bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 n.m.r. of the 8‐phosphabicyclo[3.2.1]octane system
Authors: Rudi A. , Kashman Y. 
Published: May 2005

Abstract13C Chemical shifts and 13C31P nuclear spin coupling constants have been determined for 26 8‐phosphabicyclo[3.2.1]octane derivatives, namely phosphines, phosphine oxides, phosphine sulphides and one phosphonium salt. The influence of the phosphorus configuration on δ and 2J(PC) values was examined and other factors influencing the 2J(PC) coupling constant are discussed.
Calculation of some boron nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A. 
Published: May 2005

AbstractBoron screening constants and their anisotropies have been calculated for 23 trivalent boron compounds. The calculations have been performed within a framework in which gauge‐dependent atomic orbitals are used in the molecular orbital description. Reasonable agreement with experimental chemical shifts is found when CNDO/S parameters are used; INDO calculations are less satisfactory. No correlation is found between the observed chemical shifts and those estimated from the Average Excitation Energy approach. Similarly, no correlation is found with total boron charge densities although agreement is reported with π charge density. In trimethylboron the lowest energy σ→π* transition dominates the in‐plane contributions to the local paramagnetic term while various σ→π* transitions dominate the out‐of‐plane contributions.
Sur l'Utilisation de la Stéréospécificité des Couplages Magnétiques à Longue Distance dans la Détermination des Conformations d'Aziridines Bicycliques
Authors: Rouillard Michel , Férrero Louis , Geribaldi Serge , Azzaro Marcel 
Published: May 2005

AbstractL'étude des couplages magnétiques à longue distance relevés dans les spectres RMN du proton à 60 MHz d'aziridines du type aza‐7 bicyclo[4.1.0]heptane, permet de préciser la conformation de ces composés et de démontrer sans ambiguïté l'existence de structures bloquées pour certains isomères.
NMR studies in the heterocyclic series. XVIII—Carbon‐13 NMR study of azolium salts. Attempted correlation of chemical shifts with calculated charge densities
Authors: Fayet Jean‐Pierre , Vertut Marie‐Claire , Fruchier Alain , Tjiou El Mostafa , Elguero José 
Published: May 2005

AbstractThe carbon‐13 chemical shifts and the 1J(CH) coupling constants for 18 azolium salts (di‐N‐methyl‐pyrazolium, ‐indazolium, ‐benzimidazolium and ‐benzotriazolium iodides) have been determined and assigned. The chemical shifts are discussed as a function of substituent effects, positive charge introduction and total electronic density (calculated by the CNDO/2 method). The general problem of correlations between chemical shifts and total charge densities in azoles is discussed. A statistical approach shows that these correlations are of poor quality.
Remarks on the analysis of dynamic 1H NMR spectra of A3B2 ⇌ C3D2 spin systems. Internal rotation in N,N‐diethylbenzamide
Authors: Gryff‐Keller Adam , Szczeciński Przemyslaw 
Published: May 2005

AbstractA method of analysis of dynamic NMR spectra for A3B2 ⇌ C3D2 spin systems is proposed. This method is based upon the assumption that the shape of the A–C part of the spectrum is the same as for the AB2 ⇌ CD2 spin system and the shape of the B–D part is the same as for the A3B ⇌ C3D system. By means of this simplification the iterative total line shape analysis of dynamic NMR spectra by the use of the least‐squares method becomes feasible. The method proposed is applied to the determination of the thermodynamic parameters of activation for internal rotation in N,N‐diethylbenzamide in CD3CN (ΔG = 62.6 kJ mol−1 ΔH≠ = 62 kJ mol−1, ΔS≠ = −1 J/mol−1 K−1). The determination of natural line widths is discussed in detail and a method of estimation of the effect of systematic errors on the results is proposed.
The conformation and configurational assignment of 6,7‐disubstituted 2‐oxabicyclo[3.3.0]octan‐3‐ones
Authors: De Clercq P. , Samson M. G. 
Published: May 2005

