, butadiene and 2,3‐dimethylbutadiene. The ΔδC of the olefinic carbons of the tetraene 17 also falls on the correlation line if the average of the two absorption hands at 250 and 228 nm is taken for the V←N transition energy of this compound. The chemical shift of the carbon of the methano bridge H2C‐7 is almost insensitive to the presence of one or two methylene groups at C‐2,3, in contrast with the downfield shift of 10–14 ppm observed when an endocyclic double bond is introduced into the norbornane skeleton.
Isomérie Conformationnelle autour de la Liaison Carbone–Carbone dans les Sels de Propénylylidène Ammonium
Authors: Filleux‐Blanchard Marie‐Louise , Le Botlan Denis 
Published: May 2005

AbstractL'étude par RMN protonique à des températures comprises entre −90 et 70 °C des sels de propenylylidène ammonium met en évidence la présence de deux conformères. L'examen des déplacements chimiques et constantes de couplage est an faveur d'une isomérie conformationnelle autour d'une liaison carbone–carbone, hypothèse corroborée par les résultats obtenus par spectrographie 13C. Les enthalpies libres d'activation sont données pour divers substituants.
13C, 13C coupling constants and 13C chemical shifts of aromatic carbonyl compounds. Effects of ortho‐ and peri‐interactions involving the carbonyl substituent
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractCarbon‐13 n.m.r. data have been determined for a series of 26 aromatic carbonyl compounds including benzoyl, naphthoyl and pyrenoyl derivatives 13C labelled in the carbonyl group. Doubly labelled anthraquinone has also been included. The compounds investigated comprise non‐hindered molecules and molecules in which the carbonyl substituent is subject to ortho‐ or peri‐interactions affecting conjugation of the carbonyl group with the aromatic ring. The dependence of long range 13C,13C coupling constants involving the carbonyl carbon, in particular 2J and 3J, on steric conditions is discussed, as is the possibility of deciding on the orientation of the carbonyl bond. The following results have emerged. 2J(s‐t)>2J(s‐c) for ketones and aldehydes, and the reverse is valid for acids and acid derivatives. (s‐t and s‐c refer to the orientation of the CO group relative to the aromatic bond in question with respect to the connecting single bond). For ketones 3J(t,s‐c)<3J(t,s‐t), and both of these 3J(t) values decrease with increasing angle of twist, θ, about the single bond, whereas 3J(c,s‐c) increases with θ. For acids and acid derivatives no similar regularity was found. (The initial t and c refer to the geometry of the three‐bond coupling path). Generally it is found that 3J(t)>3J(c) and 3J(t)>2J, confirming earlier results. Theoretical calculations on a few model compounds are qualitatively in accordance with the experimental results. Some sign determinations for coupling constants are presented. A short discussion is given of substituent effects on chemical shifts. Observed trends are consistent with earlier results.
Benzo‐ and indoloquinolizines. XII—carbon‐13 n.m.r. study of the conformation of the 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9a H‐pyrido[1,2‐f]phenanthridine isomers
Authors: Van Binst G. , Laus G. , Tourwé D. 
Published: May 2005

AbstractThe influence of the configuration and the conformation on the 13C n.m.r. spectrum of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f] phenanthridine was investigated. These observations, coupled with the low temperature spectrum allowed us to confirm the trans‐syn‐cis as the preferred conformation for one of the four isomers. At −40°C, 2–3% of another conformer could be detected and identified as the cis‐anti‐cis‐2.
1H and 13C studies of alkenes, epoxides and cyclic thionocarbonates
Authors: Hevesi L. , Nagy J. B. , Krief A. , Derouane E. G. 
Published: May 2005

Abstract1H and 13C chemical shift data are presented and discussed for a number of di‐ and tri‐alkyl substituted alkenes, epoxides and thionocarbonates. The completely stereospecific interconversion of these compounds, together with the n.m.r. data, allows a straightforward and quantitative stereochemical analysis. For 1H n.m.r., the most useful intermediates proved to be the thionocarbonates. The differential shieldings between cis and trans isomers are tentatively explained in terms of the conformational change of the 5‐membered thionocarbonate ring. In 13C n.m.r., either series can be useful to distinguish between stereoisomers. The conclusions stemming from the 13C n.m.r. results complement the 1H n.m.r. studies.
Conformational study of phosphoserine in aqueous solutions. II—1H n.m.r. results
Authors: Pogliani L. , Ziessow D. , Krüger Ch. 
Published: May 2005

