bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative analysis by nuclear magnetic resonance with fourier transform II13C resonance
Authors: Thiault B. , Mersseman M. 
Published: May 2005

AbstractQuantitative analyses have been carried out by 13C NMR spectroscopy using Fourier transformation. The Overhauser effect, due to the broad band decoupling of protons, has been suppressed using the two existing methods (gated decoupling and paramagnetic species), and results from each are compared. Both require a calibration curve, and the second method, when applied to aromatic substances, needs the ratio between the sample to be analysed and the paramagnetic species to be less than a certain value. Experiments have been made with pure products and blends of pure products containing both saturated and aromatic carbons. The precision of the results is given.
The 1H NMR spectra of zinc complexes of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone
Authors: Bell C. F. , Mortimore G. R. , Reed G. L. 
Published: May 2005

AbstractProton magnetic resonance spectra at 100 MHz are described for some zinc complexes of the E‐ and Z‐isomers of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone in d6‐dimethylsulphoxide solution. Chemical shift data are discussed qualitatively in relation to factors such as the charge on the metal ion, the anisotropy of ligand nitrogen atoms, electric field effects caused by the dipole moment of nitrogen lone pairs, metal‐nonbonded‐hydrogen interactions, ring current effects and the conformational changes undergone by each isomer on coordination.
13C NMR of organosulphur compounds: I—the effects of sulphur substituents on the 13C chemical shifts of alkyl chains and of S‐heterocycles
Authors: Barbarella Giovanna , Dembech Pasquale , Garbesi Anna , Fava Antonino 
Published: May 2005

AbstractThe 13C NMR spectra have been determined of: (i) aliphatic compounds having at one end a functionalized sulphur atom (SH, S−, SMe, S(O)Me, SO2Me and S+Me2) and (ii) saturated sulphur heterocycles variously substituted at the S‐atom . The results are discussed in terms of the familiar deshielding effects for α‐ and β‐carbons and shielding effects for γ‐carbons, exerted by the sulphur atom itself and/or by the atoms or groups of which the sulphur function is made up. The γ‐effect of the S‐atom appears to be nearly independent of the nature of the S‐function and of comparable magnitude to that of an aliphatic carbon (−2·5 + −3·0 ppm). Surprisingly, however, a SCH3 group shields the carbon in γ position with respect to CH3 by an amount (−5·4 ppm) which is more than twice that (−2·5 ppm) exerted by the aliphatic γ‐carbon on the S‐CH3 carbon itself. As to the cyclic compounds, the shieldings of the α‐ and β‐carbons can be rationalized in terms of the conformational orientation of the substituent at sulphur, and the equilibrium distribution of the conformers. The results confirm the great value of 13C NMR for configurational and conformational assignment of S‐heterocycles.
13C NMR spectroscopy of polycyclic aromatics. VIII—amino derivatives of quinoline, isoquinoline, acenaphthene and fluoranthene
Authors: Ernst Ludger 
Published: May 2005

AbstractComplete assignments of the 13C n.m.r. spectra have been made for 5‐aminoquinoline, 5‐aminoisoquinoline, 5‐aminoacenaphthene and 3‐aminofluoranthene. Substituent‐induced shifts are compared with those of the structurally related 1‐aminonaphthalene. Some deviations within the series can be interpreted in terms of an increase of the exocyclic peri angle. An analysis of the 1H n.m.r. spectrum of 3‐aminofluoranthene is also given.
13C NMR spectra of some N‐aryl substituted sulphur–nitrogen compounds
Authors: Kresze G. , Berger M. , Claus P. K. , Rieder W. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of four classes of N‐aryl sulphur–nitrogen compounds are discussed. The para carbon shieldings of the N‐phenyl derivatives reflect the substituents effects of the various nitrogen groups. These show large differences for the four classes of compounds due to differences in the electronic structure of the sulphur–nitrogen bond.
Nitrogen NMR spectroscopy: Application to some substituted pyrroles
Authors: King Michael M. , Yeh Herman J. C. , Dudek Gerald O. 
Published: May 2005

