bluuebunny/crossref_metadata_2025_split huggingface dataset:
Etude en RMN de l'Association des Sels de Lanthanides avec des Phénols; Application à la Détermination de Structure de Polyphénols Naturels
Authors: Davoust Daniel , Massias Marcel , Molho Darius , Platzer Nicole , Basselier Jean‐Jacques 
Published: May 2005

AbstractL'interaction des sels de lanthanide avec des phénols en solution dans le DMSO a été étudiée en RMN en vue de la détermination de structure de polyphénols naturels. Par des expériences de compétition intermoléculaire, il a étée possible de mettre en évidence des différences de réactivité en fonction de la nature et de la position des substituants. Des règles empiriques de réactivité ont été proposées; elles ont permis d'interpréter les variations de déplacements chimiques observées dans le spectre de RMN de polyphénols naturels (flavones, xanthones) en présence de sel de lanthanide.
The 13C, H coupling constants in structural and conformational analysis. III.. Long‐range carbon–hydroxyl proton couplings as evidence of hydrogen bonding in some acylphloroglucinols
Authors: Äyräs Pertti , Widén Carl‐Johan 
Published: May 2005

AbstractProton coupled 13C NMR spectra have been recorded for some acylphloroglucinol derivatives. Significant couplings over two, three and four bonds were observed between the hydroxyl proton and aromatic carbons for those compounds where the hydroxyl group is hydrogen bonded strongly enough to the carbonyl carbon of the acyl side chain. Typical values were 2J = 4.8 Hz, and 3J = 5.6 Hz or 6.7 Hz corresponding to dihedral angles of c. 0° and c. 180°, respectively; the dihedral angle is defined as the angle between the O—H bond and the plane of the aromatic ring. A stereospecific 4J(COH) value of 1.2 Hz for a ‘W’ arrangement of coupled atoms was also found. An interesting example of ‘virtual’ J(CH) coupling was observed in the proton coupled spectrum of 1‐butyrylphloroglucinol 2‐monomethyl ether in acetone‐d6 caused by the accidentally equal chemical shifts of the two ring protons.
Stereochemical aspects of proton chemical shifts. VII. The γ effects of hydroxyl, methoxyl and methyl substituents
Authors: Tavernier Dirk , Anteunis Marc J. O. 
Published: May 2005

AbstractThe 1H NMR chemical shifts of some hydroxy, methoxy or methyl substituted trans‐decalins, trans‐1, 3‐dioxadecalins and cyclohexanes are reported. It is concluded that the replacement in a g+g+ HCCCH fragment of one hydrogen by hydroxy, methoxy or methyl results in a modest (0.1 ppm) upfield shift of the other hydrogen atom. Experimental limitations to the transferability of shift increments from one molecular environment to another are demonstrated. The syntheses of 1α,5β‐dimethoxy‐ and 1β,5α‐dimethoxy‐trans‐decalin are given.
Determination of pKa values using 15N and 13C nuclear magnetic resonance spectroscopy. The case of apramycin
Authors: Paschal Jonathan W. , Dorman Douglas E. 
Published: May 2005

AbstractBy comparison of pKa values derived from 15N and 13C nuclear magnetic resonance (NMR) spectroscopies, the assignment of the 15N resonances of apramycin is completed. 13C NMR spectra appear to provide accurate pKa determinations with this aminoglycoside. Hydroxylation adjacent to one of the basic nitrogens of apramycin appears to change the pKa values of all five amines of the molecule.
Etude par RMN 13C d'Hydrocarbures Benzéniques Tricycliques Condensés
Authors: Gobert F. , Gruber R. , Cagniant D. , Cagniant P. 
Published: May 2005

AbstractQuelques benzocyclènes tricycliques ont été étudiés en RMN i3C. Il a été montré que les perturbations dues à l'interaction des deux cycles semiaromatiques restaient localisées aux carbones quaternaires.
Détermination par Résonance Magnétique Nucléaire de la Configuration d'alcools Bicycliques [4.2.0] et Tricycliques [6.4.0.02,7] ou [5.4.0.02,6]
Authors: Bouquant James , Chuche Josselin , Convert Odile , Furth Bernard 
Published: May 2005

