bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H NMR assignment and conformational analysis of glucitol: Comparison with maltitol
Authors: Hoffman Roy E. , Rutherford Trevor J. , Mulloy Barbara , Davies David B. 
Published: May 2005

AbstractThe 1H NMR spectrum of glucitol in D2O solution contains eight strongly‐coupled multiplets covering a chemical shift range of about 0.21 ppm. The spectrum is severely complicated by second‐order effects and was assigned by a combination of 2D NMR experiments and extensive spin simulation of the 1D spectra. The magnitudes of the spin coupling constants were analysed in terms of preferred conformations about each bond in the backbone of glucitol, and the results were compared with those found for maltitol in solution, with crystal conformations of both glucitol and maltitol and with low‐energy conformations computed using the MM2CARB force field. The results show a surprising degree of agreement between computed low‐energy conformations and those observed in the crystal, but little correspondence with conformations observed by NMR in solution. Although maltitol is derived from glucitol sustituted in the 4‐position with the bulky α‐D‐glucopyranose moiety, NMR measurements indicate approximately free rotation about all bonds in the glucitol moiety of maltitol. This is in contrast to glucitol, where the proton‐proton trans conformer predominates (74%) for the C4–C5 bond which, in turn, stabilizes the gauche‐gauche conformer of the adjacent C5–C6 bond (53%) and destabilizes the trans conformer of the C3–C4 bond (3%).It is found from molecular modelling studies that steric factors alone cannot explain these results, and it is postulated that intramolecular hydrogen bonding stabilizes the local conformations in glucitol whereas disruption of the hydrogen‐bond network occurs as a result of substitution of the glucitol moiety in maltitol.
1H and 13C NMR determination of the relative stereochemistry of the diastereomers resulting from the reaction of sily enol ethers with the 1‐ethoxy‐1‐propargylium dicobalt hexacarbonyl cation
Authors: Montaña Pedrero Angel M. , Nicholas Kenneth M. 
Published: May 2005

AbstractThe application of 1H and 13C NMR correlations and phase‐sensitive NOESY in the stereochemical assignment of four diastereoisomers of hexacarbonyl{μ‐η4‐[2,4‐dimethyl‐2‐(1‐ethoxy‐2‐propyn‐1‐yl)‐8‐oxabicyclo [3.2.1] octan‐3‐one]}dicobalt‐(CoCo) is reported.
Spectral artifacts in heteronuclear chemical shift correlation experiments with homonuclear decoupling via a constant evolution time
Authors: Swapna G. V. T. , Rao N. Sambasiva , Ramachandran R. 
Published: May 2005

AbstractExperimental and theoretical studies carried out to investigate the influence of strong coupling effects in the spectra generated through the commonly used heteronuclear chemical shift correlation (HETCOR) sequences involving a constant evolution time are reported. It is seen that the spectra generated via such sequences are prone to artifacts of appreciable intensity. Failure to recognize these can result in the misinterpretation of spectral data.
Dependence of vicinal 31P–31P and 31P–13C coupling constants on the dihedral angle of α, β‐diphosphonates
Authors: Grossmann G. , Lang R. , Ohms G. , Scheller D. 
Published: May 2005

AbstractSeveral α,β‐diphosphonates with a norbornane or cyclohexane skeleton were prepared, and the 31P‐31P coupling constants over three bonds for the ethyl or methyl esters, the acid and anion were obtained from the 13C NMR spectra or the 13C satellites in the 31P NMR spectra. The 3J(PP) values cover a range of about 90 Hz and are therefore well suited for conformational and configurational analysis. The dependence of 3J(PP) on the dihedral angle is well reflected by an extended Karplus relationship: 3J(PP) = A + B cos φ + C cos 2φ + D cos 3φ, with different parameters for the esters, acids and anions. For trans and gauche arrangements of the α,β‐diphosphonic acids the dependence of the P‐P coupling constants on the degree of titration is given. Investigations of the dependence of 3J(PC) on the PCCC dihedral angle show that a good curve fitting is achieved using the Karplus relationship 3J(PC) = AA + AB cos φ + C cos 2φ. A comparison of these curves with published data indicates smaller coupling constants for φ ≈ 0°. The coefficients of the Karplus equation for the 3J(PC) values obtained for esters are similar for acids and anions.
13C nuclear magnetic resonance spectra of several podocarpane and cassane diterpenoids
Authors: Abad A. , Agulló C. , Arnó M. , Domingo L. R. , Zaragozá R. J. 
Published: May 2005