AbstractA series of 15N labeled 2‐acylpyrroles was prepared and the nitrogen and proton n.m.r. spectra obtained. 15N chemical shifts for these compounds are reported for the first time. No correlation between the nitrogen chemical shift and any Hammett substituent constant could be found. No variation in J(15NH) was observed for any compound with changes in solvent, temperature or concentration, ruling out any observable tautomeric equilibria for these systems. An increase in J(15NH) with the addition of electron withdrawing groups indicates increasing polarization of the NH bond and acidity of these molecules. Two and three bond 15N couplings are also reported.
A 13C NMR investigation of some tetrakisisocyanocopper(I) tetrafluoroborate complexes: Chemical shift of, and coupling to, the isocyano carbon
Authors: Knol D. , Koole N. J. , de Bie M. J. A. 
Published: May 2005

AbstractThe 13C n.m.r. spectra twelve isocyanides, RNC, and their Cu(I) complexes, Cu(RNC)4BF4, were recorded in the solvents CDCl3 and DMSO. The resonances of the isocyano carbon, C0, could be observed for both free and coordinated isocyanides. In the spectra of the complexes this C0 resonance was present as a broad line. For some complexes the 14N13C0 coupling could only be detected after heating the sample or by adding small amounts (<7 mo1%) of Cu(CH3CN)4BF4. For the remaining complexes neither J(14N13C0) nor J(14N13C1), could be detected. No carbon‐copper coupling could be detected. The line shape of C0 is discussed in terms of exchange of an isocyanide ligand and in terms of quadrupolar nitrogen and copper relaxation. In most complexes exchange seems to be dominant, whereas in other complexes quadrupolar nitrogen relaxation is also of importance. On coordination of the isocyanide, the C0 resonance shifts upfield (15 to 20 ppm) and J(14N13C0) shows a threefold increase. The upfield shift is associated with a larger excitation energy while the increase of J(14N13C0) is ascribed to a larger effective nuclear charge on C0. The chemical shifts of the α‐carbon, the β‐carbon and the solvent effect on all n.m.r. parameters in both free and coordinated isocyanides are also discussed.
Determination of ΔH≠ and ΔS≠ by simultaneous 1H and 13C dynamic n.m.r. studies: Importance of the accuracy of temperature measurement
Authors: Piccinni‐Leopardi C. , Fabre O. , Reisse J. 
Published: May 2005

AbstractFrom ΔGTc≠ values obtained by 1H and 13C dynamic nuclear magnetic resonance studies of the same dynamic process, it is possible to estimate ΔH≠ and ΔS≠. Nevertheless, the accuracy of the temperature measurement is a factor which limits the applicability of this method. A very simple procedure for calibrating the usual temperature sensors is described, which can be applied to all types of n.m.r. probes. By the use of this procedure it is possible to measure coalescence temperatures in 1H and 13C n.m.r. with such an accuracy that ΔS≠ can be effectively determined from the difference between ΔGTc≠ values.
15N n.m.r.: Substituent effects on nitrogen chemical shifts in anilinium ions
Authors: Axenrod T. , Wieder M. J. 
Published: May 2005

Abstract15N chemical shifts were measured in a series of anilinium fluorosulfonate salts and compared with chemical shift data from a comparable series of 15N‐enriched aniline derivatives. A smaller overall range of nitrogen chemical shifts was observed for the protonated aniline series compared with that for the unprotonated anilines and is attributed to the elimination of nitrogen lone pair delocalization in the former series. Further‐more, it was found that the range of nitrogen chemical shifts in the protonated anilines is determined primarily by substituent electronic effects from the ortho ring position with almost negligible contributions from the para position.
La résonance magnétique du 77Se dans des composés organiques
Authors: Christiaens L. , Piette J‐L. , Laitem L. , Baiwir M. , Denoel J. , Llabres G. 
Published: May 2005

