bluuebunny/crossref_metadata_2025_split huggingface dataset:
350 MHz 1H NMR spectra, dipole moments and preferred conformation of 8,9‐epoxy‐6,7‐dihydro‐5H‐benzocyclohepten‐5‐ones
Authors: Huet Jean , Kotkowska‐Machnik Zofia , Zakrzewski Janusz 
Published: May 2005

Abstract350 MHz 1H NMR spectra and dipole moments showed that in the preferred conformation of 8,9‐epoxy‐6,7‐dihydro‐5H‐benzocyclohepten‐5‐one and its 1,4‐dimethoxy derivative the oxirane ring takes a pseudo‐axial position.
Carbon‐13 spectra of 2‐hetera[3](1,1′)ferrocenophanes
Authors: Piórko A. , Ratajczak A. , Dominiak M. 
Published: May 2005

AbstractThe analysis of the 13C FT NMR spectra of 2‐hetera[3](1,1′)ferrocenophanes containing an oxygen, sulphur, selenium atom, phenyl‐substituted nitrogen or a methylene group in the 2‐position of the bridge has been carried out. The electronegativity of this fragment affects both chemical shifts and coupling constants, but no simple relationship was found.
Solvent effects on 13C and 17O chemical shifts of polar molecules. Comparison between experiment and theory
Authors: Tiffon Bernard , Ancian Bernard 
Published: May 2005

AbstractExperimental solvent effects on 13C and 17O chemical shifts of acetone, and 13C chemical shifts of acetonitrile are compared with theoretical calculations by Jallali‐Heravi and Webb (solvaton model). Calculated values are, generally, in agreement with experimental results for atoms belonging to polar groups, but not for methyl carbons for which van der Waals interaction effects are predominant.
Synthesis and carbon‐13 nuclear magnetic resonance spectroscopy of 5,6‐dihydro‐2‐methyl‐1,4‐oxathiin, trans‐tetrahydro‐1,4‐benzoxathiin, 1,4‐tetrahydro‐[9,10]benzoxathiin, the 4‐oxides, 4,4‐dioxides and related acyclic compounds
Authors: Rooney Robert P. , Dyer John C. , Evans Slayton A. 
Published: May 2005

AbstractThe results of a 13C NMR spectral investigation involving 5,6‐dihydro‐1,4‐oxathiins, 1,4‐tetrahydro[9,10]benzoxathiin, trans‐tetrahydro‐1,4‐benzoxathiin, and the corresponding sulfoxides and sulfones are reported. An interpretation involving a dipolar structure with (2p→2p)π conjugation as opposed to (2p→3d)π interactions with the vinyloxy sulfides seems consistent with trends in the 13C NMR shifts. For the sulfoxides and sulfones, the substitutent‐induced chemical shift (SCS) effects at the β vinylic carbons (βSO and βSO2 effects) are considerably less than those at sp3 carbons. The γSO and γSO2 values at the sp2γ carbons indicate deshielding, in contrast to the shielding at the sp3 carbons.
13C NMR specta of 4‐quinolones and related compounds
Authors: Katritzky Alan R. , Ellison Joan , Frank Judit , Rákóczy Piroska , Radics Lajos , Gács‐Baitz Eszter 
Published: May 2005

AbstractComplete assignments are made for 23 4‐quinolones and related compounds. Literature data are used to calculate chemical shifts for 17 of these compounds: calculated and experimental shifts are in excellent agreement—all within 5 ppm for nine of the compounds and a maximum discrepancy of 7.6 ppm.
Complete assignment of the carbon‐13 NMR spectrum of chlorophyl a
Authors: Lötjönen Simo , Hynninen Paavo H. 
Published: May 2005

AbstractThe 13C NMR spectrum (at natural abundance) of monomeric chlorophyll α in acetone‐d6 has been recorded to re‐examine the assignments of the low field (aromatic‐olefinic) region of the spectrum. The assignments, made by the examination of the fully coupled spectrum and by the use of long‐range selective 1H decoupling (LSPD) with low‐power irradiation, were compared with those of the previous reports. The results of the present work clarify the ambiguities previously encountered in the assignment of the 10a‐ester, 7c‐propionyl, P‐2‐phytyl, 2b‐vinyl, γ‐ and β‐methine carbon atoms, as well as the β‐pyrrolic carbon‐6 and α‐pyrrolic carbons −16 and −17 of chlorophyll α. Reassignment of the three last carbons was found necessary. Knowledge of the chemical shifts of these carbon atoms was considered to be particularly valuable, as it yields relevant information on the delocalized π electron system which is crucial for the function of chlorophyll in photosynthesis.
Observation of steric hindrance in heteraferrocenophanes by carbon‐13 NMR
Authors: Piórko A. , Ratajczak A. 
Published: May 2005