AbstractThe conformational behaviour of 6‐alkyl‐3‐oxo‐2‐oxabicyclo[3.3.0]octan‐7‐ols and some derivatives possessing the configurations a (6‐endo‐7‐exo), b (6‐endo‐7‐endo) and c (6‐exo‐7‐endo) is discussed. It is shown that an easy configurational assignment is possible between these three series.
19F spectra—structure correlations of fluorinated quaternary phosphonium salts
Authors: Van Hamme Michael J. , Burton Donald J. , Greenlimb Peter E. 
Published: May 2005

AbstractThe 19F NMR chemical shifts and geminal FCP and FCH coupling constants are reported for a number of fluorinated quaternary phosphonium salts of the type \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm R}_3 \mathop {\rm P}\limits^ \oplus {\rm CFXY}]{\rm Z}^ \ominus $\end{document}, where generally R = alkyl or aryl; X, Y = hydrogen or halogen and Z = halogen. Spectral parameters remain relatively unaffected upon variance of R, Z−, and/or solvent, except when R is a bulky alkyl group. Linear relationships accurately describe the correlation between the summation of the electronegativities of X and Y, or simply of Y if X = F, and the 19F NMR chemical shift and geminal FCP coupling constant; geminal FCH coupling constants show no such dependence. These relationships are of demonstrated analytical value, particularly for the purpose of spectral prediction.
Etude en RMN du 13C des Effets de Substituant sur les Déplacements Chimiques du Carbone dans les Méthyl Tétrahydrofurannes
Authors: Accary Armand , Huet Jean , Infarnet Yves , Duplan Jean Claude 
Published: May 2005

AbstractLes spectres de RMN du 13C de quelques méthyltétrahydrofurannes ont été enregistrés et analysés. Les effets du groupement méthyle sur les atomes de carbone du cycle sont interprétés en fonction de l'encombrement stérique et de l'équilibre conformationnel.
A dynamic NMR study of Z, E‐isomerization in solutions of indolyl‐substituted α‐nitroacrylates
Authors: Bakhmutov V. I. , Burmistrov V. A. , Babievsky K. K. , Kochetkov K. A. , Kvasov B. A. , Belikov V. M. , Fedin E. I. 
Published: May 2005

AbstractFast Z, E‐isomerization of α‐nitro‐β‐indolylacrylates in polar solvents has been studied by dynamic 1H NMR spectroscopy. With indolylnitroacrylates having no substituents at the ring nitrogen atom, isomerization proceeds via intermediate formation of a mesomeric anion and ionization of the N–H bond as the rate determining step. For methyl‐substituted indolylnitroacrylates, no general isomerization mechanism can be suggested, and isomerization pathways depend on the structures of isomerizing species.
The torsional barrier in aromatic carbonyl compounds. V. Carbon‐13 DNMR study of stable protonated p‐substituted acetophenones
Authors: Barthelemy Jean‐François , Jost Roland , Sommer Jean 
Published: May 2005

AbstractThe barrier to internal rotation around the phenyl–carbonyl bond in a series of stable protonated p‐substituted acetophenones has been determined by means of low temperature 13C NMR and total bandshape analysis resulting in a value of ΔG = 48.1 kJ mol−1 for the unsubstituted protonated compound. The energy results and the 13C chemical shifts are in good agreement with the quasi‐planarity of the ground state in p‐substituted protonated acetophenones. The barrier heights are discussed in terms of contributions from steric and resonance effects.
Identification et Etude en Résonance Magnétique Nucléaire du Carbone‐13 des Produits de la Réaction de Quaternisation en Série Thiazolo[3,2‐d]tétrazolique
Authors: Faure R. , Galy J. P. , Vincent E. J. , Elguero J. 
Published: May 2005