AbstractLa résonance magnétique du 77Se a été observée dans vingt‐six composés organiques dont certains contiennent un atome de sélénium endocyclique. Nous avons pu ainsi compléter l'échelle de déplacements chimiques établie par McFarlane. II apparaît difficile de définir une gamme de déplacement chimique du 77Se caractéristique de son état de valence ou de sa position endo‐ ou exocyclique. Certains résultats sont discutés qualitativement. Dans le cas du sélénolo [2,3‐b]thiophène, des arguments en faveur d'un couplage 4J(Se, H) à travers l'atome de soufre ont été découverts.
13C n.m.r. spectra of 2‐substituted pyrimidines
Authors: Turner Christopher J. , Cheeseman Gordon W. H. 
Published: May 2005

Abstract13C n.m.r. chemical shifts and carbon‐proton coupling constants of 2‐substituted pyrimidines are reported. The carbon chemical shifts are correlated with π‐electron densities. Substituents which cause deshielding at the directly bound carbon (e.g. NH2, OCH3 and F) exert a more powerful effect in the benzene series than in the pyridine or pyrimidine series. The carbon‐proton coupling constants do not correlate with the electronegativity of the substituents. Carbon‐proton coupling constants and proton‐proton coupling constants over the same number of bonds do not obey the Karabatsos relationship. The changes in the carbon‐proton coupling constants in 2(1H)‐pyrimidinone and 2(1H)‐pyrimidinethione which accompany anion and cation formation are reported.
Spectres RMN de 27Al d'hydrures d'aluminium
Authors: Huet J. , Durand J. , Infarnet Y. 
Published: May 2005

AbstractLes spectres RMN de 27Al de LiAlH4, AlH3 et LiAlH (YR)3 (Y = O ou S et R = Me ou t‐Bu) ont été enregistrés. Plusieurs remarques ont pu être faites sur les paramètres obtenus (δAl, J(AlH), largeur à mi‐hauteur).
Pattern recognition of geminal proton nonequivalence and second‐order coupling in 13C single‐frequency off‐resonance decoupled spectra. Assignment criteria and structure elucidation
Authors: Hagaman Edward W. 
Published: May 2005

Abstract13C n.m.r. single‐frequency off‐resonance decoupled (sford) CH multiplet resonance which deviate from normally assumed, isolated AnX spin descriptions have been characterized. Methylene carbons whose appended protons are nonequivalent generate doublets of doublets in sford spectra provided the proton chemical shift difference exceeds c. 3 × (Jgem). The isolated moiety–CHH′–closely approximates an AMX spin system. The strong chemical shift nonequivalence of geminal aminomethylene protons induced by the nitrogen lone pair in some N‐substituted piperidine derivatives is accompanied by preferential modification of the one‐bond CH coupling constants of the α‐amino protons. In N‐methyl‐4‐t‐butylpiperidine the natural coupling constants were shown to differ by 6–12 Hz. The 13C sford resonances of protonated carbons display varying degrees of second‐order coupling depending on the coupling strength of a carbon's appended protons with a strongly coupled spin set, the number of nuclei in the spin set, and the magnitude of the carbon's residual one‐bond splitting. Qualitative criteria that allow the classification of degrees of second‐order coupling have been established and utilized in signal assignment and structure analysis.
Investigation of substituent effects of chalcones by 13C n.m.r. spectroscopy
Authors: Soĺǎniová E. , Toma Š. , Gronowitz S. 
Published: May 2005

Abstract13C chemical shifts for 23 para‐ and meta‐substituted chalcones of the types 1 and 2 have been determined. The aromatic shieldings are compared with previous results for other aromatic derivatives. Correlations of the 13C chemical shifts of vinyl carbons and carbonyl carbons as well as ring carbons with Hammett σ parameters, π electron densities and the reactivity parameters of Swain and Lupton provide a consistent picture of electronic effects transmitted through the carbon framework of the compounds studied.
Temperature effects on 13C n.m.r. chemical shifts of normal alkanes and some line r and branched 1‐alkenes
Authors: de Haan J. W. , van de Ven L. J. M. , Wilson A. R. N. , van der Hout‐Lodder A. E. , Altona C. , Faber D. H. 
Published: May 2005