AbstractThe 13C NMR spectra of stereoisomeric trans‐ and cis‐1,3‐dimethyl‐2‐oxa[3](1, 1′)ferrocenophanes, 1,2,3‐trithia[3](1, 1′)ferrocenophane and 1,3‐dithia[3](1, 1′)ferrocenophane have been recorded and analysed. The presence of steric hindrance in some of these compounds was confirmed and the conformations of the molecules were determined.
Self‐consistent perturbation‐INDO calculations of nuclear magnetic resonance carbon–carbon coupling constants for methylcycloalkanes
Authors: Stöcker Michael 
Published: May 2005

AbstractOne bond 13C,13C coupling constants have been calculated for some methylcycloalkanes, as well as for 2‐methylbutane, using the self‐consistent perturbation theory as formulated by Blizzard and Santry at the INDO (intermediate neglect of differential overlap) level of approximation. Together with previously published experimental data, the results can be interpreted satisfactorily on the basis of the Walsh model for cyclopropane and the known s character relationship 1J(13C13C) = 575·s(i)· s(j).
The 13C NMR of olefins complexed with a binuclear Ag(I)–Yb(III) chelate
Authors: Smith William B. 
Published: May 2005

AbstractThe effect of silver ion complexation on the 13C NMR of several rigid olefin structures has been determined. The silver ion induced chemical shifts (AgIS) are not amenable to easy interpretation. Addition of Yb(fod)3 forms binuclear Ag–Yb complexes with the olefin. Lanthanide induced shifts (LIS) fall off rationally with distance from the site of complexation and the averaged position of the lanthanide. The complexes may be used as probes of olefin stereochemistry.
Carbon‐13 nuclear magnetic resonance studies of thiocarbamates, S‐oxides and S,S‐dioxides
Authors: Tseng C. K. , Bowler D. J. 
Published: May 2005

AbstractThe 13C NMR spectra of four thiocarbamates and their corresponding S‐oxides and S, S‐dioxides are reported. Both βSO and β effects are deshielding and range from 20.44 to 21.68 ppm. The βSO′ effects are slightly deshielding (0.20 ∼ 0.0.77 ppm). The β′ effects, on the contrary, are shielding and range from −6.54 to −6.98 ppm. The γ′, δ′, ξ′, and ζ′ effects are also discussed.
Determination of one‐bond 14N13C coupling constants in amines using 13C T1ρ measurements
Authors: Mlynárik V. 
Published: May 2005

Abstract13C T1ρ values measured for isobutylamine, diethylamine, pyrrolidine, piperidine and triethylamine yield one‐bond 14N13C coupling constants and 14N spin‐lattice relaxation times. A decrease of 1J(14N13C) was observed in sterically hindered secondary amines.
Strained cyclobutane compounds: 1H NMR analysis of a new 1‐substituted benzobicyclo[3.1.1]heptene system
Authors: Escale R. , Khayat A. , Girard J. P. , Rossi J. C. , Chapat J. P. 
Published: May 2005

AbstractThe 1H NMR spectra of a number of new derivatives of benzobicyclo[3.1.1]heptene were examined and interpreted by using a single set of coupling constants. All the compounds belonging to this system are in a γ‐shaped configuration. Surprisingly, two different proton‐proton spin‐spin coupling constants (4J=5.5 to 6 Hz and 8.5 Hz) were obtained for the cyclobutane ring.
1H and 13C NMR studies of some aromatic dilactones (precursors of paracyclophanes)
Authors: Solladié‐Cavallo Arlette , Hilbert Marcel 
Published: May 2005

