bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 NMR spectra of substituted 2‐thiophenecarboxanilides
Authors: Amato Maria E. , Fisichella Salvatore , Musumarra Giuseppe , Bottino Francesco A. 
Published: May 2005

AbstractCarbon‐13 NMR shifts for substituted 2‐thiophenecarboxanilides of general formula XC4H2SCONHC6H4Y(X=5‐OMe, 5‐Me, H, 5‐Br, 5‐NO2; Y=H, p‐OMe, pMe, p‐NO2, m‐Me, m‐Cl, m‐NO2) in DMSO‐d6 solutions are reported.The effects of the X and Y substituents on these shifts are discussed, and correlated with substituent constants and with carbon shifts of analogous series of compounds.
Correlation of 1H and 13C NMR spectra by selective inverse INEPT. Assignment of the proton and carbon spectra of methyl (5R*, 6S*,8Z,11Z,14Z)‐5,6‐epoxyeicosa‐8,11,14‐ trienoate
Authors: Crossley Maxwell J. , Field Leslie D. , Gosper Jeffrey J. , Messerle Barbara A. 
Published: May 2005

AbstractSelective inverse INEPT and 13C → 1H → 1H heteronuclear relayed coherence transfer pulse sequences were employed to assign and correlate the proton and carbon NMR spectra of methyl (5R*,6S*,8Z,11 Z,14Z)‐5,6‐epoxyeicosa 8,11,14‐trienoate. The transfer of coherence from specific carbon nuclei in the molecule to protons was employed as a one‐dimensional method to correlate carbon and proton resonances. The one‐dimensional C→H coherence transfer experiments are particularly useful for C‐H correlation in situations where only a small amount of sample is available and two‐dimensional methods are only marginally applicable or impractical.
Sign determination of the two‐bond 15N‐15N spin‐spin coupling constant of a pyrimidine ring by a selective 15N decoupling technique
Authors: Kuroda Yoshihiro , Fujiwara Yasuhiro 
Published: May 2005

AbstractThe sign 2J(NN) of 2‐chloro‐6‐methyl‐[15N2]pyrimidine has been determined by 1H‐{1H (selective)} and 13C‐{1H (noise), 15N (selective)} triple resonance techniques. The sign was proved to be negative (‐1.6 Hz); consequently, chlorine substitution at C‐2 was found to make 2J(NN) more negative, since the magnitude of 2J(NN) of [15N2] pyrimidine is nearly equal to zero. It is stressed that sign determination for the spin couplings between hetero‐nuclei is easier to perform when the resonance of one of the hetero‐nuclei is irradiated than when that due to a proton is irradiated.
Determination of the stereochemistry of disubstituted fluoroethylenes by 13C NMR spectroscopy
Authors: Bosch M. P. , Camps F. , Fabriàs G. , Guerrero A. 
Published: May 2005

AbstractThe stereochemistry of 1,2‐disubstituted fluoroethylenes, of general formula RSH2CHCFR′, has been ascertained from the different magnitudes of the upfield shift effect promoted by fluorine on the 13C NMR absorptions of the underlined γ‐carbon of the fluorinated analogue in comparison with those of the protonated parent compounds. Likewise, this assignment was also possible from the study of the values of the 2J(CF) and 3J(CF) coupling constants in the two isomers.
Compounds with bridgehead nitrogen. 51—The NMR spectra and stereochemistry of the 6‐ethylindolizidines
Authors: Banting Lee , Crabb Trevor A. , Trethewey Andrew N. 
Published: May 2005

Abstract1H and 13C NMR spectroscopy showed that both isomers of 6‐ethylindolizidine adopt predominantly the trans‐fused conformation in CDCl3 at 298 K. ΔG for the cis‐⇌tram‐fused conformational equilibrium in indolizidine must accordingly be not less than 2.8 kcal mol−1.
Guidelines for the design of kinetic NOE experiments from computer simulation
Authors: Williamson M. P. 
Published: May 2005