AbstractLes configurations d'une série de bicyclo[4.2.0]octanols sont déterminées par résonance magnétique nucléaire du proton en présence d'un réactif lanthanidique [Eu(dpm)3]. La détermination des paramètres intrinsèques des adduits formés entre les réactifs et ces substrats a permis de dégager un certain nombre de critères d'attribution des stéréochimies. De plus, cette étude met en évidence, contrairement à ce qui est généralement admis, que la constante de couplage vicinale trans entre les protons cyclobutaniques peut ětre supérieure à celle entre protons cis. Les attributions des configurations sont confirmées par une étude en 13C. En se basant sur les résultats précédents, il est possible d'établir sans ambiguïté les configurations de tricyclo[6.4.0.02,7]dodécanols et tricyclo[5.4.0.02,6]undécanol.
Effet de Solvant en Résonance Magnétique Nucléaire du Carbone‐13. V. Autoassociation des Cétones Aliphatiques et Alicycliques Saturées
Authors: Tiffon Bernard , Dubois Jacques‐Emile 
Published: May 2005

AbstractL'influence de l'autoassociation en phase liquide de 15 cétones sur la constante d'écran en RMN du carbone du carbonyle est déterminée. On montre que le terme de constante d'écran correspondant ne dépend que du moment dipolaire et du volume molaire de la cétone, que celle‐ci soit aliphatique ou alicyclique. La distance moyenne séparant les deux carbonyles dans le modèle d'association bimoléculaire où les deux dipǒles sont antiparallèles est évaluée. Cette distance croǐt avec l'encombrement des substituants de 3,1 Å pour l'acétone à 4,75 Å pour la cétone encombrée C(Et)3COC(Me2tBu) pour laquelle l'effet de l'autoasssociation est encore important. Les cyclanones s'inscrivent dans ce modèle mais présentent un effet d'autoassociation plus marqué que les cétones aliphatiques ayant le měme nombre de carbones.
Applications of NMR spectroscopy of chiral association complexes. 6. rotation about the C(sp2)—C(aryl) bond in 2,6‐disubstituted pivalophenones
Authors: Holík Miroslav , Mannschreck Albrecht 
Published: May 2005

AbstractFor the investigation of the barrier to rotation about the C(sp2)—C(aryl) bond in non‐planar pivalophenones five derivatives were prepared and their 1H and 13C NMR spectra assigned. Methyl and bromine groups in the 3‐position have opposite substituent effects on the chemical shifts of the 1H and 13C signals of Me2 and Me4. The ΔG values were determined from the coalescence temperatures of the signal splittings generated by the addition of optically active shift reagents. The accuracy of this method was estimated by using different signals of 3‐bromo‐2,4,6‐trimethylpivalophenone and by computer simulation of the line shape. A buttressing effect of substituents in the aromatic ring was observed. A change of the twist angle by the substitution of methyl by bromine in the tert‐butyl group was suggested in order to explain the changes in ΔG and the chemical shifts.
Carbon‐13 magnetic resonance studies of cyclic compounds. 2. Carbon‐13 chemical shift parameters for equatorial and axial substituents in cyclohexane: The substituents methyl, ethyl, isopropyl, methoxy and phthalimido
Authors: Booth H. , Everett J. R. , Fleming R. A. 
Published: May 2005

AbstractCarbon‐13 chemical shift parameters for equatorial and axial substituents in cyclohexane are reported for methyl, ethyl, isopropyl, methoxy and phthalimido substituents. The usefulness of the alkyl parameters is demonstrated by the agreement between calculated and observed 13C shifts for trans‐1,4‐dialkylcyclohexanes (alkyl = Me, Et, i‐Pr) and for both conformations of cis‐1,4‐dialkylcyclohexanes (alkyl = Me, Et, i‐Pr).
13C NMR of polycyclic aromatic compounds. A review
Authors: Hansen Poul Erik 
Published: May 2005