AbstractCarbon‐13 and proton NMR data of macrocyclic diaromatic dilactones are presented. The observed behaviour of the spectra as a function of temperature shows that the energy barrier for the re‐orientation of the side chains is lower than 49 kJ mol−1 (12 kcal mol−1) and that the energy barrier for the rotation of the aromatic rings is larger than 99 kJ mol−1 (24 kcal mol−1). Hence, chiral substituted dilactones of this type will be resolvable, and the enantiomers can be easily handled at room temperature.
Molecular structure and the indirect spin–spin coupling constants in azulene—a proton NMR study in the nematic phase
Authors: Arumugam S. , Kunwar A. C. , Khetrapal C. L. 
Published: May 2005

AbstractThe proton NMR spectrum of azulene has been investigated in the nematic phase of a liquid crystal. Spectral analysis provided the direct dipole‐dipole coupling constants which were used to derive the structural information. It was found that the relative proton‐proton distances in the 7‐ and 5‐membered rings deviate significantly from those for regular heptagons and pentagons. Indirect spin‐spin couplings were also obtained. Many of the inter‐ring and long‐range couplings have magnitudes between 0.2–0.8 Hz.
Dependence of the γ carbon‐13 shielding effect on electronegativity
Authors: Lambert Joseph B. , Vagenas Adelia R. 
Published: May 2005

AbstractThree γ effects on 13C shielding in 3,3‐dimethylheteracyclohexanes as a function of the hetero‐atom X have been examined. The γ‐anti effect on the equatorial 3‐methyl group is small in absolute magnitude but strongly dependent on the polar properties of X. The plot of the 13C shielding of this carbon vs the electronegativity of X is linear, with a slope of −5.8 ppm/electronegativity unit. The γ‐gauche effects on the axial 3‐methyl group and on the 4‐carbon are large in absolute magnitude but have quite different dependences on the polar properties of X. Whereas the shielding of the 4‐carbon exhibits a linear dependence on electronegativity (slope −3.5), the axial 3‐methyl group shows little dependence (slope crudely −0.7), even though the geometric relationship between X and either carbon is almost the same. Neither gauche carbon shielding appears to be related to the steric properties of X. The polar component of both the γ‐anti effect and the γ‐gauche effect is interpreted as arising from overlap of appropriately positioned parallel orbitals. For the anti case, the pathway is the familiar zigzag arrangement of bonds. For the gauche case, the pathway may be either through space (the orbitals would be only on X and C‐α; for the 4‐carbon, this interaction would be through the center of the ring) or through bonds (there are parallel axial orbitals on all four atoms). The absence of a significant polar effect for the axial 3‐methyl group suggests that the gauche interaction requires a rigid pathway. The polar component of the general γ‐gauche effect is superimposed upon a larger contribution that is essentially independent of the nature of X and may be associated with the removal of the hydrogen on the β‐carbon and replacement with the γ‐X group.
A tropisomerism: Racemization barrier of 13‐substituted oxyprotoberberines
Authors: Solladié‐Cavallo A. , Stambach J. F. , Jung L. 
Published: May 2005

AbstractThe two possible conformations of 13‐R‐substituted oxyprotoberberines are enantiomeric. The racemization barriers are determined for three of these compounds (R=OMe, OCOMe, OCOPh) using variable temperature 1H NMR. It was found that ΔG = 39.0 kJ mol−1 when R = OMe, ΔG = 63.5 kJ mol−1 when R = OCOMe and ΔG = 63.7 kJ mol−1 when R = OCOPh. When R = H, however, the barrier is well below 35 kJ mol−1, suggesting that one of the factors influencing these racemization barriers (as in 2,2′‐bridged biphenyl systems) is steric in origin. Such low barriers to racemization do not allow easy handling of the enantiomers after resolution, but could allow better complexation of the one desired enantiomer to the receptor.
Conformational study of anticholinesterase carbamates in the furylbenzene series by 1H and 13C NMR spectroscopy
Authors: Platzer N. , Ronzani N. , Lang C. , Lange C. 
Published: May 2005

AbstractThe structural analysis of carbamates derived from 2‐(α‐furyl)benzaldoximes and 2‐(α‐furyl)benzyl alcohols was carried out by 1H and 13C NMR spectroscopy. The conjugative and steric effects of alkyl substituents introduced on the benzene rings were found to modify the relative orientation of the aromatic and furan rings. The existence of a close relationship between the stereochemistry of the studied compounds and their anticholinesterase activity has been proposed.
The rα‐structure of partially oriented phthalonitrile determined from its proton spectrum with natural abundance 13C‐ and 15N‐satellites
Authors: Diehl P. , Amrein J. , Bösiger H. , Moia F. 
Published: May 2005