AbstractThe 13C NMR spectra of several diterpenic derivatives having the podocarpane and cassane skeleton were recorded and interpreted. The most significant effects due to substituent orientation, B/C ring junction stereochemistry and conformational changes are briefly discussed.
Structure of methylenecyclopropane in a liquid crystal by 1H and 13C NMR
Authors: Turku Taoufik , Haloui Ezzeddine 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of methylenecyclopropane, both in the isotropic phase and in the Merck IV nematic phase, were analysed. The relative signs of the 13CH scalar coupling constants were determined. The complete geometry deduced from this study was compared with that from a microwave study, and the discrepancies are discussed.
1H and 13C NMR studies of the protonation of isomeric methoxysulmazole analogues
Authors: Lindon J. C. , Williams J. M. , Barraclough P. , King W. R. , Nobbs M. S. 
Published: May 2005

AbstractThe major protonation sites of six cardiotonic isomeric 2‐aryl‐n‐methoxy‐1H‐imidazo[4,5‐b]‐ and ‐[4,5‐c]‐pyridines (n = 4–7) were determined by 1H and 13C NMR methods. All the 1H‐imidazo[4,5‐c]pyridines and the 7‐methoxy derivative of sulmazole were found to protonate at the pyridyl nitrogen. Protonation occurred at the imidazo nitrogen, however, for the 5‐ and 6‐methoxy derivatives of sulmazole.
13C NMR studies on radical anions. Special solvent effects
Authors: Doctorovich Fabio , Nudelman N. S. 
Published: May 2005

AbstractThe determination of radical ions is crucial in mechanistic studies of reactions in which single electron transfer is suspected. A 13C NMR method based on the interaction of radical anions with tetrahydrofuran (THF) molecules is presented; measurements of the broadening of the THF α‐carbon signal allow determination of the substrate concentration in the range 0.2–1.2 M. The spectacular effect observed on addition of small amounts of benzene greatly improved the method. In addition, studies of the spin‐lattice, T1, and of the transverse nuclear, T2, relaxation times and of the effects of added co‐solvents allow the proposal of the bonding situation and of the degree of coordination in the radical anion‐cation‐THF molecules' complex.
Intramolecular interactions in N‐vinyl‐2‐arylpyrroles and ‐2‐heteroarylpyrroles by 1H and 13C NMR
Authors: Afonin Andrei V. , Sigalov Mark V. , Korostova Svetlana E. , Aliev Ismail A. , Vashchenko Alexander V. , Trofimov Boris A. 
Published: May 2005

AbstractThe introduction of a substituent in the 3‐position of the pyrrole ring in N‐vinyl‐2‐arylpyrroles and ‐2‐heteroarylpyrroles results in an increase in the dihedral angles between the planes of the pyrrole ring and the aryl (or heteroaryl) residue, and a decrease in the dihedral angle between the planes of the pyrrole ring and the vinyl group. Introduction of the substituent in the 5‐position of the pyrrole ring has the opposite effect on these angles. For N‐vinyl‐2‐(2′‐furyl)pyrrole, some spectral data suggest the formation of a CH…O hydrogen bond between the α‐hydrogen atom of the vinyl group and the oxygen atom of the furyl ring. This is in accord with the results of quantum chemical calculations.
Determination of the enantiomeric purity of disubstituted β‐lactams by NMR spectroscopy using a chiral shift reagent
Authors: Belleney J. , Bui C. , Carriere F. J. 
Published: May 2005