AbstractThe analysis of the 13C NMR spectra of polycyclic aromatics is discussed briefly. Basic trends of chemical shifts are mentioned, but the emphasis is placed on substituent‐induced chemical shifts (SCS). Semi‐empirical approaches and regressional analysis are treated. The factors controlling SCS are discussed and steric, mesomeric and π‐inductive effects are analysed.CH, CF, CC, CP and C, Metal coupling constants are investigated and the influence of steric effects, bond order, mesomerism and angle distortions in relation to some of these coupling constants is discussed. Relaxation times are described in a series of compounds. The effects of dissolved oxygen or radicals are shown and the use of T1 as a monitor of molecular tumbling is depicted. The impact of 13C NMR on the understanding of charged aromatic species, both positive and negative ions, is mentioned and new information about reaction intermediates in electrophilic aromatic substitution is outlined. The possibility of using 13C NMR to investigate charge transfer complexes is also discussed. Among other subjects treated are automerization, deuterium exchange and biosynthetic incorporation of labelled materials and, finally, quantitative analysis is briefly touched upon.
Sur la Similitude des Déformations du Noyau Cyclohexanonique Induites par les Groupes Tertiobutyle et gem‐Diméthyle
Authors: Grenier‐Loustalot M. F. , Iratçabal P. , Lichanot A. , Metras F. 
Published: May 2005

AbstractL'étude par RMN á 250 MHz de six chlorodiméthyl–4,4 cyclohexanones et la connaissance de deux structures cristallines permettent les conclusions suivantes: dans les séries des tertiobuty–4 et diméthyl–4,4 cyclohexanones l'influence du carbonyle et du chlore sur les constantes de couplage 2J et 3J sont similaires. Par ailleurs, les groupes gem diméthyle et tertiobutyle induisent sur le noyau cyclohexanonique des constantes de couplage 4J(H–3′–C–3–C–4–C–4–C–5–H–5′) fortes et semblables; ces observations s'interprétent bien en termes de deformation locale de structure et d'additivité de ces déformations. La détermination d'angles diédres parla méthode de Lambert et par diffraction des rayons X montre, d'une part, une bonne transférabilité des structures de l'état solide á l'état dissous, confirme, d'autre part, la trés grands similitude structurale des dérivés tertobutylés et gem diméthylés de la cyclohexanone.
Unusual carbon shielding effects of cyclopropanes and double bonds in strained bicyclo[3.1.0]hexanes and cyclopentenes
Authors: Christl Manfred , Herbert Rainer 
Published: May 2005

AbstractCarbon‐13 shieldings and one‐bond 13CH coupling constants of bicyclo[2.1.1]hexane, bicyclo[2.1.1]hex‐2‐ene, tricyclo[3.1.1.02,4]heptane and benzvalene are presented and compared to the data of related compounds. If a bicyclo[3.1.0]hexane system is part of a rigid skeleton, the cyclopropane ring exerts specific γ substituent effects of two kinds. In the case of the bicyclohexane boat form an upfield shift of the C‐3 signal is observed and in the case of the chair form a downfield shift of 15–20 ppm. Compared to the corresponding cyclopentanes the double bond in strained cyclopentenes causes downfield shifts of the C‐4 absorption. This effect increases with increasing strain, reaching a 45.9 ppm maximum in benzvalene. Hence it is the only known bicyclo[1.1.0]butane having a reversed order of carbon shieldings. The downfield shifts are explained by means of simple orbital interaction schemes.
INDO‐FPT calculations of the dihedral angle dependence of 1J(CH) in groups adjacent to a cationic carbon atom
Authors: Pachler K. G. R. , Pachter R. 
Published: May 2005

AbstractINDO‐FPT calculations of 1J(CH) in the hypothetical ethyl cation are presented in support of a recently derived empirical relationship which describes the effect of a cationic carbon on 1J(CH) in an adjacent CHn group.
13C‐NMR‐Untersuchungen zur Strukturaufklärung von Polysacchariden und deren Methylderivaten
Authors: Friebolin H. , Keilich G. , Frank N. , Dabrowski U. , Siefert E. 
Published: May 2005