AbstractThe 270 MHz n.m.r. spectra of phosphoserine (PSer) have been measured and completely analysed for seven pD values. The resulting vicinal coupling constants 3J(HαHβ) and 3J(PHβ) are used to discuss the conformations of PSer with respect to the (Hα)CαCβ(O) and (Cα)CβO(P) bond axes. The all‐trans conformer predominates for all pD values, with its fractional population being minimal at pD values close to neutrality. The CβO bond rotamer populations agree reasonably well with those obtained from 13C investigations.
1H and 31P n.m.r. spectra of the arylsulphonylamides of some chiral or prochiral organophosphoric acids
Authors: Barabás A. , Popescu R. , Mureşan V. , Almási L. 
Published: May 2005

Abstract1H and 31P n.m.r. spectra recorded for arylsulphonylamides of several organophosphoric acids confirmed the expected molecular formulae. Geminal methylenic protons of the arylsulphonylamides of diethylthiophosphinic acid, of ethoxyethanethiophosphonic acid, of ethoxycyclohexanephosphonic acid, of ethoxybenzenethiophosphonic acid and the tautomeric N‐methylated or S(or O)‐methylated derivatives are diastereotopic, showing different chemical shifts and different coupling constants to neighbouring nuclei.
The structure of 1,2‐dithioles studied by 13C n.m.r. spectroscopy
Authors: Frandsen Erik G. , Jacobsen Jens P. 
Published: May 2005

AbstractThe charge separation between the dithiole ring and oxygen in 3‐(1′,2′‐dithiole‐3′‐ylidene)‐6‐methyl‐2,3‐dihydropyran‐2,4‐diones and 3‐(1′,2′‐dithiole‐3′‐ylidene)‐2,3‐dihydrobenzo[b] pyran‐2,4‐diones has been determined by 13C and 19F n.m.r. spectroscopy. By both methods it is found that these compounds are relatively polar. A correlation is established between the 13C chemical shift of some carbon atoms and the S2p binding energies measured by e.s.c.a. in the 1,2‐dithiole derivatives. This correlation shows that these 13C shifts depend on the positive charge taken by the 1,2‐dithiole ring and can then constitute a convenient evaluation of this charge.
Equation de Karplus et l'Hybridation du Carbone. Correlation de la Constante de Couplage Vicinale 3J(Hi, Hj) et la Somme de Constantes de Couplages 1J(C, H)
Authors: Jankowski K. 
Published: May 2005

AbstractL'hybridation de carbone affecte la constante de couplage vicinale 1H1H. La constante de couplage directe 13C1H a été utilisée pour faire la corrélation de l'équation du type Karplus. Le terme correctif de cette équation a été proposé.
Carbon‐13{1H} Off‐Resonance Rauschentkopplung
Authors: Roth Klaus 
Published: May 2005

AbstractDie 13C{1H} Off‐Resonance Rauschentkopplung (ORND) kann nicht nur zur Identifizierung von Signalen quartärer Kohlenstoffatome herangezogen werden: scharfe Signale für sekundäre Kohlenstoffatome treten auf, wenn die beiden direkt gebundenen Protonen chemisch äquivalent sind. Bei chemisch nichtäquivalenten Protonen steht die Linienbreite des 13C‐Signals mit der Differenz der chemischen Verschiebungen beider Protonen im linearen Zusammenhang. Die ORND‐Entkopplungstechnik wird an einigen Beispielen demonstriert.
Calculation of some fluorine nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A. 
Published: May 2005

AbstractThe 19F screening constants and their anisotropies have been calculated for 50 fluorine molecular environments. The calculations have been performed within a framework in which gauge‐dependent atomic orbitals are used in the molecular orbital description. Calculations employing both INDO and CNDO/S standard parameterizations are reported. The molecules considered include simple binary fluorides and fluorocarbons. Both sets of calculations provide reasonable accounts of the 19F screening data for the binary fluorides. The presence of electric field effects in the aliphatic fluorocarbons are not accounted for by the present calculations. In the conjugated fluorocarbons the gross 19F chemical shift trend is reproduced except for ortho fluorines where electric field contributions are significant. The most highly screened component of σ is calculated to lie along the CF bond of various fluorobenzenes but perpendicular to the plane of 4,4′‐difluorobiphenyl, in agreement with experiment.
I. Etude de l'Influence de la Nature et de l'Orientation d'un Substituant sur les Constantes de Couplage en Série Tertiobutyl‐4 Cyclohexanonique par RMN à Haut Champ
Authors: Grenier‐Loustalot M. F. , Lectard A. , Lichanot A. , Metras F. 
Published: May 2005

