bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical IPPP analysis of 13C‐31 P through‐space indirect couplings in phosphorus‐substituted alkenes
Authors: Diz A. C. , Giribet C. G. , de Azúa M. C. Ruiz , Contreras R. H. , Aucar G. A. 
Published: May 2005

AbstractA refined version of the IPPP‐INDO method was used to analyse the difference between cis and trans 13C‐31P couplings in phosphorus‐substituted alkenes. A large through‐space transmission of the Fermi contact term is predicted for the cis 13C‐31P coupling. With the new version of the IPPP method it was assessed how different orbitals, describing chemically intuitive bonds, lone pairs and antibonding orbitals, contribute to the Fermi contact term. The importance of the P lone pair and C‐H bonds was clearly determined. The antibonding orbitals, which are very important but rarely mentioned, are also discussed.
Two‐dimensional NMR spectra of sesquiterpenes. I—NOESY study of caryophyllenes from Inula spiraeifolia
Authors: Vajs Vlatka , Jeremić Dragoslav , Milosavljević Slobodan , Macura Slobodan 
Published: May 2005

AbstractThe application of two‐dimensional NOE NMR spectroscopy (NOESY) for the stereochemical assignment of isomeric 14‐acetoxy‐13‐hydroxy‐ and 13‐acetoxy‐14‐hydroxy‐5,6‐caryophyllen‐7‐ones, and their acetylation products, is reported.
Investigation of association in purine—pyrimidine aqueous systems by 1H NMR chemical shift
Authors: Aradi Ferenc , Földesi Andras 
Published: May 2005

AbstractThe association behaviour of purine and pyrimidine has been studied in deuterium oxide at 35°C by measuring the concentration‐dependent selective changes in the chemical shifts of the CH protons. A satisfactory interpretation of the cross‐interaction, i.e. the mutually induced upfield shifts in mixed solution, required the extension of the 1:1 hetero‐association model by taking into account the self‐association of both compounds. The self‐association and the hetero‐association parameters have been determined on the basis of two‐state and three‐state models. The equilibrium constants give a decreasing tendency for association within the series purine‐purine (0.82 ± 0.08 1 mol−1) > purine‐pyrimidine (0.54 ± 0.06 1 mol−1) > pyrimidine‐pyrimidine (0.050 ± 0.002 1 mol−1), and the values of the dimer upfield shifts suggest that the association processes are dominated by the interaction of the six‐membered rings.
Nitrogen hyperfine splitting of nitroxide solutions: Differently structured and charged nitroxides as probes of environmental properties
Authors: Ottaviani M. Francesca , Martini Giacomo , Nuti Laura 
Published: May 2005

AbstractThe dependence of the nitrogen isotropic coupling constants, aN, on the structure and charge of the radicals, temperature and solvent polarity was analysed for solutions containing the following nitroxides: 4‐hydroxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (Tempol); 4‐trimethylammonium‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, iodide salt (TempTMA+); 2,2,5,5‐tetramethylpyrrolin‐1‐oxyl‐3‐carboxamide (Tempyo); and 2,2,5,5‐tetramethylpyrrolin‐1‐oxyl‐3‐carboxylate, sodium salt (Tempyca−). Polar hydrogen bond acceptor solvents and hydroxylic solvents were used. In each solvent used, Tempol and Tempyca− showed aN values which were higher, respectively, than those of TempTMA+ and Tempyo due to inductive, structural and charge effects. Such effects were analysed on the basis of the proton and 13C coupling constants. Non‐hydroxylic solvents gave temperature coefficients for aN that were almost independent of solvent polarity. Lower daN/dT values were found for charged radicals. A gradual decrease of temperature coefficients with decreasing hydrogen bond donor (HBD) properties were related to free volume changes of radical molecules. The analysis of the aN dependence on polarity parameters gave the best fitting using a simplified form of the Wertheim reaction field. Tempyca− was greatly affected by changes in polarity. A parameter to account for HBD abilities was also analysed.
Selenium‐77 NMR of coordination compounds with unsaturated selenium ligands and/or selenium (II) central ions
Authors: Dietzsch Wolfgang , Olk Ruth‐Maria , Hoyer Eberhard , Meiler Wolfgang , Robien Wolfgang 
Published: May 2005

