bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spin density distribution in dialkyl oxalate radical anions
Authors: Brix P. , Helling D. , Voss J. 
Published: May 2005

AbstractThe isotropic and anisotropic ESR spectra of dialkyl oxalate radical anions, including derivatives which were labelled with 13C or 17O in the carbonyl and 2H or 13C in the alkyl groups, were measured. The spin density distribution as determined from the experimental nuclear hyperfine coupling constants agrees very well with MNDO‐CI calculations. As a consequence of the strictly planar structure of the radical anions, E/Z isomers are observed.
13C1H shift correlation with full 1h1H decoupling
Authors: Perpick‐Dumont Marion , Reynolds William F. , Enriquez Raul G. 
Published: May 2005

AbstractA pulse sequence for obtaining 13C1H shift‐correlated spectra with full 1H1H decoupling is described and evaluated. It is concluded that the sequence provides excellent resolution, even for strongly coupled methylene groups. The sensitivity is superior to those of existing sequences based on 13C detection for organic compounds in the molecular weight range up to ca 500.
Study of disaccharide conformation by one‐and two‐dimensional NMR spectroscopy: 1,6‐anhydro‐β‐maltose hexaacetate
Authors: Dais Photis , Perlin Arthur S. 
Published: May 2005

AbstractOne‐ and two‐dimensional NMR spectroscopy were employed to determine the conformation of 2,3,4,6,2′,3′‐hexa‐O‐acetyl‐4‐O‐α‐D‐glucopyranosyl‐1′,6′‐anhydro‐β‐D‐glucopyranose in acetone‐d6 solution. Inter‐residue interproton distances, H‐1–H‐4′ and H‐1–H‐3′, determined by 2D NOE experiments are commensurate with torsional angles ϕ and Ψ of −10° and −20°, and also of 10° and −30°, about the inter‐residue glucosidic bond. Computer simulation showed that, within the limits of the experimental error (ca ±0.20 Å) of the interproton distances determined, several sets of ϕ and ψ angles are consistent with the NMR data. These ‘allowed’ conformations are presented in the form of a conformational map.
The stereochemistry of crown ethers. II —1H and 13C NMR structural study in solution
Authors: Kleinpeter E. , Gäbler M. , Schroth W. , Mattinen J. , Pihlaja K. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of a series of structurally related crown ethers have been recorded, and the signals assigned by means of 1H/13C heteronuclear correlated and 1H/1H homonuclear NOE difference spectroscopy. The NMR parameters so extracted have been used to discuss the preferred, rapidly interconverting solution conformations of the studied species. The high‐field shifts in the 13C NMR spectra, within the so‐called γ‐fragments, and also the 1H/1H homonuclear NOEs, are particularly informative in this respect. The T1 relaxation times of the 13C atoms show segmental motions within the ether segments and suggest different intramolecular flexibilities for the studied compounds.
EPR and ENDOR investigations of dynamic processes in sterically overcrowded phenoxyl‐type galvinoxyl radicals
Authors: Von Gersdorff J. , Kirste B. , Niethammer D. , Harrer W. , Kurreck H. 
Published: May 2005

AbstractThe syntheses of tert‐butylgalvinol with perdeuteriated tert‐butyl groups and of 1,4‐bicyclo[2.2.2]octanebisgalvinol are described. The EPR and ENDOR spectra of the corresponding galvinoxyl monoradicals reveal selective line broadening due to dynamic processes associated with hindered internal rotation of the phenoxy rings. Deuteriation of the central tert‐butyl group in tert‐butylgalvinoxyl gives rise to a substantial decrease of EPR line widths, allowing the determination of the kinetic parameters by means of line‐shape analyses (ΔH≠ = 21.8 kJ mol−1, ΔS≠ = −32 J mol−1 K−1). The biradical 1,4‐bicyclo[2.2.2]octanebisgalvinoxyl exhibits strong scalar and dipolar electron interactions (D = 97 MHz).
Repeatability and reproducibility of site‐specific isotope ratios in quantitative 2H NMR
Authors: Guillou C. , Trierweiler M. , Martin G. J. 
Published: May 2005

