bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long range 31P1H couplings in phosphorylated iminothiazolines and iminooxazolines
Authors: Tseng C. K. , Mihailovski A. 
Published: May 2005

AbstractLong range 31P1H coupling constants of 21 phosphorylated iminothiazolines and two phosphorylated iminooxazolines have been studied. The size of the 31P1H coupling in the HCNCNP framework is larger than that in the HCSCNP framework which is in turn larger than the HCOCNP framework. The value of the 31P1H coupling through the HCNCNP framework decreases in the order of P > PS > PO, whereas a reverse trend is observed for the HCSCNP framework. A planar zig‐zag configuration has been proposed for the long range 31P1H couplings.
Study of the intrinsic and conformational solvent effects on the chemical shift of the aldehydic proton in furfural and thiophenealdehyde
Authors: Bertrán José Fernández , Rodríguez Mario 
Published: May 2005

AbstractThe chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents. The correlation of the chemical shifts of thiophenealdehyde and benzaldehyde is excellent (r = 0·996) while it is lower for furfural–benzaldehyde (r = 0·956). The long range coupling constant Jα5 of furiurai has been measured in twelve solvents and the rotameric mole fractions determined. The chemical shifts of individual rotamers are calculated and shown to correlate with benzaldehyde, (r = 0·992; 0·993). Only one rotamer is predominant for thiophenaldehyde in all solvents. The intrinsic solvent effects of the three aldehydes are similar.
Benzo‐ and indoloquinolizine derivatives. VI—configuration and conformation of 4b,5,6,7,8,8a,10,11,16,16b‐decahydrodibenz[f,h]indolo[2,3‐a]quinolizine diastereoisomers. A 270 MHz 1H NMR study
Authors: van Binst G. , Tourwé D. 
Published: May 2005

AbstractThe synthesis of a D/E cis isomer of the title compound is described. In an attempt to obtain the other D/E cis isomer, epimerisation reactions were studied. The configuration and conformation of the isomers are determined on the basis of their 1H NMR spectra. The shift of the 16b proton on N‐9 protonation indicates the quinolizidine conformation. At 270 MHz, the ABCD system of the C‐10 and C‐11 methylenes can be analysed. The 2J(C‐10H2), together with the multiplicity of H‐8a, allows an unequivocal assignment of a cis‐anti‐cis structure to the only D/E cis isomer obtained.
Intrinsic carbon‐13 NMR solvent shifts in hydrocarbons. Relevance of long range substituent parameters
Authors: Wilson A. R. N. , van de Ven L. J. M. , de Haan J. W. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts have been measured in a number of binary mixtures of normal alkanes. Intrinsic solvent shifts are deduced from the shifts and the relevance of some small substituent effects in alkanes is discussed. A comparison is made between solvent effects and thermally induced chemical shift differences in alkanes.
Influence of methyl substituents on the chemical shift of the ring protons in mono‐, di‐ and trimethylcyclohexanes a 300 MHz study of the 1H NMR spectrum of cis‐1,3‐dimethylcyclohexane
Authors: Danneels Dirk , Anteunis M. 
Published: May 2005

AbstractFrom a 300 MHz spectral study of mono‐to trisubstituted cyclohexanes, allowing a re‐examination of some of their 1H NMR spectral parameters, it is shown that it is possible to predict with reasonable accuracy the shifts (in CCl4) of the ring protons. A substantial feature in this is the validity of the (questioned) additivity of multiple effects. It is also shown that with respect to shift alterations, equatorial ring protons behave anomalously, which cannot be explained by any existing theoretical model.
Theoretical and empirical calculations of the carbon chemical shift in terms of the electronic distribution in molecules
Authors: Martin G. J. , Martin M. L. , Odiot S. 
Published: May 2005

AbstractThe principles of the theoretical calculations of the carbon atom screening constant are reviewed. The Independent Electron, SCFMO and Valence Bond formulae are briefly discussed, and the relative importance of the different terms involved in an approximate decomposition of σ13C are pointed out. The variations of the excitation energy ΔE, the mean distance between the nucleus and 2p electrons, and the electronic charges and bond orders with the structure are presented. The nature of the steric effect is also explained. In a second part the various empirical correlations which make an evaluation of δ13C from structural and physical properties possible are shown. The actual substituent parameters of the main classes of compounds are listed and worked examples given to make the use of the tables easier. The correlations between δ13C and the electronic charge, electronegativity, Hammett‐Taft constants, electric field effects, geometrical parameters, spectroscopic data (electronic transitions, screening of other nuclei) and pH are also discussed with a view to appraising the carbon screening.
composés cycliques à six chaǐnons
Authors: Cazaux Louis , Navech Jacques 
Published: May 2005

