bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic and substituent effects in the ESR spectra of triplet biradical intermediates in lithiation reactions of 2‐alkylbenzotriazoles: A cautionary note
Authors: Dalal Nar S. , Xu Ruixin , Katritzky Alan R. , Wu Jing , Jesorka Aldo 
Published: May 2005

AbstractInvestigations of intermediates generated in the course of lithiation of four 2‐alkylbenzotriazoles revealed largescale temperature‐dependent changes in their ESR spectra. A cautionary observation was that the ESR spectra obtained under synthesis conditions exhibited lineshapes that were assignable to a monoradical, while additional, lower temperature measurements clearly showed the species to be a biradical. The electron–electron dipolar couplings yield an average distance between the two unpaired electrons in the biradical, Rav, of about 5.3 ± 0.16 Å. These Rav values are consistent with the unpaired electrons being localized on the nitrogen atoms of the two benzotriazole moieties in the biradical fragment. This conclusion is supported by oxygen trapping (nitroxide radical formation) studies. The biradicals are shown to have triplets as the ground state with a single‐triplet separation of about 26±4 kJ mol−1.
Influence of skeletal alteration of lignoids on carbon‐13 NMR chemical shifts
Authors: Agrawal Pawan K. , Pathak Ashish K. 
Published: May 2005

AbstractThe characteristic 13C NMR chemical shift ranges as a guide for the establishment of the parent skeletons of various categories and subcategories of lignoids (lignans, neolignans and oxyneolignans) and for the determination of the substitution pattern of the side‐chain are tabulated.
Carbon NMR assignment for gnaphaliin 7‐methyl ether
Authors: Reinecke Manfred G. , Minter David E. , Jia Qi 
Published: May 2005

AbstractThe 13C NMR spectrum for gnaphaliin 7‐methyl ether is reported and assigned from XCORFE and HETCOR studies which also suggest a revision in the assignments for the other 5‐hydroxy‐3,7,8‐tri‐methoxyflavones flindulatin and ternatin.
Kinetics and reaction mechanisms of diazo compounds and iodonium salts as studied by chemically induced dynamic nuclear polarisation
Authors: Gragerov I. P. , Levit A. F. , Kiprianova L. A. , Buchachenko A. L. 
Published: May 2005

AbstractCIDNP phenomena in various reactions of diazo compounds and iodonium salts are described. The various reaction pathways leading to the formation of polarised aromatic products are analysed in detail.
Carbon chemical shifts of 1,1‐diphenylethylene and α‐methylstyrene dimer dianions
Authors: Takahashi Kensuke , Yamada Kaoru , Wakata Kazuyoshi , Asami Ryuzo 
Published: May 2005

AbstractThe natural abundance C‐13 NMR spectra of 1,1‐diphenylethylene and α‐methylstyrene dimer dianions have been obtained using the proton noise decoupling technique. The extra negative charge distributions in the carbanions have been discussed and compared with those obtained from the proton chemical shifts. The chemical shifts of the two ortho carbons in a phenyl ring are equivalent to each other for the former carbanion but not for the latter.
The nuclear magnetic resonance of heterocyclic compounds related to anthracene
Authors: Sharpless Norman E. , Bradley Robert B. , Ferretti James A. 
Published: May 2005

AbstractThe NMR spectra of a series of heterocyclic compounds analogous to anthracene have been investigated at 220 and 60 MHz. Correlations have been made with molecular geometry and parameters calculated from semi‐empirical MO theory. For planar molecules, the chemical shift of the proton ortho to the heteroatom is linear with respect to the electron density on the heteroatom, but otherwise chemical shifts are independent of electron density. Planarity of the molecules is also a factor in some of the coupling constants.
Etude par RMN 13C de quelques époxydes exo et endo dans la série du bicyclo[2.2.1]heptane
Authors: Zimmermann D. , Reisse J. , Coste J. , Plénat F. , Christol H. 
Published: May 2005

AbstractL'étude RMN 13C de composés époxybicyclo[2.2.1]‐heptaniques fait ressortir une forte influence de l'orientation endo ou exo de l'hétérocycle sur le glissement chimique du 13C pontal. La différence entre les variations de glissements chimiques en 13C et 1H montre que l'effet de courant de cycle ne peut seul rendre compte des résultats observés.
Carbon‐13 NMR spectra of arylmethyl carbanions
Authors: Takahashi Kensuke , Kondo Yoshiharu , Asami Ryuzo , Inoue Yoshio 
Published: May 2005