AbstractDie 13C‐NMR‐Spektren einer Reihe von Polysacchariden und ihrer Methylderivate wurden aufgenommen, zugeordnet und für die methylierten Polysaccharide außerdem die Kopplungskonstanten 1J(CH) bestimmt. An Beispielen wird gezeigt, daß die Zahl der 13C‐Signale und deren Lage im Spektrum Aussagen über den Aufbau der Polysaccharide, sowie über die Verknüpfungsstellen der glykosidischen Bindung gestatten. Während aus den Signallagen die anomere Konfiguration nicht eindeutig zu ermitteln ist, gelingt dies bei den methylierten Polysacchariden mit Hilfe der Kopplungskonstanten 1J(C‐1, H); diese weisen Unterschiede von durchschnittlich 12 Hz (aber mindestens 5 Hz) zwischen den α‐ und β‐Anomeren auf, wobei die gröβeren Werte den α‐Anomeren entsprechen.
Application de la Résonance Magnétique de l'Azote 15 à l'Etude de la Délocalisation Electronique dans les Anilines, Aminopyridines et Enamines
Authors: Dorie Jean , Mechin Bernard , Martin Gérard 
Published: May 2005

AbstractLa spectrososcopie 15N en abondance naturelle a été appliquée à l'étude de la délocalisation électronique dans des anilines ortho, méta et para substituées. Les relations qui permettent d'estimer le degré de délocalisation électronique de la paire libre de l'atome d'azote (en unités de ΔG≠T) à partir de δ 15N, ont été étendues aux amino‐pyridines, ‐pyrimidines et à quelques nucléosides. La cohérence des résultats obtenus dans la série des anilines (et énamines) a été vérifiée par comparaison avec les données d'une étude antérieure réalisée sur les amides et composés analogues. Les données de la spectros copie 15N permettent ainsi d'établir des échelles de délocalisation électronique dans de nombreuses séries de composés azotés.
Ring inversion in a substituted 3,4‐dihydro‐2H‐thiopyran
Authors: Brunskill John S. A. , De Asish , Ewing David F. 
Published: May 2005

AbstractActivation parameters have been determined for ring inversion in a 3,4‐dihydro‐2H‐thiopyran and this system has been compared with analogous 6‐membered ring systems.
Etude en RMN: Couplages a Longue distance dans les Perfluoro‐alkyl‐1 Dihydro‐3,4 Isoquinoléines et Perfluoro‐alkyl‐1 Isoquinoléines
Authors: Pastor R. E. , Cambon A. R. , Musso J. 
Published: May 2005

AbstractDans l'étude en RMN du proton et du fluor des perfluoro‐alkyl‐1 dihydro‐3,4 isoquinoléines et perfluoro‐alkyl‐1 isoquinoléines, nous avons pu observer de nombreux couplages à longue distance. Outre le couplage homoallylique avec les protons méthyléniques en 3 dans les perfluoro‐alkyl‐1 dihydro‐3,4 isoquinoléines et le couplage interbenzylique en 7J avec les groupements méthyles en 4 dans perfluoro‐alkyl‐1 méthyl‐4 isoquinoléines, les fluors α des chaines perfluoro‐alkyles sont couplés avec les protons H‐8 dans tous les composés étudiés. Ce dernier type de couplage en5J entre un proton aromatique et un atome de fluor est mis en évidence pour la première fois. Les divers types de couplages à longue distance ont pǔ ětre expliqués par des considérations d'ordre géométrique, stérique et électronique.
Geometrical isomerism and 13C spectra of the β‐substituted Enones R1C(1)OC(2)HC(3)HR2
Authors: Kozerski Lech , Kamieńska‐Trela Krystyna , Kania Lidia 
Published: May 2005

AbstractThe 13C chemical shifts of the unsaturated carbons were measured in 31 cis and trans pairs of β‐substituted enones R1C(1)OC(2)HC(3)HR2. In these polarized ethylenes the chemical shifts of the olefinic carbons are simply related by the equation δc=δt+A. The steric and electronic effects introduced by the R1 and R2 substituents influence the chemical shifts of C‐2 and C‐3 in both isomers. It is shown that the sign and magnitude of the intercept A mainly reflect the π‐charge electronic density changes which arise in the cis isomer and are transmitted via the π‐framework. The effect of the steric interaction on the chemical shift of C‐3 in the cis isomers is postulated to be related to the symmetry of the substituents. Therefore, the differential shielding of C‐3 is indicative of the conformational structure of the cis molecule.
Carbon‐13 magnetic resonance: γ‐anti substituent effects
Authors: Forrest T. P. , Webb J. G. K. 
Published: May 2005