AbstractThe repeatability and reproducibility of quantitative deuterium NMR at the natural abundance have been determined according to the ISO norms in a collaborative studyThis study was organized by the Community Bureau of Reference, EEC (Bruxelles). The list of the participants is given at the end.
involving 16 spectrometers.A repeatability of better than 0.8% and a confidence interval of 0.25% have been determined from the results obtained in the 15 different European laboratories that participated in the collaborative study. The reproducibility of the measurements carried out on very different NMR systems is of the order of 2–3%, but this can be improved to 1% with more homogeneous spectrometer systems.The influence of the spectrometer performances on the precision of the quantitative data has been analysed in terms of statistical inference, variance analysis and multidimensional factorial representation. The results indicate the advantages of using highly automated procedures to decrease the random error in the measurement.
Experimental test of karplus‐type relationships for 3J(Sn, C) and 3J(Sn, H)
Authors: Mitchell T. N. , Podesta J. C. , Ayala A. , Chopa A. B. 
Published: May 2005

AbstractMultinuclear (1H, 13C, 119Sn) NMR data are presented for a series of compounds of the type XMe2SnCHRCHR'CO2Me (X = Me, Cl; R, R' = Me, Ph). Values of 3J(H, H), 3J(Sn, H) and 3J(Sn, C) were used to assign the preferred conformations of these compounds and at the same time to test the empirical relationships proposed previously for 3J(Sn, C) and (indirectly) 3J(Sn, H); the validity of these relationships was confirmed.
Compounds with bridgehead nitrogen. 56—The 1H NMR spectra and stereochemistry of some perhydrooxazolo[3,4‐a]quinolines and 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines
Authors: Crabb Trevor A. , Heywood Geoffrey C. 
Published: May 2005

AbstractThe configurations and preferred conformations of some perhydrooxazolo[3,4‐a]quinolines and of the related 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines have been assigned on the basis of their 1H NMR spectra. Comparison of the spectra of the two sets of compounds shows the effect of replacement of the alicyclic ring in the fully reduced compounds by the aromatic ring in the 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines on the 1H NMR parameters of the NCH2O protons.
Carbon‐13 NMR study of 1‐(trifluoromethyl)‐dihydro‐ and ‐tetra‐hydro‐naphthalenes
Authors: Bonnet‐Delpon D. , Ourevitch M. 
Published: May 2005

Abstract13C NMR data for variously functionalized and substituted 1‐CF3‐tetrahydronaphthalenes are reported. A complete assignment of the chemical shifts has been achieved.
13C NMR spectroscopic study of the rearrangement of 16β‐hydroxy‐17‐oxo steroids to 17β‐hydroxy‐16‐oxo isomers
Authors: Doller Darío , Gros Eduardo G. 
Published: May 2005

AbstractThe acid‐catalysed rearrangement of 3β, 16β‐dihydroxyandrost‐5‐en‐17‐one to 3β, 17β‐dihydroxyandrost‐5‐en‐16‐one was studied by 13C NMR spectroscopy. The spectra indicated that the reaction is produced by an intramolecular 1, 2‐shift of hydride from C‐16α to C‐17α.
Long‐range CH correlation 2D NMR spectroscopy. 4—Complete spectral assignments of the pesticide metabolite S‐(2,3‐dihydroxy‐1‐propyl)glutathione
Authors: Krishnamurthy V. V. , Casida John E. , Dohn David R. 
Published: May 2005

