bluuebunny/crossref_metadata_2025_split huggingface dataset:
Concerning the fluorine NMR spectra of steroidal phosphorofluoridates
Authors: Jennings W. Brian , Tolley Malcolm S. , Cooper G. H. , Chittenden Rosemary A. 
Published: May 2005

AbstractAdditional spectral evidence suggests that the previously reported signal doubling in the 19F NMR spectra of certain steroidal phosphorofluoridates is better interpreted in terms of diastereoisomerism than by restricted rotation around the PO bond.
13C NMR spectra of benzofuroxan and related compounds
Authors: Anet F. A. L. , Yavari Issa 
Published: May 2005

AbstractThe 13C n.m.r. spectrum of benzofuroxan at −15°C is assigned on the basis of selective decoupling experiments and by comparison with the 13C chemical shifts of model compounds. The 13C spectra were also measured in trifluoroacetic acid as a solvent. From the temperature dependence of the 13C spectrum of benzofuroxan in CDCl3, a barrier of 14·0 ± 0·2 kcal mol−1 is obtained for the degenerate tautomerism in this compound.
Nuclear magnetic resonance spectroscopy of Schiff bases: II—imines extracted from aqueous solution
Authors: Pesek Joseph J. , Frost Jack H. 
Published: May 2005

AbstractNuclear magnetic resonance spectroscopy is used to study netural imines formed from various aldehydes and primary amines in aqueous solution. The imines are then extracted into CDCl3 and their formation constants in the aqueous phase are calculated as a function of pD. The results are in agreement with previous studies. Decoupling experiments are used to prove that additional splitting of the proton spectrum is due to long range coupling rather than syn‐anti isomerism. The possibility of utilizing the formation of Schiff bases in aqueous solution for synthetic purposes is discussed and the 13C magnetic resonance spectrum of the imine, isolated from the reaction of 2‐thiophenecarbaldehyde and n‐butylamine, is reported.
Sterisch behinderte Rotation in monosubstituierten Ansa‐Verbindungen
Authors: Brink Maud 
Published: May 2005

AbstractDie Rotationsbarriere um die Pivot‐Bindungen in

equation image

mit n = 8 oder 10 und R = CH2C6H5, CH2COOH, CH2COOCH3 oder CH(CH3)2 wurde studiert; ΔG≠ Werte wurden > 24 Kcal/Mol. gefunden. Die Lösungsmittel‐, Temperature‐ und Konzentrationsabhängigkeit der doppelten, magnetisch nichtäquivalenten Methylenprotonen bzw. Methylgruppen wurde untersucht.
A 1H NMR study of hydrogen bonding and complexation processes of trimethylacetic acid in acetone
Authors: Balevichius V. , Kimtys L. 
Published: May 2005

AbstractThe carboxyl proton chemical shifts of trimethylacetic acid, which was dissolved in acetone and in binary mixtures of acetone and cyclohexane, have been measured as a function of concentration at temperatures of 0, +15, +30, +45 and +60 °C. The results obtained for the system studied, using the equilibrium constant method for interpretation of experimental data, indicate that the molecular association through hydrogen bonds occurs as a monomer‐cyclic dimer‐1:1 complex equilibrium process in the low concentration range (up to 0·08 mol fraction). The equilibrium constants of complexation and dimerization, the chemical shifts of the acid in the complex, and the thermodynamic parameters of complexation and dimerization have been calculated.
Etude stereochimique par RMN du 13C des α‐halogenocyclohexanones
Authors: Jantzen R. , Tordeux M. , de Villardi G. , Chachaty C. 
Published: May 2005

AbstractL'étude en RMN 13C des halogéno‐2 t‐butyl‐4 cyclohexanones cis et trans permet de mesurer l'influence de la nature et de la stéréochimie des halogènes sur les déplacements chimiques des différents carbones de la molécule. Les incréments sont comparés à ceux obtenus en série cyclohexanique. Par comparaison entre les valeurs des déplacements chimiques expérimentaux et calculés (à l'aide du jeu d'incréments trouvés précédemment) on montre sur des molécules mono‐ et dihalogénées de stéréochimie et de conformation connues, que ces incréments sont à la fois additifs et fonction linéaire de la valeur de la position de l'équilibre conformationnel.
A 1H NMR study of tautomerism in some 1‐arylamino‐3‐aryliminopropenes
Authors: Richards C. P. , Webb G. A. 
Published: May 2005