AbstractThe proton spectra of phthalonitrile, including 13C‐ and 15N‐satellites at natural abundance in isotropic and oriented solvents, have been analysed. The entire rα‐structure is derived from the direct couplings. The AISEFT method has been used for obtaining the pure satellite information.
13C NMR and force field investigations of hydrindane conformations
Authors: Schneider Hans‐Jörg , Nguyen‐ba Nghe 
Published: May 2005

Abstract13C NMR shifts of trans‐ and cis‐annelated bicyclo[4.3.0]nonanes with substituents R in position 8 (R  H, OH, Cl, Br) and 1‐hydroxy derivatives were analysed on the basis of force field calculated torsional angles using Allinger's MM1 program. Shielding increments for the 6 membered ring agree with corresponding cyclohexane values within ± 0.8 ppm maximal deviation. 13C NMR line shape analysis with cis‐hydrindane between 148 and 180 K yielded ΔH* = 37.0 ± 0.4 kJ mol−1 and ΔS* = 28 J mol−1 K−1 for the topomerization. The force field calculated reaction profile showed ΔH* = 37 kJ mol−1, in close agreement.
Assignment of the 13C nuclear magnetic resonance spectra of three 27‐hydroxyfriedelanes
Authors: Gunatilaka A. A. Leslie , Nanayakkara N. P. Dhammika , Sultanbawa M. Uvais S. , Wazeer Mohamed I. M. 
Published: May 2005

Abstract13C NMR spectra of 27‐hydroxyfriedelane, kokoonol (27‐hydroxyfriedelan‐3‐one) and kokoononol (27‐hydroxyfriedelan‐3,21‐dione) have been recorded and signals assigned using the off‐resonance decoupling, inversion recovery and lanthanide induced shift techniques.
Substituent effects on 13C and 1H chemical shifts in 3‐benzylidene‐2,4‐pentanediones
Authors: Solčániova E. , Hrnčiar P. , Liptaj T. 
Published: May 2005

AbstractSubstituent effects on the 13C and 1H chemical shifts have been studied for derivatives of 3‐benzylidene‐2, 4‐pentanedione. A significant correlation has been found between chemical shifts of the Z carbonyl group (C‐2) and Hammett constants, while no correlation has been found for the E carbonyl group (C‐4). Attempts have been made to determine the structural factors which influence these effects. The conformation of 3‐benzylidene‐2, 4‐pentanediones has been determined by 13C and 1H NMR spectroscopy.
Deuterium isotope effects on 13C nuclear shielding as a measure of tautomeric equilibria
Authors: Hansen Poul Erik , Duus Fritz , Schmitt Peter 
Published: May 2005

AbstractLarge deuterium isotope effects of both signs have been observed on the 13C nuclear shielding in proton‐chelating tautomeric forms of β‐thioxoketones, and small isotope effects of both signs have been found in related forms of Schiff's bases of salicylaldehydes. These effects are interpreted in terms of shifts in the tautomeric equilibria on deuterium substitution of the enolic proton. The observation of deuterium isotope effects is suggested as a useful method for the detection of fast tautomeric equilibria in systems of the following type.
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13C NMR spectra of diazastilbenes. II—Torsion angles of trans‐pyridinalanilines and trans‐benzylideneaminopyridines
Authors: Denecke Egon , Müller Klaus , Bluhm Thorsten 
Published: May 2005

AbstractThe torsion angles of trans‐pyridinalanilines and trans‐benzylideneanilines were derived from the chemical shifts of the para‐carbon atoms. The N‐torsion angle is between 33 and 59°. For the C‐torsion angle, a value of approximately 10° is obtained for the benzylideneaminopyridines and the C‐torsion angle for the pyridinalalines is estimated to be in the same range.
Carbon‐13 chemical shifts of 3‐substituted thietanes, thietane 1‐oxides and thietane 1,1‐dioxides
Authors: Dittmer Donald C. , Patwardhan Bhalchandra H. , Bartholomew John T. 
Published: May 2005

