bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molar paramagnetic solvent NMR shifts of galvinoxyl in toluene. Kinetics of the reaction between galvinoxyl and tertiary amines at high radical concentrations
Authors: Screttas Constantinos G. , Heropoulos Georgios A. 
Published: May 2005

AbstractThe molar paramagnetic solvent NMR shifts of galvinoxyl (1, G′) in toluene were measured at 34°C and found to be 2.21 and 2.39 ppm mol−1 for the aliphatic and the aromatic proton signals of toluene, respectively. The implications of the inequality of the two molar shifts are discussed. The paramagnetic solvent shift of G. in toluene in the presence of tertiary amines decays according to a first‐order rate law. The apparent first‐order rate constants were found to be linearly related to the initial concentration of the amine. The kobs vs. [R3N]0 regression lines in some cases exhibit a positive intercept, indicating the involvement of the solvent in the reaction. The logarithms of the second‐order rate constants are shown to be linear with respect to the ionization potentials of the amines. The reaction products of galvinoxyl with n‐Bu3N are hydrogalvinoxyl, GH and the enamine n‐Bu2NCH=CHEt whereas, with N/N‐dimethylaniline. the products are hydrogalvinoxyl and the hemiaminal ether of formaldehyde, derived from the combination of the radical PhN(Me)CH2. with G. through the oxygen of the latter. A mechanistic scheme is proposed involving a rate‐determining electron‐transfer step.
Accurate determination and analysis of the temperature dependence of long‐range spin–spin couplings in 2‐chlorobenzaldehyde
Authors: Laatikainen Reino , Tuppurainen Kari , Hiltunen Yrjö , Lötjönen Simo 
Published: May 2005

AbstractThe proton‐proton spin‐spin couplings of 2‐chlorobenzaldehyde were determined accurately for acetone‐d6 and CD3CN solutions at several temperatures. The sign and temperature dependence of the para‐benzylic six‐bond coupling, 6Jα4, was also obtained, although the observed value of this indicator of the formyl–ring co‐planarity was in the range −24 to −31 mHz. The fitting of the temperature dependence suggests that 6J0 (the value of the coupling when the formyl‐ring dihedral angle is 0°) is very small and probably positive, in contrast, for example, to styrene. The results are discussed on the basis of some modified INDO/FP calculations. A simple resolution enhancement technique is also described.
Spectroscopic electronegativities correlated with the 13C NMR shifts of metal (Ia, IIa, IIIa) 2‐ethoxyethoxides
Authors: Micha‐Screttas Maria 
Published: May 2005

AbstractSpectroscopic electronegativities of Li, Na, K, Mg, Ca, Sr and Al bear a linear relationship with the C‐1 chemical shifts in the corresponding sequence of metal 2‐ethoxyethoxides. The unusual feature of this correlation is that it accommodates data for derivatives of metals belonging to different groups. The observed correlation implies that there is a linearity between χspec and the mean excitation energy.
29Si and13C NMR spectra of 4‐substituted 2‐methoxytrimethylsiloxybenzenes. Factors determining the chemical shifts in models of lignin constituents
Authors: Schraml Jan , Kvíčalová Magdalena , Chvalovský Václav , Elder Thomas , Brežný Robert 
Published: May 2005

Abstract29Si and13C NMR chemical shifts are reported for a series of twenty 4‐substituted 2‐methoxytrimethyl‐siloxybenzenes; the set of substituents incorporates a basic set of ten substituents differing in their relative polar and resonance effects and ten other substituents which model substituents encountered in lignins. The factors affecting the chemical shifts are discussed using a comparison with the NMR data for a similar series of compounds, correlations with substituent parameters and electronic charges calculated by a quantum chemical method (MNDO calculations on force‐field optimized molecular geometries) for the basic set. It is concluded that the methoxy group in theorthoposition to the trimethylsiloxy group takes, for most of its time, the conformation in which the methyl group lies in the plane of the benzene ring and is turned away from the trimethylsiloxy group which assumes a perpendicular conformation. Proximity deshielding effects observed on both the methoxy and trimethylsiloxy groups are influenced by the substituents in position 4, which is in agreement with the notion that these effects are due to an interaction of the vicinal oxygen atoms or their unshared electrons. The dependence of the29Si chemical shifts on σpis not substantially affected by the presence of theorthomethoxy group.
Assignment of carbonyl carbon and acetyl methyl proton resonances of acetylated saccharides by the use of two‐dimensional NMR techniques
Authors: Uhrínová Stanislava , Petráková Eva , Ruppeldt Juraj , Uhrín Dušan 
Published: May 2005

