bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ab initio IGLO calculations of 31P NMR shielding tensors of thiophosphoryl compounds. I—dithiadiphosphetanes and dithioxophosphoranes
Authors: Krüger Kerstin , Grossmann Gisbert , Fleischer Ulrich , Franke Robert , Kutzelnigg Werner 
Published: May 2005

AbstractBy means of the IGLO method the 31P NMR chemical shift, δiso, the principal values, σii, and the orientation of the principal axes of the shielding tensor were calculated for a number of dithiadiphosphetanes [RP(S)S]2 and of dithioxophosphoranes RPS2 with RH, CH3 or C6H5. The calculated compare well to the available experimental data from solid‐state NMR and can be taken as predictions where no experimental data are available. The dependence of the principal values σii on geometry changes and the substitution was studied. The shielding tensors were calculated as sums of contributions of localized molecular orbitals. These contributions were used to discuss the effects observed. They provide valuable insights into relationships between geometrical structure and the principal values of σ.
DNA–protein interaction in solution: NMR studies of the 13C‐site‐specifically labelled Lac operator–Lac repressor complex
Authors: Lancelot Gérard , Maurizot Jean‐Claude , Chassignol Marcel , Thuong Nguyeng T. , Chanteloup Luc , Beau Jean‐Marie 
Published: May 2005

AbstractCarbon‐13 and proton resonance assignments for a DNA fragment complexed with its regulatory protein were obtain with the use of a selectively 13C‐labelled oligonucleotide. Data obtained on the Lac operator–Lac repressor complex from the HMQC–NOESY maps of the free and complexed Lac operator demonstrate that only minor conformational modifications are induced on complexation.
17O NMR spectroscopic investigation of steroids at natural abundance
Authors: Kählig H. , Robien W. 
Published: May 2005

AbstractNatural abundance 17O NMR spectroscopic data, in toluene‐d8 at 90°C, were obtained for different classes of steroids, including androstanes, estranes, pregnanes, cholanes and cholestanes. Only routine acquisition parameters were used in combination with linear prediction methods during the processing for eliminating acoustic ringing artifacts. The results are discussed in terms of stereochemical effects on the 17O chemical shift of the various oxygen‐containing functionalities.
Gradient selection of coherences in experiments with carbon detection
Authors: Willker Wieland , Leibfritz Dieter 
Published: May 2005

AbstractCoherence pathway selection with gradients in carbon‐detected experiments is demonstrated. Gradient selection (gs) offers excellent suppression of artifacts and unwanted magnetization, and in practice the signal‐to‐noise ratio is at least as good as for the equivalent phase cycled experiment. A selective gs‐1D‐13C‐COSY is used to correlate one carbon resonance with its neighbours. The gs‐INADEQUATE is used to select multi‐quantum coherences; this can be performed as a 1D or a 2D experiment. Complete elimination of t1 noise is obtained in the gs version only. Applications to labelled glucose, 3‐phenylpropan‐1‐ol and natural abundance menthol are presented. Interference from high‐frequency stray radiation in the gradient cable is removed by inserting a low‐pass filter between the gradient wiring and the probe.
Determination of stability constants of metal complexes from NMR chemical shifts and relaxation rates using a spreadsheet computer program
Authors: Huskens Jurriaan , Lammers Hendrik , van Bekkum Herman , Peters Joop A. 
Published: May 2005

AbstractThe versatility of multinuclear magnetic resonance techniques in the determination of stability constants of metal complexes is demonstrated for three cases in which potentiometry is impossible or less suitable. The complexation of cyclo‐trimetaphosphate to lanthanide aminopolycarboxylate complexes was investigated in a dilution experiment using 31P NMR shifts. The stabilities of CdL and CdL2 [L = 1‐(2‐aminoethylamino)‐1‐deoxy‐D‐galactitol] were determined by 113Cd NMR speciation, in which the occurring species were in slow exchange. Competition experiments using both 31P NMR shifts and 13C and 31P relaxation rate enhancements were performed to determine the stabilities of Nd(NTA)(PPP) and Nd(PPP)2 (PPP = tripolyphosphate). Where possible, the results were compared with potentiometric data and found to be in good agreement.
15N NMR chemical shifts of NH‐pyrazoles in the solid state and in solution at low temperature
Authors: Aguilar‐Parrilla Francisco , Männle Ferdinand , Limbach Hans‐Heinrich , Elguero José , Jagerovic Nadine 
Published: May 2005