AbstractCarbon‐13 chemical shifts of the α‐ and β‐carbon atoms for 12 thietane 1,1‐dixides, 9 thietane 1‐oxides and 7 thietanes with a variety of 3‐substituents [H, CH(CO2Et)2, SEt, Br, SPh, Ph, Cl, NMe2, OH, OSiMe3, OAc, OEt] are correlated according to the nature of the sulfur atom (Y=sulfone, sulfoxide, sulfide) and the nature of the 3‐substituent (X) by the equations δα= aY+bX and δβ=aX+bY, where a and b are parameters characteristic of X and Y. One‐bond coupling constants [J(CH)] are reported for 21 compounds. The chemical shifts for the α‐ and the β‐carbon atoms of the sulfones show the ‘fore‐membered ring sulfone effect’ (α‐carbon unusually deshielded, β‐carbon unusually shielded), but the α‐carbon‐hydrogen coupling constants are similar to those of the sulfoxides and sulfides; the β‐carbon‐hydrogen coupling constants are sensitive to the nature of the substituent (X) but no special β‐effect is observed. Comparison of the chemical shifts of the α‐methylene carbon atoms of 3‐phenyl‐, 3‐(β‐naphthyl)‐ and 3‐(α‐thienyl)‐thietes with those of the coresponding sulfones also reveals the ‘four‐membered ring sulfone effect’ cis‐ and trans‐3‐Substituted thietane 1‐oxides may be distinguished by the greater downfield shift for the β‐carbon atom in the trans‐isomer.
A new method for differentiating between solvent effect mechanisms on 13C chemical shifts
Authors: Sugiura Makiko , Takao Narao , Ueji Shinichi 
Published: May 2005

AbstractA new method of differentiating between the different mechanisms operative for 13C solvent effects is proposed. This approach, in which the 13C solvent shifts of C‐1 of tert‐butylcyclohexane are selected for the reference solvent shifts, allows the study of 13C solvent shifts measured from an internal TMS reference. Using this method, the solute factor related to the van der Waals contribution can be estimated, and specific solvent effects other than the van der Waals effect can also be detected.
Relationships between the acidity of the Z and E isomers of N‐Nitroso‐N‐alkyl‐α‐amino acids and their conformations
Authors: Liberek Bogdan , Ciarkowski Jerzy , Plucińska Krystyna , Stachowiak Krystyna 
Published: May 2005

AbstractThe acidity constants of both Z and E conformational isomers of five N‐nitroso‐N‐alkyl‐α‐amino acids, ONN(R1)CH(R2)COOH, are determined by the observation of selected pH titrated 1H NMR signals. For two glycine derivatives (1, R1CH3, R2H, ONSar; 2, R1C2H5, R2H, ONEtGly) and two alanine derivatives (3, R1CH3, R2CH3, ONMeAla; 4, R1C2H5, R2CH3, ONEtAla) the E isomers appear to be stronger acids than the Z while for the third alanine derivative (5, R1n‐C3H7, R2CH3, ONPrAla) the opposite is observed. These results, also including anisotropy effects associated with the NNO group, are discussed in terms of conformations. A 7‐membered ring conformation with an NO…HOOC intramolecular hydrogen bond is proposed to be statistically important in the Z isomers of 1, 2, 3 and, to a lesser extent, 4.
1H NMR investigations on the conformation of the spirodioxolanes derived from vicinal diols. II—The ketal of cyclohexanone and racemic 1,2‐propanediol
Authors: Csunderlik C. , Chirilǎ T. , Bacaloglu R. 
Published: May 2005

AbstractThe methylene, methine and methyl protons at C‐2 and C‐3 from the dioxolane moiety in 2‐methyl‐1,4‐dioxaspiro[4.5]decane constitute an ABMX3 coupling system. The analysis data obtained and, also, the application of the Karplus rule to the value of the J(AB) vicinal coupling constant, confirm the axial orientation of the A methine proton and the pseudoequatorial orientation of the B methylene proton. These findings agree with a ‘half‐chair’ conformation of the 1,3‐dioxolane ring.
NMR spectrum of benzo[b]furan in a nematic phase
Authors: Arumugam S. , Kunwar A. C. , Khetrapal C. L. 
Published: May 2005