AbstractNous avons montré que les produits obtenus lors de la quaternisation du thiazolo[3,2‐d]tétrazole, et de deux de ses dérivés, phényl‐3 thiazolo[3,2‐d]tétrazole et tétrazolo[5,1‐b]benzothiazole, sont des sels de tétrazolium. Nous avons discuté des effets dus à la quaternisation en fonction des résultats de la RMN du 13C.
A colour‐coded set of capillaries for improved deuterium locking and shimming of viscous samples
Authors: O'Neill I. K. , Stuart B. 
Published: May 2005

AbstractCoaxial capillaries containing deuterated materials provide better 2H‐locking and magnet shimming for the 13C and 31P FTNMR observation of viscous samples. A series of capillaries is necessary for the accurate shimming of materials with differing polarities and magnetic susceptibilities.
1H and 13C NMR study of the prototropic tautomerism of 4(5)‐vinyl‐1,2,3‐triazole in dimethylformamide as solvent
Authors: Toppet S. , Wouters G. , Smets G. 
Published: May 2005

AbstractCarbon‐13 NMR study of 4(5)‐vinyl‐1,2,3‐triazole in dimethylformamide at −55°C allows direct observation of the three separate tautomers. The 13C chemical shift values of the three forms, as well as their percentages in the tautomeric mixture, are given.
NMR spectral studies. XIV. Carbon‐13 nuclear magnetic resonance studies on β‐lactams
Authors: Bose Ajay K. , Srinivasan P. R. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of a variety of mono‐ and bicyclic β‐lactams have been measured and the chemical shifts of the ring carbon atoms have been assigned unambiguously. Effects of substituents on the chemical shifts of these carbons are also discussed.
The dynamic stereochemistry of dimesityl‐2,4,6‐trimethoxyphenylmethane: A 1H NMR study at 270 MHz
Authors: Willem R. , Hoogzand C. 
Published: May 2005

AbstractThe spectral behaviour of dimesityl‐2,4,6‐trimethoxyphenylmethane (1) was examined by 1H NMR spectroscopy at 270 MHz in order to resolve an isochrony of resonances observed in the low temperature spectra of 1 at 60 MHz. At 270 MHz the spectra of 1 exhibit well resolved o‐methyl resonances at low temperature so that the two‐ring flip mechanism, previously proposed as the threshold mechanism by Mislow et al., receives new independent experimental support.
Characterization of coupling constants to nitrogen. Carbon‐13 chemical shifts and carbon–nitrogen coupling constants of substituted benzaldoximes
Authors: Danoff Ann , Franzen‐Sieveking Marcia , Lichter Robert L. , Fanso‐Free Samuel N. Y. 
Published: May 2005

AbstractCarbon‐13 chemical shifts and 13C−15N coupling constants of substituted benzaldoximes and of two non‐aromatic oximes have been determined. The coupling constants display little variation as a function of the nature or position of substitution, which suggests that perturbations in the π electron distribution have little effect. The values are compared with the markedly different ones reported for mesitaldoxime, and, in conjunction with the observed solvent effects, are discussed within the Schulman‐Venanzi framework for assessing the role of the lone‐pair.
Determination of hydration equilibrium constants and pKa values of 4‐piperidones in buffered water solutions
Authors: Van Luppen J. J. , Lepoivre J. A. , Dommisse R. A. , Alderweireldt F. C. 
Published: May 2005

Abstract1H and 13C chemical shift parameters are given for 4‐piperidones and their derivatives in buffered aqueous solution. The 13C shift increments of methyl substituents on the nitrogen atom are discussed. The pH‐shift dependence is studied in detail and pKa values are given for ketone forms and hydration products. The hydration equilibria are measured as a function of pH and temperature.
13C NMR spectra of polymethoxy‐ and methylenedioxyflavonols
Authors: Calvert D. J. , Cambie R. C. , Davis B. R. 
Published: May 2005

AbstractThe 13C NMR spectra of 20 polymethoxy‐ and/or methylenedioxyflavonols are reported. In key cases assignments have been made by examination of fully coupled spectra.
Substituent group effects on the NQR frequency of Cl in certain chloromethane derivatives
Authors: Ramanamurti D. V. , Venkatacharyulu P. , Premaswarup D. 
Published: May 2005