AbstractCarbonyl carbons in peracetylated saccharides are coupled via three‐ and two‐bond couplings with ring protons and acetyl methyl protons, respectively. Using their mean values, the optimum setting for 2D heterocorrelated experiments (Freeman–Morris and COLOC sequences) designed for the assignment of carbonyl carbon and acetyl methyl proton resonances is presented. Selective inversion of the methyl proton resonances in the middle of the refocusing period is introduced. This modification eliminates the effect of 2J(CO,CH3) on the intensity of the carbonyl carbon‐ring proton cross‐peaks, which is essential in the assignment procedure. The carbonyl carbon, acetyl methyl and ring proton resonances can be used for the determination of the primary structure of complex saccharides.
Study of solvent effects on the nitrogen NMR shieldings of some indolizines
Authors: Witanowski M. , Sicińska W. , Grabowski Z. , Webb G. A. 
Published: May 2005

AbstractSolvent effects on the nitrogen NMR shieldings of indolizine and three azaindolizines are presented for a range of thirteen solvents. The results are discussed in terms of hydrogen‐bonding an solvent polarity effects. ‘Pyridine‐type’ nitrogen atoms show a much larger range of solvent effects than do ‘pyrrole‐type’ nitrogens; solvent to solute hydrogen bonding is the dominant contribution to the changes in shielding for the ‘pyridine‐type’ nitrogen atoms as the solvent is varied. Solvent polarity effects are important for both types of nitrogen atom in azaindolizines and can be attributed to a solvent‐induced electronic charge separation between the nitrogen atoms concerned.Quantum chemical calculations involving the solvaton model are used to provide supporting evidence for the importance of solvent polarity effects on nitrogen shieldings in azaindolizines.
A question of assignments in the 13C NMR of estrone and related structures
Authors: Smith William B. 
Published: May 2005

AbstractThe initial assignments for C‐6 and C‐8 in the carbon spectrum of estrone [3‐hydroxyestra‐1,3,5(10)‐triene‐17‐one] were reversed by a subsequent group of investigators. Recent respected reference publications have reproduced these conflicting sets of data, reflecting an uncertainty regarding the correct assignments. The implied question has been answered with the aid of APT, 2D COSY and HETCOR experiments.
13C NMR study of polyaryl‐ and poly‐C‐heteroaryl‐carbinols and their carbonium salts
Authors: Avendaño Carmen , de Diego Carmen , Elguero José 
Published: May 2005