AbstractThe proton NMR spectrum of benzo[b]furan has been investigated in the nematic phase of a liquid crystal. Dipolar couplings obtained from the spectral analysis have been used to derive the interproton distance ratios. The phenyl ring geometry differs from that in benzo[b]thiophene. The deviations have been explained in terms of bond polarization effects.
13C NMR study of some derivatives of 1,3,4‐oxadiazoles, 1,3,4‐thiadiazoles and isosydnones
Authors: Aranda Gérard , Dessolin Michèle , Golfier Michel , Guillerez Marie‐George 
Published: May 2005

AbstractThe assignment of all ring carbons of 37 derivatives of 1,3,4‐oxa‐ or thiadiazoles and of seven isosydnones is described. In some cases, 13C‐labelled compounds were used. The analysis of substituent effects and the calculation of charge densities of some of the derivatives suggest that the two nitrogen atoms form a protective screen against electron perturbation and play the role of an ‘electronic buffer’. A notable variation of chemical shifts could be observed only when oxygen is replaced by sulphur.
The combined effects of two chlorine substituents and the non‐additivities of chemical shifts in aliphatic dichloro esters
Authors: Pitkänen Maija 
Published: May 2005

AbstractCarbon‐13 NMR spectra were measured for 25 methyl esters of aliphatic dichlorocarboxylic acids for substituted propanoic to hexanoic acids. Observed 13C shifts are compared with calculated shift values obtained from the shifts of the corresponding monochloro esters by applying a simple sum method. The greatest failures from additivity are observed for αβ and αα substituted carbons. The combined effects of two chlorine substituents were determined, and compared with those obtained from chlorine substituent effects in monochloro esters by assuming additivity. The trends displayed by the combined effects, and also by the non‐additivity effects, are discussed.
Configurational and conformational studies of N,N‐dimethylpiperidinium derivatives by 13C and 1H NMR spectroscopy
Authors: Casy A. F. , Ogungbamila F. O. 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of a series of methiodides of mono‐ and di‐C‐methyl derivatives of 1‐methyl‐4‐phenyl‐4‐piperidinols are reported and chemical shift data analysed in terms of configurations and conformations of isomeric sets. Results demondtrate the value of quaternary salt NMR data as an aid to configurational assignment, and the evaluation of non‐bonded interactions governing conformational equilibria in piperidine derivatives.
Isotopic perturbation of a degenerate valence isomerization. A 13C NMR study of deuterio‐1,5‐dimethylsemibullvalene
Authors: Askani Rainer , Kalinowski Hans‐Otto , Weuste Burkhard 
Published: May 2005

AbstractMono deuterio‐1,5‐dimethylsemibullvalene is studied by the isotopic perturbation method with respect to the equilibrium of the valence isomerization. It emerges that deuterium prefers the cyclopropane position. From the temperature dependence of the splittings in the 13C NMR spectra the ground state enthalpy difference in mono deuterio‐1,5‐dimethylsemibullvalene is calculated to be 484 J mol−1.
Chemistry of the SO Bond. 8—A stereochemical investigation of some methyl‐substituted trimethylene sulphites (1,3,2‐Dioxathian 2‐Oxides) via 13C nuclear magnetic resonance
Authors: Hellier Desmond G. , Phillips Andrew M. 
Published: May 2005

Abstract13C NMR chemical shifts for trimethylene sulphite and 35 derivatives are presented. From the magnitudes of the β shifts it has been possible to establish chemical shift additivity relationships for a series of compounds. The results are discussed in terms of probable conformations in solution.
Study of different association processes in the bicyclo[3.2.1]octan‐3‐ol series by 13C relaxation time measurements
Authors: Zahra J. P. , Waegell B. , Faure R. , Vincent E. J. 
Published: May 2005

AbstractThe measurements of T1 relaxation times in 13C NMR spectroscopy are used to determine solute‐solvent interactions. endo‐ and exo‐Bicyclo[3.2.1]octan‐3‐ol and the corresponding bromohydrins are used as substrates. In a non‐polar solvent, such as cyclohexane, solute‐solvent interactions occur exclusively, whereas in the more polar acetone only solute‐solvent interactions are observed. In chloroform, which is of intermediate polarity, the two types of interactions (solute‐solute and solute‐solvent) occur simultaneously.