AbstractAn empirical method is suggested for estimating the NQR frequencies of substituted chloromethanes. The frequencies are given by the equation νCl = νo + ∑imi, where the parameters mi are characteristic of the substituent groups, with additive properties in the case of multiple substitution for substituted chloromethanes. The calculations reveal that (i) as in chlorobenzenes, the effect of substituent groups on the NQR frequencies is additive to a first order of approximation, (ii)the effect is much larger in chloromethanes than in chlorobenzenes, (iii) the relative effects of different substituent groups are similar in the two sets, (iv) where there is more than one substituent group their mutual interaction is of the same order of magnitude as the crystal field effects.
15N nuclear magnetic resonance studies of [1‐15N]nicotinamide adenine dinucleotides
Authors: Oppenheimer Norman J. , Davidson Robert M. 
Published: May 2005

AbstractThe synthesis of [1‐15N]nicotinamide adenine dinucleotide is described. Chemical shift data from 15N NMR studies are presented for the pyridine ring nitrogen of labeled NAD and related compounds. The results indicate a 15N label in the N‐1 position to be highly sensitive to the redox‐state of the pyridine moiety, with an upfield shift of over 100 ppm observed upon reduction of NAD+ to NADH. The feasibility of conducting 15N NMR studies of pyridine nucleotide binding to dehydrogenases is discussed.
Carbon‐13 nuclear magnetic resonance studies of creatine, creatinine and some of their analogs
Authors: Dietrich Robert F. , Marletta Michael A. , Kenyon George L. 
Published: May 2005

AbstractCreatine (N‐methyl‐N‐amidinoglycine), creatinine (1‐methyl‐2‐aminoimidazolin‐4‐one) and a series of 38 of their close structural analogs have been examined using natural abundance 13C NMR spectroscopy at 25.16 MHz. Both proton‐coupled and proton noise‐decoupled spectra were recorded. Unequivocal assignments of the carbon resonances could be made in the vast majority of cases. Both 13C NMR chemical shifts and 1J(CH) values can be used to characterize and to differentiate readily between analogs of creatine and analogs of creatinine. For example, the 1J(CH) coupling constants for the α‐carbons of the acyclic creatine analogs were all in the 140–142 Hz range, whereas the corresponding coupling constants for the related, cyclized creatinine analogs were all in the 150–152 Hz range.
Assignment and sign determination of (C, H) and (H, H) coupling constants in N‐acetylimidazole with selective population inversion experiments
Authors: Pachler K. G. R. , Wessels P. L. 
Published: May 2005

AbstractThe assignment of the (C, H) couplings in N‐acetylimidazole and the determination of the relative signs of all (C, H) and (H, H) couplings with SPI experiments are described. All coupling constants are of the same, positive, sign as the directly‐bonded (C, H) coupling constants. Some advantageous features of the SPI technique, such as selectivity and increased sensitivity, are discussed in comparison to conventional double irradiation methods.
Hindered rotation in the N(2,2,2‐trichlorocarboethoxy)nortropanes. An NMR study
Authors: Scheiber P. 
Published: May 2005

AbstractA rarely occurring type of hindered rotation was observed by 1H NMR in some N‒(2,2,2‒trichlorocarboethoxy)nortropanes. A complete lineshape analysis gave the activation energy Ea = 56.9 kJ mol‒1 for the rotation around the CH2OCO bond.
1H NMR study of some substituted acyclic silaethanes, 2‐silapropanes and 2‐methyl‐2‐silapropanes and their rotameric populations around the SiC bond
Authors: Carleer Robert , Anteunis Marc J. O. 
Published: May 2005

