bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemically Activated Glassy Carbons as potential Supercapacitors and substrates for fixed mediators
Authors: El‐Rahman H. A. Abd 
Published: May 2005

AbstractGlassy carbon electrodes were prepared in various electrolytes by cyclic voltammetry and constant potential methods under various conditions to explore the factors affecting the response of GC after the electrochemical pretreatment (ECP), including the high pseudo‐capacitance, the great ability to absorb and strongly hold redox species and the facilitation of kinetics of electron transfer. Deepening the oxidation via increasing the oxidation potential and the oxidation time or the number of cycles and the final potential in cyclic voltammetry were found to increase the amount of redox species loaded onto GC and the pseudocapacitance due to formation of thicker carbon oxide layer. The increase in the rate of electron transfer reactions on deepening the oxidation is, however, attributed to the generation of more cleaner surface and more reactive sites. The order of increasing the efficiency of ECP; NaOH>KCl>HCl>NaClO4(MeCN), signifies the role of water and pH on the formation and thickness of the oxide layer formed after ECP. The results support the predominance of the faradaic origin of the pseudo‐capacitance of GC after ECP.
Determination of single PCB congeners in fish by on‐line LC‐GC
Authors: Hyvönen Helena , Auvinen Tuula , Riekkola Marja‐Liisa , Himberg Kimmo 
Published: May 2005

AbstractAn on‐line coupled LC‐GC technique was applied to the analysis of polychlorobiphenyls (PCBs) in Baltic herring. The liquid chromatographic (LC) and gas chromatographic (GC) instruments were coupled with a loop‐type interface and concurrent solvent evaporation was used in transferring the sample to the GC. A cyano phase with hexane as eluent was used for the LC separation and an NB‐54 column was used for the GC separation. On‐line LC‐GC is a good alternative to GC for the analysis of PCB compounds in biological material. The number of sample propurification steps is fewer and, the risks of sample contamination and loss are reduced.
Conformation and intermolecular interation of the antidepressant drugs nitroxazepine and imipramine in aqueous solutions and model membranes
Authors: Srivastava Sudha , Phadke Ratna S. , Govil Girjesh , Nagarajan K. 
Published: May 2005

AbstractComplete assignments of the proton magnetic resonance spectra of nitroxazepine and imipramine have been made using 1D and 2D techniques. The drugs are found to aggregate through stacking intereactions between the tricyclic moieties at higher concentrations in aqueous solutions. The changes in the chemical shifts with increasing concentration of the two antidepressant drugs show qualitative agreement with the stacking patterns and conformations observed in crystal structures. The conformations of the propyl moiety of the two drugs in aqueous solution and in lipid bilayers are very different. In D2O, the drugs exist in an extended chain conformation which is similar to the crystal structure. In lipid bilayers they acquire a folded structure. The folded structures probably facilitate the binding of the hydrophobic regions of the drugs to the interior of lipid bilayers.
A substituent chemical shift (SCS) effect study by 13C and 19F NMR of para‐substituted phenylhalodiazirines
Authors: Terpinski Jacek , Denney Dorothy Z. , Beveridge Richard , Cox D. Phillip , Moss Robert A. 
Published: May 2005

AbstractA range of 3‐(para‐substituted‐phenyl)‐3‐halodiazirines have been prepared and their 13C and 19F NMR spectra measured. Calculated with these data were the susceptibility coefficients ρI and ρR of the inductive (σI) and resonance (σR0) effects, respectively, to substituent‐induced chemical shift differences at the diazirine carbon (13C NMR) and the 3‐fluorine (19F NMR of the 3‐fluorodiazirine series). An inverse relationship was found between the susceptibility parameters and the electronegativity of the halo substituent at the diazirine carbon.
Long‐range two‐dimensional heteronuclear chemical shift correlation
Authors: Martin Gary E. , Zektzer Andrew S. 
Published: May 2005