AbstractThe enantiomeric purities of disubstituted β‐lactams were determined by 1H and 13C NMR spectroscopy using tris[3‐(trifluoromethylhydroxymethylene)‐d‐camphorato]europium(III), Eu(tfc)3, as a chiral shift reagent. Using a [Eu(tfc)3]/[lactam] ratio of 0.5, most of the resonances were split into signal pairs due to the respective enantiomers. The method gives quantitative enantiomeric compositions. 13C NMR spectroscopy is more advantageous than 1H NMR, which is of limited use owing, for example, to the significant line broadening observed in the 1H spectra at [Eu(tfc)3]/[lactam] > 0.8. Assignments of the proton and carbon signals were obtained for the two enantiomers of the complexed lactams.
Assignment of relative configurations and conformational study of acyclic diastereomeric ketones
Authors: Alvarez‐Ibarra C. , Arias‐Pérez M. S. , Moya E. 
Published: May 2005

AbstractThe conformational analysis and the assignment of relative configurations [(RR, SS) and (RS, SR)] to the dia‐stereomeric racemates of two acyclic ketones with two asymmetric carbons, ±‐2,2,7,7‐tetramethyl‐5,6‐diphenyloctan‐3‐one and ±‐5,5‐dimethyl‐1,3,4‐triphenylhexan‐1‐one, have been achieved by analysis of1H‐1H geminal and vicinal coupling constants, 13C–1H direct coupling constants and 13C chemical shifts. This study allows the establishment of the monoconformational character of the (RR, SS) diastereomers. The application of the empirical equation of Haasnoot et al. supports this hypothesis.
Study of lithium tetrafluoroborate–cyano complexes by NMR in thermotropic liquid crystals
Authors: Gowda G. A. Nagana , Suryaprakash N. , Weiss R. G. , Khetrapal C. L. , Diehl P. 
Published: May 2005

AbstractLithium tetrafluoroborate‐acetonitrile complexes were studied in two liquid crystals, trans,trans‐4‐n‐propyl(1,1′‐bicyclohexyl)‐4′‐carbonitrile (ZLI‐1184) and trans‐4‐pentyl‐1‐(4‐cyanophenyl)cyclohexane (S‐1114). The results indicate the formation of tetrahedral lithium‐acetonitrile complexes and the coordination of lithium from LiBF4 and LiClO4 with the cyano group of ZLI‐1184. No evidence was found to support either lithium ion complexation with S‐1114 or tetrafluoroborate ordering in any of the systems investigated.
1H and 13C NMR study of the neomenthyl halides: A very high field proton shift in the iodide
Authors: Lange Gordon L. , Gottardo Christine 
Published: May 2005

AbstractComplete analyses o the 1H NMR spectra of neomethyl iodide (1), the bromide (2) and the chloride (3) are reported. Of paticular interest is the very high‐field resonance at −0.16 ppm in 1 which is assigned to H‐4. The same poton in the bromide is also found upfield at 0.78 ppm. H‐4 in these neomenthyl derivatives is tertiary and β‐antipeiplanar to the halogen atom. A similar upfield shift has been reported previously for the tertiary proton in trans‐9‐iododecalin. The reasons or these unusual shifts are not readily apparent and the 13C NMR spectra of 1 and 2, which are reported here for the first time, provide no additional clues to explain the shifts.
An empirical extension of the karplus equation
Authors: Imai Keisuke , Ōsawa Eiji 
Published: May 2005

AbstractThe Karplus equation is expanded to contain 11 mutually independent structural terms and 22 adjustable parameters. These terms are selected on an empirical basis and combined linearly (Eqn 4). The new equation reproduces 198 NMR vicinal 1H‐1H coupling constants determined in less polar solvents with a standard deviation of 0.33 Hz. The equation can be applied to norbornene derivatives, for which some of the previous modifications did not work well. Among new factors introduced in this modification to the Karplus‐type equation are Mullay's group electro‐negativity used in the evaluation of the α‐ and β‐substituent effects, the CC length and the CCH valence angles of the coupled HCCH system, and the through‐space interactions between a coupled proton and a non‐bonded atom within the molecule. The four most important terms are the two cosine functions, originally used by Karplus, one form of the α‐substituent effect and the CCH valence angles. These four terms alone give an accuracy of 0.42 Hz.
Direct observations of 1J(11B, 14N) coupling constants by 11B NMR spectroscopy
Authors: Ouassas Abdeljalil , Duplan Jean‐Claude , Fenet Bernard , Frange Bernard 
Published: May 2005