AbstractThe carbon‐13 chemical shifts of a series of trisubstituted methanols with phenyl, p‐dimethylaminophenyl, 9‐fluorenyl, 2‐N‐methylpyrrolyl, 2‐furyl, 2‐thienyl, 2‐N‐methylindolyl, 2‐benzofuryl and 2‐benzothienyl substituents (26 compounds) are discussed. Those of the sp3 carbon atoms bearing the OH group, and the ipso carbons carrying the COH group, follow additive models with high accuracy. The corresponding central carbon atom of the carbonium ions, which were stable enough to be studied in chloroform (eight compounds), also follows an additive pattern which allows the prediction of the chemical shifts of derivatives not studied in this work.
1H and 13C NMR spectra of pseudomorphine and dimethylpseudomorphine
Authors: Graden D. W. , Caldwell G. W. , Villani F. J. , Maryanoff C. A. , Grant A. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 7,7′,8,8′‐tetradehydro‐4,5:4′,5′‐diepoxy‐17,17′‐dimethyl‐[2,2′‐bimorphinan]‐3,3′,6,6′‐tetrol; [2,2′‐bimorphine] (pseudomorphine) and 7,7′,8,8′‐tetradehydro‐4,5:4′,5′‐diepoxy‐17,17′‐dimethyl‐[2,2′‐bimorphinan]‐3,3′‐dimethoxy‐6,6′‐diol; 2,2′‐bimorphine (dimethylpseudomorphine) were measured and assigned using DEPT, COSY, HETCOR, NOESY, NOE difference techniques and selective proton decoupled carbon NMR experiments.
13C cross‐polarization/magic angle spinning and 2H NMR studies of the structure and dynamics of the (deoxycholic acid)2–ferrocene inclusion compound
Authors: Heyes Stephen J. , Dobson Christopher M. 
Published: May 2005

AbstractThe channel‐type inclusion complex, (deoxycholic acid)2–ferrocene [(DCA)2–;ferrocene], was studied by 13C cross‐polarization/magic angle spinning NMR spectroscopy. The spectra indicate that two different DCA molecules are present in the crystalline structure. Relaxation data indicate a relatively restricted degree of reorientational freedom of the included ferrocene molecules. 2H NMR spectra of the inclusion complex with perdeuterated ferrocene reveal rapid, anisotropic librations of the principal axes of the ferrocene molecules about their mean positions, varying from <ca. ± 1° at 160 K to ca. ± 28° at 350 K. The anisotropic, librational nature of this molecular reorientation may be rationalized in terms of the packing features of the sheet‐like nature of the structures of such deoxycholic acid compounds.
Silicon‐29 MAS NMR investigations of Na2O · SiO2 glasses: Refinement of the binary distribution model
Authors: Grimmer Arnd‐RÜDiger , Thomas Berthold , Seifert Gudrun , Sarv Priit 
Published: May 2005

AbstractSilicon‐29 MAS (9 kHz) NMR spectra at 11.7 T, combined with an improved deconvolution procedure, are used to refine the Qn/Qn‐1 distribution model for binary glasses x Na2O · SiO2 (0.18 < x < 0.49). Using the fictitious temperature concept the binary distribution is shown to be the low‐temperature limiting case for the distribution of structural units Qn, Observed deviations from the strict model tending to random distribution can be explained by the model of Dorfeld. Additional structural information can be derived from 29Si chemical shift and line‐width data.
Complete 1H and 13C NMR spectral assignment of some polynitropolycyclic cage molecules by 2D NMR spectroscopy
Authors: Axenrod T. , Liang B. , Dave P. R. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of several saturated polynitropolycyclic molecules were unambiguously assigned using aromatic solvent‐induced shifts, NOE difference spectra, 1H–1H COSY spectra and 2D 13C–1H shift correlated spectra, optimized either for one‐bond or long‐range 13C–1H couplings.
1H NMR investigation of selected heptafulvenes
Authors: Bönzli Peter , Neuenschwander Markus 
Published: May 2005

AbstractThe 1H NMR spectra of selected heptafulvenes 2a–e were analysed under high‐resolution conditions. The results are in agreement with a symmetrical boat conformation for 2a and with a nearly planar conformation of 2e. Within the series 2a–e, ring planarization and π‐delocalization increase. Substituent effects on NMR parameters are discussed.
1H NMR structural analysis of isomeric tetrazole‐substituted spirostan steroids: Shielding effects and conformational study
Authors: Silwood Christopher J. L. , Davies David B. 
Published: May 2005