Abstract77Se NMR spectra of coordination compounds containing unsaturated dithio, thioseleno or diseleno ligands are reported. NiII, ZnII, SeII and TeII were used as central ions. The shielding of the Se donor atoms of the same ligands depends on the central ion, following the series SeII < ZnII < TeII < NiII. The greater is the concentration of selenium atoms in the coordination sphere of identical central ions, the more their signals are shifted to lower field. Comparisons are made between mixed ligand complexes and the corresponding selenium containing parent compounds.The chemical shifts found for the selenium donor atoms in the planar NiII complex {Ni[Se2 CC(CN)2]2}2‐ and the octahedral NiIV complex {Ni[Se2CC(CN)2]3}2‐ differ by 265 ppm. The most downfield shifts of all the investigated compounds were found for donor atoms in 1,2‐diselenolene compounds.
Solvent dependence of 13C relaxation times and reorientational dynamics in tribromobenzene
Authors: Chen A. F. T. , Wang S. P. , Schwartz M. 
Published: May 2005

AbstractThe 13C spin–lattice relaxation times and nuclear Overhauser enhancements of protonated carbons in 1, 3, 5‐tribromobenzene were measured in a number of solvents of widely varying viscosity, Derived reorientational correlation times were found to increase approximately linearly with solution viscosity, as predicted by hydrodynamic theories of rotational diffusion.Rotational correlation times calculated from the perrin stick model were two to three times longer than the measured τc values. Similarly, correlation times predicted by the Hu–Zwanzig slip model were too small by a factor of two. On the other hand, application of the newer Hynes–Kapral–Weinberg theory furnished reorientational correlation times that were in virtually quantitative agreement with the experimental results.
Comparison of substituent‐induced proton NMR shift in steroids and decalins
Authors: Schneider Hans‐Jörg , Jung Marion 
Published: May 2005

AbstractThe proton shifts of trans‐decalin and of its 9‐hydroxy derivative were determined by 2D NMR methods, supported in the latter case by lanthanide‐induced shifts. Based on these shifts and on literature data, substituent (X)‐induced chemical shifts (SCS) were obtained for the 9‐X‐trans‐decalins for X = OH, Cl, Br, I and Ch3. Comparisons with corresponding secondary cyclohexyl derivatives, derived from androstane measurements, usually showed good correlations; 38 SCS values out of 40 (for X = Hal, OH) deviate by < ±0.08 ppm and are in line with earlier linear electric field effect calculations. Only two literature values for Br and I on the antiperiplanar tertiary H‐10 exhibit unusual upfield shifts which, however, cannot be related to dihedral angle changes.
Configurational assignment of β‐phenylaspartic acids in solution by 1H and 13C nuclear magnetic resonance
Authors: Barrelle M. , Gey C. , Béguin C. G. 
Published: May 2005

AbstractVicinal 3J(HH) and 3J(13CH) coupling constants are reported for the two diastereoisomers of β‐phenylaspartic acid at various pH values. A comparison between these coupling constants and those expected from the possible conformations of these molecules allows configurational assignments to be made. In strong acidic medium we observed intermediate values for 3J(HH) for both isomers, for one isomer two intermediate values for 3J(Co‐α, H‐β) and 3J(Co‐β, H‐α), and for the other isomer a very small value for 3J(CO‐α, H‐β) and an intermediate value for 3J(Co‐β, H‐α). The discussion shows that the former has the RR/SS configuration and the latter the RS/SR configuration.
Configurational assignment of 2‐alkylsulphinyl‐1‐arylethanol diastereomers by 13C NMR
Authors: Alcudia F. , Fernández I. , Llera J. M. , Trujillo M. , Zorrilla F. 
Published: May 2005