AbstractDiverses méthodes de calcul sont proposées pour calculer l'angle de torsion de la liaison CC dans les composés cycliques à six chaǐnons. Elles fournissent un ordre de grandeur correct de cet angle par comparaison avec les mesures aux rayons X. La limite de cette détermination est montrée.
Long range substituent effects relfected in the 13C NMR spectra of allyl alcohols and their derivatives
Authors: Wenkert Ernest , Gašić Miroslav J. , Hagaman Edward W. , Kwart L. D. 
Published: May 2005

AbstractAcylation of allyl alcohols induces strong carbon shifts, shielding γ and deshielding δ effects. These shifts are a consequence of through‐bond polarization of the olefinic carbons. Allyl ethers show similar, but milder perturbations. The olefinic carbon shifts reveal a strong concentration dependence. This effect, in greatly reduced form, is also observed in non‐oxygenated alkenes. Hydrogen bonding by alcohols enhances the chemical shift difference in olefinic carbon pairs by increased polarization.
Carbon‐13 nuclear magnetic resonance chemical shifts and 13C‐199Hg coupling constants for symmetrical dialkylmercurials
Authors: Casanova J. , Rogers H. R. , Servis K. L. 
Published: May 2005

AbstractThe carbon‐13 chemical shifts and coupling constants (J[13C199Hg]) have been determined for a series of eleven symmetrically substituted organomercurials. Empirical substituent parameters can be calculated which correlate observed and predicted chemical shifts for dialkylmercurials.
A NMR investigation of proline and its derivatives. II—Conformational implications of the 1H NMR spectrum of L‐proline at different pH
Authors: Pogliani L. , Ellenberger M. , Valat J. 
Published: May 2005

AbstractThe 250 MHz 1H NMR spectrum of L‐proline is comprehensively analysed by computer simulation for different pH values. A fast endo–exo interconversion has already been proposed from chemical shift and coupling constant data. A critical comparison of the vicinal coupling constants leads to the conclusion that in basic solution the equilibrium is shifted towards a more endo conformation. The position of the carboxylic plane in the ring space is given by the relative intramolecular chemical shift of the geminal protons and by the typical patterns of the Hα multiplet. These results are applied to the analysis of the spectra of ProNH2 and AcProNH2.
Reaction de redistribution entre le tripropylbore et ses produits d'oxydation: Etude par résonance du Noyau 11B
Authors: Cros G. , Costes J. , Laurent J‐P. 
Published: May 2005

AbstractL'étude par résonance magnétique nucléaire (11B) des systèmes formés par le tripropylbore et l'anhydride borique met en évidence l'intervention de réactions de redistribution entre le tripropylbore et ses produits d'oxydation, c'est‐à‐dire de redistributions mettant en jeu des groupements monofonctionnels (C3H7) et difonctionnels (O) sur des atomes de bore tricoordonnés.
Proton NMR spectrum of indene oriented in the nematic phase
Authors: Diehl P. , Vogt J. 
Published: May 2005

AbstractThe proton NMR spectrum of the 8‐spin system of indene has been studied in the nematic phase of N‐(p‐ethoxybenzylidene)‐p‐n‐butylaniline. Orientation parameters and ratios of interproton distances have been derived and are compared with the results of an electron diffraction study.
Hochauflösungs‐13C‐NMR‐Spektroskopie. II—Die Spektren von (2‐Dimethylamino‐1‐propenyl)triazinen
Authors: Braun S. , Frey G. , Bachmann M. 
Published: May 2005

AbstractDie unentkoppelten 13C‐NMR‐Spektren der bei der Reaktion von Methyltriazinen mit 1‐Äthoxy‐1‐(dimethylamino)‐äthylen entstandenen Produkte wurden mit Hilfe der Puls‐Fourier‐Transform‐Technik aufgenommen und analysiert. Der Vergleich der beobachteten 13C‐chemischen Verschiebungen und 13CH‐Kopplungskonstanten mit denen der Ausgangstriazine und des 2‐Dimethylamino‐2‐penten‐4‐ons bestätigt die (2‐Dimethylamino‐1‐propenyl)triazin‐Struktur. Die Daten werden im Hinblick auf sterische Effekte sowie die Konfiguration und Konformation der Seitenkette diskutiert.
Unresolvable long range spin–spin coupling as a source of systematic error in proton NMR total bandshape analysis
Authors: Drakenberg Torbjörn , Carter Robert E. 
Published: May 2005