AbstractCarbon‐13 chemical shifts of three arylmethyl carbanions have been determined by changing solvents and counter ions. The charge distributions in the carbanions are discussed and compared with those obtained from the 1H chemical shifts.
Studies in organometallic rearrangements IV—proton and carbon nuclear magnetic resonance spectra of group IVA substituted indenes and indenyl anions
Authors: Taylor Glenn A. , Rakita P. E. 
Published: May 2005

AbstractThe proton and carbon NMR spectra for a series of substituted indenes [C9H7R, R = H, CH3, Si(CH3)3] are reported. The proton and carbon resonances for the 5‐membered ring exhibit pronounced changes as a function of the substituents.
The anion radical of azobispyridin N‐oxide
Authors: Eargle Dolan H. , Ventura‐Batista Maria Isabel , da Silva José Dias 
Published: May 2005

AbstractThe anion radical of the fully aromatic di‐N‐oxide system of azobispyridine N‐oxide was prepared and studied by ESR. Utilising computer simulation and CNDO computation the ESR spectrum was interpreted as follows:

Using appropriate equations the spin densities were calculated at

Ths semi‐quinoidal nature of the radical suggests a possible use as a spin label.
Carbon‐13 NMR spectra of coumarin and methoxycoumarins—a reinvestigation of charge density/Chemical Shift Relations
Authors: Günther Harald , Prestien Jörn , Joseph‐Nathan Pedro 
Published: May 2005

AbstractThe carbon‐13 NMR spectra of coumarin, 6‐, 7‐, 8‐methoxycoumarin, and 5,7‐, 7,8‐, 5,8‐ and 6,7‐dimethoxycoumarin have been measured and assigned. It is shown that substituent induced chemical shifts S(δ) in the mono‐ and disubstituted systems correlate well with the HMO atom‐atom polarisibilities πij of the parent compound: Si(δi) = 80.13 πij with a standard deviation of 1.42 ppm and a correlation factor of 0.994. Correlations between δ(13C) values and charge densities calculated by various semi‐empirical methods are less successful.
13C NMR spectra of thiophenes. III—Bromothiophenes
Authors: Sone Tyo , Fujieda Kunimi , Takahashi Kensuke 
Published: May 2005

AbstractThe 13C NMR spectra of all bromo substituted thiophenes have been obtained at 15·085 MHz. 13C signal assignments for monobromothiophenes have been confirmed by comparison with the spectra of their partially deuteriated derivatives; a revision is made for the assignment in 3‐bromothiophene. The substituent effect of bromine is generally additive for the 13C chemical shifts. The substituent effect on various types of 13C, 1H coupling constants is also obtained and discussed.
13C‐NMR‐spektroskopische und stereochemische Untersuchungen: XI—Konformationen von Bicyclo[3.3.1]nonanen und ihre Unterscheidbarkeit durch lanthanideninduzierte Verschiebungen
Authors: Schneider Hans‐Jörg , Lonsdorfer Michael , Weigand Eckehard F. 
Published: May 2005

AbstractEin Vergleich von gemessenen und aus stereospezifischen Inkrementen berechneten 13C‐Verschiebungen zeigt für Bicyclo[3.3.1]nonan und die entsprechende 9‐Hydroxy‐ und 9‐Oxo‐Verbindung eine dominierende Sessel‐Sessel‐Konformation CC an; einen ähnlichen Schluß ergibt das 1H‐NMR‐Spektrum des Ketons. 13C‐NMR‐Tieftemperaturmessungen sowie die Analyse der Temperaturabhängigkeit von 13C‐Verschiebungen in Bicyclo‐[3.3.1]nonan erlauben die Festlegung eines unteren Grenzwertes für den Energieunterschied zwischen der CC‐ und einer Boot‐Sessel‐Konformation BC von ΔG ≧ 5,85 kJ mol.−1 Die Möglichkeit zur Differenzierung flexibler Geometrien wie CC, BC und BB durch lanthanideninduzierte 1H‐ und 13C‐Verschiebungen wird unter Einschluß einer Fehlerbetrachtung untersucht. Das Auftreten mehrerer bzw. flacher Minima bei der computergestützten Geometrieanalyse der Pseudokontaktverschiebungen erlaubte nur den Ausschluß von BB‐Konformationen.
Eine neue Methode zur Beobachtung von Reaktionen im NMR‐Spektrometer. Oxidation von Trialkylboranen mit Luftsauerstoff
Authors: Friebolin H. , Rensch R. 
Published: May 2005