AbstractComplete 13C and 1H spectral peak assignments of S‐(2,3‐dihydroxy‐1‐propyl)glutathione (1) (an in vivo metabolite of the pesticide 1,2‐dibromo‐3‐chloropropane) were made using various 2D NMR techniques. Long‐range CH correlation 2D NMR unambiguously assigned the key methylene resonances adjacent to sulfur. Appropriate delays for optimum cross‐peak intensities in the long‐range correlation experiment were chosen with response intensity curves, generated using estimated long‐range coupling constants. These curves, although generated assuming a first‐order coupling network, are useful even in systems with strong second‐order couplings as in 1.
Generation of quinone cation radicals via photo‐induced electron transfer: ESR evidence
Authors: Liu Zhong‐Li , Wu Lung‐Min , Liu You‐Cheng 
Published: May 2005

AbstractBenzoquinone cation radicals of 1,4‐benzoquinone and methyl‐, 2,5‐dimethyl‐ and 2,6‐dimethyl‐1,4‐benzoquinone were formed from the corresponding parent quinones by in situ UV photolysis in trifluoroacetic acid at ambient temperature, and detected by ESR. The cationic character of the radical species was confirmed by the electron transfer between the quinone cation radicals and N,N,Ń,Ń‐tetramethyl‐p‐phenylenediamine (TMPD). In the case of tert‐butyl substituted benzoquinones, instead of the corresponding cation radicals, cyclized radicals, i.e. the 3,3‐dimethylcoumaran‐5‐oxy and 3,3‐dimethyl‐7‐tert‐butylcoumaran‐5‐oxy radicals and the 3,3‐dimethyl‐6‐tert‐butylcoumaran‐5‐hydroxy cation radical were detected from tert‐butyl, 2,6‐di‐tert‐butyl‐ and 2,5‐di‐tert‐butyl‐1,4‐benzoquinones, respectively. A mechanism involving electron transfer between the photoexcited quinone and that in the ground state is proposed.
Aromatic substituent chemical shifts and J(CF) coupling constants in fluoro‐substituted benzenes
Authors: Newmark Richard A. , Hill James R. , Tiers George V. D. 
Published: May 2005

AbstractAromatic substituent chemical shifts are reported for the difluoromethylthio, trifluoromethoxy, pentadecafluoroheptyl and fluosulfonyl groups. Long‐range coupling to the ortho and para carbons is observed in all cases except the trifluoromethoxy group.
Microcomputer simulation of solid‐state 13C NMR line shapes affected by quadrupolar nuclei
Authors: Olivieri Alejandro , Frydman Lucio , Grasselli Mariano , Diaz Luis 
Published: May 2005

AbstractSolid‐state 13C NMR spectra of 14N‐containing compounds obtained under CPMAS conditions often show asymmetric doublets arising from the unaveraged 13C,14N residual dipolar coupling. A similar result has recently been noticed in deuteriated samples, whose 13C resonances showed the combined effect of 13C,2H dipolar and scalar couplings. A simple approach, easily adaptable to a desk microcomputer, is described for simulating 13C line shapes for arbitrary values of quadrupole parameters, CX (X = 14N, 2H) distances, external field and orientation of the internuclear vector in the axis system where the electric field gradient tensor is diagonal.
Solubilization of aromatics in aqueous bile salts. IV—Two‐dimensional 1H NMR study on intra‐ and inter‐molecular interactions in aromatic solubilizate–cholate systems
Authors: Kolehmainen E. 
Published: May 2005

AbstractSolubilization of aromatics in aqueous bile salts was studied by two‐dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY) for three model systems: benzene, anisole and veratrole solubilized in aqueous sodium cholate. The observed intra‐ and inter‐molecular cross‐relaxation properties are discussed in terms of different solubilization sites available for different solubilizates. The cholate anions located in the micelles seem to maintain their intramolecular cross‐relaxation characteristics during the mixed micelle formation. A molecular mechanical calculation of the cholate anion was performed in order to determine the non‐bonded internuclear distances between the NOE‐connected nuclei.
Complete assignment of the 13C NMR spectra of bleomycin A2 and its zinc complex by means of two‐dimensional NMR spectroscopy
Authors: Akkerman M. A. J. , Haasnoot C. A. G. , Pandit U. K. , Hilbers C. W. 
Published: May 2005