AbstractThe relative configurations of erythro‐ and threo‐2‐alkylsulphinyl‐1‐phenyl(or 2‐thiophen or 2‐furyl)ethanol have been correlated with 13C NMR data. A general rule for determining the configuration of this type of compound is presented.
EPR and ENDOR investigation of daunomycin and adriamycin semiquinones
Authors: Jülich Thomas , Scheffler Klaus , Schuler Paul , Stegmann Hartmut B. 
Published: May 2005

AbstractElectron spin resonance and ENDOR spectra of semiquinones from daunomycin, adriamycin, their derviatives and model compounds are reported. Hyperfine coupling constants were assigned with the help of TRIPLE resonance and partial deuteration. In contrast to published results, the data obtained were interpreted on the basis of a rapid conformational interconversion of ring A with participation of half chair and boat conformers.
13C NMR chemical shift assignments for some 1‐aminopyrrole derivatives
Authors: Attanasi Orazio A. , Grossi Mario , Perrulli Francesca R. , Santeusanio Stefania , Serra‐Zanetti Franco , Bongini Alessandro , Tugnoli Vitaliano 
Published: May 2005

AbstractThe 13C NMR spectra of various 1‐aminopyrrole derivatives are reported and the chemical shift assignments are discussed. The NMR assignments were confirmed by MNDO calculations.13C NMR chemical shifts 1‐Aminopyrrole derivatives.
Structure of two stereoisomers of Pt(trans‐MeO2CCHCHCO2Me)2[P(cyclohexyl)3]: Complete assignment of the 11 non‐equivalent tricyclohexylphosphine protons using DQF‐COSY and 13C, 1H two‐dimensional methods
Authors: Rüegger Heinz 
Published: May 2005

AbstractThe 1H NMR spectrum of the Pt(0) complex Pt(trans‐MeO2CCHCHCO2Me)2[P(cyclohexyl)3] was measured and the structures of the two isomeric forms, which differ with respect to olefin coordination, were assigned. The structural study made use of a complete analysis of the 11 non‐equivalent protons of the P(cyclohexyl)3 in one isomer, and this was accomplished via DQF‐COSY and 13C,1H inverse heteronuclear correlation methods.
17O NMR spectroscopic study of substituted 9‐fluorenones
Authors: Boykin D. W. , Nowak‐Wydra Barbara 
Published: May 2005

AbstractThe 17O NMR chemical shift data for 23 9‐fluorenones in acetonitrile at 75°C are reported. 17O NMR data for the 3‐substituted 9‐fluorenones are correlated with 17O NMR data for 4‐substituted acetophenones. Chemical shift data for 1‐halogeno‐9‐fluorenones are deshielded relative to the 3‐isomers, suggesting important repulsive van der Waals interactions. The keto carbonyl signal for 9‐fluorenone‐1‐carboxylic acid is substantially shielded, as expected, from intramolecular hydrogen bonding. The data for several multi‐substituted 9‐fluorenones demonstrate that substituent effects are additive for the 9‐fluorenones.
Determination of dynamic parameters in amino acids from 17O NMR line width measurements
Authors: Tritt‐Goc J. , Fiat D. 
Published: May 2005

AbstractThe viscosity and temperature dependence of the 17O NMR line width of glycine, alanine, proline, leucine, histidine and phenylalanine were investigated at pH 2, 7 and 12.5. The observed viscosity/temperature (η/T) dependence of the reorientation correlation time, τc, is compared with that given by hydrodynamic models. It was found that for amino acids the Gierer–Wirtz model is superior to the Stokes–Einstein–Debye and Hu–Zwanzig models. The 17O quadrupole coupling constant for glycine, alanine and histidine was determined in water solution; the activation energies for molecular tumbling were evaluated, and the hydration of the amino acids in their cationic zwitterionic and anionic ionization states is discussed.
Analysis of low‐resolution, low‐field NMR relaxation data with the Padé‐Laplace method
Authors: Tellier Charles , Guillou‐Charpin Marion , Le Botlan Denis , Pelissolo François 
Published: May 2005