AbstractNous avons enregistré les spectres RMN 1H de six α‐halogéno tertiobutyl‐4 cyclohexanones (composés 2 à 7) afin d'examiner les variations des constantes de couplage (2J, 3J, 4J) en fonction de la nature, la position, l'orientation et le nombre de substituants (CO, Cl, tBu). Les résultats observés sont interprétés en termes de déformations géométriques ou d'effets de substituants.
Bandshape analysis with internal resolution standard. Barriers to internal rotation in 3,5‐dimethyl‐4‐(N,N‐dimethylthio‐carbamoyl)pyrazoles
Authors: Berg U. , Karlsson S. , Sandström J. 
Published: May 2005

AbstractThe barriers to rotation of the dimethylamino group in a series of 4‐N,N‐dimethylthiocarbamoylpyrazoles have been determined by the 1H n.m.r. technique. For one of the compounds the rate constants have been determined over a temperature interval of 113 degrees by monitoring the exchange rate in the fast and slow exchange regions by the intensity of the resonances of the exchanging protons relative to an internal reference signal, and in the intermediate region by the conventional complete bandshape technique. The entropy and enthalpy of activation have been calculated, and the values obtained by the intensity method are in reasonable agreement with those obtained by the complete bandshape analysis. For the other compounds the usual coalescence approximation has been used. The thiocarbamoylpyrazoles were prepared by reaction between N,N‐dimethyl‐α,α‐diacetylthioacetamide and the appropriate hydrazines.
Unterscheidung enantiotoper/diastereotoper Protonen und regioselektive Spinentkopplung in metallorganischen Komplexen mit Hilfe von Shiftreagenzien
Authors: Kläui Wolfgang , Neukomm Heinrich 
Published: May 2005

AbstractDimethylphosphonat HP(O)(OCH3)2 und die Dimethylphosphonat‐Komplexe [(C5H5)MX{P(O)(OCH3)2}{P(OCH3)3}] (M = Co, Rh; X = I; CH3), [(C3H5) Co{P(O)(OCH3)2}2{P(OH)(OCH3)2}] und [(C5H5)Ni{P(O) (OCH3)2}{P(OCH3)3}] werden 1H‐NMR spektroskopisch untersucht. Es wird gezeigt, dass sich die enantiomeren Formen von [(C5H5)MX{P(O)(OCH3)2}{P(OCH)3)}] in Gegenwart des chiralen Shiftreagens Eu(tfc)3 getrennt beobachten lassen. Man findet einen starken Einfluss des Substituenten X auf die Unterscheidbarkeit der diastereotopen Phosphonat‐Methoxylgruppen in [(C5H5)MX{P(O)(OCH3)2}{P(OCH3)3}]. Die enantiotopen Phosphonat‐Methoxylgruppen in HP(O)(OCH3)2 werden durch Wechselwirkung mit Eu (tfc)3 unterscheidbar. Die gleichen Gruppen in [(C5H5)Ni{P(O)(OCH3)2}{P(OCH3)3}] werden durch Zugabe von Eu(tfc)3 von 31P entkoppelt. Der entkoppelt. Der komplex [(C5H5)Co{P(O)(OCH3)2}2P(OH)(OCH3)2}] reagiert als Chelatligand mit Eu(tfc)3 unter Freisetzung von tfcH.
N.m.r. studies of the keto–enol tautomerism of acylthioacetamides
Authors: Klose G. , Ludwig E. , Uhlemann E. 
Published: May 2005