AbstractThe 15N chemical shifts of thirteen NH‐pyrazoles in the solid state and of seven NH‐pyrazoles in [2H8] THF solution at 170–175 K (with frozen annular tautomerism) are reported. The solid‐state values are discussed using an additive model. The differences in chemical shifts between the solid state and solution are due to the different intermolecular hydrogen bonds present in the various environments.
Preparation and NMR determination of structures of tri‐, tetra‐ and pentacyclic isoindolone derivatives
Authors: Sohár Pal , Frimpong‐Manso Samuel , Stájer Géza , Bernáth Gábor 
Published: May 2005

AbstractFrom the reactions of 3‐endo‐benzoyl‐6‐exo‐phenylbicyclo[2.2.1] heptane‐2‐endo‐carboxylic acid (2) and α,ω‐diamines or o‐aminophenol/thiophenol, different tri‐, tetra‐ and pentacyclic phenyl‐substituted norbornane‐condensed heterocycles were prepared. With ethylenediamine, 2 furnished two isomeric imidazolo[2,1‐a]isoindolones. In the formation of one of them, an end→oexo isomerizaton was observed. The stereostructures (configurations and conformations) of the compounds were elucidated by 1H and 13C NMR spectroscopy, with the aid of routine spectra and also DR, DNOE, DEPT, COLOC and 2D‐HSC measurements.
13C and 15N NMR study of mesoionic type A and type B tetrazoles with four nitrogen atoms in the exocyclic group
Authors: Koźmiński Wiktor , Jaźwiński Jarosaw , Stefaniak Lech , Webb Graham A. 
Published: May 2005

Abstract13C and 15N NMR measurements are reported from a study of five mesoionic compounds containing either the 2,3‐diphenyl‐ or 1,3‐diphenyltetrazolium ring, and either the 2,3‐diphenyltetrazolium ring or its linear analogue as an exocyclic group. Three 15N‐labelled compounds were synthesized for signal assignment purposes. Some 15N13C and 15N15N coupling constants were determined. A proton was found to be located on the exocyclic groups of two of the compounds.
EPR study of Bi‐, Ter‐ and quaterthiophene radical cations
Authors: Kirste Burkhard , Tian Peizhu , Kossmehl Gerhard , Engelmann Gunnar , Jugelt Werner 
Published: May 2005

AbstractRadical cations of a series of α‐methyl‐substituted bi‐, ter‐ and quaterthiophenes were investigated by EPR and, in part, ENDOR spectroscopy. In the case of terthiophenes, the electronic and steric effects of methyl substituents were studied. The experimentally determined spin density distributions were rationalized by means of semi‐empirical quantum‐mechanical calculations (MNDO, PM3, RHF‐INDO/SP). Sterically non‐hindered oligothiophene radical cations are planar and form mixtures of cis and trans conformers, whereas uniform species were observed in the case of sterically hindered, non‐planar radical cations.
Solid‐state mercury‐199 NMR of hexakis (dimethyl sulphoxidé) mercury (II) trifluoromethanesulphonate: A new standard for mercury‐199 CP/MAS experiments
Authors: Hook James M. , Dean Philip A. W. , van Gorkom Leon C. M. 
Published: May 2005

AbstractHexakis(dimethyl sulphoxide)mercury(II) trifluoromethanesulphonate, [Hg(dmso)6](O3SCF3)2, is a stable, readily synthesized compound which is an excellent standard for setting up CP/MAS experiments in solid‐state 199Hg NMR. The isotropic chemical shift, δISO ‐2313 ppm, is to lower frequency than that measured for the same material in solution. The static spectrum exhibits of powder pattern indicative of axial symmetry about the mercury atom, with a chemical shift anisotropy of 122 ppm.
Multinuclear magnetic resonance study of some mesoionic 1,3,4‐triazoles
Authors: Bocian Wojciech , Jaźwiński Jaroslaw , Stefaniak Lech , Webb Graham A. 
Published: May 2005

