bluuebunny/crossref_metadata_2025_split huggingface dataset:
The NMR spectra and conformations of dihydropyran derivatives—I: The conformations of 2‐alkoxy‐5,6‐dihydro‐α‐pyran‐6‐carboxylic esters
Authors: Achmatowicz O. , Jurczak J. , Konowal A. , Zamojski A. 
Published: May 2005

AbstractOn the basis of NMR spectra of trans‐ and cis‐2‐alkoxy‐5,6‐α‐pyran‐6‐carboxylic esters it was found that, at room temperature, the trans‐compounds exist exclusively in the conformation with equatorial carbalkoxy and pseudoaxial alkoxy groups. The cis‐isomers appear to be in conformational equilibrium between a form with equatorial carbalkoxy and pseudoequatorial alkoxy groups and that with axial and pseudoaxial substituents. In the latter case, the axial carbalkoxy group is bent out off its normal position by about 15°.
CNDO calculations of diamagnetic shielding in molecules
Authors: Sadlej Andrzej J. 
Published: May 2005

AbstractAn approximate procedure for the calculation of diamagnetic shielding in molecules is presented. The method proposed is based on the ‘complete neglect of differential overlap’ (CNDO) molecular wave functions and is formulated according to the zero differential overlap (ZDO) approximation. The results obtained with several CNDO‐type wave functions for diatomic and polyatomic molecules are in very good agreement with non‐empirical SCF calculations. The 14N diamagnetic shielding constants in several molecules were computed and some approximations usually adopted in the interpretation of 14N chemical shifts are critically discussed. It was shown that in some cases the observed 14N chemical shifts cannot be interpreted solely in terms of the paramagnetic contribution to the shielding constant.
Transferts Protoniques de Sels D'ammonium. Substitues—II: Vitesse D'inversion a L'azote Par la Methode de ‘Protonation Competitive’
Authors: Delpuech Jean‐Jacques 
Published: May 2005

AbstractL'inversion de l'azote pyramidal d'une amine peut ětre ralentie, de manière calculable, par une protonation presque totale dans un milieu d'acidité variable. Un traitement théorique complet permet de calculer sa vitesse à partir de la durée de vie moyenne du sel d'ammonium déterminée par résonance magnétique nucléaire. On peut ainsi fixer les conditions de validité de la formule approchée de Saunders et Yamada: la vitesse de protonation de l'amine doit ětre largement supérieure à la vitesse d'inversion; la vitesse de déprotonation du sel d'ammonium peut, par contre, ětre quelconque. Au cas où l'in version se produit entre deux molécules isomères différentes, ce traitement fournit également le rapport, à l'équilibre, des concentrations des sels isomères correspondants.
Inequivalence Magnetique Due a la Presence d'un Atome de Phosphore Asymetrique ou Pseudo‐Asymetrique
Authors: Marty Raymond , Houalla Doureid , Wolf Robert , Riess Jean 
Published: May 2005

AbstractDans les phosphinates d'alcoyle RPH(O)OR′, la présence de l'atome de phosphore asymétrique induit des inéquivalences magnétiques au niveau de protons ou groupes méthyles géminés. Si le reste alcoxy OR' comporte lui aussi un atome de carbone asymétrique, la résonance magnétique de 31P et de 1H, permet de mettre en évidence la formation des deux diastéréoisoméres attendus, en proportions égales.Par ailleurs, la résonance magnétique de 31P révèle le caractère de centre de pseudo‐asymétrie de l'atome de phosphore dans les esters phosphoneux de l'alcool butylique secondaire.
Chemical shift non‐equivalence of ring protons in N‐substituted β‐lactams
Authors: Vigevani A. , Gioia B. , Gallo G. G. 
Published: May 2005

AbstractA study is reported on the chemical shift non‐equivalence of the diastereotopic protons at C‐4 in identically 3,3‐disubstituted β‐lactams having an asymmetric carbon atom in positions ranging from β to ε of the chain attached to the nitrogen atom. The non‐equivalence has been correlated with the nature of the substituents bonded to the chiral centre and to its distance from the C‐4 protons.
Conformational analysis and J(HCOH) of α‐hydroxy‐N‐caproylhydrazobenzene, a degradation product of phenylbutazone
Authors: Neville G. A. , Awang D. V. C. 
Published: May 2005