AbstractThe structures of two pairs of tetrazole‐substituted spirostan steroids were characterized by the use of one‐ and two‐dimensional 1H NMR measurements. The conformation of the seven‐membered spirostan ring A of the steroid was determined by analysis of proton spin coupling constants and confirmed by 1D and 2D NOE experiments showing interactions between the methyl group and ring protons. The conformation of the tetrazole‐substituted ring A was found to be the same for the four isomers, allowing them to be differentiated by the analysis of the effect of tetrazole‐ring isomerization on the chemical shifts of neighbouring protons.
Influence of the phosphorus lone pair on coupling constants in vinylphosphines
Authors: Mitchell Terence N. , Heesche‐Wagner Kerstin , Belt Heinz‐Joachim 
Published: May 2005

AbstractMultinuclear NMR data are presented and discussed for a variety of vinylphosphines in which the vinyl group bears one, two or three substituents; these include organic and trimethylstannyl residues. The orientation of the phosphorus lone pair can be determined from two‐bond phosphorus‐carbon coupling constant values. The magnitudes of the 3J(PCCSn), 4J(PCCSnC) and 5J(PCCSnCH) coupling constants are clearly determined by a throughspace interaction when P and C are in a cis configuration.
Multinuclear magnetic resonance study of 1,3,3‐trimethylbicyclo [2.2.1]heptan‐2‐one (fenchone) oxime, its five monochloro derivatives and a dehydrochlorination product
Authors: Kolehmainen Erkki , Laihia Katri , Korvola Jorma , Kauppinen Reijo , Mänttäri Pia , Rissanen Kari 
Published: May 2005

AbstractFenchone oxime, 5‐exo‐chlorofenchone oxime, 6‐exo‐chlorofenchone oxime, 7‐anti‐chlorofenchone oxime, 8‐chlorofenchone oxime, 9‐chlorofenchone oxime and a dehydrochlorination product of 10‐chlorofenchone oxime were synthesized from fenchone and the corresponding chlorofenchones. The 1H, 13C and 17O NMR spectra of the oximes and the dehydrochlorination product were recorded. The NMR data were compared with the corresponding parameters obtained earlier for fenchone and monochlorofenchones in order to determine the differences between the carbonyl and oxime substituents from the NMR spectroscopic point of view, and to assign the stereochemistry of the oxime group. This stereochemistry could not, however, be assigned solely by NMR spectroscopy.
1H NMR spectra of some 5‐substituted‐thianthreniumyl perchlorates
Authors: Lochynski Stanislaw , Hoque A. K. M. M. , Shin Seung Rim , Shine Henry J. 
Published: May 2005

Abstract1H NMR spectra of 21 5‐substituted‐thianthreniumyl perchlorates are reported that allow chemical shift and structural assignments to be made.
Carbon‐13 NMR spectral investigation of organosulfur compounds. Substitutent‐induced chemical shift (SCS) effects in acyclic saturated organosulfur compounds
Authors: Dyer John C. , Evans Slayton A. 
Published: May 2005

AbstractThe 13C NMR shielding effects on proximal carbon atoms caused by oxidation of sulfenyl sulfur to sulfinyl, sulfonyl and sulfonium species are diagnostic indicators and extremely useful in the structural characterization of organosulfur compounds.
Determination of polyaminocarboxylate ligand denticity by 13C NMR paramagnetic line broadening
Authors: Popov K. , Vendilo A. , Djatlova N. 
Published: May 2005

AbstractThe 13C NMR characteristics of sodium acetate and complexes of ethylenediaminetetraacetic acid (EDTA, H4edta) with La3+ and VO2+ in the presence of the paramagnetic relaxant [Gd(H2O)n edta]− are reported. The observed selective paramagnetic line broadening of the uncoordinated glycinate arms in [VO2edta]3− permits an assignment of the 13C resonances and independent ligand denticity determination. For COO resonances the selectivity was found to be ca. 18. A large difference was also observed between the 13C transverse relaxation times for the uncoordinated COO groups of CH3COO− and the coordinated COO groups of [La(H2O)3edta]−. The magnitude of the selectivity provides clear advantages in aiding the 13C NMR assignment and the establishment of the true denticity for the complexes of polydentate ligands.
Loss in conformational rigidity of bradykinin on replacement of the Phe‐8 by tyrosine
Authors: Srivastava Sudha , Haram S. , Phadke Ratna S. 
Published: May 2005