Abstract1H, 13C, 14N and 15N NMR data are reported for a series of mesoinoic 1,3,4‐triazoles and some of their salts. The results obtained show that the molecules studied exist in the cyclic mesoionic form with delocalization of the positive charge over the ring atoms. The corresponding negative charge occurs on the atoms of the exocyclic groups, which also act as the site of protonation and salt formation. The most important experimental data for these interpretations are found to be the nitrogen shieldings and that for C‐5.
Pulsed field gradient one‐dimensional NMR selective ROE and TOCSY experiments
Authors: Dalvit Claudio , Bovermann Günter 
Published: May 2005

AbstractA pulsed field gradient one‐dimensional NMR selective ROE (rotating frame NOE) experiment was designed and successfully tested. The resulting spectra are of high quality and devoid of artefacts. Hence reliable quantification of very weak ROEs necessary for the three‐dimensional structure determination of a molecule is now possible. A similar experiment was designed for the selective 1D TOCSY pulse sequence.
Stereochemistry and synthesis of precursors to strigol analogues
Authors: Tóth Gábor , Halász Judit , Kádas István , Árvai Géza , Mikló Katalin , Haessner Rainer 
Published: May 2005

AbstractThe relative configuration and conformation of the 8‐methyl‐5‐nitro‐1‐oxo‐Δ8(8a)‐octahydronaphthalene isomers were elucidated by various 1H and 13C NMR methods. The structure of the tricyclic by‐products was also determined.
Complete 1H and 13C NMR assignments of two steroid 5, 6β‐epoxides using 1D TOCSY and 2D HMQC TOCSY experiments
Authors: Over Diana E. , Bardet Michel , Marchon Jean‐Claude , Ramasseul René 
Published: May 2005

AbstractThe complete assignments of 1H and 13C data for two steroid epoxides, 3β‐acetoxy‐5,6β‐epoxyandrostan‐17‐one and 3β‐acetoxy‐5,6β‐epoxycholestane, based on DEPT, 1H1H DQF COSY, HMQC, 1D TOCSY and 2D HMQC TOCSY sequences are described. Especially the 1D TOCSY and 2D HMQC TOCSY techniques were essential to the structure elucidation of theses steroids.
17O NMR spectra and conformation of cyclic vinyl ethers
Authors: Taskinen Esko , Ora Mikko 
Published: May 2005

AbstractThe 17O NMR spectra of a number of heterocyclic vinyl ethers were recorded in CDCl3 and DMSO‐d6 solutions. The oxygen chemical shifts reveal substantial differences in the strength of p‐π conjugation between the five‐ and six‐membered ring compounds, especially between those with an exocyclic CC bond. The conformations of the title compounds were estimated by force‐field calculations; the calculated torsional angle of the COCC moiety appears to be a linear function of the 17O NMR shift data, corrected by appropriate structural factors.
Solid‐state 13C NMR spectroscopy. 2‐titanium tetrachloride‐ketone complexes. Structure and mechanism of isomerization
Authors: Maier Günther , Kalinowski Hans‐Otto , Weber Claudia , Henrich Markus 
Published: May 2005

AbstractThe solid‐state 13C NMR spectra of a series of titanium tetrachloride‐ketone and titanium tetrachloride‐ester complexes are presented. The kind of complexation is discussed. The activation energy and the mechanism (planar inversion) for the syn‐anti isomerization at the oxygen atom was evaluated.
13C and 1H NMR assignments for a series of dehydroabietic acid derivatives
Authors: Gigante Bárbara , Santos Lina , Marcelo‐Curto Maria João , Ascenso José 
Published: May 2005

AbstractReliable assignments were made for a series of nitro and amine C ring‐substituted dehydroabietic acid derivatives, the main resin acid present in disproportionated rosin and an important intermediate in the chemical industry. A combination of 1D and 2D NMR techniques, including HETCORR, COSY and DEPT experiments, was used. Quaternary carbon atoms, mainly aromatic substituted, require care owing to assignment difficulties that are based on calculated data and are confirmed by long‐range 1H, 13C NMR correlation with selective INEPT and the proton‐detected HMBC experiment.
Theory and application of fully anisotropic overall molecular tumbling, with restricted group internal rotation: 13C NMR relaxation studies of sodium taurocholate and ginsenoside‐Re
Authors: Wang Dehua , Xu Xiaolong , Deng Nianyong , Pen Lianqang , Zhang Wenbin , Stark Ruth E. 
Published: May 2005