AbstractLong‐range heteronuclear chemical shift correlation has undergone a period of burgeoning growth during the past 4 years. Initially, such correlations were made by simply reoptimizing the conventional heteronuclear chemical shift correlation sequence originally devised by Freeman and Morris. Problems inherent in the reoptimization of the Freeman–Morris sequence have led to the development of a number of other of experiments, most recently, including reverse (proton) detected heteronuclear multiple quantum techniques. The techniques now in use are compared and the inherent problems of each are identified and weighed against advantages. Applications of each technique are also presented.
Comparative study of the 13C nuclear magnetic resonance shifts of carbonyl and thiocarbonyl compounds
Authors: Katritzky Alan R. , Sobiak Stanislaw , Marson Charles M. 
Published: May 2005

AbstractThe 13C spectra of nine novel and fifteen known derivatives YC(:X)Z with X = O or S are reported and compared with literature data. Two linear relationships between 13CO and 13CS are established depending on whether or not Y or Z is linked through an O atom to the CX group. General equations for 13CO and 13CS in terms of the attached groups are also deduced. The 13C chemical shifts of n‐butyl and n‐octyl groups attached to the heteroatoms in this series of compounds are recorded and discussed.
Chemistry of the SO bond. 10—Conformational analysis of cyclic sulphates via 13C and 17O NMR spectroscopy
Authors: Hellier Desmond G. , Liddy H. G. 
Published: May 2005

AbstractThe conformational analysis of cyclic sulphates with 5–7‐membered rings is discussed on the basis of 13C and 17O NMR spectroscopic studies.
1H and 13C NMR studies of third‐generation cephalosporin esters sulphoxides and sulphones
Authors: Lee Moses , Micetich Ronald G. , Singh Rajeshwar , Spevak Paul , Singh Maya Prakash , Maiti Samarendra N. 
Published: May 2005

AbstractThe 1H and 13C NMR signals of 13 third‐generation cephalosporin esters have been assigned, and the effects of the sulphoxide and sulphone groups on the chemical shifts are discussed.Cephalosporin ester sulphoxides and sulphones 13C NMR 1H NMR Stereochemistry.
Structural elucidation of germine esters isolated from Veratrum nigrum L. Total assignment of 1H and 13C nuclear magnetic resonances by two‐dimensional NMR techniques
Authors: Han Xiuwen , Grossmann Peter , Rüegger Heinz 
Published: May 2005

AbstractThe application of two‐dimensional phase‐sensitive COSY, ROESY and 13C–1H shift correlation spectroscopy in the structural elucidation and stereochemical assignment of the steroidal alkaloids 15‐(2‐methylbutyryl)germine, 3‐(2‐hydroxy‐2‐methylbutyryl)‐15‐(2‐methylbutyryl)germine and 16‐(2‐methylbutyryl)germine is reported. It is shown that two‐dimensional 13C–1H heteronuclear long‐range correlation spectroscopy is an invaluable method for the stereochemical assignment of proton resonances which overlap in 1H NMR and homonuclear correlation spectra.
1H NMR and molecular mechanics studies of epimeric ethyl esters of 20(R, S)‐hydroxy‐23‐norcholanoic acids
Authors: Maier M. S. , Seldes A. M. , Gros E. G. 
Published: May 2005

AbstractProton chemical shifts for the C‐18, C‐21, CO2CH2CH3 and CO2CH2CH3 protons of epimeric ethyl esters of 20(R,S)‐hydroxy‐23‐norcholanoic acids were measured in deuteriochloroform and pyridine‐d5. The observed solvent shifts due to specific OH—pyridine hydrogen‐bonded complexes allowed the quantification of the epimeric mixtures by analysis of the pyridine‐d5 1H NMR spectra. The main features of the pyridine‐induced shifts are rationalized in terms of the preferred conformations for the 20R‐ and 20S‐epimers, which are predicted by molecular mechanics calculations.
Paramagnetic resonance in bipyridyl adducts of copper(II) salicylhydroxamates
Authors: Khadikar Padmakar V. , Ghadrian Taghi 
Published: May 2005