AbstractA FORTRAN computer program has been written that calculates the time course of NOEs in spin systems of arbitrary complexity. The program first calculates spin‐lattice and cross‐relaxation rates from the molecular parameters, and then calculates all NOEs simulataneously by a numerical integratio of the Solomon equations. This method is extremely fast and easy to program, and may be applied to calculation of truncated drive NOEs or transient NOEs. The program is applied to peptide and protein structures using various correlation times, in order to develop a picture of the behaviour of the NOE under various conditions. The results are used to suggest guidelines for the design of NOE experiments to ensure that the structural information is recovered in an efficient way, and that experiments are not misinterpreted. The distinction of α helix from 310 helix by NOEs is discussed.
Conformational analysis of the repeated sequence of glutelin‐2, a maize storage protein
Authors: Pons Miquel , Feliz Miguel , Celma Carles , Giralt Ernest 
Published: May 2005

AbstractThe presence of repeated proline‐rich sequences constitutes a common trend in several cereal storage proteins. The protected hexapeptide Boc‐Val‐His‐Leu‐Pro‐Pro‐Pro‐OH (1), with the sequence of the repeated region of glutelin‐2 (28 kD) from maize, has been studied by proton and 13C NMR in D2O, DMSO‐d6, CDCl3 and CDCl3‐CD3OD at different temperatures. Spectra were assigned mainly by using 2D correlation techniques. The spectra in D2O and DMSO‐d6 suggest that peptide 1 has a random coil, all‐trans conformation. In CDCl3 1 presents a folded conformation, stabilized by hydrogen bonds, with one of the methyl groups of the valine residue situated over the histidine ring. In CDCl3‐CD3OD 1 is present as a mixture of different conformations. The spectral data are discussed taking as a reference the known conformation of polyproline.
17O NMR studies of the effect of mixed ligands on the bound water in aqueous solutions of amino acids and Co(II)
Authors: Gotsis Efstathios D. , Fiat Daniel 
Published: May 2005

AbstractThe effect of mixed ligands on the lifetime and 17O hyperfine coupling constant of water bound to Co2+ in aqueous solutions of proline, glycine and alanine was determined, as a function of pH, by means of 17O NMR. The lifetime of the coordinated water molecules decreased from 4.9 X 10−7 s (for the pure aqueous complex) to 3.5 × 10−8 at pH 8, where more than one complex of proline were present. Smaller changes were measured for the 17O hyperfine coupling constant of water [from ‐ 1.7 × 107 Hz for Co(H2O) to ‐1.45 × 107 Hz measured at pH 6 in the presence of proline], and the enthalpy of activation of the first‐order exchange from the first coordination sphere of Co2+ (from 7.4 ± 0.2 kcal mol−1 for the pure aqueous complex to 6.2 ± 0.4 kcal mol−1 at pH 8 in the presence of proline).
Total assignment of the 1H and 13C NMR spectra of new 1‐phenyl‐ and 1‐cyano‐substituted 3,3‐dimethyl‐2‐thiatricyclo[3.2.1.16,8]nonane 2,2‐dioxide through the application of two‐dimensional NMR techniques
Authors: Faure Robert , Vacher Bernard , Samat André , Chanon Michel 
Published: May 2005

AbstractTotal assignment of 13C and 1H NMR spectra of the new compounds 1‐cyano‐ and 1‐phenyl‐substituted 3,3‐dimethyl‐2‐thiatricyclo[3.2.1.16,8]nonane 2,2‐dioxide was achieved using the concerted application of two‐dimensional homonuclear and heteronuclear chemical shift correlations. This unequivocal structure determination rules out the formation of a six‐membered ring during the intramolecular cyclization of the α‐sulphonyl‐C centred radical originating from 5‐endo‐isopropylsulphonyl‐5‐exo‐substituted norbornene.
An internal deuterium NMR thermometer
Authors: Roth Klaus 
Published: May 2005