Abstractγ‐anti Substituent effects of the first row elements (CH3, NH2, OH, F) and the higher‐row halogens on 13C chemical shifts are shown to have separate linear relationships with element electronegativity. The halogens generally show an increasing upfield shift with increasing electronegativity, but the response of the effect of the first‐row elements to changing electronegativity is dependent upon the substitution pattern of the atoms involved. In molecules with the substituent at a bridgehead, increasing electronegativity causes increasing downfield shift of the γ‐anti carbon, whereas in other systems which have the substituent at a secondary carbon, increasing electronegativity causes an increasing upfield shift. Examples are cited to show that the γ‐anti effect of a hydroxyl group is more shielding (by about 2 ppm) when a 1,3‐diaxial interaction between an α and a γ hydrogen is present, than when this interaction is removed by replacement of either of the hydrogens. This correlation is taken as evidence of this hydrogen‐hydrogen interaction as one pathway for the transmission of the γ‐anti substituent effects of first‐row elements.
Contribution of the trityl group to magnetic asymmetry in N‐trityl amino acid benzyl esters
Authors: Matsoukas J. , Theodoropoulos D. 
Published: May 2005

AbstractThe magnetic nonequivalence of the O‐methylene protons of certain N‐trityl amino acid benzyl esters is reported. It is shown that magnetic asymmetry arises from hindered internal rotation of the α‐benzyl group. The degree of proximity of the bulky N‐trityl to the α‐benzyl group, and consequently the degree of free rotation of the latter, is dependent on the nature of the amino acid side‐chain R.
Chemical shifts for tritons in chlorobenzene, bromobenzene, fluorobenzene and toluene as determined by tritium NMR spectroscopy
Authors: Long Mervyn A. , Lukey Christopher A. 
Published: May 2005

AbstractChemical shifts for tritons in chlorobenzene have been measured in the pure compound and in a dilute solution in cyclohexane using a 64 MHz NMR spectrometer. The order of shifts is o>m>p. Triton shifts in pure bromobenzene, fluorobenzene and toluene have also been measured and the influence of CCl4 solvent on the aromatic triton shifts in toluene explored. Complete resolution of the three aromatic triton positions is achieved in pure toluene, but the ortho and para shifts are not resolved in 25% solution in CCl4.
Tritium labelling of hexamethyldisiloxane for 3H NMR referencing
Authors: Long Mervyn A. , Garnett John L. , Lukey Christopher A. 
Published: May 2005

AbstractTritium labelled hexamethyldisiloxane is a suitable material for the internal referencing of 3H NMR spectra. Such a referencing procedure is necessary where the instrument is not capable of scanning 1H resonance under identical experimental conditions. Hexamethyldisiloxane may be tritiated to high activity (typically 1 Ci ml−1) by Raney nickel catalysed exchange with elemental tritium in a simple one‐step procedure. A variety of heterogeneous catalysts are shown to be inactive in the common labelling method involving exchange with tritiated water.
Carbon‐13 NMR analysis of cyclobutane dimers from benzocycloalkenes
Authors: Browne C. E. , Ruehle P. H. , Dobbs T. K. , Eisenbraun E. J. 
Published: May 2005

Abstract13C NMR Spectra for a series of 11 substituted cyclobutanes derived from photodimerization of benzocycloalkenes were recorded. Comparison of the carbon chemical shifts for the head‐to‐head and head‐to‐tail cis‐syn‐cis and cis‐anti‐cis isomers reveals shielding trends which should facilitate structural and stereochemical assignments for related compounds. The head‐to‐head isomers show a larger separation of cyclobutane carbon resonances than the head‐to‐tail isomers. The cis‐syn‐cis isomers relative to the cis‐anti‐cis isomers exhibit distinctive upfield shifts of all carbon resonances, except those of aromatic carbons ortho to alkyl‐substituted aromatic carbons.
Etude en Résonance Magnétique Nucléaire du Carbone‐13 de N‐Aryl Pyrazolines‐2 Diversement Substituées. Effets de Substituant et Etude Conformationnelle
Authors: Faure Robert , Llinares Jeanine , Vincent Emile‐Jean , Elguero José 
Published: May 2005