Abstract13C NMR spectra of free bleomycin A2 at pH 4 and 6.7 and of its zinc complex at pH 6.7 were completely assigned by making use of two‐dimensional 1H13C correlated spectroscopy. Differences in resonance positions between the spectra of the free bleomycin at pH 4 and 6.7 are observed for the β‐hydroxyhistidine and the β‐aminoalanine residues, obviously because of protonation/deprotonation of these moieties in the pH region considered. Also, shifts are observed for the carbon resonances of the gulose residue. Upon complex formation between zinc(II) and bleomycin large 13C shifts are observed for the carbon atoms in the pyrimidinepropionamide, β‐hydroxyhistidine, β‐aminoalanine, α‐L‐gulose and α‐D‐mannose fragments. Although for some residues the observed shifts correspond with the position of the zinc(II) binding sites in bleomycin proposed on the basis of earlier 1H NMR experiments, a simple correlation between the location of the zinc(II) binding sites and the 13C shifts cannot be drawn.
Two‐dimensional6Li,1H heteronuclear Overhauser spectroscopy (HOESY) in magnitude and pure absorption representations. Application to a dimer–monomer equilibrium of a 1,4‐dilithio compound
Authors: Bauer Walter , Schleyer Paul Von Ragué 
Published: May 2005

Abstract6Li,1H HOESY was used both for the detection of short lithium–proton distances and for proton spectral assignments of 1,8‐dilithio‐1,2‐diphenylhex‐1‐ene, which exists as a monomer–dimer equilibrium mixture in tetrahydrofuran (THF‐d8). Experiments using magnitude mode, pure absorption and pseudo‐steady‐state mode representations are described. Pure absorption6Li,1H HOESY proved to be the superior method.
Total assignment of the 1H‐ and 13C‐NMR spectra of dinaphtho[1,2‐b:1′,2′‐d]thiophene through the concerted use of two‐dimensional NMR techniques
Authors: Johnston Milton D. , Castle Raymond N. , Salazar Miguel , Kruger Diana K. , Martin Gary E. 
Published: May 2005

AbstractThe 1H‐ and 13C‐NMR spectra of dinaphtho[1,2‐b:1′2′‐d]thiophene (1), a sulfur‐containing polynuclear heteroaromatic, have been totally assigned using a combination of two‐dimensional NMR techniques. Techniques applied were standard proton‐proton COSY, proton zero‐quantum coherence (ZQCOSY, optimized to 7 Hz and to 1.75 Hz), proton double quantum coherence (DQCOSY, optimized to 7 Hz), broad‐band decoupled (both dimensions) proton‐carbon chemical shift correlation, long‐range proton‐carbon chemical shift correlation, and proton‐carbon heteronuclear relayed coherence transfer. A comparison of these methods on 1 showed the most useful information concerning connectivities to be obtained from the zero‐quantum coherence and long‐range heteronuclear correlation experiments. A detailed critique of each type of experiment is given in the context of applications to polynuclear aromatics.
Extraction of 1H1H and 1H13C dipolar couplings from spectra acquired in inhomogeneous magnetic fields
Authors: Kay Lewis E. , Thomson D. S. , Prestegard J. H. 
Published: May 2005

AbstractExperimental procedures are presented for the extraction of 1H1H and 1H13C dipolar couplings from molecules oriented in high magnetic fields without a requirement for high field homogeneity. These couplings impose restrictions on structure in a manner similar to NOE distances and can serve as useful additional constraints for defining structure. The experimental procedures involve pulse sequences which refocus the effects of magnetic field inhomogeneities but which retain dipolar couplings, scalar couplings and, in cases of chemically distinct groups, chemical shift differences. The methods are important for the extension of experiments to higher fields and more complex media where field homogeneity is hard to maintain. The experiments are illustrated using samples containing sodium acetate‐99% 13C2 or alanine‐99% 13C3 dissolved in a nematic liquid crystal and oriented in an inhomogeneous magnetic field. Coupling constants obtained from the studies are in good agreement with couplings extracted from one‐dimensional spectra obtained in homogeneous fields.
Indirect two‐dimensional heteronuclear NMR spectroscopy of low‐γ metal nuclei (M = 183W, 57Fe, 103Rh, 61Ni)
Authors: Benn Reinhard , Rufińska Anna 
Published: May 2005