AbstractThe reaction B(NCS)4− + BX4− (X = F, Cl, Br) leads to mixed BXn(NCS) (n = 1, 2, 3) species easily detected in solution by 11B NMR. Further, with X = Cl, 1J(11B, 14N) values could be measured from the 11B NMR spectra (25.6, 24.5 and 21.4 Hz for n = 3, 2 and 1, respectively). For X = F, the relevant 1J(11B, 14N) values (24.3, 25.2 and 28 Hz for n = 3, 2 and 1, respectively) increase in the same order as the related 1J(11B, 19F) (5.5, 12.7 and 20.0 Hz, respectively). No such 1J(11B, 14N) could be resolved for X = Br.
Substituent‐Induced chemical shifts of 2‐phenylthiazolidines—1H NMR study
Authors: Umarani R. 
Published: May 2005

AbstractThe 1H NMR 270‐MHz spectra of substituted 2‐phenylthiazolidines were recorded and the substituent‐induced chemical shifts (SCS) of the benzylic proton plotted against σ, the correlation coefficient being 0.801 and −ρ = 10.29 Hz. Halogens show deviations in the SCS plots. When the halogen‐substituted derivatives are omitted, the correlation with σ is greatly improved. The applicability of dual‐substituent correlations using Swin‐Lupton parameters (F and R) and Taft's σ1, σR parameters has been studied.
17O NMR and molecular mechanical studies of arylmethylenemalonaldehydes
Authors: Kolehmainen Erkki , Král Vladimir 
Published: May 2005

AbstractThe 17O NMR spectra of six different arylmethylenemalonaldehydes were measured for various solvents and temperatures. The 17O NMR chemical shifts and line widths of the carbonyl oxygens of the malonaldehyde fragment show a clear variation in the series of monoaryl compounds studied. The differences between the 17O NMR chemical shifts of the formyl oxygens correlate well with two conformationally dependent 1H–1H and 1H–13C coupling constants for the same compounds. Molecular mechanical calculations were also performed in order to relate the present data with the conformational preferences of the malonaldehyde fragment of the arylmethylenemalonaldehydes.
Full proton NMR assignment of the reduced form of a repeat unit tetrasaccharide derived by keratanase digestion of keratan sulphate
Authors: Huckerby T. N. , Dickenson J. M. , Nieduszynski I. A. 
Published: May 2005

AbstractThe full assignment of the ambient‐temperature high‐field 1H NMR spectrum for the reduced form of a repeat‐unit β‐linked tetrasaccharide derived by keratanase digestion from keratan sulphate, GlcNAc(6‐SO4)13Gal(6‐SO4)14GlcNAc(6‐SO4)13Gal‐ol, was achieved using two‐dimensional COSY and RELAYED‐COSY experiments. The problem of the choice of the measurement temperature for 1H NMR spectra from keratan sulphate oligomers and polymers is discussed. A modified protocol for the preparation of keratanase‐derived oligosaccharides is proposed.
13C NMR data for chlorine‐ or nitro‐substituted azomethine dyes
Authors: Haessner Rainer , Hennig Lothar , Gaca Jerzy 
Published: May 2005

AbstractThe 13C NMR spectra of 1‐aryl‐substituted 3‐methyl‐2‐pyrazolin‐5‐ones and their azomethine dyes have been recorded and assigned. ortho‐Substituents (Cl and NO2) on the phenyl ring in the 1‐position of the pyrazoline moiety show a small influence on the chemical shift of the azomethine bond carbon atom, C‐4.
Determination of the barrier to CN bond rotation in captopril: Application of reference deconvolution to line‐shape analysis
Authors: Green Darren V. S. , Hillier Ian H. , Morris Gareth A. , Whalley Lesley 
Published: May 2005