AbstractUnresolvable long range spin‐spin coupling which is not explicitly taken into account in total NMR bandshape analysis is demonstrated to be a potentially important source of systematic error, leading to ΔH≠ and δS≠ values incorrect by c. 1 kcal/mol and 2 to 4 cal/(mol K), respectively.
Etude par RMN du carbone des systèmes CN: imines, phénylhydrazones, semicarbazones, amidines, iminoéthers
Authors: Naulet N. , Filleux M. L. , Martin G. J. , Pornet J. 
Published: May 2005

AbstractCe travail présente une étude par RMN de carbone‐13 de composés comportant une double liaison CN simple et conjuguée (iminoéthers, imines aliphatiques, imines éthyléniques, amidines, oximes, phénylhydrazones, semicarbazones). L'influence de la stéréoisomérie Z/E, des substituants et le rǒle de l'effet stérique sur le déplacement chimique sont discutés.
1H NMR spectra of E and Z pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone and related compounds
Authors: Bell C. F. , Mortimore G. R. 
Published: May 2005

AbstractProton magnetic resonance spectra at 100 MHz are reported for the E‐ and Z‐isomers of pyridine‐2‐carbaldehyd 2′‐ pyridylhydrazone in carbon tetrachloride, d6‐dimethylsulphoxide and d6‐benzene solutions, and for various monomethylated derivatives in d6‐dimethylsulphoxide. The spectral parameters obtained by analysis with the help of LAOCOON 3 are discussed in terms of solvent effects and the chemical shift changes consequent upon isomerisation are evaluated. Some conclusions are reached concerning the preferred conformations of the E‐ and Z‐isomers of pyridine‐2‐carbaldehyde 2′‐pyridylhydrazone.
Parameter errors in LAOCOON 3 calculations
Authors: Ewing D. F. 
Published: May 2005

AbstractSome model calculations with LAOCOON 3 have been used to show that the mean error in the calculated coupling constants is linearly related to the root mean square error in the transition frequencies. On the basis of this linearity it is shown that the ‘probable’ error parameter of LAOCOON 3 should be increased by a factor of 2·5 to give more realistic errors.
13C NMR spectroscopy of four tertiary methyl norbornenols and norbornanols
Authors: Paasivirta Jaakko , Laihia Katri 
Published: May 2005

AbstractCarbon chemical shifts and direct 13C1H coupling constants of 2‐endo‐methyl‐5‐norbornen‐2‐exo‐ol, 2‐exo‐methyl‐5‐norbornen‐2‐endo‐ol, 2‐endo‐methylnorbornan‐2‐exo‐ol and 2‐exo‐methylnorbornan‐2‐endo‐ol have been measured from single samples using a dual probe pulse Fourier transform method.
35Cl/37Cl isotope effects on 13C chemical shifts. Assignment of carbon‐13 NMR lines of polychlorinated hydrocarbons
Authors: Buchner W. , Scheutzow D. 
Published: May 2005

AbstractAn isotope effect of about 0·1 Hz at 25 MHz (0·004 ppm) on the 13C chemical shifts due to directly bonded chlorine has been observed at −50°C for hexachloropropene, hexachlorobutadiene and tetrachlorobutenyne. This effect yields an unambiguous assignment of 13C NMR lines to specific carbon atoms in these polychlorinated hydrocarbons.
Vicinal C,H spin coupling in substituted alkenes. Stereochemical significance and structural effects
Authors: Vogeli U. , von Philipsborn W. 
Published: May 2005

AbstractVicinal C,H spin coupling (3JC,H) in substituted alkenes has been investigated systematically. Emphasis is laid on the stereochemical significance (Jtrans/Jcis) and on the various structural factors which influence 3JC,H, such as π‐bond order, torsional angle ϕ, bond angle θ, electronegativity of substituents and steric effects. A new type of γ‐effect is observed in 3JtransC,H which appears to have the same origin as the γ‐shift effect. By comparison of 3J and 3JH,H, it was found that the relation 3JC,H ≈︁ 0·6 3JH,H holds for both trans and cis coupling constants. Finally, it is concluded that 3JC,H constitutes a valuable criterion to distinguish E‐ and Z‐isomers, particularly in trisubstituted alkenes. Applications to natural products are presented.
15N nuclear magnetic resonance spectroscopy. Natural abundance 15N NMR of monosubstituted indoles
Authors: Rosenberg E. , Williamson Kenneth L. , Roberts John D. 
Published: May 2005