AbstractEs wird ein Verfahren beschrieben, das eine Reaktion direkt im Spektrometer zu beobachten erlaubt, bei der kontinuierlich ein gasförmiger Reaktand über eine Glaskapillare in das rotierende 5 mm‐Proberöhrchen eingeleitet wird. Bei richtiger Versuchsführung werden die Signale durch die Kapillare und die aufsteigenden Gasblasen nur unwesentlich verbreitert (Halbwertsbreiten < 1 Hz). Eine Versuchsanordnung mit zwei Kapillaren gestattet, gleichzeitig zwei gasförmige Reaktanden zuzuführen and deren Reaktion zu verfolgen. Als Beispiel für die Anwendungsmöglichkeiten dieser Methode werden die bei der Autoxidation von Trialkylboranen aufgenommenen Protonenresonanzspektren gezeigt.
On the dimerization of α‐mercaptoacetone: An n.m.r. study
Authors: Cook Michael J. , El‐Khouly Abdel‐Azim 
Published: May 2005

Abstract1H n.m.r. is used to show that α‐mercaptoacetone is formed as a mixture of monomer and a dimer. No evidence is found to support the previously claimed isolation of two dimeric species. The dimer dissociates to the monomer on standing as a solution in chloroform, but the monomer is dimerized by grinding. 1‐Mercapto‐3‐phenylpropan‐2‐one behaves similarly.
13C n.m.r. spectra of quercetin and rutin
Authors: Lallemand J. Y. , Duteil M. 
Published: May 2005

AbstractThe noise‐decoupled and gated‐decoupled 13C n.m.r. spectra of quercetin and rutin are studied and assignments are proposed. The previous assignments of carbons 2 and 4′, carbons 5 and 9, carbons 6 and 8 have been reversed.
Carbon‐13 n.m.r. spectra of branched carboxylic acids and their derivatives
Authors: Terent'ev A. B. , Dostovalova V. I. , Kh. Freidlina R. 
Published: May 2005

Abstract13C n.m.r. spectra have been measured for 39 compounds with branched structures including carboxylic acids, their methyl and ethyl esters, nitriles and chlorinated esters. The results obtained indicate that the 13 C n.m.r. technique is applicable to structure assignment of acids and their derivatives containing various numbers of substituents on the chain. The dependence of the carboxylic carbon chemical shift on the number and structure of α‐positioned substituents has been determined. Calculation of the chemical shifts for branched carboxylic acids, esters and nitriles from the corresponding increments using the additivity scheme is shown to be possible in principle.
Systèmes Aromatiques à 10 Électrons π Dérivés de l'Aza‐3a‐pentalène: XXVI—Etude de quelques Dérivés Polyazapentaléniques en Résonance du Carbone‐13
Authors: Faure Robert , Vincent Emile‐Jean , Claramunt Rosa‐Maria , Elguero José 
Published: May 2005

AbstractL'étude en RMN du 13C de neuf azapentalènes a été effectuée. Tous les signaux ont été attribués. Dans un cas on a mis en évidence des couplages entre les atomes de carbone et l'hydrogène porté par l'azote pyrrolique, fait exceptionnel dans le cas des hétérocycles aromatiques polyazotés. On démontre l'utilité de la RMN du 13C pour l'étude de la tautomérie annulaire.
Effets de Substituants en Série Diazolique et Diazinique‐1,3—Etude par Résonance Magnétique Nucléaire du Carbone‐13
Authors: Faure R. , Vincent E.‐J. , Assef G. , Kister J. , Metzger J. 
Published: May 2005