AbstractA theory is presented for fully anisotropic overall molecular tumbling with restricted group internal rotation. This formalism is used with 13C NMR relaxation data and results from molecular mechanics to compute the rotational diffusion rates and methyl group internal rotation rates for sodium taurocholate and ginsenoside‐Re in organic solvents. Although existing theories for steroid derivatives describe methyl internal rotation in terms of free isotropic motion, methyl rotation in ginsenoside‐Re is found to be both sluggish and spatially restricted. The energetic barrier to methyl internal rotation increases significantly with the bulkiness of flexible side‐chains in a series of steroid natural products.
15N NMR studies of guanidines. I—hydrogen bonding and electronic effects in conformationally flexible guanidines
Authors: Bedford Geoffrey R. , Taylor Peter J. , Webb Graham A. 
Published: May 2005

AbstractHydrogen bonding and electron distribution in some heterocyclic guanidines were studied by 15N NMR spectroscopy, using other substituted guanidines as points of reference. Solvent effects were used to distinguish the 15N NMR signals for their two sp2 nitrogen atoms, since ring nitrogen forms an intramolecular hydrogen bond and so is much less sensitive to solvent than is the guanidine unit. The effect of substituent is discussed in terms of competition between through‐resonance and the more localized resonance of the π‐inductive effect. These are favoured, respectively, by oxygen (nitro, acyl) and nitrogen (cyano) acceptor groups, whereas heterocycles, also nitrogen acceptors, occupy an intermediate position. Among the latter class, there are indications that the balance between these forms of resonance may be influenced by competitive conjugation with ring π‐donor heteroatoms.
15N NMR studies of guanidines. II—the fused‐in guanidine unit of some oxoheterocycles: A combined 15N NMR, 13C NMR and IR study
Authors: Bedford Geoffrey R. , Taylor Peter J. , Webb Graham A. 
Published: May 2005

Abstract15N NMR spectroscopy was used to extend previous studies, by 13C NMR and IR spectroscopy, of fused oxoheterocycles which contain the guanidine unit. These compounds fall into three clearly definable structural types, through‐conjugated, ring‐conjugated or imide‐like, any or all of which may result from the cyclization reactions used for their synthesis. It is shown that 15N NMR and IR criteria are of equal value in distinguishing these, whereas 13C NMR is in general unhelpful. A qualitative correlation exists between v(CN) for the guanidine unit, and the summed 15N NMR chemical shifts for the two π‐donor nitrogen atoms. The present observations should help to establish spectroscopic criteria for structural elucidation.
Neutral hyperconjugation challenged: No support from one‐bond CC coupling constants
Authors: Kamieńska‐Trela Krystyna 
Published: May 2005

AbstractA significant decrease in 1J(Cipso, CH2) coupling constants from a value typical of C(sp2)C(sp3) bonds (43.5 Hz or smaller) to the unexpectedly low value of 36 Hz typical of C(sp3)C(sp3) bonds was reported by Lambert and Singer on passing from XC6H4CH2Sn(CH3)3 to XC6H4CH2C(CH3)3 (X = H, CH3, OCH3, NO2). This trend was invoked by these authors as the first evidence for neutral hyperconjugation in terms of coupling constants. However, the present measurements reveal that also in C6H5CH2C(CH3)3 and p‐O2NC6H4CH2C(CH3)3 the 1J(Cipso, CH2) coupling constant bears a value typical of this type of bonding (43.8 and 42.6 Hz, respectively). Thus, at variance with Lambert and Singer's observation, a slight increase in 1J(CC) coupling constants occurs on passing from Sn to C derivatives. This contradicts not only their experimental data but also conclusions concerning hyperconjugation in the neutral ground state.
Total assignment of the 1H and 13C NMR chemical shifts of four bufadienolides by 2D NMR spectroscopy
Authors: Reynolds William F. , Maxwell Anderson , Telang Balchandur , Bedaisie Kishore , Ramcharan Gangadeen 
Published: May 2005