Abstract15N chemical shifts of twenty‐four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2‐, 3‐ and 5‐ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl3. 13C NMR data for previously unreported compounds are also reported.
13C nuclear magnetic resonance studies on some substituted isoxazoles
Authors: Gainer James , Howarth Graham A. , Hoyle William , Roberts Stanley M. 
Published: May 2005

Abstract13C n.m.r. spectra of some substituted isoxazoles have been examined to ascertain the reactive site in the metallation of 4‐substituted 3,5‐dimethylisoxazoles. The results obtained indicate that metallation occurred exclusively at the C‐5 methyl.
13C, 15N coupling constants in substituted 1,2,4‐triazines‐4‐15N
Authors: Braun S. 
Published: May 2005

AbstractThe 13C,15N coupling constants in three 1,2,4‐triazine‐4‐15N derivatives and in a substituted pyrimidine‐1‐15N have been determined and are compared with those in pyridine and quinoline. Of special interest are the data of the 5‐(2‐dimethylamino‐1‐propenyl)‐3,6‐dimethyl‐1,2,4‐triazine‐4‐15N, since one observes a characteristic alternation of the absolute value of J(13C,15N) along the sidechain and a hitherto unobserved very large 13C,15N coupling constant through four bonds of 3·9 Hz, the origin of which is attributed to the influence of the lone pair orbital on the 15N at position 4.
Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques
Authors: Gobert F. , Combrisson S. , Platzer N. , Ricard M. 
Published: May 2005

AbstractLes conséquences en RMN 1H et 13C de l'effet péri induit par un phényle ont été étudiées en série anthracénique. On a pu montrer que les contributions stériques s'élevaient à 25% de l'effet total. Le modèle de Johnson et Bovey est susceptible de décrire correctement la zone de blindage du phényle seul. En RMN 13C, les blindages et déblindages inattendus observés chez les dérivés très encombrés sont probablement liés à des distorsions du squelette anthracénique.
13C Fourier transform n.m.r.: XIII—reassignment of the 13C spectrum of ergosterol
Authors: Cushley Robert J. , Filipenko J. Douglas 
Published: May 2005

AbstractThe complete labeling pattern of ergosterol isolated from Saccharomyces cerevisiae grown with [1‐13C] acetate is detailed and the results of this study have led to a reassignment of carbons 5, 8, 12, 16, 22 and 23 in the 13C n.m.r. spectrum of ergosterol.
Proton n.m.r. spin‐tickling studies of 13C‐labeled compounds. The correlation of J(C,H) and J(H,H)
Authors: Marshall James L. , Seiwell Ruth 
Published: May 2005

AbstractA tabulation has been compiled for twenty 13CH coupling constants of various carboxylic acids and includes 2J(C,H), 3J(C,H) and 4J(C,H) values of olefins (both cis and trans); 3J(C,H), 4J(C,H) and 5J(C,H) values of aromatics; 3J(C,H) and 4J(C,H) values of acetylenes; and 2J(C,H) and 3J(C,H) values of rigid aliphatics. This tabulation has been completed in the present study by the spin‐tickling proton n.m.r. study of 13C‐carboxyl‐endo‐1,2,3,4,7,7‐hexachloronorbornene‐5‐carboxylic acid, which has established that the 2J(C,H) value is negative and the 3J(C,H) values (both cis and trans) are positive in this system. A plot of these twenty J(C,H) values vs the corresponding J(H,H) values of geometrically equivalent model systems (where there is a proton in place of a carboxyl group) gives a correlation coefficient of 0·975 (with a slope of 0·62), indicating that carbon–proton and proton–proton couplings operate by similar mechanisms throughout this broad series of structural types.
Conformational investigations on cyclic dipeptides containing a proline residue by means of 13C n.m.r. spectroscopy
Authors: Siemion Ignacy Z. 
Published: May 2005