AbstractThree series of substituted silaalkanes, (i) SiH3CH2X, (ii) MeSiH2CH2X and (III) Me2SiHCH2X, have been prepared (X=Cl, Br, I, NMe2, OMe, SMe), and the shifts and coupling constants extracted from their1H NMR spectra. Coefficients averaged over three rotameric states can be obtained from the first series which are used for the correction of coupling constants resulting from the presence of the electronegative substituents X. With the aid of the Karplus‐Conroy angular dependence of the interproton coupling constants in silaethane† fragments, corrected for electronegative substitution, approximate rotameric populations in series ii and iii were obtained. Except for X=NMe2, there is always a preference for asynclinalX/CH3relationship, even for sandwiched situations (series III).
The stereochemistry of the 6‐membered ring of cedranone
Authors: Rodríguez Mario , Bertrán José Fernández 
Published: May 2005

AbstractEvidence from the coupling constants and solvent shifts of the protons in cedranone rules out the boat and chair conformations of the cyclohexanone ring. Linear correlation of the solvent shifts of the C‐15 methyl protons of cedranone with those of the α‐methyl groups of fenchone indicates a nearly planar conformation of the cedranone ring. Site factor analysis of the ASIS effect of the methyl protons of cedranone provides conclusive evidence of a quasi‐chair conformation of the 6‐membered ring.
Ligand conformation in lanthanide complexes by NMR paramagnetic shifts: L‐proline and L‐valine
Authors: Mossoyan J. , Asso M. , Benlian D. 
Published: May 2005

AbstractA fitting procedure is descdribede to establish the conformation and molecular dynamics of flexible molecules co‐ordinated to lanthanide cations from NMR paramagnetic shift data of 1H and 13C resonances. The results from L‐proline and L‐valine in aqueous solution at low pH values are consistent with peak assignments given by independent methods. A free rotation of the pyrrolidine ring is proposed in the case of L‐proline, and a rigid lock in the case of L‐valine, and angle and distance values are given for the cation and ligand positions in the complex.
Aromatic imine stereochemistry as studied by 13C and 1H NMR of 15N‐enriched materials
Authors: Buchanan Gerald W. , Dawson Brian A. 
Published: May 2005

AbstractA series of thirteen 15N‐enriched N‐aryl imines derived from benzaldehydes and acetophenones have been prepared and examined by 13C and 1H NMR. Preferred conformations of the C‐arvl and N‐aryl rings have been deduced from 13C chemical shifts and 13C‐15N couplings. Evidence for steric inhibition of resonance in O‐alkylated materials is presented. Relative signs of 1J(CN) and 2J(CCN) have been determined in some compounds. An E: Z interconversion barrier of 21.6 kcal mol−1 has been obtained from 1H NMR coalescence data.
Additive of substituent effects on the chemical shift of the formyl proton in disubstituted benzaldehydes
Authors: Castañeda H. O. , Contreras R. H. , de Kowalewski D. G. 
Published: May 2005

AbstractAn additivity relationship of substituent effects on the formyl proton chemical shift has been tested with ten disubstituted benzaldehydes. In most cases it is found that the formyl proton chemical shift, extrapolated to infinite dilution in nitromethane, is in good agreement with that calculated using the additivity relationship.
Prediction of anti and gauche vicinal proton‐proton coupling constants in carbohydrates: A simple additivity rule for pyranose rings
Authors: Altona Cornelis , Haasnoot Cornelis A. G. 
Published: May 2005

AbstractThe effect of the relative orientation and electronegativity of substituents on the magnitude of 3J(aa), 3J(ae) and 3J(ee) is well predicated by a simple set of additivity constants, valid for pyranose rings in carbohydrates. The proposed set of parameters is used to calculate 327 coupling constants [3J(HH)] in a variety of pyranosides and related compounds. A comparison with experimental values taken from the literature shows that couplings in molecules which are conformationally pure and underformed can be predicted with a surprising accuracy. An overall root‐mean‐square agreement of 0.29 Hz is attained for a selected group of 305 coupling values. A statistical breakdown of ΔJ(aa) and ΔJ(ae) [ΔJ=J(exp)‐J(calc)] along each carbon‐carbon bond in the pyranose systems reveals an unexpected degree of geometrical homogeneity.
The molecular structure of allenes and ketenes. XIV—semi‐empirical descriptions of 13C chemical shifts of ketene imines and deduced from the effects of isoelectronic substitutions in allenes
Authors: Runge Wolfgang 
Published: May 2005