AbstractESR spectra of bipyridyl(Bipy) adducts of copper(II) salicylhydroxamates were obtained at room and liquid nitrogen temperatures in polycrystalline samples. The bonding ability of Bipy is discussed on the basis of N‐superhyperfine coupling (N‐Shf) while the magnitude of CuL bonding is discussed on the basis of ESR parameters. The room temperature magnetic moment values indicated tetragonal distortion. The nature of distortion is also discussed on the basis of N‐Shf coupling.
Quadrupole effects in crown ether–salt complexes: A solid‐state NMR study
Authors: Pietrass T. , Burkert P. K. 
Published: May 2005

Abstract7Li, 23Na and 13C solid‐state NMR spectroscopy under static and magic angle spinning conditions was used to study the salt complexes of lithium chloride, lithium bromide, lithium perchlorate and lithium nitrate with 12‐crown‐4 and of sodium nitrate with 15‐crown‐5, Structural and dynamic features of the compounds are discussed, focusing on the quadrupolar interaction and temperature‐dependent phenomena.
Angular dependence of geminal spin–spin coupling constants in a prototype CH2 group. J(H,H) versus interbond angle in methane
Authors: Geertsen Jan , Oddershede Jens , Raynes William T. 
Published: May 2005

AbstractCorrelated ab initio calculations of the dependences of the proton–proton spin–spin coupling constant J(H1, H2) in methane with the variation of the H1CH2 interbond angle are reported. The other coupling constants, including J(C, H), were simultaneously calculated. The coupling constants J(H1, H2) and J(C, H1) increase nearly linearly with the opening of the interbond angle whereas J(H2, H3) and J(C, H3) decrease. J(H3, H4) is only very slightly affected. The changes are due almost solely to changes in the Fermi contact term. The angular dependence is slightly larger at the SCF level of calculation than at the correlated level. The change in the geminal coupling constant J(H1, H2) with respect to equilibrium geometry is given to within 0.025 Hz by ΔJ(H1, H2) (Hz) = 41.57 sin α12 − 8.90 sin2 α12, where α12 is the increase in the interbond angle with respect to equilibrium ( − 10° ⩽ α12 ⩽ 10°).
77Se, 13C and 1H NMR spectra of acyclic phenylselenenylalkanes and ‐alkenes and some of their selenoxides
Authors: Duddeck Helmut , Wagner Petra , Rys Barbara 
Published: May 2005

AbstractThe 77Se, 13C and 1H NMR spectra of 57 mostly new compounds with phenylselenenyl groups attached to acyclic alkanes, alkenes and phenylalkanes and of 10 corresponding selenoxides are reported. Substituent effects on the chemical shifts of these nuclei were determined and are discussed in terms of the conformation and configuration. The results suggest that, in contrast to PhSeCCSePh fragments, CCCSe chains prefer a gauche conformation.
19F NMR properties of some trifluorovinyl‐ and pentafluoropropenyl‐substituted aromatics
Authors: Koroniak Henryk , Palmer Keith W. , Dolbier William R. , Zhang Hua‐Qi 
Published: May 2005

Abstract19F NMR chemical shifts and coupling constants are given for a series of aryl (phenyl, naphthyl and phenanthryl) substituted trifluorovinyls and (E)‐ and (Z)‐perfluoropropenyls. The relationship between the 19F NMR chemical shifts and the configurational orientation of the perfluoroalkenyl substituents is discussed.
Nitroxide radical as a probe for molecular conformation. Part I. 13C NMR study of the interaction of N,N‐dimethylamides with nitroxide radical
Authors: Wawer Iwona , Ströhl Dieter , Kleinpeter Erich 
Published: May 2005

Abstract13C NMR contact shifts induced by the 2,2,6,6,‐tetramethylpiperidine nitroxide radical (TMPN) were measured for N,N‐dimethyl‐para‐substituted benzamides and N,N‐dimethyl‐β‐bromo‐ and ‐α,β‐methylacrylamides. The shifts were linear functions of radical concentration, cr. It was found that N‐methyl group anti to the carbonyl group is a better acceptor site than the syn‐N‐methyl group and that there is a relationship between Δδ/dcr and the non‐planarity of molecules of amides with an s‐skew conformation. The electrostatic potential of amide molecules obtained from MNDO calculations was used to predict the stereospecific interaction with radicals.
Configurational effects in 17O NMR chemical shifts of hydroxyl‐substituted, bicyclo [2.2.1]heptenes and ‐heptanes, their methylated derivatives and some related compounds
Authors: Kolehmainen Erkki , Laihia Katri 
Published: May 2005