Abstract13C NMR was used to study the cis‐trans isomerization of 1‐[(2S)‐3‐mercapto‐2‐methyl‐1‐oxopropyl]‐L‐proline (captopril) in D2O solution over the temperature range 50–100°C. Measurements of the rate of cis‐trans interconversion were made by line‐shape analysis and saturation transfer techniques. The combined results yielded a value for the activation energy of 89 ± 2 kJ mol−1 (21.3 ± 0.5 kcal mol−1) for the C‐N bond rotation. For line‐shape analysis the experimental data were treated by reference deconvolution, using a small amount of labelled acetonitrile as reference, before processing. It was found that the deconvolution process significantly improved the reliability of the analysis.
1H and 13C NMR spectra of rac‐2,3‐bis(palmitoyloxy)propyl(2‐trimethylarsonioethyl)phosphonate, an arsenic‐containing phosphonolipid
Authors: Amato Maria E. , Irgolic Kurt J. , Junk Thomas , Pappalardo Giuseppe C. , Perly Bruno 
Published: May 2005

AbstractThe 1H (500 MHz), 13C (300 MHz) and 31P (202 MHz) NMR spectra of rac‐2,3‐bis(palmitoyloxy)propyl(2‐trimethylarsonioethyl)phosphonate were recorded in CDCl3 (3 M) solution. Homonuclear 1H‐1H and heteronuclear 13C–1H chemical shift correlation experiments (COSY) were performed. All resonances were assigned. The shifts of the arsenic‐containing phosphonolipid were compared with the shifts of the N‐containing phospholipids. The most significant shift differences were found for the groups directly bonded to arsenic. Spectral evidence was indicative of free rotation about the CH2 CH2 bond in the arsenocholine fragment.
Chemical shift changes on conversion of benzofurans to dihydrobenzofurans; the large effect on the proton ortho to the furan oxygen
Authors: Kalidhar Suraj B. 
Published: May 2005

AbstractA comparison of the 1H NMR spectra of benzofuran and its dihydrofuran shows that the benzene proton ortho to the furan oxygen undergoes a larger change in chemical shift than those for the other protons. This observation is useful for locating the fusion sites of the furan ring in naturally occurring benzofuran derivatives.
An investigation of the keto‐enol tautomerism in 2‐acetyl‐1‐tetralone by 2D NMR spectroscopy
Authors: Agrawal Pawan K. , Thakur Raghunath S. , Frahm August W. , Schneider M. 
Published: May 2005

AbstractLong‐range CH correlation and long‐range selective proton decoupling (LRSPD), together with other standard NMR techniques, led to the complete 13C and 1H NMR spectral assignments of 2‐acetyl‐1‐tetralone and demonstrated its existence in the endo‐enolic form.
Stereochemical study of a new heterocyclic system: Decahydro‐1H‐oxepino[3′,4′:4,5]isoxazolo [2,3‐a]pyridin‐1‐one
Authors: Cid P. , Figueredo M. , Font J. , Jaime C. , de March P. , Virgili A. 
Published: May 2005

AbstractThe stereochemistry and conformational behaviour of a new heterocyclic system obtained by the 1,3‐dipolar cyclo‐addition of 3,4,5,6‐tetrahydropyridine 1‐oxide to hex‐2‐en‐6‐olide has been studied by 1H{1H} and 13C{1H} NOE techniques and MM2 calculations.
Transmission of electronic effects through 2‐[donor]‐1‐[acceptor]‐cyclopropane
Authors: Alonso Miguel E. , Pekerar Sarah V. , Borgo Maria L. 
Published: May 2005

AbstractThe through‐ring conjugation between π‐donor and attractor substitutents on vicinal carbons of cyclopropane with the direct participation of the ring was assessed using proton and 13C NMR. Appropriate 1H NMR correlations were obtained between σp and δH of the trimethylene protons. However, aryl through‐space field effects were found to obscure individual conjugative effects. Conversely, the 13C NMR data implied the occurrence of competitive conjugation of π‐groups with the ring but gave no proof for the existence of the actual transmission of conjugative effects through the C‐1–C‐2 bond of the ring.
Complete assignments of the 1H and 13C NMR spectra of the macrolide antibiotic flavofungin; intramolecular hydrogen bonding and conformation
Authors: Szilágyi László , Sándor Péter 
Published: May 2005