AbstractThe temperature of an NMR sample can be indirectly determined by using a suitable deuteriated reference compound and the lock channel for observing the deuterium rapid‐passage NMR spectrum. By calculating the autocorrelation spectrum by two forward Fourier transformations, the relative chemical shift differences can easily be determined. The procedure can be performed on most commercial spectrometers and is completely independent of the frequency of the observed nucleus and/or any high‐power proton decoupling of the sample.
Carbon‐13 NMR studies of multicyclic lactams. Structures and 13C assignments by lanthanide induced shifts, relaxation studies and MINDO/3 calculations
Authors: Barfield Michael , Babaqi Abdulla S. 
Published: May 2005

AbstractCarbon‐13 NMR studies were performed with a series of nineteen multicyclic lactams. The solution conformations of most of these were determined using the lanthanide induced shift (LIS) method in combination with x‐ray and/or MINDO/3 optimized geometries. These analyses show that E‐caprolactam and 3‐azabicyclo[4.3.1]decan‐4‐one have at least two conformations in solution. The LIS structural analyses were further confirmed by means of 13C T1 relaxation times with Gd(dpm)3 and Gd(fod)3 as relaxation reagents. However, relaxation data for carbons in proximity to the complexation site are not reliable for this purpose, probably because of the occurrence of mechanisms other than dipole‐dipole. It is also noted that it is better to compare carbons having the same number of bonded hydrogens. With the help of the LIS data it was possible to assign unambiguously the chemical shifts of the carbons in all of the lactams in this study.
29Si hyperfine splittings in the EPR spectra of silyl‐substituted alkyl and propynyl radicals
Authors: Walton John. N. C. 
Published: May 2005

AbstractThe 29Si satellites were observed in the EPR spectra of 3‐trimethylsilylprop‐2‐ynyl, 1‐trimethylsiloxyprop‐2‐ynyl and trimethylsiloxymethyl radicals. Comparison of the experimental a(29Si) values with spin densities calculated by semi‐empirical MO methods led to a value of 810 G for Qsi. The magnitude and postive temperature dependence of the a(29Si) values in the siloxy‐substitued radicals showed that their preferred conformations are staggered with the silicon atom in the nodal plane of the orbital containing the unpaired electron. This contrasts with the analogous β‐trialkylsilkylethyl radicals, which adopt eclipsed confromations. The rotaton barrier baout the C‐αO bond in trimethylsiloxymethyl radicals was estimated to be 3.8 keal mol−1. The preference of β‐oxamethyl radicals for the staggered conformation was attributed to the comparatively large stablization due to the interacton of the unpaired electron with the adjacent oxygen, and an attempt was made to quantify this effect.
Magnitude and sign of C,C coupling constants in acetylenes and allenes
Authors: Lambert JöRg , Klessinger Martin 
Published: May 2005

AbstractOne‐ and two‐bond C,C coupling constants and the signs of ten of the two‐bond coupling constants were determined from the INADEQUATE and SLAP spectra of four acetylenes and one allene. The geminal C,C coupling constants involving sp‐hybridized carbons are found to be positive and to correlate linearly with the corresponding s character products. In contrast, INDO‐SCPT calculations yield negative values for these coupling constants, and no correlation with the s character products. A separation of those parts of the coupling information transmitted by the σ and π electron framework, based on INDO‐FPT‐PRMO calculations, reveals some possible reasons for the poor performance of the INDO‐SCPT method for systems with π‐electrons.
A rare example of extremely strong carbon—carbon coupling: Analysis of 13C and 1H NMR spectra of a 13C2‐acetylenic ketone
Authors: Auchus Richard J. , d'Avignon André , Covey Douglas F. 
Published: May 2005