AbstractWell resolved natural abundance 17O NMR spectra of 27 mono‐, di‐, tri‐ and tetrahydroxybicyclo[2.2.1]heptenes and ‐heptanes (norbornenes or norbornanes), their methylated derivatives and some related compounds were measured for 0.5 M or saturated solutions in acetonitrile at 65°C. In addition, the 17O NMR chemical shifts of 14 aliphatic and alicyclic alcohols were also determined for reference purposes. The 17O NMR chemical shifts of all compounds were assigned. Both methyl‐ and hydroxyl‐induced deshielding β‐effects were consistent with those reported in the literature. Similarly, observed shielding γ‐effects were in agreement with the earlier observations and characteristic especially for mutual γ‐gauche and ‐eclipsed orientations of substituents. In addition, clear shielding δ‐effects (up to 10 ppm) were observed in tri‐ or tetrahydroxynorbornanes. These δ‐effects can be related to the attractive van der Waals interactions observed earlier in 13C NMR chemical shifts.
Non‐equivalence Magnetique en Resonance Nucleaire—IV. Influence de Plusieurs Types de Dissymetries sur les Deplacements Chimiques et les Couplages Relatifs a des Systemes OCH2CH3 et SCH2CH3
Authors: Martin Mme Maryvonne L. , Lefevre M. François , Lapeyre Mme Denise , Martin M. Gérard J. , Mantione M. Richard 
Published: May 2005

AbstractLa non‐équivalence magnétique des protons méthyléniques de groupements ACH2CH3 est étudiée dans plusieurs séries de composés. Les effets sont comparés d'une part dans les séries A = O et A = S, d'autre part dans les composés présentant un carbone asymétrique, un carbone de type cétal ou une dissymétrie allénique. L'influence de la substitution sur le carbone en α de AEt est discutée en relation avec les conformations. Une variation de la constante de couplage entre les protons méthyléniques géminés en function de la nature des substituants lointains est mise en évidence.
Studies in nuclear magnetic resonance—IX. Rotational barriers in substituted N,N‐dimethylbenzamides
Authors: Jackman L. M. , Kavanagh T. E. , Haddon R. C. 
Published: May 2005

AbstractThe barriers to rotation about the CN bond in eighteen substituted N,N‐dimethylbenzamides have been determined by complete line shape analysis of the NMR spectra of the N,N‐dimethyl protons. The barriers have been correlated with the substituent constants σ and σ+. It has been shown that polar solvents increase the barrier in N,N‐dimethylbenzamide.Acid catalysis of rotation about the amide CN bond in N‐(p‐N,N‐dimethylcarboxamidobenzyl)‐pyridinium bromide has been investigated. 18O exchange studies show that catalysis is due to N‐protonation rather than the formation of a tetrahedral intermediate. The rate of rotation is a function of the Hammett acidity function, H0, and the water activity, and it is shown that proton exchange between the N‐ and O‐protonated species involves the intermediacy of a water molecule.The differences in chemical shifts for the non‐equivalent N, N‐dimethyl groups of the benzamides are also a function of the substituents. Possible explanations of this phenomenon are discussed.
Electron transfer processes—X: Radical ions with hydrogen bridges derived from 1,1′,3,3′‐tetraketo‐Δ2,2′‐biindan, 5,6,11,12‐naphthacenetetrone, 1,4,9,10‐anthracenetetrone, and 1,4,5,8‐naphthalenetetrone
Authors: Russell Glen A. , Neugebauer Franz A. 
Published: May 2005