Abstract—Intramolecular OH… N hydrogen bonding between the hydroxylic and terminal amino groups of α‐hydroxy‐N‐caproylhydrazobenzene (5) permits J(HCOH) to be observed in most solvents. The configuration and conformation of 5 are discussed and an HCOH dihedral angle (ϕ) of 145° is calculated. Solvent effects on J(HCOH) as well as the role they appear to exert in restricting internal rotation of the phenyl substituents of 5 are discussed.
The proton resonance spectra of heterocycles—VI: The correlation of substituent effects on chemical shifts in bicyclic compounds
Authors: Katritzky A. R. , Takeuchi Y. , Ternai B. , Tiddy G. J. T. 
Published: May 2005

AbstractThe proton chemical shifts are reported for monosubstituted naphthalenes, quinolines and quinoxalines. Together with literature data, these chemical shifts are compared with the parent compounds and substituent effects evaluated statistically. The effect of substituents parallels that in benzenes, but is modified by bond fixation, steric hindrance and other effects which can, at least qualitatively be understood. The treatment enables estimation of likely chemical shifts for ABC spectra in fused aromatic systems which should facilitate the solution of such spectra.
NMR experiments on acetals—XXV: Conformational energy for the chair‐twist interconversion of the 1,3‐dioxane system
Authors: Anteunis M. , Swaelens G. 
Published: May 2005

AbstractTrans‐4‐t‐Bu‐6‐R‐1,3‐dioxanes (R = Me, Pri and cyclohexyl) show temperature‐dependent values for 2J(H—2) and 3J(H—4(6), H—5) in their PMR spectra. This is the result of the presence of twist‐boat conformations. With the aid of typical limit‐values of 2J(H—2) for the chair and twist forms, the amount of flexible conformations were determined as a function of temperature (Table 2), allowing the determination of the enthalpy change for chair‐twist interconversion in 1,3‐dioxane itself (6·2 ± 0·3 kcal/mole). Typical values for 2J(H—2) were obtained from a study of low temperature spectra and from appropriate model compounds of which 4‐(1′‐adamantyl)‐6‐t‐Bu‐1,3‐dioxane served as the model for a genuine twist form with a twofold axis through C‐2/C‐5.
Determination of 2,4‐dichlorophenol in dichlorophenol isomers by NMR
Authors: Esumi Naohumi , Suzuki Teruo , Hayashi Shoichi 
Published: May 2005

AbstractQuantitative analysis of isomers by NMR has been carried out in the measurement of species whose components present simple and sufficiently isolated spectra. Generally, the substituted aromatic proton splits into complicated spectral lines due to spin‐spin coupling. The ring proton spectra of dichlorophenol isomers show a pattern peculiar to the three spin system. It was found that some of the signal attributable to these compounds appear in a position slightly isolated from each other. Therefore, we established the quantitative analysis method for dichlorophenol, using the signal intensity method. From the result of the quantitative analysis, the lowest detectable concentration was 1·1% (±0·3% at the standard deviation). The accuracy of the peak intensity method was found to be ±1·8% within the 50 to 80 mol% concentration range of 2,4‐dichlorophenol isomer.
Determination de Susceptibilites Paramagnetiques par les Methodes de RMN
Authors: Widenlocher Mm. Gérard , Dayan Elie 
Published: May 2005

AbstractLes susceptibilités magnétiques jouent un rǒle important en RMN, mais leurs valeurs ne sont pas toujours connues; ici, les auteurs donnent une méthode de mesure de susceptibilités paramagnetiques et proposent une explication pour la dépendance linéaire de la susceptibilité magnétique en fonction de déplacement observé.
Conformations of highly hindered aryl ethers—IV PMR studies of 2,4‐ and 2,6‐ dinitroaryl ethers
Authors: Lehmann F. Pedro A. 
Published: May 2005