AbstractNous avons enregistré les spectres de RMN du carbone‐13 de thiones et de thioethers, en série diazolique et diazinique‐1,3, diversement substitués sur les atomes d'azote par des groupements alkyles, ainsi que certaines des structures oxygénées homologues. Toutes les raies de résonance ont été attribuées. Dans le cas des dérivés thiocarbonylés, nous montrons que l'équilibre thiol ⇄ thione est déplacé vers la forme thione, mais que la RMN du carbone‐13 ne peut conduire qu'à une évaluation qualitative de la position de cet équilibre. L'analyse des effets de substituant montre que, contrairement aux composés oxygénés, le groupement isopropyle adopte dans les dérivés soufrés une conformation privilégiée par suite de l'encombrement stérique dǔ à l'atome de soufre. La substitution par un groupement tertiobutyle conduit à des valeurs des effets γ inattendus. Nous attribuons ce phénomène à des déformations de cycle ou à des variations des angles valentiels de l'azote porteur du substituant, provoquées par des interactions stériques entre le substituant et le cycle correspondant. Nous relions ces modifications à certaines modalités de la réactivité, et à des résultats de spectroscopie photoélectronique.
The 13C n.m.r. spectra of polysubstituted benzenes. 1—the use of hexachlorobenzene as a reference for the structure elucidation of multisubstituted polychlorobenzenes
Authors: Heaton C. A. , Hunt M. H. , Meth‐Cohn O. 
Published: May 2005

AbstractThe use of 13C n.m.r. for structure elucidation of a series of products obtained by reaction of dialkylamines with 1,2‐dinitrotetrachlorobenzene has shown that the general problem of non‐additivity of substituent effects of contiguously substituted benzenes may be overcome, with these products, by the choice of a suitable standard. In this case hexachlorobenzene was used and the difference between the actual and calculated chemical shifts was small, allowing unambiguous structural assignment.
Protonenresonanz‐ und Röntgenstrukturuntersuchungen an unsymmetrisch substituierten Aminoboranen. III—Substituentenabhängigkeit der Struktur
Authors: Friebolin H. , Morgenthaler H. , Autenrieth K. , Ziegler M. L. 
Published: May 2005

AbstractEine Reihe unsymmetrisch substituierter N‐Methylaminoborane mit je einem Phenylring am Stickstoff und am Bor wurde synthetisiert und das in verdünnten Lösungen 1H NMR‐spektroskopisch bestimmte cistrans‐Isomerenverhältnis in Abhängigkeit von der Größe der aromatischen Reste und vom Zweitsubstituenten am Bor diskutiert. Die Strukturbestimmung aller untersuchter Verbindungen folgte aus der Lage des N‐Methylsignals mit Hilfe eines Zuordnungskriteriums, das durch die Röntgenstrukturanalysen von Methyl(4‐Br‐phenyl)amino‐chlorphenylboran und Methyl(2‐methyl‐4‐Br‐phenyl)amino‐chlor(2‐methylphenyl)boran erstellt wurde. Von Methylphenylamino‐chlorphenylboran ist im thermischen Gleichgewicht das Isomere mit cis‐ständigen Phenylringen stark begünstigt (90%). Beim Ersatz eines Phenylringes durch den 2‐Methyl‐ oder 2,6‐Dimethylphenylrest nimmt stets der Anteil des cis‐Isomeren ab. Substitution des Chloratoms am Bor durch Brom oder die Methylgruppe führt ebenfalls zu einer Verschiebung des Isomerenverhältnisses zum trans‐Isomeren hin. Absolut betrachtet sind jedoch nur bei den Verbindungen mit einer Methylgruppe oder mit einem 2,6‐Dimethylphenylrest am Bor, sowie bei denen mit je einem 2‐Methylphenylrest am Stickstoff und am Bor die trans‐Isomeren energetisch günstiger als die cis‐Isomeren. Für die gefundenen Substituenteneffekte werden sterische Hinderung und elektronische Abstoßung verantwortlich gemacht. Die Experimente zeigen außerdem, daß in allen Fällen das im Kristall bevorzugte Isomere auch im Lösungsgleichgewicht überwiegt.
Carbon‐13 n.m.r. studies of substituted bisalkylamino‐s‐triazines in acidic media
Authors: Tseng C. K. , Mihailovski A. 
Published: May 2005