AbstractAcetylthioacetamides exist as different keto and enol isomers in chloroform solutions. The keto form with intramolecular hydrogen bonding between the NH and the carbonyl group is the dominant keto isomer. On the other hand the enol forms with intramolecular hydrogen bonding between the OH and the thioketo group are the dominant enol isomers in the temperature range 60°C to −60°C. The thermodynamic data of the keto‐enol equilibria were obtained by measuring the intensities of appropriate high resolution proton signals as a function of temperature. At low temperatures all lines characteristic of the enol forms are doubled in the N‐phenyl‐substituted derivatives because the rotation of the NHC6H5 group around the CN bond becomes slow and the chemical shifts characteristic of the E and Z isomers are different. We estimated approximate thermodynamic data of the E/Z equilibrium in some of the compounds. The changes of the line shape as well as the chemical shifts as a function of temperature indicate the presence of various additional exchange processes. In order to obtain further information we performed curve fittings of the chemical shifts of one acetylthioacetanilide and of a series of monothio‐β‐diketones (studied in another paper) assuming a fast two site exchange process. On the basis of the results obtained a reaction scheme for N‐substituted acylthioacetanilides in solution is proposed.
A case of negative homoallylic coupling constants: 3‐cyclopentenone
Authors: Lemarié B. , Ripoll J. L. 
Published: May 2005

AbstractThe 1H n.m.r. spectrum of 3‐cyclopentenone has been analysed and all (except the geminal) HH couplings obtained with their signs. The results are compared (i) with those obtained previously for the derivatives of cyclopentene and (ii) with those calculated by CNDO/2 and INDO finite perturbation methods. The coupling constants are discussed in order to define the factors contributing to the couplings.
13C19F spin–spin coupling in some monofluoro‐substituted polycyclic aromatic hydrocarbons
Authors: Hansen P. E. , Berg A. , Jakobsen H. J. , Manzara A. P. , Michl J. 
Published: May 2005

AbstractThe determination and complete assignment of the 13C19F coupling constants and 13C chemical shifts for 15 monofluoro derivatives of nine polycyclic aromatic hydrocarbons are reported. Fluorine substitutent effects on the 13C chemical shifts are given and their regular behaviour, making comparisons between different compounds possible, is discussed. The numerical values of the 13C19F long range coupling constants are found, with a few exceptions, to decrease in an alternating manner along the periphery of the molecules. In several cases the signs of the coupling constants have been determined. It appears that the signs alternate, but additional evidence is required. The magnitudes of different types of coupling constants are discussed in terms of steric and electronic effects. CNDO/2 and INDO calculations of the 13C19F coupling constants in the fluoronaphthalenes have been performed using the ‘sum‐over‐states’ method with the aim of examining the orbital and spin–dipole contributions to the various couplings.
N.m.r. characterization of functional groups: 5—on the nature of olefinic end groups in polyisobutylenes
Authors: Manatt Stanley L. , Ingham John D. , Miller Joseph A. 
Published: May 2005

AbstractProton n.m.r. signals for two types of olefinic end groups, ‐CH2C(CH3)CH2 (δ4.68 and δ4.87) and ‐CHC(CH3)2 (δ5.21), have been observed in high molecular weight polyisobutylenes. Comparable amounts of both these end groups exist in commercial and laboratory prepared samples of polyisobutylenes contrary to previous reports that the former group is by far predominant. That different catalysts produce different relative concentrations of these end groups is demonstrated. Evidence for the presence of a third type of unsaturation from the ‐CH2C(CH2)CH2‐ structure is discussed.
Etude en RMN du carbone 13 de dicoumarols substitués
Authors: Convert Odile , Deville Catherine , Godfroid Jean‐Jacques 
Published: May 2005

AbstractLes spectres de RMN en 13C des dicoumarols substitués sur le carbone du pont sont interprétés dans le but d'obtenir des informations structurales pour des relations structure‐activité quantitatives. Les résultats sont en accord avec ceux obtenus en RMN du 1H: ces dicoumarols présentent une double rotation restreinte autour des liaisons du pont.
Détermination du Site de Protonation de l'Azido‐2 thiazole et du Thiazolo[2,3‐e]tétrazole à Partir de la Largeur des Raies des Signaux Protoniques
Authors: Faure R. , Galy J.‐P. , Vincent E.‐J. , Elguero J. 
Published: May 2005

AbstractLes signaux des protons fixés sur un atome de carbone en α d'un azote pyridinique en série thiazole et en γ en série thiazolo[2,3‐e]tétrazolique sont élargis à cause de la présence d'atomes d'azote 14N; cet élargissement disparait par irradiation, par refroidissement et en milieu acide (dans ce cas, cela permet la détermination du site de protonation des deux molécules).
Concerning carbon‐13 n.m.r. spectroscopy of 5β‐hydroxylated phytoecdysones
Authors: Krepinsky J. , Findlay J. A. , Danieli B. , Palmisano G. , Beynon P. , Murakami S. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of the 5β‐hydroxylated phytoecdysones polypodine B, muristerone A and kaladasterone are presented and briefly discussed together with the spectrum of makisterone A. Comparisons with previously reported spectra of ecdysone, ecdysterone and poststerone are made and allow a correction for the C‐20/C‐24 assignment for ecdysone.
A general purpose n.m.r. microcell system suitable for volatile, air sensitive and toxic samples
Authors: Al‐Rawi Jassim M. A. , Bloxsidge James P. 
Published: May 2005