Abstract1H n.m.r. spectra at ambient temperatures reveal that an equilibrium exists between the ‘all‐trans’ and ‘all‐cis’ isomers of some of the 1‐arylamino‐3‐aryliminopropenes. The ‘all‐cis’ isomer predominates in nonpolar solvents, whereas the ‘all‐trans’ isomer is favoured in hydrogen bonding solvents. From a consideration of the magnitudes of the 3J coupling constants, it is reported that the ‘cis‐trans’ isomer is the most stable form of the 4‐nitrophenyl derivative in dimethyl sulphoxide.
13C n.m.r. chemical shifts of carbodiimides
Authors: Anet Frank A. L. , Yavari Issa 
Published: May 2005

AbstractThe 13C n.m.r. chemical shifts of the sp‐hybridized carbons in dialkylcarbodiimides have values of δc ≃ 140. These shifts are compared with those of similarly hybridized carbons occuring in other classes of compounds.
Conformational analysis: XIV—A 1H n.m.r. conformational study of methyl substituted 2‐oxo‐1,3,2‐dioxathians to confirm the predominance of chair forms in the trimethylene sulphite series
Authors: Nikander Hannu , Mukkala Veli‐Matti , Nurmi Timo , Pihlaja Kalevi 
Published: May 2005

AbstractSeven isomeric 4,5,6‐trimethyl‐2‐oxo‐1,3,2‐dioxathians, cis‐4‐trans‐6‐dimethyl‐r‐2‐oxo‐1,3,2‐dioxathian and two isomeric 4,5,5,6‐tetramethyl‐2‐oxo‐1,3,2‐dioxathians were prepared and their 1H n.m.r. spectra analysed. The values of the vicinal coupling constants reported earlier for the cis‐4‐trans‐6 compound were shown to be erroneous. In all cases the values of the vicinal coupling constants (and those of the chemical shifts) are indicative of a single chair conformation or a chair‐chair equilibrium, in contrast to earlier reports on the significant contribution of twist forms but in agreement with an electron diffraction study. The chair form is ≳ 31 kJ mol−1 thermochemically more stable than the twist form.
13C n.m.r. spectroscopy: Comparison of the spectra of some dimeric Catharanthus alkaloids and their derivatives
Authors: Dorman Douglas E. , Paschal Jonathan W. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of some dimeric Catharanthus alkaloids are reported and assigned. Methods devised to aid in the assignment of resonances in complex molecules are described. The 13C n.m.r. spectra of several derivatives of vinblastine are discussed.
Carbon‐13 n.m.r. studies of some saturated 1,2‐oxazepine derivatives
Authors: Rice Kenner C. , Wasylishen Roderick E. 
Published: May 2005

AbstractThe influence of incorporating an group, an oxygen atom and the fragment in a saturated 7‐membered ring system on carbon‐13 n.m.r. chemical shifts is examined, and also, the influence of the dioxolane ring moiety on the 13C chemical shifts in these ring systems. Substituent effects are generally additive except in cases where the ring is heavily substituted with methyl groups. A large upfield steric shift (γ effect) of 7–8 ppm is observed in two of the derivatives. An example of long range nonequivalence is also observed. Assignments of the 13C n.m.r. spectra have been made by comparison with model compounds, and from proton coupled 13C n.m.r. spectra. The synthesis of several new compounds is described.
Effets stériques des groupes alkyle sur le déplacement chimique des hydrogènes d'un méthyle: Correlation avec les termes Es de Taft
Authors: Roussel C. , Gallo R. , Chanon M. , Metzger J. , Bernassau J. M. 
Published: May 2005

AbstractL'effet des groupements alkyle de la série Me, Et, i‐Pr, t‐Bu sur le déplacement des hydrogènes d'un groupe méthyle, situé en ortho, est relié linéairement aux paramètres d'effets stériques (Es) de Taft dans des structures du type 1.