AbstractAn integral transform technique, the Padé‐Laplace method, was adopted to calculate the number of discrete exponential components and the corresponding parameters from NMR spin relaxation decay curves. The results thus obtained can be improved by injection into an iterative program. This ‘Padé‐Laplace plus iterative’ method was tested on simulated data of up to five relaxation times and then on experimental data obtained with a tube containing four manganese chloride‐doped water samples. The results extracted from the low‐resolution, low‐field NMR signals of complex chemical and biological products are discussed.
EPR and ENDOR investigations of chrysazin and aclacinomycin A semiquinones
Authors: Jülich Thomas , Stegmann Hartmut B. , Krohn Karsten , Eickhoff Astrid 
Published: May 2005

AbstractDifferent assignments of the coupling constants to distinct positions of chrysazin are given in the literature. Several methyl derivatives, particularly the hitherto unknown 1,8‐dihydroxy‐2,3‐dimethyl‐9,10‐anthraquinone, were prepared, and their radical anions were investigated by EPR and ENDOR spectroscopy to achieve a reliable attribution of these values. The data obtained show a remarkable solvent dependence of the spin density distribution. Thus, the discrepancy mentioned above can be explained in terms of intermolecular hydrogen bond formation. Therefore, the requirements for an investigation of the semiquinones of the antitumour drug aclacinomycin A and 7‐deoxyaklavinone are fulfilled. The splitting constants of the radical anions are assigned using model compounds, TRIPLE experiments and the solvent dependence. In contrast to the results obtained for daunomycin radicals, the data can be interpreted in terms of an almost rigid half‐chair conformation of the A ring.
Studies of the π‐electron distribution in push–pull alkenes by 1H and 13C NMR spectroscopy—II
Authors: Kleinpeter E. , Thomas St. , Uhlig G. , Rudorf W.‐D. 
Published: May 2005

AbstractA wide variety of push–pull alkenes were studied by means of variable‐temperature 1H and 13C NMR spectroscopy with respect to the configuration/conformation and the barriers to rotation about partial CC and CN double bonds. For the assignment of the 13C NMR spectra especially the semi‐selective INEPT pulse sequence and an incremental system for estimating the 13C chemical shift values of aromatic carbon atoms proved useful. The influence of thioether, sulphone and sulphoxide moieties in the acceptor part of the push–pull system on the π‐electron distribution is critically considered.
Reinvestigation of 1H and 13C NMR spectra of 1,8‐bis(dimethylamino)naphthalene complexes with mineral acids
Authors: Dega‐Szafran Zofia , Nowak‐Wydra Barbara , Szafran Miroslaw 
Published: May 2005

AbstractHydrogen and carbon‐13 NMR chemical shifts of five complexes of 1,8‐bis(dimethylamino)naphthalene with strong acids were measured in acetonitrile‐d3 and nitromethane‐d3 and identified by 2D, NOE difference and long‐range enhanced COSY spectra. The assignments of the resonances corresponding to H‐2,7, H‐4,5, C‐3,6 and C‐4,5 obtained in this study differ from those reported previously.
Quantitative silicon‐29 NMR investigations of highly concentrated high‐ratio sodium silicate solutions
Authors: Harris Robin K. , Bahlmann Elke K. F. , Metcalfe Kenneth , Smith Edward G. 
Published: May 2005