AbstractA microcell system that is convenient to fill and which can be evacuated and/or filled with gas or vapour has been developed for handling tritiated n.m.r. samples and has subsequently proved to have a more general application. A 3 mm tube, after the removal of a 5 mm filling extension, is sleeved into a 5 mm n.m.r. tube or used directly in a reduced diameter probe.
Calculation of the nitrogen screening constants of some N‐heterocycles
Authors: Ebraheem K. A. K. , Webb G. A. , Witanowski M. 
Published: May 2005

AbstractAbsolute nitrogen screening constants and chemical shifts of some N‐heterocycles are calculated within the CNDO/S level of approximation to Pople's model. Satisfactory agreement between calculated and observed nitrogen chemical shifts is obtained in most cases. The application of the results to the study of tautomeric equilibria is discussed. ‘Pyridine‐type’ nitrogen chemical shifts are dominated by n → π* transitions together with significant contributions from π → σ* and σ → π* transitions whereas the latter two are the dominant ones for ‘pyrrole‐type’ nitrogen nuclei.
1H and 13C n.m.r. study of butatriene‐bis‐tricarbonyliron complexes. Assignment of geometric orientation by comparative J(CCCH) values
Authors: Victor Rae , Ringel Israel 
Published: May 2005

AbstractA number of substituted butatriene‐bis‐tricarbonyliron complexes have been studied by 13C and 1H n.m.r. spectroscopy. Long range coupling values, J(CCCH), have confirmed chemical shift results that methyl and phenyl groups assume opposite orientations at the coordinated double bonds with the methyl group preferentially trans to carbon and the phenyl group preferentially trans to iron.
The proton spectrum including 13C‐satellites of π‐benzenechromium tricarbonyl in a nematic solvent
Authors: Diehl P. , Kunwar A. C. 
Published: May 2005

AbstractThe proton spectrum of π‐benzenechromium tricarbonyl with 13C‐satellites due to ring‐ and carbonyl‐carbons at natural abundance has been investigated in a nematic solvent. The structural data are found to be in agreement with those from electron and neutron diffraction measurements. The proton–proton indirect coupling constants have also been determined.
Time‐dependence of the polarized intensity ratio in CIDNP investigations
Authors: Kende Imre 
Published: May 2005

AbstractThe time‐dependence of the polarized intensity ratio within a product molecule has been studied by a kinetic method. The kinetic analysis of polarized product formation shows that considerable changes in CIDNP ratios occur during the reaction but characteristic curves can be obtained under different experimental conditions. A method is proposed to evaluate the relative enhancement coefficients on the basis of these characteristic curves, and to obtain information on the kinetics of the reaction.
Proximity and the heteroatom effects on the carbon‐13 chemical shifts of methyl‐substituted phenols, anilines and thiophenols
Authors: Netzel Daniel A. 
Published: May 2005

AbstractUpfield substituent‐induced 13C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH3 (X = CH3, NH2, OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A −2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a −3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The 13C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair‐interaction term associated with the through‐space electronic influence of the heteroatom.
ESR study of N‐acyl‐N‐alkyl nitroxide radicals from photolysis of N‐nitrosoamides
Authors: Flesia Elio , Surzur Jean‐Marie , Tordo Paul 
Published: May 2005

AbstractA new method of generation of N‐acyl‐N‐alkyl nitroxide radicals by photolysis of N‐nitrosoamides is described. ESR parameters are reported for 17 radicals of the general formula RCON(R′)O.; the high resolution obtained allows conformational analysis which shows a preferred trans conformation around the CON bond and hindered rotation around the NR′ σ‐bond.
Long range substituent‐induced chemical shifts in the 13C NMR spectra of N‐benzylidenebenzylamines
Authors: Arrowsmith John E. , Cook Michael J. , Hardstone David J. 
Published: May 2005

AbstractCarbon‐13 chemical shifts for N‐benzylidenebenzylamines are affected by substituents up to eleven bonds away from the substituent group. The data correlate well with Hammett constants.