equation image
Une équation Δδ = δR – δMe = λ′Es rend compte des résultats expérimentaux. λ′ dépend du solvant et du modèle utilisé. Les calculs des déplacements chimiques suivant les approches d'ApSimon et de Buckingham confirment la prépondérance des effets stériques sur l'effet de substituant observé.
RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique
Authors: Grenier‐Loustalot M. F. , Iratçabal P. , Forchioni A. , Metras F. 
Published: May 2005

AbstractNous avons enregistré les spectres RMN du 13C d'une série de quatorze chlorocyclohexanones afin d'examiner les variations du déplacement chimique du 13C en fonction de la position de l'orientation et du nombre de substituants chlore. On détermine par comparaison entre les valeurs des déplacements chimiques expérimentaux et calculés de molécules chlorée, des incréments Δδ13C et les conditions de leur additivité. La comparaison des déplacements chimiques observés et calculés dans le cas de molécules mono et dichlorées en interconversion, montre que les effets du chlore sont additifs.
2,3,5,6‐Tetramethylmorpholine: II—1H n.m.r. structural studies of the isomers of 2,3,5,6‐tetramethylmorpholine
Authors: Hernestam Sven , Nilsson Bertil 
Published: May 2005

AbstractThe structures of the six isomers of 2,3,5,6‐tetramethyl‐morpholine have been determined by means of proton nuclear magnetic resonance studies at 100 MHz. The spectra have been analysed in terms of spin–spin coupling constants and population distributions of the possible conformers at low temperatures. Also included in this paper are results from n.m.r. studies on the six 4‐benzyl‐2,3,5,6‐tetramethylmorpholine derivatives, which give information about the stereochemistry of the methyl groups α to the amine group.
Natural abundance nitrogen‐15 n.m.r. spectroscopy. Spin–lattice relaxation in organic compounds
Authors: Levy George C. , Holloway Clive E. , Rosanske Richard C. , Hewitt James M. , Bradley Craig H. 
Published: May 2005

AbstractThe small negative magnetogyric ratio (γ) of the 15N nucleus decreases the efficiency of 15N1H dipole‐dipole relaxation to about 25% of that for an analogous 13C nucleus. This may lead to greater competition from other relaxation mechanisms in 15N n.m.r. and consequent partial or total quenching of the negative nuclear Overhauser effect (NOE). In unfavorable circumstances nulling of the 15N resonance can occur. Previous 15N relaxation studies have examined isotopically enriched, low molecular weight compounds. The present study examines several small to intermediate size organic compounds containing nitrogen at natural isotopic abundance. In contrast to some of the earlier studies, 15N1H dipolar relaxation was found to be dominant for protonated nitrogen atoms, even for two tertiary nitrogens (the tertiary amine nitrogen in 1,2,3,4,6,7,12,12b‐octahydroindolo[2,3‐a] quinolizine and the oxime nitrogen in 3‐methyl‐2‐pentanone ketoxime). The magnitude of the NOE and the moderate value of T1 indicate effective dipolar relaxation from neighboring but not directly bonded protons in these cases. Nitro groups were found, as expected, to have predominant contributions from non‐dipolar mechanisms, and in one case (2‐methyl‐2‐nitro‐1, 3‐propanediol) signal nulling (NOE of η = −1) was observed. The effect of paramagnetic impurities was demonstrated for ethanolamine, which contains a basic nitrogen. In this case T1DD(15N1H) = 4·3 s; added Ni(acac)2 at 1 × 10−4 Molar reduced the 15N T1 to 0·065 s and consequently the NOE to η = 0.
13C n.m.r. spectroscopy of diethyl alkyl‐ and benzyl‐phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds
Authors: Ernst Ludger 
Published: May 2005