Abstract13C n.m.r. chemical shifts of a number of 1,1‐disubstituted ethylenes are presented. Moreover, effects of changing temperatures on the 13C n.m.r. chemical shifts of some of these compounds as well as of three normal alkanes are given. These variations in chemical shifts are attributed to varying amounts of sterically induced shifts in the different conformational equilibria. In addition to the well‐known 1,4 interaction between two alkyl groups shielding effects on the carbon atoms of the connecting bonds are also proposed. No definite explanation of this effect is presented at this time. It is further shown that no simple correlations exist between 13C n.m.r. chemical shifts and calculated total charge densities at this level. Instead, the experimental results in 1‐alkenes are rationalized by assuming a linear dependence of the 13C n.m.r. chemical shifts of C‐1 and C‐2 via rehybridizations on changes in bond angles for small skeletal deformations caused by steric interactions. These changes in geometries, as well as conformational energies in three 1‐alkenes, were calculated by means of VFF calculations. Finally. upfield shifts for both C‐2 and C‐4 are proposed for those conformations of 1‐alkenes in which the C‐3C‐4 group interacts with the pz‐orbital of C‐2.
13C n.m.r. spectra of some thiobenzamides. Correlation between 13C and 1H n.m.r. spectra and signal assignments of syn and anti CH2 groups
Authors: Piccinni‐Leopardi C. , Fabre O. , Zimmermann D. , Reisse J. , Cornea F. , Fulea C. 
Published: May 2005

Abstract13C n.m.r. spectra of a series of N,N‐disubstituted thioamides have been recorded and signal assignments were performed. Separate signals are observed for methylene groups fixed on the nitrogen atom. Since the carbon atom syn to the thiocarbonyl sulfur resonates at higher field than the anti carbon, the syn‐anti assignment in 1H n.m.r. is easily obtained by selective double irradiation. This method, which is rapid and reliable, affords a rather general solution to the interesting problem of resonance assignments in tertiary amides and thioamides (and in analogous molecules such as oximes and nitrosamines).
Pteridine studies: III—13C n.m.r. data of pteridine, some of its derivatives and their covalent σ‐adducts with ammonia and water
Authors: Geerts J. P. , Nagel A. , van der Plas H. C. 
Published: May 2005

Abstract13C n.m.r. spectral data of pteridine and nineteen of its derivatives (containing one or more chloro, methylthio, methyl, t‐butyl or phenyl substituents) are reported. The 13C n.m.r. spectrum of the title compound has been assigned conclusively. 13C n.m.r. substituent effects are shown to be very useful in discerning between 6‐ and 7‐substituted pteridines. Additionally, the 13C n.m.r. spectra of several covalent amination products, i.e. the 3,4‐dihydro‐4‐ amino‐ and the 5,6,7,8‐tetrahydro‐6,7‐diaminopteridine derivatives, formed by dissolving the appropriate pteridine in liquid ammonia, have been recorded. The 13C n.m.r. spectra of the corresponding covalent hydrates are also reported.
High resolution proton coupled 13C spectrum and structure of butadieneiron tricarbonyl
Authors: Bachmann K. , von Philipsborn W. 
Published: May 2005

AbstractA complete analysis of the proton coupled 13C spectrum of butadieneiron tricarbonyl is presented. The structure of the diene ligand is discussed on the basis of vicinal C,H and H,H coupling constants as well as 2J(HH), 1J(CH) and 1J(CC) data. These data are interpreted in terms of a non‐planar C,H skeleton in which C,C bond lengths are nearly equal and the terminal carbon atoms exhibit some rehybridization towards sp3. The results obtained from the complex in solution agree with a structural model from X‐ray data of substituted butadieneiron tricarbonyl complexes.
1H n.m.r. spectra and ensuing conformational evidence on carbon–carbon double bonded systems. (Electrically neutral organic Lewis acids—33)
Authors: Haslinger E. , Wolschann P. 
Published: May 2005