AbstractThe amounts of boat (A) and planar (B) forms for the equilibrium state in D2O and CD3OD/d6‐DMSO (1:1) were calculated for seven proline‐containing cyclic dipeptides from their 13C n.m.r. spectra. For c‐Pro‐Val the thermodynamic functions for the conversion between the boat and planar forms have been obtained from measurements of equilibrium constants at different temperatures.
Theoretical calculations of nuclear spin coupling of phosphorus to carbon and hydrogen by the finite perturbation method
Authors: Albright Thomas A. 
Published: May 2005

AbstractFinite perturbation calculations using CNDO/2 wave functions are presented for the determination of 31P13C and 31P1H couplings. The calculations were carried out on 46 molecules and a comparison with experimental values is given. The groups of compounds considered were phosphonium cations, phosphine oxides, alkylidenephosphoranes, phosphine sulfides, phosphoranes and phosphines. With the exception of phosphines, the finite perturbation approach reproduces the experimental couplings with fair accuracy. It is found that there is a good correlation with the calculated 1J(P, C) and the phosphorus 3s‐carbon 2s bond orders for tetra‐ and pentavalent phosphorus compounds. This lends support to the growing body of evidence for the direct relationship of the magnitude of 1J(P, C) and percent s character in the hybrid orbital on the carbon comprising the PC bond. The finite perturbation technique was also used to explore the effects of geometrical changes on PC and PH couplings. Finally, the effect of deleting d orbitals on phosphorus is discussed briefly.
Sélénophènes substitués. Additivité de l'influence des substituants sur les couplages J(HH) et J(SeH)
Authors: Simonnin M. P. , Pouet M. J. , Cense J. M. , Paulmier C. 
Published: May 2005

AbstractLes différents couplages J(HH) et J(SeH) mesurés dans divers sélénophènes 2‐ et 3‐substitués, dont les signes ont été déterminés par double résonance, ont été reliés aux constantes de réactivité de Swain et Lupton par des équations linéaires J = i + fF + rR. L'importance relative de la contribution des effets inductifs et mésomères est discutée. Dans les sélénophènes 2,4‐disubstitués, l'effet des deux substituants sur les couplages J(HH) et J(SeH) est additif. Cette loi d'additivité rend compte du changement de signe de 3J(SeH) observé dans le dinitro 2,4‐sélénophène. Les conformations préférentielles des formyl 2‐ et 3‐sélénophènes, déduites des couplages à longue distance, sont respectivement SeO cis et SeO trans.
The use of the selective population inversion technique in the assignment of carbon‐13 n.m.r. resonances in 3,6‐epoxy‐pentacyclo[6.2.1.02,7.04,10.05,9]undecane
Authors: Dekker T. G. , Pachler K. G. R. , Wessels P. L. 
Published: May 2005

AbstractDifferent applications of the selective population inversion technique in an n.m.r. study of 3,6‐epoxypentacyclo‐[6.2.1.02,7.04,10.05,9] undecane have been demonstrated. The intensity gain accompanying heteronuclear 13C—{1H} experiments allowed the detection of fine structure due to long range CH couplings otherwise hidden in normal proton coupled 13C spectra. Definite assignments of two very similar, directly bonded, CH couplings within a methylene group have been made.
13C spin relaxation studies of the basic pancreatic trypsin inhibitor
Authors: Wüthrich Kurt , Baumann Rudolf 
Published: May 2005

AbstractThe longitudinal 13C spin relaxation times T1 and the 13C{1H} nuclear Overhauser enhancement were measured in a concentrated aqueous solution of the basic pancreatic trypsin inhibitor. The correlation time for overall rotational motions of the basic pancreatic trypsin inhibitor molecules was found to be τR ≈ 2 × 10−8 s. In connection with previous 1H n.m.r. studies of intramolecular motions of the aromatics, we were particularly interested in the correlation times τG for intramolecular segmental motions of the aromatic rings. The present experiments revealed no manifestation of intramolecular motions of the aromatics, indicating that τG ≫ 2 × 10−8 s for the aromatic ring carbon atoms. On the other hand, rapid segmental motions were evidenced for the peripheral carbon atoms of aliphatic amino acid sidechains. Comparison of the 1H and 13C n.m.r. data on the basic pancreatic trypsin inhibitor indicates that the time scale of high resolution 1H n.m.r. at high fields may in many instances be more appropriate for studies of the molecular dynamics in globular proteins than the time scale of spin relaxation measurements.