AbstractRadical anions and cations have been prepared by the reduction of the title compounds or their diprotonated derivatives. The same radical ions have been observed by oxidation of the dihydro derivatives. Electron spin resonance hyperfine splitting constants have been assigned on the basis of Hückel and McLachlan calculations and selective substitutions. The hyperfine splitting by the bridging hydrogen atoms in the radical anions was much weaker (0·5 to 0·7 gauss) than for the corresponding radical cations (2 to 3 gauss) for the naphthacene, anthracene, and naphthalene dihydrotetrones. This is interpreted to be a result of orbital symmetry since, in the highest occupied MO for the anion but not for the cation, a nodal plane passes through the bridging hydrogen atom.
Substituent effects on magnetic non‐ equivalence in acetals
Authors: Rattet Lana S. , Goldstein J. H. 
Published: May 2005

AbstractThe proton and 13CH satellite spectra of five diethyl haloacetals have been analyzed and their spectral parameters obtained. The parameters for the ethoxy methylene protons indicate the extent of their magnetic nonequivalence. It has been found that these parameters are dependent on the degree of halogen substitution in the group Z, which is bonded to the central carbon atom, and correlate well with the corresponding group electronegativity values, a′ z, proposed by Huheey. The parallel behavior of the methylenic J(CH) and chemical shifts indicates that a primarily through‐bond mechanism is responsible for propagation of both the electronic and symmetry effects observed. Transmission factors calculated from the spectral data agree with independent estimates reasonably well, thus supporting the conclusions reached here.
Applications of proton magnetic resonance spectroscopy to structural problems—XXXIV: Partial bond fixation in bicyclic heteroaromatic compounds
Authors: Boulton A. J. , Halls P. J. , Katritzky A. R. 
Published: May 2005

AbstractNMR spectral parameters are reported for benzofurazan, 1,2,3‐ and 2,1,3‐benzothiadiazole, and 1‐methyl‐ and 2‐methyl‐benzotriazole. The coupling constants are discussed in connection with the aromaticity of these compounds and the occurrence of partial bond fixation.
Etude par resonance magnetique nucleaire des interactions noyau‐substituant dans les acetanilides para‐substitues
Authors: Bennett J. , Delmas M. , Maire J. C. 
Published: May 2005

AbstractLes spectres de RMN de quinze acétanilides para‐substitués XC6H4·NH·CO·CH3 (X = NH·CO·ME; NH2; CO·OEt; COOH; Cl; OEt; F; H; OMe; CH3; NO2; C6H5;NNC6H5; Me3Si) ont été étudiés. Il y a une relation linéaire entre δ et δNH et les constantes σP de Hammett. Le couplage J(o‐HH) entre les protons aromatiques est relié plutôt à σR0. La constante J (13CH) dans le groupe CH3, est indépendante de X.
The NMR spectra of some iodo‐ and bromo‐fluorobenzenes. A novel solvent effect on ortho fluorine‐fluorine couplings
Authors: Cooper M. Ashley 
Published: May 2005

AbstractThe NMR spectral parameters for some bromo‐ and iodo‐substituted fluorobenzenes are presented, and the derived meta‐ and para‐ fluorine‐fluorine couplings are shown to be in accord with the predictions made by Abraham et al., using an additive substituent constant scheme. While the approximation of additive substituent effects is quite good, it is shown, however, that with highly accurate experimental values there are small deviations from perfect additivity. The existence of a large solvent effect on 3JFF is demonstrated and the mechanism of this effect is discussed. It is emphasized that certain discrepancies in the literature between various values of the same 3JFF may be due to this large, hitherto unrecognized solvent dependence.
Etude de la Basicite de Composes Organophosphores Typiques dans Leurs Complexes de Lewis Avec le Trifluorure de Bore
Authors: Elegant Lucien , Azzaro Marcel , Mańkowski‐Favelier Raymonde , Mavel Gérard , Morize Nicole 
Published: May 2005