AbstractThe carbon‐13 n.m.r. spectra of six substituted bisalkylamino‐s‐triazines are reported. The site of protonation of 2‐methoxy‐s‐triazines is shown to be at N‐1 or N‐3. The effect of trifluoroacetic acid on 2‐chloro‐s‐triazines is also discussed.
Long range 13C13C coupling constants. A review
Authors: Hansen Poul Erik 
Published: May 2005

AbstractA large number of 13C13C coupling constants from a diversity of compounds are now available. Attempts have been made to classify this information in order to illustrate how these data are obtained, how signs are determined and how both two‐ and three‐bond couplings can lead to structural information. Coupling constants in aromatic compounds are now well documented, substituent effect trends have been established and correlations with bond orders are noticed. Comparison of 13C13C couplings with 13C1H couplings is mentioned. Theoretical calculations are dealt with, and these can now be properly evaluated as both magnitudes and signs of the experimental couplings are known. Finally, the occurrence of long range couplings in biosynthetic material is briefly surveyed.
Etude en RMN du 13C de Mérocyanines Benzimidazoliniques
Authors: Besse J‐P. J. , Samat A. M. , Le Gall J. Y. , Guglielmetti R. J. , Le Beuze A. J. 
Published: May 2005

AbstractUne série de mérocyanines α‐oxo benzimidazoliniques diversement substituées sur la partie ‘phénolate’ et possédant une chaǐne grasse sur l'un des azotes hétérocycliques, a été étudiée en RMN du carbone‐ 13. Des substituants donneurs d'électrons provoquent une augmentation de la densité électronique sur le carbone méthinique C‐3 et une augmentation de l'alternance de la distribution de charge sur le pont diméthinique 3,4. Corrélativement un déplacement bathochrome de la transition électronique de plus basse énergie est observé. Par ailleurs, l'apparition de la résonance à champ faible du proton méthinique H‐3 semble due à une interaction spécifique intervenant entre ce proton et l'atome d'oxygène ‘phénolate’, ce qui suppose l'existence d'une configuration trans privilégiée pour les mérocyanines.
Carbon‐13 NMR studies of quinolines and isoquinolines. II. Chlorine–nitrogen interactions and N‐oxide effects
Authors: Su Ja‐An , Siew Ernest , Brown Ellis V. , Smith Stanford L. 
Published: May 2005

AbstractCarbon‐13 chemical shift assignments are reported for four chloroquinolines, six chloroisoquinolines, one dichloroquinoline, four dichloroisoquinolines, four methylchloroquinolines, two methylchloroisoquinolines, quinoline N‐oxide, isoquinoline N‐oxide, five methylquinoline N‐oxides, two methylisoquinoline N‐oxides and three chloroisoquinoline N‐oxides. Chlorine substituent chemical shift (SCS) effects are reported for the alpha, ortho, meta, para and peri positions. Consistent patterns are observed for the para and peri positions, a vinylogous ortho pattern is reported and the additivity of these SCS effects is demonstrated. Alpha SCS effects vary widely from 1.1 ppm upfield in 1‐chloroisoquinoline to 6.7 ppm downfield in 4‐chloroquinoline. These results, together with those in the literature, permit the definition of steric and nitrogen lone‐pair contributions which modify the ‘normal’ chlorine SCS effect, and these modifying contributions are shown to be roughly additive.Large (6–16 ppm) upfield shifts are observed for the carbons ortho and para to the N‐oxide group. The individual magnitudes of these shifts and their sum are constant and the effects are additive in substituted systems. A 9.5 ppm upfield shift is also observed for C‐8 in quinoline N‐oxides which is attributed to a space–charge interaction. Substituent chemical shift (SCS) effects for the chloro and methyl groups and the chemical shifts of the methyl carbons are essentially the same in the N‐oxides as in the parent heterocycles and are additive, except for those molecules where the substituent is adjacent to the N‐oxide moiety, in which cases substantial interactions are observed.
Carbon‐13 NMR studies of a series of benzylphenols
Authors: Nakai Yoshimi , Yamada Fukiko 
Published: May 2005