AbstractThe n.m.r. spectra of various derivatives of the cyclic acylal of malonic acid and of dimethylbarbituric acid are described. From the long range coupling constant, conformational evidence on the dihedral angle θ between the aromatic ring and the diketodioxane ring or the N,N‐dimethylbarbituric acid ring can be derived. The investigated substances show a dependence of θ on the aromatic substitution.
Constituents of Satureia calamintha. Application of Eu(fod)3 to the assignments of the methyl resonances of triterpenes related to 12‐ursene
Authors: Romeo G. , Giannetto P. , Aversa M. C. 
Published: May 2005

AbstractThe n.m.r. spectra of triterpenoids related to 12‐ursene have been examined using the shift reagent Eu(fod)3. The assignment of all the methyl resonances has been achieved for ursolic acid derivatives and the corresponding compounds of the 3‐epi series, which have not been investigated previously. The additive shielding effects of various substituents on the methyl resonance frequencies have been deduced from the results.
Zur theoretischen Interpretation von NMR‐chemischen Verschiebungen tetrakoordinierter zentralatome. IV—CNDO/2‐Berechnungen von 29Si‐NMR‐chemischen Verschiebungen. Der Einfluß der ΔE‐Näherung
Authors: Wolff R. , Radeglia R. 
Published: May 2005

AbstractAuf der Basis des CNDO/2‐Verfahrens werden paramagnetische Abschirmungskonstanten für das Zentralatom tetrasubstituierter Siliciumverbindungen Me4–nSiXn (X = F, OMe, NMe2, C1) mit und ohne ΔE‐Näherung berechnet und mit den experimentellen 29Si‐NMR‐chemischen Verschiebungen verglichen. Die aus dem Vergleich der berechneten Werte erhaltenen ‘mittleren Anregungsenergien’ ΔE sind von der Ladung am Zentralatom abhängig und können für quantitative Betrachtungen nicht als konstant angesehen werden.
Conformational analysis of N,N‐diisopropylamides by combined use of n.m.r. lanthanide‐induced shifts and conformational energy calculations
Authors: Graham Laurine L. , Vanderkooi Garret , Getz Joseph A. 
Published: May 2005

AbstractA new method of conformational analysis has been developed, in which energy minimization calculations are combined with lanthanide‐induced shift data. First, exhaustive energy calculations are carried out on the free molecules in order to determine the conformations of lowest energy. Then, the coordinates of all low energy conformations or pairs of conformations are used in the pseudocontact shift equation for lanthanide‐induced shifts in order to find which of the theoretically obtained conformation(s) gives the best agreement with experiment. The molecules complexed to the lanthanide shift reagent were N,N‐diisopropylformamide (DIPF) and N,N‐diisopropylacetamide (DIPA). Two different lanthanide shift reagents were used, Eu(fod)3Fod is the anion of 1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyl‐4,6‐octanedione‐d27.
and Pr(fod)3, in order to check the validity of the method. Proton magnetic resonance spectra were taken at 6 °C in carbon tetrachloride solution. The principal conformation found was different for each amide. DIPF was found to exist as a mixture of I (39 mol%) and II (61 mol%) with Eu(fod)3, and a mixture of I (37%) and II magnified image (63%) with Pr(fod)3. DIPA was found to exist as a mixture of I (79%) and IV (21%) with Eu(fod)3 and a mixture of I (87%) and IV (13%) with Pr(fod)3. For both molecules, the two conformations of lowest computed energy were also the pair which gave the best fit to the lanthanide shift reagent data. The location of the principal magnetic axis of the complex was found to lie between 0° and 14° from the lanthanide atom–oxygen atom bond axis. The technique of combining lanthanide shift reagent data with energy calculations shows great promise in conformational analysis.
13C n.m.r. spectra ofN,N‐dialkylamides
Authors: Fritz Hans , Hug Paul , Sauter Hanspeter , Winkler Tammo , Logemann Enno 
Published: May 2005