AbstractFour known bufadienolides, marinobufagin (1), telocinobufagin (2), bufalin (3) and resibufogenin (4), were isolated from the toad Bufo marinus. The 1H and 13C NMR spectra were completely assigned by using a combination of 13C DEPT and 2D NMR experiments (1H1H COSY, HMQC, HMBC and NOESY). The full 1H NMR data for 1–4 and 1H and 13C NMR data for 2 are reported for the first time.
Multinuclear magnetic resonance study of N,N′,N″‐tris(trimethylsilyl)borazine
Authors: Wrackmeyer Bernd , Schwarze Bernd , Durran D. Michael , Webb Graham A. 
Published: May 2005

AbstractThe nuclear spin relaxation rate of the quadrupolar 14N nuclei in N,N′,N″‐tris(trimethylsilyl)borazine (1) is surprisingly slow [T1(14N)=0.1 s]. This allows one to measure 1J(29Si14N) (9.6 Hz) directly from the 29Si NMR spectra and also to compare signs of coupling constants 1J(29Si14N) (<0) and 3J(14NSiC1H) (>0) by 2D 29Si/1H HETCOR experiments. Since the transverse relaxation time T2(14N) in 1 is governed by scalar relaxation of the second kind, the magnitude of 1J(14N11B) can be evaluated (23 ± 0.5 Hz). 11B, 14N and 29Si NMR data for N,N′‐bis(trimethylsilyl)borazine (2) were also obtained, and 11B and 14N NMR spectra of the parent borazine [HBNH]3 (3), and of [HBNMe]3 (4) were remeasured. Calculation of the tensor components of the 14N electric field gradient shows that eqzz in 1 and in 2 for 14N(Si) is significantly smaller than for other borazines [HBNR]3, e.g. with R=H (3) or Me (4), in agreement with the experimental results.
A 1D H, C correlation with homonuclear cross‐polarization
Authors: Zangger Klaus , Sterk Heinz 
Published: May 2005

AbstractA 1D H, C correlation ROESY experiment is suggested and applications for signal assignments via through‐bond and through‐space correlations are demonstrated using glutathione and 1‐O‐methyl‐4,6‐O‐benzylidene‐α‐D‐glucopyranoside.
Intramolecular hydrogen bonding and conformation of a dipyrrolic derivative
Authors: Díaz E. , Galeazzi E. , Nava J. L. , Muchowski J. M. , Guzmán A. , van Calsteren M. R. , Jankowski K. 
Published: May 2005

AbstractThe conformation of 1‐phenyl‐1‐(1,2‐dimethyl‐5‐pyrrolyl)‐2‐(2‐methyl‐5‐benzoyl‐1‐pyrroly)ethanol, with characteristics of a molecular propeller, is stabilized by intramolecular hydrogen bonding as detected by 1H NMR, NOE difference experiments, 2D NMR, COSY, 13C NMR, HETCOR, HMBC and 1H NMR variable‐temperature experiments.
Magnetization transfer NMR study of nitrogen inversion in 2,2‐dimethylaziridine
Authors: Johnston Eric R. 
Published: May 2005

AbstractThe slow inversion at pyramidal nitrogen in 2,2‐dimethylaziridine was investigated by NMR spectroscopy at 304 K using one‐dimensional spin locking methods and two‐dimensional exchange spectroscopy. The activation free energy was found to be 17.5 kcal mol−1 (73.2 kJ mol−1) at this temperature. This value represents a lower limit for the unimolecular inversion barrier height as autocatalytic and water‐catalyzed inversion pathways can in principle also contribute to the observed rate. The spin locking experiments described employ non‐selective pulses and are particularly useful for the quantitative study of slow chemical exchange between nuclei of similar resonance frequency where selective magnetization transfer experiments are difficult or impossible.
Distinguishing two‐bond and three‐bond 13C1H connectivities by 2D BIRD‐decoupled difference spectra: The DODO pulse
Authors: Reynolds William F. , Yang Ji‐Ping , Enriquez Raul G. 
Published: May 2005