AbstractPMR studies of a series of 2,4‐ and 2,6‐ dinitrophenyl‐ and 2,4‐dinitronaphthyl‐ aryl ethers strongly indicate the existence of preferred conformations. Extensive conjugation of the ether linkage with the dinitro ring, resulting in their coplanarity, is an important stereochemical influence. In the ensuing skew conformation the dinitro ring is positioned in such a way that the 6‐substituent is proximal to the other ring. In the case of the 2,4‐dinitrophenyl ethers (1) this is the 6‐proton, which shows the expected shielding due to the ring current in the other ring. In the 2,6‐dinitrophenyl‐(2) and 2,4‐dinitronaphthyl‐(3) ethers, this is a nitro group, twisted out of coplanarity to fit over the other ring, whose magnetic anisotropy is reflected in the shielding experienced by the 6′‐protons. When there is a 2′‐substituent magnified image present the ring which bears it twists in such a way as to bring the 6′‐proton closer to the proximal nitro‐group, explaining the greater shielding observed in these cases. Variable temperature studies provided further evidence in favor of these conformations since no significant changes were observed from −55° to + 155°, even for compounds with four substituents flanking the ether linkage. Nevertheless, the compounds studied here are not frozen in these conformations, but probably inter‐convert via concerted rotation with others.
NMR studies of silver ion and 1,3,5‐trinitrobenzene complexes
Authors: Deb K. K. , Cole T. C. , Bloor J. E. 
Published: May 2005

AbstractA study, using NMR techniques, of the propensity of complex formation of silver ions with hydrocarbons and heterocyclic compounds containing nitrogen, oxygen and sulphur is described. The results are compared with similar data using 1,3,5‐trinitrobenzene as an acceptor. The differences in the two sets of data are interpreted in terms of localized and delocalized interactions in the formation of weak complexes.
The NMR spectra of some fluorinated pyridine derivatives
Authors: Thomas W. A. , Griffin G. E. 
Published: May 2005

AbstractThe 1H and 19F spectra of a variety of mono‐ and di‐ fluorinated pyridines are examined, and compared with the corresponding spectra of the pyridinium ions. The magnitudes and signs of the 1H19F coupling constants are in general in accord with those observed for the corresponding 1H1H couplings, with an exaggerated range. Large changes in the NMR parameters are observed on protonation of the nitrogen, 3J(HF) changing sign in some of the α‐fluoropyridine derivatives.
Acetate‐methyl signals in the NMR spectra of peracetylated derivatives of chondroitin sulfates and their desulfated derivatives
Authors: Hirano Shigehiro 
Published: May 2005

AbstractChondroitin 4‐sulfate (Ch4S), chondroitin 6‐sulfate (Ch6S), dermatan sulfate, chondroitin and desulfated dermatan sulfate were peracetylated and the derivatives isolated in yields of 45 to 88%. Acetate‐methyl signals in the NMR spectra of these derivatives in D2O were analyzed using a correlation of the chemical shifts to the orientations. The lC conformation of hexopyranosiduronic acid moieties was estimated in these derivatives. No significant change of the chemical shifts was observed with the NMR spectra measured in D2O, in 7 M urea solution, in the various diluted solutions, and in the temperature range of 2 to 95° in D2O.
Linewidth variation in the dinitronitrosomethyl dianion radical in the slow exchange mode
Authors: Russell Glen A. , Norris Robert K. 
Published: May 2005

AbstractThe treatment of nitromethane or dinitromethane in aqueous alkaline solutions (1 to 2·5 M hydroxide) with nitrogen dioxide yields the dianion radical of dinitronitrosomethane [C(NO2)2(NO)\documentclass{article}\pagestyle{empty}\begin{document}$ \buildrel\textstyle.\over= $\end{document}] which at 30° has hfsc of a = 10·75 and 0·65 and aNNO = 5·80 g. Restricted rotation about the CNO bond causes magnetic non‐equivalence of the two nitro groups which can slowly exchange giving rise to line broadening. The use of 15N labeled nitrogen dioxide gave the dianion radical

which exists in two equally populated conformations, each of which shows the expected line broadening for a ‘slow exchange’ process in which the nitro groups are being interconverted.
Complete PMR analysis of naphthalene as an eight spin system
Authors: Crecely R. W. , Goldstein J. H. 
Published: May 2005