Abstract13C chemical shifts and31P13C spin–spin coupling constants are reported for 10 alkyl‐, 20 benzyl‐ and 3 (naphthylmethyl)‐phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects onJ(PC) are studied and discussed.nJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates andnJ(PP) (n = 5, 6, 7) were obtained from the13C satellites in the31P n.m.r. spectra of the isomeric diphosphonates, C6H4[CH2P(O)(OEt)2]2. Comparison of those13C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH3C6H4CH2P(O)(OEt)2, yielded the relative signs ofnJ(PC) (n = 2–6).
Nuclear magnetic resonance studies: VII—13C and 15N n.m.r. of diazo compounds
Authors: Albright Thomas A. , Freeman Walter J. 
Published: May 2005

AbstractThe 13C and 15N n.m.r. results for a series of diazo compounds are reported. It is found that the diazo carbon is shielded by an extraordinary amount compared with normal sp2 hybridized carbons. The 15N chemical shifts reveal that the terminal nitrogen is deshielded relative to the central one. This is contrary to that expected from charge effects but support is found for this phenomenon in other systems. One‐bond 13C14N coupling in diazomethane is also reported for the first time. INDO MO calculations of the charges and finite perturbation calculations of 13C14N and CH couplings are compared with the experimental results.
N.m.r. spectra of prostaglandin metabolites and precursors and of related pyrazoline adducts
Authors: Rackham David M. , Cowdrey Sarah E. , Gutteridge Norman J. A. , Osborne David J. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of the major human urinary metabolite of prostaglandin PGE2 and PGE1 are discussed together with some unsaturated precursors. Δ‐2‐Pyrazolines, formed by addition of diazomethane to the 11‐oxo dienediones in this series, were identified by 13C and 1H n.m.r. and by other physical methods.
13C n.m.r. investigation on the first and second nitrogen protonation in the diazanaphthalenes
Authors: van de Weijer Peter , van den Ham Dirk M. W. , van der Meer Douwe 
Published: May 2005

AbstractThe 13C chemical shifts of the diazanaphthalenes have been recorded as a function of the pH value, providing classical titration curves. From these curves the pK1 and pK2 values have been determined taking into account the activity coefficients. The changes in 13C chemical shift under the influence of nitrogen protonation (Δδ) can be described by two protonation parameter sets.
Kernresonanzspektroskopische Untersuchungen ancis‐(CH3)2Pt[P(OCH3)3]2
Authors: Hägele Gerhard , Lorberth Jörg 
Published: May 2005

Abstract100 MHz1H NMR Spektren voncis‐ (CH3)2Pt[P(OCH3)3]2werden als Superposition von [AR3X9]2‐und [AR3X9]2M ‐Systemen analysiert. Diecis‐Struktur wird abgeleitet von den KopplungskonstantenJ(PP) undJ(PtP).
Carbon‐13 n.m.r. analysis of selected strychnos alkaloids
Authors: Leung J. , Jones Alan J. 
Published: May 2005

AbstractThe carbon‐13 chemical shifts of strychnine and ten closely related analogues have been assigned and confirmed in several cases using selective proton decoupling techniques. Where additivity relationships are used the importance of having data on an array of structural analogues is emphasized. Quaternization at N‐19 exerts long range polarization effects throughout the molecular framework. The effects of N‐oxide formation on the carbon‐13 shifts of 5 to 9‐membered ring heterocycles and strychnine are discussed as aids to structural assignment. A Zwitterionic structure for strychnic acid is deduced.
Carbon‐13 n.m.r. studies. 65—13C spectra of some tricyclo[3.2.1.02,4]octane derivatives
Authors: Cheng A. K. , Stothers J. B. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of 18 derivatives of the tricyclo[3.2.1.02,4]octanes have been determined. This series includes methyl, hydroxyl and oxo substituted examples to compare the effects of these substituents on the skeletal carbon shieldings with those observed for the corresponding norbornanes and bicyclo[3.2.1]octanes. In general, the trends are similar and the perturbations associated with closely neighboring groups follow a consistent pattern. The shielding data for the exo–exo and exo–endo isomers of tetracyclo[3.3.1.02,406,8]nonane are also reported.
Determination of the conformation of 1,4‐diheterocyclanes. I—The1H n.m.r. spectrum and ring conformation of 3‐methyl‐2‐oxo‐1,4‐dioxepane
Authors: Äyräs Pertti , Partanen Annikki 
Published: May 2005