AbstractIn concentrated alkaline sodium silicate solutions a consistent decrease in the amount of silicate monomer Q0, end‐groups Q1, cyclic trimer Q groups and middle groups Q2, and also branching groups in ring formations Q, is observed with increasing molar ratio of SiO2 to Na2O (RM), whereas for branching groups Q3 and cross‐linking groups Q4 a consistent increase is found. The interest of this work is particularly focused on the Q4 region, which may indicate the formation of colloidal silicate particles. For this region the 29Si background signal from the NMR probe and the glass tube can cause problems, so the subtraction technique was used. Spin‐lattice relaxation times, not previously reported for silicate solutions of concentrations and molar ratios as high as those studied here, are given for all structural units, including Q4. It was found that sodium silicate solutions of RM = 2.0 do contain a Q4 region when they are extremely highly concentrated in SiO2 (38 wt% SiO2) or aged.
Structural reinvestigation of two diastereoisomeric aspidosperma–eburnea type bis‐indoles by NMR methods. Detection of a ‘hidden’ exchange partner and implications in noe analysis
Authors: Szántay Csaba , Demeter Ádám , Honty Katalin , Kolonits Pál , Szántay Csaba 
Published: May 2005

AbstractFull 1H and 13C assignments are reported for two aspidosperma—eburnea type diastereoisomers. Homonuclear NOE difference measurements revealed that the previously reported configurational assignment of these compounds is in error. More interestingly, rotation about the bond connecting the two indole units is hindered in both molecules and gives a strongly biased two‐site chemical exchange system. At room temperature the exchange rates are slow on the chemical shift time‐scale with regard to certain 1H signals. In addition, the exchange rates are such that the signals due to the minor component are broadened to the extent that they escape detection in a conventional 1H spectrum, whereas only a very small amount of broadening is observed on the main signals. The presence of this ‘hidden’ exchange partner can give rise to peculiar effects in the NOE difference spectra. Such spurious effects can be the source of misinterpretation if the existence of the ‘silent partner’ goes unnoticed. Thermodynamic parameters are evaluated based on earlier work addressing the problem of the ‘hidden’ exchange partner.
NMR data for sulphur and selenium analogues of furocoumarin (psoralen)
Authors: Jakobs Andreas , Llabres Gabriel , Baiwir Marcel 
Published: May 2005

Abstract1H, 13C and 77Se chemical shifts of sulphur and selenium analogues of furocoumarin are given. These data are very similar to the values obtained from benzofuran, coumarin and their sulphur and selenium analogues.
Multiple magnetic resonance studies of some para‐substituted derivatives of triphenyl phosphine
Authors: McFarlane W. 
Published: May 2005

Abstract19F and 31P decoupling experiments are used to simplify the proton spectra of para‐substituted derivatives of triphenyl phosphine, prior to 1H‐{1H} tickling experiments. 3J(31P…︁H) and 4J(31P…︁H) are positive, and 5J(31P…︁19F) is negative in the trivalent phosphorus derivatives, and all become more positive as the valency of the phosphorus atom is increased. A triple resonance experiment is used to show that 7J(31P…︁H) in [p‐CH3C6H4CH2P⊕(C6H5)3] is negative. The double resonance technique is used to relate the 31P chemical shifts to the tetramethylsilane resonant frequency.
NMR‐Untersuchungen an Dialkylsubstituierten Piperidinen–I. Konfigurationsbestimmung der 2,3‐, 2,4‐ und 3,4‐Dimethylpiperidine und die Analyse Ihrer NMR‐Spektren
Authors: Feltkamp Herbert , Naegele Walter , Wendisch Detlef 
Published: May 2005

AbstractDie Gemische der stereoisomeren 2,3‐, 2,4‐ und 3, 4‐Dimethylpiperidine warden durch katalytische Hydrierung der entsprechenden Lutidine dargestellt. Die einzelnen Isomeren warden durch fraktionierte Destillation getrennt. Die Konfigurationsaufklärung erfolgt kernresonanzspektroskopisch durch Analyse der 100 und 220 MHz NMR Spektren. Es gelingt eine weitgehende Zuordnung aller Protonen des Piperidinringes.
Konformative Beweglichkeit Flexibler Ringsysteme—X. Untersuchungen mit Hilfe der Protonenresonanz‐Spektroskopie. Substituentenabhängigkeit der Ringinversion bei 1.3‐Dioxanen, 1.3‐Dithianen und 1.3‐Oxathianen
Authors: Friebolin Horst , Schmid Helmut G. , Kabuß Siegfried , Faißt Wilhelm 
Published: May 2005