AbstractThe complete resonance assignments and the conformation of the hormone [Tyr8]‐bradykinin, a nonapeptide, in DMSO‐d6 have been determined using 2D 1H NMR techniques. NMR parameters such as the chemical shifts, coupling constants, temperature coefficients of the backbone NH protons and NOEs have been analysed in the light of the known conformation of the native peptide. The results indicate that the peptide loses conformational rigidity on the replacement of Phe‐8 by Tyr.
NMR analysis of fluorinated corticosteroids related to fluocinonide: Detection of long‐range 1H–19F couplings using the heteronuclear equivalent of the COSY experiment
Authors: Hughes Donald W. , Bain Alex D. , Robinson Valerie J. 
Published: May 2005

AbstractThe analysis of the 1H and 19F NMR spectra of the corticosteroid fluocinonide and five related steroids is reported. The 500 MHz 1H NMR spectra revealed several previously undetected long‐range 1H–19F coupling constants. These couplings were assigned by the application of the heteronuclear equivalent of the COSY pulse sequence. The fluorine substituent effects and long‐range heteronuclear couplings were examined in relation to structures derived from molecular mechanics (MMX) calculations.
Correlation of the crystal structure and solid‐state 13C NMR spectrum of pyromellitic dianhydride
Authors: Wolfe Roger A. , Schwartz Willis T. , Dinan Frank J. 
Published: May 2005

AbstractThe interatomic distances for crystalline pyromellitic dianhydride (PMDA) were calculated from x‐ray crystallographic data. The CP‐MAS 13C NMR spectrum of PMDA was found to be consistent with and accountable for in terms of these distances after literature assignment errors were corrected. An anomalous peak was observed in the differential scanning calorimetry thermogram of PMDA. The entropy change associated with this transition indicates that a two‐fold change in symmetry occurs approximately 60°C below the melting point of PMDA. Attempts to observe this transition by CP‐MAS 13C NMR were unsuccessful.
Liquid‐phase stereochemistry of cationic [Rhbisphosphinediene]+ and neutral [RhbisphosphinedieneCl] complexes. 1H, 31P and 13C NMR and molecular mechanics study
Authors: Szalontai Gábor , Sándor Péter , Bakos József 
Published: May 2005

AbstractThe liquid‐state stereochemistry of cationic [Rh(I)dienebisphosphine]+ and neutral [Rh(I)dienebisphosphineCl] complexes is reported on the basis of their 1H, 13C and 31P NMR spectra. In solution the 400‐MHz 1H spectra indicate C2 symmetry for the cationic species and a strongly solvent‐ and temperature‐dependent equilibrium for the neutral five‐coordinated species. Gas‐phase molecular mechanics calculations on the cationic complexes predict local energy minima for the skew(diequatorial), chair and boat conformations of the six‐membered phosphine chelate. The 2D exchange spectra of the neutral complex prove a slow exchange between identical forms of the bidentate chelate, but no such exchange exists between the diene atom pairs; the origin of the observed pairwise identify of the diene atoms is therefore not fully understood. In principle, several stereoisomers can exist in such complexes, depending on the actual conformation of the bisphosphine chelate and/or on the cis or trans relationship of the fifth coordinating point and the rest of the phosphine. The existence of the traditionally asssumed trigonal‐bipyramidalsquare‐pyramidal equilibrium is unlikely. As an alternative, the fluxional nature of the aliphatic part of the phosphine chelate could explain the phenomena. This motion, however, should be restricted to a chair—boat equilibrium which does not significantly change the axial—equatorial positions of the phenyl rings.
Molecular modelling, NOED and spin—lattice relaxation study of the stereochemistry of some terpenoids
Authors: Qing Ning , Colebrook Lawrence D. , Commodari Fernando 
Published: May 2005