AbstractNMR spectra are reported for an acetylenic ketone enriched with 13C in the acetylenic carbon atoms that exhibits extremely strong C‐C coupling. Chemical shifts and coupling constants have been extracted from computer simulations of the second‐order 1H and 13C spectra. The two acetylenic carbon atoms exhibit a Δ ν/J ratio of 0.2. Owing to the strong coupling, the double‐quantum coherence 13C spectrum requires an unusually long (58 ms) interpulse delay time in order to obtain a good spectrum. NMR spectra of this compound provide a unqiue example of strong coupling in a CCH (AB or ABX) spin system.
Effect of intramolecular and intermolecular exchange processes on the 1H NMR spectra of 2‐chloro‐1,3,2‐dioxarsolanes
Authors: Song S. K. , Watkins C. L. , Krannich L. K. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of solutions of 2‐chloro‐4,4,5,5‐tetramethyl‐1,3,2‐dioxarsolane (1) and 2‐chloro‐1,3,2‐dioxarsolane (2) are reported as a function of temperature, concentration and solvent. These data indicate rapid intramolecular conformational averaging for (1) and (2) under all the conditions investigated. Additionally, intermolecular conformational averaging processes are shown to be present. The kinetic parameters for intermolecular exchange were obtained from line shape analysis of the 1H NMR data. These results indicate the intermolecular exchange to be bimolecular in nature, involving a four‐centered transition state. The OCH2CH2–O torsional angle of (2) has been calculated from the analysis of its AA′BB′ 1H NMR spectral patterns, obtained at low concentrations in the absence of intermolecular exchange.
A 59Co NMR chemical shift and relaxation study of preferential solvation toward tris(acetylacetonato)cobalt(III)
Authors: Grahn Hans , Edlund Ulf , Holak Tadeusz A. 
Published: May 2005

AbstractA 59Co NMR chemical shift and relaxation study of the preferential solvation of tris(acetylacetonato)cobalt(III) was undertaken by varying the solute concentration in cyclohexane. As expected, the preferred solvation is most pronounced for hydrogen‐bond donating solutes, such as chloroform and methanol. However, the expected levelling of the 59Co chemical shift curve on increasing the alcohol molar fraction is not observed because of competing solute‐solute interactions in bulk solution. The order of preference is close to that proposed using paramagnetically induced relaxation times or shifts in solutions doped with tris(acetylacetonato)chromium(III). The 59Co line‐width measurements correlate with Co(acac)3 rotational correlation times. Contrary to earlier proposals, the 59Co relaxation is claimed to be controlled by modulation of the static quadrupolar tensor of Co(acac)3.
Calculation of 2J(HH) and 1J(CH) for transition metal methyl compounds; evidence for geometric dependence of 2J(HH)
Authors: Green Jennifer C. , Payne Martin P. 
Published: May 2005

AbstractCalculations of 2J(HH) and 1J(CH) for CH4, TiCl3CH3, Mn(CO)5CH3 and Zn(CH3)2 as a function of C‐H distance and MCH angle have been carried out, based on the extended Hückel method. The positive geminal coupling constant found for TiCl3CH3 is shown to be caused by the small TiCH angle, and the results suggest that the sign and magnitude of the geminal coupling constant in methyl groups could be a useful probe of their solution structure.
1H and 13C NMR spectra of derivatives of 2‐hydroxy‐3‐methylbut‐3‐enenitrile and 2‐hydroxy‐3‐methylbut‐2‐enenitrile
Authors: Jaroszewski Jerzy W. , Ettlinger Martin G. 
Published: May 2005

AbstractA series of derivatives of 2‐hydroxy‐3‐methylbut‐2‐ and ‐3‐enenitrile, including β‐D‐glucopyranosides, were obtained and their 1H and 13CNMR spectra were investigated. The spectra were assigned using lanthanide‐induced shifts, NOE difference spectroscopy and deuterium labelling.
N‐methylene chemical shifts of N‐benzylpyridinium salts
Authors: Munavalli S. , Hsu F.‐L. , Szafraniec L. L. , Beaudry W. T. , Poziomek E. J. 
Published: May 2005

AbstractThe chemical shifts of N‐benzylpyridinium salts have been measured in D2O, and the substituent induced chemical shifts of the methylene protons are in substantial agreement with those expected from the overall electronic effects of the substituents. An additivity effect of the substituents on the methylene resonance is also observed.
1H NMR and a study of the anomalous temperature dependence of the 35Cl NQR frequencies in 2‐chloro‐3‐pyridinol
Authors: Raghoottama P. S. , Soundararajan S. , Ramakrishna J. 
Published: May 2005