AbstractCarbon‐13 NMR spectra of a series of benzylphenols and their O‐alkylated derivatives were recorded to find the substituent effects of the benzyl, hydroxybenzyl and alkoxybenzyl groups on the 13C chemical shifts. It was found that the methylene bridge carbons show signal shifts mainly due to the mesomeric effects of the OH and OCH3 substituents, and that in the case of ortho‐substituted benzyl compounds, the methylene carbon signals exhibit upfield shifts due to both mesomeric and steric effects.
Etudes d'Hétérocycles Pentagonaux Polyhétéroatomiques par RMN du 13C. Effets de Substituant, de la Benzocondensation et Etude de la Tautomèrie Prototropique en Série Benzothiazolique
Authors: Faure R. , Elguero J. , Vincent E. J. , Lazaro R. 
Published: May 2005

AbstractLes spectres de résonance magnétique nucléaire due carbone‐13 de 43 benzothiazoles ont été enregistrés dans le diméthylsulfoxyde hexadeutérié. Tous les carbones ont été attribués de facon non ambiguë, grǎce aux effets de substituant sur les positions 4, 5, 6 ou 7. Nous discutons des variations des déplacements chimiques en fonction de la nature du substituant en 2 (équation triparamétrique du type: Δδ = aF+bR+cQ+d′), de l'annélation en série benzohétérocyclique et de la tautomérie prototropique en série benzothiazolique (dans le cas où le substituant en position 2 représente un groupement OH, SH ou NHR).
Some features of the 13C NMR of cephalosporins
Authors: Dereppe J. M. , Schanck A. , Coene B. , Moreau C. , Van Meerssche M. 
Published: May 2005

Abstract13C NMR spectra of 4 cephalosporins have been interpreted. Some spectral characteristics are presented, allowing easy peak assignment of the 13C resonances of the cephalosporanic ring atoms. Quaternary carbon resonances were differentiated with the aid of relaxation time measurements.
Détermination de la Conformation et de la Configuration de Sulfoxydes à Sept Chainons, Intermédiaires de Synthèse d'un Analogue de la Biotine
Authors: Lacombe Liliane , Lavielle Solange 
Published: May 2005

AbstractLa conformation des deux sulfoxydes du diaza‐8,10 dibenzyl‐8,10 thia‐4 bicyclo[5.3.0]décanone‐9 est étudiée par RMN. L'examen des constantes de couplage permet de conclure que ces deux sulfoxydes existent sous des conformations chaises à liaison S→O axiale.
Détermination par RMN 1H et 13C de la Conformation Favorisée des Ozonides d'Acènes
Authors: Gobert F. , Altenburger‐Combrisson S. , Albouy J. P. 
Published: May 2005

AbstractL'existence d'une conformation favorisée pour l'ozonide du diméthyl‐9,10 anthracène a été démontrée par RMN 1H et 13C. On retrouve cette měme conformation dans l'ozonide du diméthoxy‐9,10 anthracène et dans celui de l'anthracène qui a pu ětre observé pour la première fois en solution.
Dynamic 13C NMR studies on the internal rotation in tetraarylallyl anions
Authors: Bauer H. , Angrick M. , Rewicki D. 
Published: May 2005

AbstractProton noise decoupled 13C NMR spectra of lithium 1,1,3,3‐bis (2,2′‐biphenylylene)propenide and lithium 1,1,3,3‐tetraphenylpropenide have been studied, and complete assignments have been made based on several methods, e.g. 13C13C coupling constants of selectively labelled compounds and low‐temperature splitting of temperature dependent signals. The barriers to rotation about the partial double bonds of the allyl group have been determined by 13C DNMR resulting in the thermodynamic parameters of activation ΔG = 57 kj mol−1, ΔH≠ = 56.5 kj mol−1, ΔS≠ = −3J mol−1K−1 and ΔG = 55.5 kj mol−1, ΔH≠ = 63 kj mol−1, ΔS≠ = 26 kJ mol−1K−1, respectively. The results are discussed, including the hitherto known data about the topomerisation process.
A theoretical study of solvent effects on the 13C chemical shifts of some polar molecules
Authors: Jallali‐Heravi M. , Webb G. A. 
Published: May 2005

AbstractCalculations of the dependence of 13C chemical shifts on the dielectric constant, ϵ, of the medium are reported using the INDO/S parameterized version of Pople's method together with the solvaton model. Satisfactory agreement with the available experimental data is obtained. The rather sensitive dependence of chemical shift upon ϵ suggests that polar solute—solvent interactions in aprotic media should be taken into account when considering 13C chemical shifts.