AbstractOn a étudié, en résonance du proton et du fluor (à température variable) ainsi qu'en résonance du bore et du phosphore, un certain nombre de complexes entre BF3 et des composés organo‐phosphorés typiques. En ce qui concerne BF3, la résonance de bore reste insensible à la force du complexe; par contre, la résonance du fluor suggéère l'existence de plusieurs types de complexes, soit sur le groupe phosphoré, soit sur les hétéroatomes (par example N, O) de la molécule. Ces complexes sont vraisemblablement de type σ pur. Le déplacement chimique des protons dans la molécule organo‐phosphorée subit sensiblement les mêmes perturbations que dans les autres molécules complexables (amines, esters, etc.); ces perturbations peuvent provenir avant tout d'effets d'anisotropie magnétiques; par contre, les couplages proton‐phophore suivent la modification de l'électronégativité de ce dernier.
Interactions Intramoleculaires—X: Etude par RMN des Équilibres Conformationnels de Cyclohexènes Monosubstitutés en 4 et du Dicyano‐1,2 Cyclohexane trans
Authors: Aycard Jean‐Pierre , Bodot Hubert , Garnier Roger , Lauricella Robert , Pouzard Guy 
Published: May 2005

AbstractLes enthalpies libres conformationnelles des substituants CN, Cl et COOC2H5 ont été évaluées à partir de l'étude des spectres RMN des cyclohexènes (D4‐3,3,6,6) monosubstitués en 4.Les spectres RMN du dicyano‐1,2cyclohexane (D4‐3,3,6,6)trans ont permis une estimation de l'équilibre conformationnel (dans différents solvants) ainsi que de l'énergie d'interaction gauche diéquatoriale entre les deux groupements CN.
Substituentenabhängigkeit der Ringinversion des Ungesättigten Siebenringes bei Benzocycloheptenderivaten. Konformative Beweglichkeit flexibler Ringsysteme—XIV: Untersuchungen mit Hilfe der Protonenresonanzspektroskopie
Authors: Kabuß S. , Schmid H. G. , Friebolin H. , Faißt W. 
Published: May 2005

AbstractBei insgesamt 20 Benzocycloheptenderivaten mit 1, 2 und 3 Paaren geminaler Substituenten wurden die konformativen Umwandlungen des ungesättigten Siebenringes PR‐spektroskopisch untersucht.Bei allen Verbindungen ist das Umklappen des Ringes bei − 80°C ‘eingefroren.’ In nachweisbarer Menge liegt bei dieser Temperatur in allen Fällen nur ein Konformeres vor, vermutlich dasjenige mit der Sesselform des Siebenringes.Die Werte der freien Aktivierungsenthalpie ΔG≠ der Sesselinversion liegen zwischen 9,9 und 13,7 kcal/Mol. Bei di‐ und tetrasubstituierten Benzocycloheptenen hängt der ΔG≠‐Wert von der Stellung der Liganden ab: Bei den disubstituierten Derivaten ist ΔG≠ am größten bei 5‐ Stellung und am kleinsten bei 3‐ Stellung der Substituenten. Bei den tetrasubstituierten Derivaten ist das Umklappen des Ringes im Verhältnis zu den vergleichbaren Dimethylverbindungen erschwert, wenn die Ligandenpaare in 3,6‐ oder 3,7‐ Stellung stehen, jedoch erleichtert, wenn sie in 3,5‐ oder 4,6‐ Stellung angeordnet sind. Der bei 3,5‐ bzw. 4,6‐ Stellung der Ligandenpaare beobachtete Effekt wird auf die transanulare Abstoßung synaxialer Substituenten zurückgeführt, durch die der Cycloheptensessel abgeflacht wird. Eine solche Abstoßung fehlt bei 3,6‐Stellung der Liganden. Bei den Verbindungen mit 3,7‐ständigen Liganden führt die trans‐anulare Abstoßung hingegen zu stärkerer Wellung (puckering) des Sessels; das Umklappen könnte dadurch erschwert sein.Für Benzocyclohepten wurden die für die gegenseitige Umwandlung von Sessel‐, Wannen‐ und Twist‐Konformeren (S, W und T) erforderlichen Werte der Aktivierungsenergie durch Modellrechnungen ermittelt. Günstigster Weg für das Umklappen des Sessels ist der Versionsweg S→W über die Übeergangskonformationen V56. Die hierfür berechnete Aktivierungsenergie (14,6 kcal/Mol) stimmt mit der experimentell ermittelten (13 ± 1,5 kcal/Mol) gut überein. Für die Aktivierungsenergie der Pseudorotation W → T wurde mit 11,1 kcal/Mol ein nur wenig neidrigerer Wert berechnet.