AbstractAn essentially algebraic model for semi‐empirical calculations of 13C chemical shicts of ketene imines and ketenes is presented which utilizes geometrical and non‐geometrical aspects of symmetry. In particular, emphasizing isoelectronic substitution as a generalized symmetry principle, it is shown that approximation functions for the description of 13C chemical shifts of ketene imines and ketenes can be deduced from those used for the allenes, and that the parameters which are necessary for the calculations of the carbon resonances of the heterocumulenes are simply related to those used for the allenes. A comparison between calculated and experimental 13C chemical shifts of complex ketene imines and ketenes demonstrates the relevance of the suggested model.
Vitamin B6 and derivatives. II—13C NMR study of systems formed by pyridoxal phosphate or pyridoxal with octopamine
Authors: Haran Raymond , Laurent Jean‐Pierre , Massol Michel , Nepveu‐Juras Francoise 
Published: May 2005

AbstractSchiff base formation by condensation of pyridoxal phosphate or pyridoxal with octopamine in aqueous or methanolic medium was investigated by 13C NMR. Enolimine forms are favoured in methanolic solution, whereas in aqueous solution the predominant ketoenamine forms show a hydrogen bond between the iminium proton and the C‐3‐O− phenolate anion of the pyridoxal phosphate. The addition of Cu++ ions is consistent with the hypothesis of chelation of Cu++ by the nitrogen of the aldimine function and the phenolate function of pyridoxal phosphate.
The configuration of β‐halogenoenamines. The use of a new procedure for NOE measurements
Authors: Granger Pierre , Chapelle Stella , Poirier Jean‐Marie 
Published: May 2005

AbstractThe configurations of 16 different β‐halogenoenamines have been determined using the proton NOE effect, and the same results were obtained as when the 2J(CH) coupling constants were used. A new procedure called the ‘repetitive shift frequency’ is presented for the NOE determinations which allows better reproducibility and improves the precision.
13C NMR Studies: Effect of steric compression on chemical shifts of carbons in diastereoisomers
Authors: Prashad Mahavir , Seth M. , Bhaduri A. P. , Banerji Avijit 
Published: May 2005

Abstract13C NMR of diastereoisomeric pairs of 2,3‐diaryl‐2‐methylbutyronitriles revealed a difference in the chemical shift of the carbon atoms between the diastereoisomers and the observed shifts were greatly influenced by the presence of an ortho substituent in the 3‐phenyl ring.
11B13C coupling constant in LiB(CH3)4
Authors: Yanagisawa Masaru , Yamamoto Osamu 
Published: May 2005

AbstractCoupling constants between 11B and 13C, 13C and 1H, and 11B and 1H were obtained for LiB(CH3)4 in 1,2‐dimethoxyethane, in which the anion B(CH3) is belived to exist as a separate ion pair. The correlations of the coupling constants with the effective nuclear charge of boron, and with the s character of the BC bond, are discussed.
The conformation of (1R,2S,4R,5S)‐2,4‐dimethoxybicyclo[3.3.1]nonan‐9‐one and some related compounds
Authors: Camps P. , Jaime C. 
Published: May 2005

AbstractA mixture of stereoisomers of 2,4‐dimethoxybicyclo[3.3.1]nonan‐9‐one was prepared, separated by column chromatography and characterized by 60 MHz 1H NMR spectroscopy using Eu(fod)3. A double chair conformation with axial methoxyl groups is established for (1R,2S,4R,5S)‐2,4‐dimethoxybicyclo[3.3.1]‐nonan‐9‐one on the basis of the J(12), J(2,H‐3 exo) and J(2,3 endo) values and the chemical shifts for H‐2(4). The conformation of some related compounds is subsequently inferred.