AbstractThe PMR spectrum of naphthalene has been completely analyzed as an eight‐spin system for the first time. It was found that inter‐ring long‐range couplings exist between all combinations of the α and β protons on adjacent rings. The signs and magnitudes of the coupling values have been determined and compared to couplings reported in the literature for other polynuclear compounds.
Protonenresonanzuntersuchungen an Polysacchariden—III: Amylose–und dextranderivate
Authors: Keilich G. , Siefert E. , Friebolin H. 
Published: May 2005

AbstractDie Protonenresonanzspektren einiger Methyl‐, Acetyl‐ und Benzoylderivate der Polysaccharide Amylose und Dextran sowie der α‐D‐Glucose und β‐Maltose wurden analysiert. Aus den relativen Signallagen und den Kopplungskonstanten der Ringprotonen kann die Konfiguration und Konformation des Monomerbausteins sowie die Art der glycosidischen Bindung bestimmt werden.
Etude des Signes des Constantes de Couplage 3J(PXCH) et 4J(FPXCH) dans les Diaza‐, Dioxa‐ et Dithiaphospholanes Fluores
Authors: Albrand J.‐P. , Cogne A. , Gagnaire D. , Martin J. , Robert J.‐B. , Verrier J. 
Published: May 2005

AbstractOn a réalisé l'analyse complète des spectres de RMN des fluorophospholanes (1 à 3). Les signes absolus des constantes de couplage 3J(PH) et 4J(FH) ont été déterminés, par rapport au signe absolu connu de la constante 1J(PF), à partir d'expériences de double résonance hétéronucléaire sélective. Les constantes 3J(POCH) et 3J(PNCH) observées sont toutes positives. Les deux constantes 3J(PSCH) du dithiaphospholane (2) présentent des faibles valeurs de signes opposés, la plus grande étant positive. Toutes les constantes 4J(FPXCH) sont positives et ces constantes semblent peu stéréospécifiques.
Tritium nuclear magnetic resonance spectroscopy—I: Technique, internal referencing and some preliminary results
Authors: Bloxsidge J. , Elvidge J. A. , Jones J. R. , Evans E. A. 
Published: May 2005

AbstractRoutine measurement of triton magnetic resonance spectra is described for the first time, using a micro‐bulb sample tube assembly to obviate radiological hazards. Levels of isotope abundance and chemical concentration, the problem of self‐radiolysis and the general usefulness of the technique are discussed. Results are given for a selection of compounds including glucose, amino‐acids, thymidine and uridine. The self‐radiolysis of the last is followed.
The detection of hidden proton magnetic resonance signals by means of INDOR
Authors: van Deursen F. W. 
Published: May 2005

AbstractThe INDOR technique appears to be a very useful and rapid tool for the detection of hidden proton lines as an aid in the elucidation of the structure of complex organic molecules. The experimental conditions for obtaining optimum results in a limited time are discussed. Analysis of the INDOR spectra of a number of selected spin systems are given; these show the capabilities of this method. Examples are given in which this technique is applied.
Chemical shift non‐equivalence of methylene protons adjacent to an asymmetric nitrogen atom
Authors: Vigevani A. , Gioia B. , Cavalleri B. , Gallo G. G. 
Published: May 2005

AbstractThe chemical shift non‐equivalence of the methylene protons adjacent to the quaternary nitrogen in compounds of the type has been investigated. The behaviour of the examined compounds is interpreted in terms of different rotation rates around the three CN⊕ bonds. The vicinal and geminal coupling constants of the non‐equivalent methylene protons are also reported and discussed in terms of steric factors.
An abnormal trend in J(13CCH) values in some aldehydes
Authors: Ewing D. F. 
Published: May 2005

AbstractThe 2J(13CCH) couplings involving the formyl proton of α‐halogeno‐aldehydes have been found to decrease with increasing halogen electronegativity. This trend may be rationalised in terms of inductive withdrawal and a conformation dependent hyperconjugative effect. The direct J(13CH) couplings are also anomalous.
Solvent effects in NMR spectra induced by benzene in methyl benzoic esters—IV
Authors: Alexandrou N. E. , Hadjimihalakis P. M. , Pavlidou Miss E. G. 
Published: May 2005