AbstractIndirect two‐dimensional (X, M) (X = 1H, 31P) triple resonance spectroscopy is presented for the detection of the NMR parameters of insensitive metal nuclei M = 57Fe, 103Rh, 183W and 61Ni which exhibit a scalar coupling to the more sensitive X nucleus. The versatlity of this approach is demonstrated and compared with the previously used detection schemes by recording δ(M) and J(M, X) for a series of organometallic phosphorus tungsten(IV), rhodium(I), iron(0), iron(II) and nickel(0) complexes. The NMR data of the complexes are discussed.
An alternative approach to multi‐dimensional NMR spectroscopy
Authors: Freeman Ray , Friedrich Jan , Davies Simon 
Published: May 2005

AbstractMulti‐dimensional NMR spectroscopy must satisfy the Nyquist sampling condition in all frequency dimensions. This entails very long experiments and very large data arrays, and may mean that fine structure of cross‐peaks cannot be adequately digitized. This sampling restriction can be sidestepped in an alternative approach which explores the new frequency dimensions by scanning selective radiofrequency pulses in small steps over narrow frequency ranges. A pulse envelope shaped according to the first half of a Gaussian curve is particularly well suited to this task. Thus a form of double resonance experiment can be used to generate two‐dimensional correlation spectra that have all the features of the well known COSY experiment, with an additional ‘zoom’ capability that reveals the detailed fine structure information. For systems of three coupled spins the corresponding triple resonance experiment generates a three‐dimensional correlation specrum, the frequency scans being restricted to the region of interest (the 3D cross‐peak) based on information from the conventional NMR spectrum. For correlation spectroscopy of higher dimensionality no frequency search is employed, the selective pulses simply being set at predetermined chemical shift frequencies. A four‐dimensional correlation experiment is described which uses population transfer to establish that four non‐equivalent protons are coupled in a chain ISRP. It employs an initial ‘ZZ‐pulse’ applied at the I‐spin frequency to excite longitudinal two‐spin order (2IzSz) which is then propagated along the chain by the application of selective ‘ZZZ‐pulses’ to the intermediate spins S and R, creating an antiphase intensity perturbation (2RzPz) on the P multiplet. The procedure is recursive and can in principle be extended to N spins coupled pairwise in a ‘linear’ chain. This is a powerful diagnostic tool for structure determination and can be adapted to recognize other topological features such as chain branching and ring closure.
A practical guide to combined rotation and multiple‐pulse NMR spectroscopy of solids
Authors: Jackson Peter , Harris Robin K. 
Published: May 2005

AbstractTechnical details are given for the successful operation of CRAMPS techniques to obtain high‐resolution proton NMR spectra of solids. Matters addressed include probe construction, tunning procedures, optimization of pulses, spectral calibration and referencing. In practice, the MREV‐8 sequences is preferred to BR‐24. It is suggested that CRAMPS operation deserves more widespread application.
139La NMR as a tool for kineic studies
Authors: Ducommun Y. , Helm L. , Laurenczy G. , Merbach A. E. 
Published: May 2005