AbstractA 35Cl NQR study of 2‐chloro‐3‐pyridinol showed the presence of four NQR signals at 77 K. One of the lines showed a positive temperature coefficient of the NQR frequency. 1H NMR studies showed the presence of intramolecular hydrogen bonding, and the anomalous NQR temperature dependence has been explained in terms of Bayer and hydrogen bond effects. The room temperature x‐ray structure and the low‐temperature NQR data suggest the presence of a phase transition.
Comparison of four pulse sequences for the routine application of proton‐carbon shift correlation
Authors: Kessler H. , Griesinger C. , Zimmermann G. 
Published: May 2005

AbstractFour different pulse sequences for proton‐carbon shift correlation via 1J(CH) couplings are compared using amacrolide as a practical example. These are the COLOC sequence, a new improved variant of COLOC, the 2D‐DEPT‐COSY sequence and its new constant‐time variant. It emerged that the 2D‐DEPT‐COSY and the modified COLOC sequences are the most appropriate for the purpose of routine proton‐carbon shift correlation via direct coupling.
Peptide—lanthanide cation equilibria in aqueous solution. III—Temperature dependence of l‐carnosine‐Ln3+ bound shifts. Isomorphous substitution and side‐chain folding
Authors: Mossoyan J. C. , Ouarzazi J. , Benlian D. 
Published: May 2005

AbstractThe temperature dependence of paramagnetic shifts induced for proton resonances has been investigated for lanthanide (Dy, Ho and Yb) complexes of L‐carnosine. Two different methods of data reduction were used to separate contact, pseudo‐contact and diamagnetic contributions to the paramagnetic shift, one using induced bound shifts and the other based on temperature plots of the induced shift ratios. These studies revealed that diamagnetic effects, which include conformational changes, inductive effects and direct field effects, cannot be neglected. In the Dy, Ho and Yb complexes the side‐chain is folded, but isomorphous replacement and axial symmetry are retained.
Stereostructure of cycloadducts of norbornane/ene‐fused dihydro‐1,3‐ and ‐3,1‐oxazines
Authors: Sohár P. , Stájer G. , Bernáth G. 
Published: May 2005

AbstractThe steric structures of the tetracyclic mono‐ and the pentacyclic bis‐adducts formed in the cycloadditions of norbornane‐ and norbornene‐fused 1,3‐ and 3,1‐dihydrooxazine dipolarophiles with diphenylnitrilimine or benzonitrile oxide were investigated. These reactions could yield 2–8 annellation and positional isomers. The structures of the products were proved by 1H and 13C NMR spectroseopy, and the various potentially stable conformations of the flexible hetero rings were evaluated. The assignments were confirmed by double resonance and DEPT measurements; the steric structures were supported by the results of DNOE experiments.
Carbon‐13 NMR shift data of some 3H‐1,4‐benzodiazepine‐2,5(1H, 4H)‐diones
Authors: Mohiuddin Ghulam , Reddy Padala Satyanarayana , Ratnam Chengalvala Venkata 
Published: May 2005

AbstractCarbon‐13 chemical shifts of eight 3H‐1,4‐benzodiazepine‐2,5(1H, 4H)‐diones are reported. The carbonyl chemical shifts have diagnostic value for distinguishing these diones from the isomeric 1,3‐benzodiazepine‐2,5‐dione structures.
The tautomerism and stereochemistry of β‐sulphinyl enamines
Authors: Kozerski L. , Kawęcki R. , Bednarek E. 
Published: May 2005

AbstractThe tautomeric equilibrium of β‐sulphinyl enamines in solution and the stereochemistry of its components have been studied by 1H and 13C NMR. The parent aliphatic β‐sulphinyl enamines bearing secondary alkylamino residues exist in two tautomeric forms in chloroform solution; the Z‐enamine form always predominates over the E‐imine form. α‐Alkyl‐substituted tertiary compounds exist in solution as a 4:1 mixture of E and Z isomers. NOE enhancements were measured in the two groups of compounds to confirm the stereochemical conclusions derived from the chemical shift interpretation.
1H NMR spectra of pyranocoumarins
Authors: Manzini Paolo , Rodighiero Paolo , Pastorini Giovanni , Guiotto Adriano 
Published: May 2005