AbstractNMR solvent effects induced by benzene in methyl substituted benzoic esters can be effectively used in the interpretation of complex NMR spectra. A 1:1 collision complex between solvent and solute is proposed, supported by dilution curve experiments and the geometry of the ‘complex’ is discussed.
Intensitätsformel für Hyperfeinstrukturlinien bei n aequivalenten Kernen mit beliebigem Spinmoment—I
Authors: Kuss E. , Brehm U. 
Published: May 2005

AbstractDie relativen Intensitäten der kernmagnetischen Hyperfeinstrukturlinien sind bei n aequivalenten, benachbarten Protonen (I = ½) bekanntlich durch die Binomialkoeffizienten und das Pascalsche Dreieck gegeben. Bei n aequivalenten, benachbarten Kernen mit I > ½ ist eine einfache Berechnungsformel für die relativen Intensitäten nicht bekannt, andrerseits ist die Ermittlung der sehr großen Zahlen aus den Anordnungsmöglichkeiten der Spins sehr umständlich.Ordnet man die Zahlen wiederum in n Reihen an, so erhält man ‘Pascalsche Dreiecke höherer Ordnung’. Sie sing (a) symmetrisch, (b) Die Summe der Zahlen der n‐ten Reihe ist stets (2I + 1)n und (c) Es ergibt sich jede Zahl in irgendeinem der Dreiecke als Summe der r darüberstehenden Zahlen, wobei r = 2I + 1 ist.Für die Berechung der v‐ten Zahl in der n‐ten Reihe eines beliebigen Dreiecks höherer Ordnung wird eine Rekursionsformel angegeben.Weitergehend wird gezeigt, daß auch eine direkte Berechnung, ohne Kenntnis der Zahlen der voraufgehenden Reihe, bei beliebig hohen Werten von n und I aus der Beziehung:

möglich ist. Darin ist a die größte ganze, psotive Zahl ≦(v – 1)/r und ≦n.Unter der Voraussetzung, daß die Hyperfeinstruktur‐Aufspaltung J klein gegenüber der chemischen Verschiebungsdifferenz Δν* ist, lassen sich die relativen Intensitäten der Hyperfeinstrukturlinien aus der Formel in sehr einfacher Weise berechnen, wie an einigen Beispielen gezeigt wird.
Structure des Complexes de Meisenheimer Complexes de Courte Duree de Vie et Complexes Stables Formes par Action des Ions Méthoxydes sur les Dinitro‐4,6 Anisoles X‐2 Substitues
Authors: Terrier François , Hallé Jean‐Claude , Simonnin Marie‐Paule 
Published: May 2005

AbstractL'étude RMN de l'interaction des ions CH3O− avec les dinitro‐4,6 anisoles X‐2 substitués (X = CN, CF3, Cl, F) a permis d'identifier divers complexes de Meisenheimer résultant de l'attaque des ions CH3O− sur les carbones −5 et −3 non substitués. Ces complexes −1,5 et −1,3, dont la durée de vie est très courte, se transforment rapidement au profit des complexes stables −1,1. Les déplacements chimiques des anisoles et des différents complexes reflètent les effets électroniques et stériques des substituants X. L'influence de la charge négative portée par le cycle et les modifications géométriques du squelette sont mises en évidence en comparant les paramètres RMN des anisoles et des complexes correspondants. Lorsque X = F, l'étude des signes des constantes de couplage montre que 3J(FH) et 5J(FH) sont de signes contraires dans l'anisole et dans le complexe −1,1.
NMR spectra of the cycloaddition adducts between tetracyanoethylene oxide and norbornadiene derivatives
Authors: Shen Kei‐Wei , Shen Yvonne Hua , Winters Lawrence J. 
Published: May 2005