AbstractA modified BIRD pulse, called the DODO pulse, was developed and incorporated into one version of the FLOCK sequence. Addition of the two‐dimensional spectra obtained with this modified sequence and with the unmodified FLOCK sequence produces a normal indirectly bonded 13C1H shift correlation spectrum. Subtraction of one spectrum from the other generates a difference spectrum which allows a clear distinction between two‐bond and three‐bond 13C1H connectivities among protonated carbons.
Investigation of structural inhomogeneities in soft‐block modified methacrylate resins
Authors: Clayden Nigel J. , Smyth Gerard 
Published: May 2005

AbstractWideline 1H NMR and selective high‐resolution 13C cross‐polarization magic angle spinning (CP/MAS) NMR spectroscopy was used to investigate the polymer structure in methacrylate thermoset resins modified by the incorporation of a polyether soft‐block. Spin diffusion experiments indicate phase separation between a hard‐ and soft‐block phase. Similar soft‐block domain sizes were found regardless of the soft‐block content, reflecting the discriminatory nature of the delay used to create the magnetisation gradient. The main effect of increasing the polyether content is to ensure that more of the sample adopts a two‐phase hard/soft morphology. The selective 13C CP/MAS NMR spectra show that partial mixing of the methacrylate resin and polyether must occur and adding a Goldman‐Shen preparation period establishes that the mixing occurs through the bulk and is not simply interfacial.
2,5‐dihydro‐1,2,5‐azasilaborole derivatives studied by 15N and 29Si NMR using Hahn‐echo and pseudo‐BIRD experiments
Authors: Wrackmeyer Bernd , Kupče ĒRiks , Köster Roland , Seidel Günter 
Published: May 2005

Abstract15N and 29Si NMR data of 2,5‐hydro‐1,2,5‐azasilaborole derivatives and related compounds were determined with emphasis on coupling constants 1J(29Si 15N) which cannot be measured from 15N NMR spectra of most boron‐nitrogen compounds. In the case of compounds with an SiNH fragment ψ‐Bird pulse sequences, combined with HMQC or HSQC, served for 1H detection of the 29Si resonance with preselection of the 15N‐1H spin pair. This permitted the measurement of 1J(29Si 15N) and the determination of its absolute sign (>0). In the absence of an NH group, the coupling constants 1J(29Si 15N) were measured from the 15N satellites in 29Si NMR spectra recorded by using the Hahn‐echo extended (HEED) refocused INEPT pulse sequence. Isotope induced chemical shifts 1Δ 15/14N(29Si) were also measured by this technique for all the compounds. The 1J(29Si 15N) values cover the range 8.4–17.0 Hz, depending on the substituents at boron, silicon and nitrogen and on the complexation of the heterocycle.
The 15N‐isotopomers of cis‐ and trans‐difluorodiazine; A 19F NMR investigation of the two [AX]2 spin systems of 15N2F2
Authors: Aubke F. , Hägele G. , Willner H. 
Published: May 2005

AbstractThe decomposition of 15N3F at −20°C leads to cis‐ and trans‐15N2F2. The corresponding 19F NMR spectra were analysed as [AX]2 systems. 19F, 15N and 14N NMR spectra were simulated using the novel PC program systems DSYMPCD, DCYMPCD and WIN‐DAISY running under WIN‐NMR. Stereospecific coupling constants were obtained for both isomers. Comparison of the 19F NMR spectra from both the [1/2A1/2X]2 and the [1A1/2X]2 systems in 15N2F2 and 14N2F2 overcomes the inherent ambiguities of the [AX]2 analysis.
Highly selective 1D CH correlations
Authors: Stelten Johannes , Leibfritz Dieter 
Published: May 2005

AbstractSemi‐selective 1D one‐bond 1JCH correlations with 13C or 1H detection and multiple‐bond nJCH correlations with 1H detection are described. In these methods INEPT is used for the polarization transfer and pulsed field gradient coherence transfer pathway selection. The pulse sequences are designed particularly with regard to solving efficiently sterochemical problems in organic molecules with minimum acquisition time. The methods also allow easy quantification of heteronuclear nJCH coupling constants.