AbstractThe1H n.m.r. spectrum of 3‐methyl‐2‐oxo‐1,4‐dioxepane was recorded at 300 and 60 MHz. The ring conformation was considered in terms of the spectral parameters and shown to be a twisted boat where the lactone grouping is approximately planar.
Analyse du spectre de RMN protonique du cyclobutanedithiol‐1,1
Authors: Fournier Claude , Lemarié Bernard , Braillon Bernard , Paquer Daniel , Vazeux Michel 
Published: May 2005

AbstractCette note traite de la synthèse et de l'analyse du spectre de RMN protonique à 90 MHz du cyclobutanedithiol‐1,1. Les déplacements chimiques et les constantes de couplage sont rapportés et la discussion de ces dernières a permis de préciser la conformation de cette molécule.
Étude en RMN du 13C de Dérivés de la Pipéridone‐4 Stériquement Encombrés et des Oximes Correspondantes
Authors: Geneste P. , Kamenka J. M. , Brevard C. 
Published: May 2005

AbstractLes différences de déplacements chimiques régiospécifiques introduites par la fonction oxime permettent, à l'aide de paramètres (Δδ et Δδ), d'estimer les modifications conformationnelles directement à partir des spectres de 13 C. En particulier, les conformations croisées résultant de l'oximation de pipéridones stériquement encombrées sont détectées sans ambiguité.
Carbon‐13 n.m.r. study of 31P13C spin–spin coupling constants in dichloro‐ and monochloro‐vinyl phosphate derivatives
Authors: Szalontai Gábor 
Published: May 2005

AbstractCarbon‐13 chemical shifts and J(PC) coupling constants of 29 vinyl phosphate derivatives are presented. In the series of compounds (R1O)2P(O)OC1(R)C2X2 (where 3 in R indicates the first carbon of the R2 substituent) large differences were found between the 3J(P, O, C‐1, C‐3) and 3J(P, O, C‐1, C‐2) coupling constants of the chlorinated (XCI) and the unsubstituted (XH) derivatives. A possible explanation of this phenomenon is given on the basis of Jameson's s bond character theory. Strong stereospecificity of 3J(P, O, C‐1, C‐3) coupling constants was observed in the series of compounds (R1O)2 P(O)OC1(R)C2HR3. Coupling constants varied between 3.2–4.9 Hz in the E isomers, while peaks could not be resolved in the Z isomers. The 3J(P, O, C‐1, C‐2) coupling constants were regularly 20–30% greater in the Z than in the E isomers.
Temperature dependence of the chemical shifts of commonly employed proton n.m.r. reference compounds
Authors: Cross Bradford P. , Schleich Thomas 
Published: May 2005

AbstractThe temperature dependence of the chemical shifts of ten commonly employed 1H n.m.r. reference compounds of interest to both organic and biological workers was determined using the temperature independent standard ethane at low density. The water soluble standards sodium 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate and sodium 3‐trimethylsilylpropionate‐d6 exhibited very small chemical shift changes over the range of 20–65 °C. Outside of this temperature interval the chemical shift is distinctly nonlinear, but still is sufficiently small to be neglected for many n.m.r. studies. In contrast, the temperature dependence of seven neat organic liquid reference standards was observed to be linear over a significant temperature range with slopes varying between 0.0009 and 0.0023 ppm °C−1. Only tetramethylammonium chloride (in 2H2O) exhibited a small but pronounced nonlinear temperature dependence over the full range investigated.
Carbon‐13 n.m.r. investigation on the nitrogen methylation of the mono‐ and diazanaphthalenes
Authors: van de Weijer Peter , Mohan Chandra , van den Ham Dirk M. W. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of the N‐methylated mono‐ and diazanaphthalenes have been recorded and analysed. It has been shown that N‐methylation as well as N‐protonation in cinnoline occur predominantly at the β‐nitrogen atom. N‐methylation and N‐protonation show a similar effect on the 13C chemical shifts.
The interpretation of carbon nuclear magnetic resonance shifts. 3.. The variation of the local diamagnetic shielding term in 13C N.m.r., as determined by calculation and by X‐ray photoelectron spectroscopy
Authors: Mason Joan 
Published: May 2005