AbstractNOED, COSY and HETCOR experiments in conjunction with molecular mechanics calculations, were used to assign the 1H and 13C NMR spectra of the terpenoids α‐ionone and methyl O‐methylpodocarpate and to investigate their stereochemistry. These compounds were used as models to investigate the ability of molecular mechanics and associated calculations to predict 1H spin—lattice relaxation rates in molecules of this type.
133Cs, 1H two‐dimensional heteronuclear Overhauser effect spectroscopy (HOESY): Structural analysis of organic caesium compounds by detection of short Cs,H contacts
Authors: Bauer Walter 
Published: May 2005

AbstractTransient heteronuclear Overhauser effects were observed between 133Cs and 1H by two‐dimensional heteronuclear Overhauser effect spectroscopy (HOESY). In caesium tetraphenylborate (CsBPh4) dissolved in pyridine‐d5, Cs+ is tightly attached to the BPh4− anion, thus forming a contact ion pair (CIP). By contrast, after addition of one equivalent of the crown ether 18‐crown‐6, caesium is located intimately at the site of the crown ether whereas the tetraphenylborate anion is remote (solvent‐separated ion pair, SSIP). The results are in agreement with experiments described earlier by Mei et al. Similar observations were made for caesium 3‐methylpentyl 3‐oxide in tetrahydrofuran‐d8 solution. 133Cs, 1H HOESY indicates the presence of a contact ion pair. Steady‐state 133Cs {1H} experiments on the latter compound reveal weak fractional enhancements of 0.2%.
13C CP‐MAS NMR spectra and fluxional behaviour of [M2(ηHCCCMe2)(CO)4(ηC5H5)2]+ [BF4]− (M = Mo, W) complexes in the solid state
Authors: Galakhov M. V. , Bakhmutov V. I. , Barinov I. V. 
Published: May 2005

AbstractInternal rotation about the C‐2–C‐3 bond was observed in the 13C CP‐MAS NMR spectra of the solid complexes [M2(ηHC1C2C3Me2)(CO)4(ηC5H5)2]+ [BF4]− where M = Mo or W.
Direct determination of proton‐exchange kinetics by 320‐MHz tritium NMR spectroscopy
Authors: Dixon Richard E. , Williams Philip G. , Saljoughian Manouchehr , Long Mervyn A. , Streitwieser Andrew 
Published: May 2005

AbstractThe first application of tritium NMR spectroscopy to the direct observation of proton‐exchange kinetics is described; this technique allows the study of milligram amounts of substrates and for substrates with multiple exchangeable positions. The examples include benzene and the ring and methyl positions of p‐xylene reacting with cesium cyclohexylamide in cyclohexylamine, and the enolate positions of cyclohexanone and methyl 7,12‐dihydroxy‐3‐ketocholan‐24‐oate reacting with heptafluorobutyric acid in dioxane.
Carbon‐13 NMR study of 5‐triphenyl‐phosphoranilydeneaminopyrazoles
Authors: Arques Antonio , Molina Pedro , Vinader María Victoria , Elguero José 
Published: May 2005

Abstract13C chemical shifts and 13C–31P coupling constants are reported for nineteen pyrazoles bearing an NPPh3 substituent at position 5. The three heterocyclic carbons are coupled with the phosphorus (2J, 3J and 4J). These couplings are very sensitive to the nature of the subtituent at position 4 [CHO, CHCHCOMe, CH(CH2NO2)2, CHNR, CH2NHR and CH2N(COR)Ar].
Protonated XH heteroatom (X = O, N, S) analysis in oil fractions from morocco oil‐shale using 29Si multiple‐pulse NMR
Authors: Béguin Claude G. , Bennouna Chakib , Bitar Hassane , Dahbi Abderrahman , Léna Louis 
Published: May 2005

AbstractThe characterization and determination of the protonated heteroatom content of the XH type (X = O, N, S) in oil fractions was carried out using 29Si NMR on silylated derivatives of the heteroatomic compounds. The analysis was achieved on a mixture of standard compounds and on two oil fractions from Morocco oil‐shale: asphaltenes and the aromatic and polar components.