AbstractThe 1H NMR spectra of variously annulated pyranocoumarins are reported. The complete assignment of chemical shifts was achieved by using coupling constants and the shift effects induced by the introduction of methyl groups at various positions on the pyranocoumarin nucleus, and by comparison with the spectra of known compounds.
13C spin—lattice relaxation in all‐trans retinal: Effect of the chemical shift anisotropy
Authors: Pattaroni Christian , Lauterwein Jürgen 
Published: May 2005

AbstractThe 13C spin‐lattice relaxation times and nuclear Overhauser enhancement factors of all‐trans‐retinal were measured in acetone‐d6 at two different magnetic field strengths. The extent to which the chemical shift anisotropy mechanism was found to contribute to the relaxation rate of the quaternary olefinic carbons was between 23 and 37% at 4.70 T and between 48 and 66% at 8.45 T. Assuming anisotropic molecular motion and an asymmetric chemical shift tensor, the shielding anisotropies of carbons C‐5, C‐6, C‐9 and C‐13 were calculated to be 185, 172, 188 and 228 ppm, respectively. These are qualitatively similar to those obtained in a recent 13C NMR study of all‐trans‐retinal in the solid state. In contrast, the quaternary aliphatic carbon C‐1 was much less relaxed by the chemical shift anisotropy mechanism (contribution <11%). The relaxation of the proton‐bearing carbons was independent of the magnetic field and determined only by the dipole—dipole interaction mechanism.
Structural and NMR assignment study of the O‐linked glycopeptides of calf fetuin
Authors: Berman Elisha 
Published: May 2005

AbstractTwo O‐linked glycopeptides were isolated by protease digestion of calf fetuin. Using 13C and 1H NMR spectroscopy, it was established that both carry identical trisaccharide side‐chains, but they were found to possess different peptide moieties. Therefore, they must originate from different regions of the polypeptide backbone of fetuin. The two glycopeptides carry a total of three oligosaccharide chains, in accordance with previously published data. One glycopeptide was found to carry two side‐chains: one is linked to a serine and the other to a threonine that are separated by one alanine only. The other glycopeptide carries one sugar chain linked to a serine residue. It was not possible to isolate any glycopeptide which contained a second sialic acid residue directly linked to the N‐acetylgalactosamine, as reported earlier. Some long‐range chemical shift effects were observed in the NMR spectra of the glycopeptide, indicating a specific conformation for this glycopeptide as a result of the proximity of the two oligosaccharide side‐chains.
ENDOR spectra of vanadyl complexes in asphaltenes
Authors: Atherton Neil M. , Fairhurst Shirley A. , Hewson Geoffrey J. 
Published: May 2005

AbstractIt has been suggested, on the basis of electron spin resonance measurements, that the coordination of vanadyl complexed in asphaltenes is porphyrin‐like. We have examined a number of asphaltenes using electron nuclear double resonance (ENDOR) spectroscopy and obtained spectra from 14N and 1H nuclei. Comparison of the spectra with those of vanadyl octaethyl‐ and tetraphenyl‐porphyrins confirms that the porphyrin structure does indeed occur in the asphaltenes.
A 31 P NMR study of O,O′‐dialkyldithiophosphates: An unusual coupling
Authors: Ray G. Joseph , Caspari Gunter 
Published: May 2005

AbstractA series of O,O′‐dialkyldithiophosphoric acids have been studied by 31P NMR, and a four‐bond 31P‐1H scalar coupling has been detected. This coupling is unusual because it is observed between phosphorus and only one of two available protons located on the same carbon, even when the alkyl fragment is simply an alkane that should not show any conformational preference. Variation of the structural features of the alkyl group showed that this coupling involved a “W” pathway.