AbstractThe application of 139La NMR to study the kinetics of substitution reactions is described. Rate constants associated with fast substitution reactions on La3+ complexes in the presence of excess of the aqua‐ion can be obtained by measuring the line widths of the corresponding signals. Measurements as a function of temperature allow the separation of the kinetic and quardrupolar relaxation effects. The rate of aquation of La(2,6‐dicarboxy‐4‐hydroxypyridine)+ was measured in aqueous solution. The dissociation rate constant and the activation parameters obtained for this process are k298r = 207 ± 51 s−1, ΔH = 38.3 ± 3.1 kJ mol−1 and ΔS = −72 ± 8 J K−1 mol−1. The spin–spin relaxation rates of the lanthanum(III) in the two environments are described by 1/T = 550 ± 83 s−1 and EA = 26.4 ± 5.8 kJ mol−1 for the aqua‐ion and by 1/T = (2.00 ± 0.08) × 104 s−1 and EB = 16.3 ± 1.6 kJ mol−1 for the mono‐complex.
NMR of the methylene group: Artifacts in the proton–proton decoupled heteronuclear two‐dimensional chemical shift correlation experiment
Authors: Bain Alex D. , Hughes Donald W. , Hunter Howard N. 
Published: May 2005

AbstractWhen the proton–proton decoupled heteronuclear two‐dimensional chemical shift correlation experiment is applied to a molecule containing methylene groups, the spectra show not only the expected signals at the two proton chemical shifts, but also a strong artifact. This artifact appears at the average of the two proton chemical shifts, and arises from coherence transfer between the two protons caused by the BIRD pulse. It is not caused by strong coupling between the protons, and so may appear in any spectrum. The dependence of this artifact on experimental conditions was analysed, and is illustrated with results obtained on the methylene groups from the cyclophane ring in N6′,N9‐octamethylenepurinecyclophane.
Unusual two‐bond 13C,13C coupling constants in sulphones
Authors: Rücker Christoph , Fritz Hans 
Published: May 2005

AbstractA measurable coupling between carbon atoms through the SO2 group is observed in a series of structurally diverse sulphones. In open‐chain (single coupling path) sulphones this 2J coupling ranges from 5.5 to 27.2 Hz, while in cyclic (multiple coupling path) sulphones values ranging from 4.3 to 21.6 Hz are observed. Sulphides and sulphoxides do not exhibit a corresponding coupling of comparable magnitude. A positive sign for this coupling is derived from the data of cyclic sulphones. Whereas substituents and branching at the coupling termini exert minor influences on the coupling, the most important factor determining the magnitude of the 2J(CSC) coupling is the hybridization of the coupling carbon atoms. A linear relationship between the 2J value and the s character product of the CS bond forming C orbitals is estalished.
Application of data processing for sensitivity and resolution enhancement of 31P and 13C NMR spectra of humic substances
Authors: Kupka Teobald , Pacha Jerzy , Dziȩgielewski Jan O. 
Published: May 2005

AbstractThe application of various methods of data processing of a raw, untreated free induction decay (FID) to improve the quality of noisy and overcrowded spectra is shown. The use of complex interpolation of fragments of a typical 31P NMR spectrum of humic substances from forest soil in D2O, combined with two‐stage apodization of the FID, results in better defined signals and a higher accuracy of the integration of signals partially overlapped in the initial spectrum. Convolution difference resolution enhancement was used to enhance the spectral resolution of overlapped orthophosphate ion and orthophosphate monoester signals, while the noise was attenuated by a decreasing exponential.An attempt to detect carbon signals buried in the noise by applying a rapidly decaying exponential (line broadening of 10 or 50 Hz) to a noisy FID, and the use of resolution enhancement, are also described for the 13C NMR signals from soil extracts.
NMR spectra of organogermanium compounds. 8—73Ge, 13C and 1H NMR spectra of methylvinylgermanes
Authors: Takeuchi Yoshito , Inagaki Hiroko , Tanaka Katsumi , Yoshimura Shin 
Published: May 2005

AbstractA series of methylvinylgermanes were prepared and their 1H, 13C and 73Ge NMR spectra were determined. The chemical shifts were compared with those of the corresponding methylvinylsilanes and a very good correlation was found. The origin of the chemical shifts could not be simply attributed to the electron densities as estimated by MNDO calculations.