AbstractLes déplacements chimiques du carbone‐13 de la phényl‐1 pyrazoline‐2 et de vingt‐cinq N‐nitrophényl pyrazolines‐2, diversement substituées sur l'hétérocycle, ont été complétement attribués. Ces valeurs sont discutées en fonction des contraintes électroniques et stériques des différents substituants. Les effects stériques entrainent des modifications de la conformation aussi bien du groupement nitrophenyle, que du cycle pyrazoline‐2, ce qui explique les variations de certains déplacements chimiques.
13C‐NMR‐Untersuchungen an Steroiden. IV—Substituenteneffekte an 16‐mono‐ und 16,17‐disubstituierten 3‐Methoxyöstra‐1,3,5(10)‐trienen
Authors: Engelhardt Günter , Zeigan Dieter , Schönecker Bruno 
Published: May 2005

AbstractDie 13C‐NMR‐Spektren einiger stereoisomerer 16‐mono‐ und 16,17‐disubstituierter 3‐Methoxyöstratriene (16‐Substituent: OH, Br, N3, NHAc, SCN, SeCN, SH, NCS; 17‐Substituent: OH) wurden aufgenommen und vollständig zugeordnet. Für die 16‐monosubstituierten Verbindungen zeigt sich, daß die durch den 16‐Substituenten induzierten Verschiebungseffekte wietgehend unabhängig von dessen sterischer Anordnung (16α oder 16β) snd und somit zur Konfigurationsbestimmung nicht verwendet werden Können. Die Untersuchung der Substituenteneffekte in den 16,17‐disubstituierten Verbindungen ergibt, daß die vicinale Disubstitution z̀ beträchtlichen Abweichungen von der Additivität besonders für die substituierten C‐Atome führt, die bis nahezu 14 ppm betragen können.
Concerning the chemical shifts of the ring protons of toluene as determined by 1H NMR spectroscopy of deuterated material
Authors: Schaefer T. , Hutton H. M. 
Published: May 2005

AbstractChemical shifts of the ring protons are determined by 1H NMR of 99% deuterated toluene. At low temperatures the deuterons relax rapidly, yielding sharp 1H peaks for the ortho, meta and para protons. These are compared with shifts obtained by other methods.
Solvent and temperature studies of some indenyl‐ and fluorenyllithiums using13C NMR spectroscopy
Authors: Edlund Ulf 
Published: May 2005

Abstract13C NMR spectra of indenyl‐ and fluorenyllithium and some of their methyl substituted derivatives have been obtained. The shielding differentials induced by varying the temperature or coordinating ability of the solvent are discussed in terms of an equilibrium between discrete ion pairs or differences in external solvation. An increase of the coordinating ability of the solvent induces shift differentials of similar signs as those given by lowering the temperature. Methyl substituents close to the cation location are found to have only a minor effect on the observed ion pair ratio but seem to influence the preferred cation position in the tight ion pair structure.
Angular dependence of the vicinal interproton spin–spin coupling in silacyclohexanes. The conformational energy term of the methyl group in 1‐methyl‐1‐silacyclohexane
Authors: Carleer Robert , Anteunis Marc J. O. 
Published: May 2005

AbstractAn approximate Karplus‐Conroy relationship between the vicinal coupling constantsJ(HSiCH) in a silaethane fragment and the corresponding torsional angles τ in silacyclohexanes is proposed. The relationship3J(HSiCH)VSτ is asymmetric. The1H NMR parameters and conformational features ofcis‐ andtrans‐3,5‐dimethyl‐1‐silacyclonexane and 3‐silabicyclo[3.2.1]octane are discussed, and the conformational energy term for the methyl group in 1‐methyl‐1‐silacyclohexane is found to be approximately 1.45 kJ mole−1in favour of the axial position for the methyl group, in good agreement with previously calculated values.