AbstractMittels der Temperaturabhängigkeit der Protonenresonanzsignale wurden für 1.3‐Dioxane, 1.3‐Oxathiane und 1.3‐Dithiane mit ein und zwei Paaren geminaler Methylsubstituenten Geschwindigkeitskonstante k, freie Aktivierungsenthalpie ΔG‡ und Aktivierungsenergie Eα der Sesselinversion bestimmt. Die Geschwindigkeit der Sesselinversion hängt bei den drei genannten Ringsystemen in unterschiedlicher Weise von der Zahl und der Stellung der Substituentenpaare ab:Beim Dioxanring wird k nur dann erniedrigt, wenn ein Paar Methylgruppen in 5‐Stellung eingeführt wird; k wird jedoch erhöht, wenn die Substituenten in 2‐ oder 4‐Stellung angegliedert werden. Dieser letztere Effekt ist bei Einführung von zwei Paar Methylgruppen in 4‐ und 6‐Stellung besonders stark.Eine ähnliche Substituentenabhängigkeit von k wird auch bei den Oxathianen beobachtet, während die Inversionsgeschwindigkeit des 1.3‐Dithianringes von Substituenten nur wenig beeinflußt wird.Die durch 2‐ und 4‐ständige Methylgruppen verursachte Erleichterung der Sesselinversion des 1.3‐Dioxanringes kann auf die Deformation (Abflachung) des Sessels zurückgeführt werden, die bei 1.3‐Abstoßung der synaxialen Liganden auftreten muß. Ein solcher Effekt ist beim 1.3‐Dithianring infolge der langen CS‐Abstände nicht möglich. Beim Oxathiansystem ist eine eindeutige Erklärung der beobachteten Substituenteneffekte durch die Unsymmetrie des Ringsystems erschwert.
Konformative Beweglichkeit Flexibler Ringsysteme–XI Untersuchungen mit Hilfe der Protonenresonanzspektroskopie Ringinversion bei Methyl‐ und Alkoxylcyclohexanen
Authors: Friebolin H. , Schmid H. G. , Kabuß S. , Faißt W. 
Published: May 2005

AbstractMittels der Temperaturabhängigkeit der Protonenresonanzsignale wurde die sesselinversion von Cyclohexanderivaten mit ein, zwei und drei Paaren geminaler Methyl‐ und Alkoxylgruppen untersucht.Die Geschwindigkeit der Sesselinversion hängt von der Zahl und der relativen Stellung der Ligandenpaare sowie von der Größe der Liganden ab.Ein Paar geminaler Liganden verändert die Inversionsgeschwindigkeit nur unwesentlich.Zwei Liganden‐Paare erschweren die Inversion, wenn sie in 1‐ und 4‐Position zueinander stehen, erleichtern sie jedoch, wenn die in 1‐ und 3‐Position zueinander angeordnet sind. Beide Effekte sind bei Methoxylgruppen kleiner als bei Methylgruppen.Drei Liganden‐Paare erhöhen die Umklapphäufigkeit besonders stark, wenn sie in 1‐, 3‐ und 5‐ Position zueinander stehen, vermindern sie hingegen, wenn sie in 1‐, 2‐ und 4‐Position angeordnet sind.Der Effekt 1,3‐ständiger Substituenten wird auf Erhöhung des Energieinhaltes des Grundzustandes der Molekeln, der Effekt 1,4‐ständiger Substituenten auf Erhöhung des Energieinhaltes des Übergangszustandes der Sesselinversion zuriückgeführt.