Abstract1H and 13C NMR spectra of the 32‐membered pentaene macrolide flavofungin‐I (identical with mycoticin A) in DMSO‐d6 solution were fully assigned employing a combination of various 1D and 2D homo‐ and hetero‐nuclear experiments. Secondary deuterium isotope shifts measured in the 1H NMR spectrum indicated that three of the eight hydroxyl groups are involved in intramolecular hydrogen bonds, which can lead to restricted mobility within the polyol part of the molecule. These results and inferences made from H, H coupling constants suggest that the conformation of the macrocycle is very similar to that found for roxaticin by x‐ray crystallography. All double bonds are in the E configuration, and the conjugated pentaene chain assumes a fully extended s‐trans conformation.
1H NMR chemical shift study on the stacking interaction between purine and 6‐methylpurine
Authors: Aradi Ferenc 
Published: May 2005

AbstractMutually induced proton chemical shift changes were measured for purine‐6‐methylpurine solutions in deuterium oxide at 35° C. The chemical shift vs. concentration profiles were analysed using a three‐state decomposition model based on simultaneous, competitive dimer equilibria. The association parameters for purine‐6‐methylpurine hetero‐association provide some additional information about the effect of methylation on the stacking interaction between nucleic acid bases. The equilibrium constant (2.54 ± 0.17 and 2.57 ± 0.29 I mol−1, calculated from the experimental data on purine and 6‐methylpurine, respectively) suggests the dominant role of the methylated counterpart in the association. The upfield dimer shifts indicate that the methyl group perturbs the plane‐to‐plane or stacking‐like arrangement in the associated state.
Attenuation of spin–spin effects in carbon‐13 T1ρ NMR experiments by multipulse proton homonuclear decoupling
Authors: Tekely Piotr , Canet Daniel , Delpuech Jean‐Jacques , Virlet Joseph 
Published: May 2005

AbstractIn crystalline polyoxymethylene, a system with tightly coupled protons, it is shown experimentally that the averaging of the dipolar local field of protons by multipulse proton homonuclear decoupling leads to a decrease in the spin–spin contribution to the 13C rotating frame relaxation rate.
Cryogenic NMR: Spectrometer design for studies of matrix‐isolated materials
Authors: Espidel Joussef E. , Harris Robin K. 
Published: May 2005

AbstractThe construction of equipment capable of studying the 1H NMR of samples down to 26 K is described. The system includes a facility for obtaining matrix‐isolated compounds at cryogenic temperatures. Samples can be changed without removing the cryogenic equipment from the probe area. An NMR method of obtaining the true temperature at the sample is described. Illustrative spectra of both pure compounds and a matrix‐isolated system are provided.
NMR studies of the reorientational motions of cyclopentadienyl ligands in solid cis‐ and trans‐[(η5‐C5H5)2Fe2(CO)2(μ2‐CO)2]
Authors: Aime Silvio , Botta Mauro , Gobetto Roberto , Orlandi Alessandra 
Published: May 2005

AbstractChemical shift anisotropies and spin‐lattice relaxation times, T1, were determined for bridging and terminal carbonyls in c's and trans isomers of [(η5‐C5H5)2Fe2(CO) 2(μ2‐CO)2]. The relaxation path of the 13CO resonances occurs through the dipolar interaction with the cyclopentadienyl protons modulated by the reorientational motion of the C5H5 (Cp) rings around their five‐fold axes. Wide‐line proton spin‐lattice relaxation times, T1, at variable temperature allow the evaluation of the activation energies associated with the internal rotation of the cyclopentadienyl rings. In the cis isomer, the two crystallographically non‐equivalent Cp ligands rotate at different rates (Ea = 7.2 and 15.8 kJ mol−1, respectively). Carbon‐13 spin‐lattice relaxation times in the rotating frame of the cyclopentadienyl carbons of the cis isomer support this view. Finally, good agreement is found between our work, the results obtained from crystallographic data and theoretical calculations on the energy barriers for the rotation of the Cp rings.