AbstractExperimental values of ‘chemical shifts’The term ‘chemical shift’ is used in the general sense, as by physicists and physical chemists (cf. chemical shifts in Mössbauer spectroscopy, or as here, X‐ray photoelectron spectroscopy). The chemical shift δ, as measured in n.m.r. spectroscopy, is then the algebraic sum of the ‘chemical shift’ in the local diamagnetic shielding term, ΔσAp in the paramagnetic term, ΔσAp and, the contribution from the rest of the molecule, in the local term approximation.
in the local diamagnetic term σAd for carbon in a wide range of groupings have been obtained from X‐ray photoelectron spectroscopic measurements of chemical shifts in the C‐Is binding energy. Eb. This conversion is possible because σAd and Eb both depend directly on the electrostatic potential within the valence shell; thus Eb increases, and σAd calculated by an extended Flygare method (in which CNDO‐calculated atomic charges are used to interpolate Hartree‐Fock values of σd for the free atom A and ± ions) show that the extended Flygare method values are reliable, differential relaxation effects in the photo‐emission process being small. Agreement is also good with published ab initio values of σAd. The range of variation in σAd for carbon is 7–8 ppm from C2H2 to CF4, or 10 ppm if one includes negative ions such as CN−. Some problems of the local term approximation are discussed, and comparison made with the atom‐plus‐ligand ‘local’ term approximation.
Résonance Magnétique Nucléaire. V.—Etude de Chlorures Vinyliques par RMN 1H. Incréments spécifiques des radicaux alkyle
Authors: Abudarham J. P. , Meyet J. , Smadja W. , Levisalles J. 
Published: May 2005

AbstractIsolés et identifiés, vingt‐cinq chlorures vinyliques ont été caractérisés par résonance magnétique du proton (RMN 1H), par chromatographie en phase vapeur (CPV) et, pour certains, par voie chimique. De nouveaux incréments spécifiques du groupe alkyle géminé au proton vinylique sont proposés. L'effet du chlore sur les hydrogènes vinyliques allyliques et homoallyliques est décrit, ainsi que l'effet de solvant du benzène.
1H n.m.r. spectra of N‐phenylmaleimide in isotropic and nematic phases
Authors: Khetrapal C. L. , Diehl P. , Kunwar A. C. 
Published: May 2005

Abstract1H n.m.r. spectra of N‐phenylmaleimide have been investigated in isotropic as well as nematic phases; the chemical shifts, the direct dipolar and the indirect spin–spin coupling constants have been determined. The direct dipolar coupling constants are consistent with rapidly interconverting energetically equivalent twisted conformations of C2 symmetry. Under the assumption that only two such conformers are predominantly present, the angle between the phenyl and the maleimide planes is determined as 52.9±0.9°.
Etudes d'Alkylidènehydrazono‐2 Méthyl‐3 Dihydro‐2,3 Benzothiazoles par RMN 1H en Présence d'Eu(fod)3
Authors: Richer Jean‐Claude , Beljean Martine , Pays Michel 
Published: May 2005

AbstractL'étude des spectres RMN 1H, en présence d'Eu(fod)3, d'une série d'alkylidènehydrazono‐2 méthyl‐3 dihydro‐2,3 benzothiazoles démontre que le site de coordination du complexe de lanthanide sur les deux azotes de ces azines varie en fonction de facteurs qui peuvent étre stériques ou polaires.Cette étude permet également de déterminer les configurations Z ou E des azines étudiées ainsi que les proportions relatives des isomères en solution dans différents solvants.
Carbon‐13 nuclear magnetic resonance of the azomethine group. II—(II.II) conjugation and twist angles
Authors: Solladié‐Cavallo A. , Solladié G. 
Published: May 2005

AbstractTorsional angles in some mono‐substituted conjugated benzenes were determined from the chemical shift of the para carbons. Similar results were obtained from ketones and imines, and the torsional angles increase, as expected, with steric hindrance. It is possible to assign a syn or anti stereochemistry for the imines from the value of the torsional angle.