AbstractThe NMR spectra of the cycloaddition adducts between tetracyanoethylene oxide (TCNEO) and norbornadiene derivatives have been studied. It was shown that there was significant long‐range coupling between 7‐anti and endo hydrogens in the adducts and that this long‐range coupling was solvent dependent. Based on the present study it is concluded that the long‐range coupling between endo and anti hydrogens can be as high as 4·1 Hz when an electronegative substituent is attached to the carbon which bears endo hydrogen.
Conformational studies on pyranoid sugar derivatives by NMR spectroscopy. Correlations of observed proton—proton coupling constants with the generalized Karplus equation
Authors: Durette Philippe L. , Horton Derek 
Published: May 2005

AbstractProton spin‐spin coupling values measured for a wide range of tetrasubstituted tetrahydropyran ring‐systems obtained from aldopentopyranose sugars have been correlated with values calculated from a generalized version of the Karplus equation which takes into account the electronegativities of the various atoms in the molecule and the configurations of these substituents. Minor discrepancies between observed and calculated values can be attributed to slight flattening of the tetrahydropyran ring as a result of steric interactions of the substituents. The magnitude of the geminal coupling J5e,5a of these aldopentopyranose derivatives provides a rough measure of the conformational population; when H‐4 is axial [Cl(D) or 1C(L) conformation] J5e,5a is ∼10.9 Hz, and is ∼13.4 Hz when H‐4 is equatorial [1C(D) or Cl(L) conformation].
Etude par RMN des 2,2′‐Dihalogeno‐Diethylethers—I: Effet de Température
Authors: Haloui Ezzeddine , Canet Daniel , Granger Pierre 
Published: May 2005

AbstractLes spectres RMN d′éthers disubstitués de formule (XCH2CH2)2O avec X = Cl, Br, I, d′une part, à température ambiante et à l′état pur et, d′autre part, en solution dans CS2 et à différentes températures, ont été analysés avec précision. Les déplacements chimiques de chacun des groupements CH2 ont pu ětre attribués. Les rotaméres prépondérants ont été déterminés à l′état pur et à différentes températures. De plus, il est montré que pour ces trois halogénures dissous dans CS2, les formes gauches relatives à chaque branche deviennent plus stables en refroidissant. Les auteurs ont mis au point une procédure permettant, par décomposition de raies, de traiter les spectres de type AA′BB′ ayant l′aspect de spectres de type A2B2.
NMR‐Untersuchungen bei Prolin‐enthaltenden Diketopiperazinen
Authors: Siemion Ignacy Z. 
Published: May 2005

AbstractBei NMR‐Untersuchungen der cis‐ und trans‐Reihe Prolin‐enthaltender Diketopiperazine konnten Unterschiede zwischen den Signalen pseudoaxialer und pseudoäquatorialer Substituenten (α‐Proton, α‐Methylgruppe, α‐iso‐Propylgruppe) festgestellt werden.
Nuclear magnetic resonance studies of internal rotation—III Rotational barriers in META‐ and PARA‐substituted N, N‐dimethylcinnamamides
Authors: Spassov S. L. , Dimitrov V. S. , Agova M. , Kantschowska I. , Todorova R. 
Published: May 2005

AbstractThe rotational barriers about the CN bond of eight m‐ and p‐substituted N, N‐dimethyl cinnamamides have been determined by the iterative total line shape NMR method. The ΔG values have been correlated with the substituent constants σ, σn and σ+. By comparison of the results with literature data, some conclusions about the accuracy of the barrier determination as well as the transmittance of polar effects in conjugated amides have been drawn.
A semi‐empirical MO calculation of 13C chemical shifts—I: Alkanes
Authors: Solkan V. N. , Mamayev V. M. , Sergeyev N. M. , Ustynyuk Yu. A. 
Published: May 2005

Abstract13C shielding constants have been calculated for a series of alkanes, methane to pentane. The quantities σd and σp have been obtained, using an average excitation energy approximation and the extended Hückel MO wave functions in terms of the Pople method. The results fit the experimental data and the VB results of Grant et al. fairly well. The quantity σd varies within a wide range for carbon atoms of various degrees of substitution. Two conformations of the hydrocarbons studied have been calculated. The results show that the 13C chemical shifts may be used for conformational analysis.