AbstractCarbon‐13 n.m.r. spectra of formic, acetic, propionic and butyric acid amides withN,N‐di‐n‐alkyl substituents have been completely assigned with the aid of extensive double resonance experiments. The data obtained were used to study long range steric effects on chemical and solvent shifts.
13C spectra of some vicinal dimethylene derivatives of cyclic hydrocarbons
Authors: Pfeffer H. U. , Klessinger M. 
Published: May 2005

AbstractCarbon chemical shifts of cyclic dimethylene compounds were determined and interpreted. It is suggested that steric compression leads to additional shielding of the exo‐methylene group, the chemical shifts of this group being a useful measure of the amount of steric hindrance.
Deuterium isotope effects in solutions of 2,4‐pentanedione
Authors: Leipert Thomas K. 
Published: May 2005

AbstractProton and deuterium n.m.r. measurements in acetylacetone and 3,3‐d2‐acetylacetone are reported. Deuterium‐isotope effects on chemical shifts and keto–enol equilibria as a function of concentration in the two solvents triethylamine and pyrrole are determined. A strong solvent concentration dependence for d‐isotope effects is observed in triethylamine; in pyrrole no dependence is obtained. The results are interpreted in terms of an equilibrium between the symmetrical (C2v) and asymmetrical (Cs) enolic forms in acetylacetone. The usefulness of 2H n.m.r. for the study of exchange processes is demonstrated.
1H n.m.r. spectra of 6‐acetoxy‐2,4‐cyclohexadienones
Authors: Bubb W. A. , Fallick C. J. , Sternhell S. 
Published: May 2005

Abstract1H n.m.r. spectra of 36 derivatives of 6‐acetoxy‐2,4‐cyclohexadienones were analysed. All available evidence indicates that all members of the series have similar conformations which do not depart significantly from planarity. Substituent‐induced chemical shifts and interproton coupling constants correlate well with those in the analogously substituted ethylene and benzene derivatives. In particular, it appears that a substituent on the central carbon atom exerts a similar influence on 4J(HH) across a ‘W’ path when the three intervening carbon atoms are a part of a benzene ring, an allylic system (i.e. sp3–sp2–sp2), a localized sp2–sp2–sp2 system or a saturated (i.e. sp3–sp3–sp3) system.
Calculation of some nitrogen nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A. 
Published: May 2005

AbstractSome nitrogen screening constants and their anisotropies are calculated within the CNDO/S level of approximation. Satisfactory agreement is found with available experimental data in most cases. In general the reported results are in closer agreement with experiment than are those found from ab initio calculations. The calculated data for the isoelectronic molecules N2O and CH2N2 would be in better agreement with experiment if the assignments of the two nitrogen nuclei were reversed in both cases. A reasonable correlation is obtained with some observed nitrogen chemical shifts. Contributions arising from electronic transitions are reported for N2, HCN, CH3CN, CH3NC, NO2+ and NO2−.
Study of molecular motions and 14N quadrupolar coupling in 1,3‐ and 1,4‐ diethylpyridinium bromides using 13C and 14N relaxation time measurements
Authors: Ghesquière Denis , Chachaty Claude 
Published: May 2005

AbstractThe internal and overall motions of 1,3‐ and 1,4‐diethylpyridinium bromides have been studied by 13C relaxation. The enthalpies of activation for the rotation of the ethyl groups in positions 1 and 3 are deduced from the temperature dependence of the T1 values of the methylene and methine carbons. The 14N quadrupolar relaxation time, Tq, together with 13C relaxation data provide an estimate of the 14N quadrupolar coupling constants.