bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron paramagnetic resonance investigation of the complexes of grignard reagents with 9,10‐phenanthrenesemiquinonate
Authors: Pan Kai , Cheng Kung‐Lung , Ho Tong‐Ing 
Published: May 2005

AbstractThe substituent effect on the proton hyperfine splitting constants (hfsc) of the charge‐transfer complexes of Grignard reagents (RMgBr, R = CH3, C2H5, CH3CHCH) with seven 3‐substituted 9,10‐phenanthroquinones is reported. A back‐donation bonding interaction between phenanthrenesemiquinonate anion radical π* and the magnesium p orbital is revealed by the hfsc analysis.
Ring a conformation in steroids. 3—Cyclosteroids and cyclopropanosteroids
Authors: Marat Kirk , Templeton J. F. , Ling Yangzhi , Lin Weiyang , Gupta R. K. 
Published: May 2005

AbstractProton and carbon NMR data are provided for 21 ring A and ring B cyclosteroids and cyclopropano (or methylene) steroids. Shift assignments were made using standard 2D NMR techniques, while ring A proton subspectra were extracted with a 1D TOCSY experiment. Coupling constants were obtained from iterative spin system simulation of these sub‐spectra. Ring A conformations were determined from the two‐ and three‐bond proton‐proton couplings and NOE measurements. The utility and limitations of extended Karplus‐type equations, the effect of cyclopropyl groups on vicinal and geminal couplings and cyclopropane‐induced chemical shifts are discussed.
Conformational analysis of oligomeric flavanoids. 2—methyl ether acetate derivatives of profisetinidins
Authors: Steynberg Jan P. , Brandt E. Vincent , Ferreira Daneel , Helfer Carin A. , Mattice Wayne L. , Gornik Dominika , Hemingway Richard W. 
Published: May 2005

AbstractThe profisetinidins are the most important polyflavanoids of commerce, making up the major constituents of wattle and quebracho tannins. Even within the dimeric profisetinidins, substantial complexity exists because of stereo‐, regio‐, rotational and conformational isomers. Definition of the stereochemistry of the upper and lower flavan units, the location of the interflavanoid bond, the conformation of the heterocyclic rings in the upper and lower flavan units and the conformations of major and minor rotational isomers in a series of methyl ether acetate derivatives of dimeric profisetinidin diastereomers is possible by application of COSY and NOE experiments. All compounds studied were present in two rotameric forms with the more compact conformation favored. The heterocyclic ring in the upper chain extender unit was predominantly in an E‐conformation (i.e. half‐chair in 2R,3S isomers and a ‘reverse’ half‐chair in the 2S,3R isomers). The heterocyclic ring conformation of the terminal cate‐chin unit, although mostly in an E‐conformation, was often represented by significant proportions of A‐conformers.
1H and 13C NMR spectra of the methanolic allomerization products of 132(R)‐chlorophyll a
Authors: Hyvärinen Kristiina , Helaja Juho , Kuronen Pirjo , Kilpeläinen Ilkka , Hynninen Paavo H. 
Published: May 2005

AbstractThe spontaneous autoxidation (allomerization) of 132(R)‐chlorophyll a in methanol produces seven main products containing three epimer pairs. The 1H and 13C NMR spectra of these products in acetone‐d6 were recorded on a 500 MHz spectrometer and fully assigned using two‐dimensional HMQC and HMBC techniques. The absolute configurations of the oxidized carbons, originally C‐132, were determined using the ROESY technique. In comparison with 132(R)‐chlorophyll a, the steric repulsion between the C‐17 side‐chain and the bulky substituents of the oxidized C‐132 causes steric strain in the chiral part of an allomer, relieved by conformational changes in rings D and E and to a lesser extent also in the whole macrocycle. These changes were estimated for each allomer from the Δδ values of the carbon and proton resonances and from proton‐proton coupling constants. Information about the orientation of the front part of the phytyl chain in 132(R)‐chlorophyll a and its methanolic allomers was obtained by analysing the variation in the form of the P1‐CH2 signal.
Oxygen‐17 and carbon‐13 NMR studies of diarylketenes
Authors: Cerioni Giovanni , Plumitallo Antonio , Frey Joseph , Rappoport Zvi 
Published: May 2005

AbstractNatural abundance 17O and 13C NMR spectra for eleven diarylketenes are reported. 17O shifts show invariance with para substitution and a shielding due to ortho substitution. A buttressing effect is observed for bis(2,3,4,5,6‐pentamethylphenyl)ketene. A comparison between ketenes and isocyanates is made. The importance of cylindrical symmetry for half‐height linewidths is discussed.
Nitrogen NMR assessment of interactions between nitroso, cyano and acetyl groups across aliphatic systems
Authors: Witanowski Michal , Biedrzycka Zenobia , Konopski Leszek , Grela Karol 
Published: May 2005

AbstractThe nitrogen NMR shieldings (Δσ, equivalent to —Δδ on the frequency scale of chemical shifts) of the NO group in nitrosoalkanes are shown to be a sensitive probe to electron‐withdrawing effects of substituents and to steric strain effects. The former produce high‐field (low‐frequency) shifts, which can amount to about 90 ppm, while the latter result in considerable low‐field (high‐frequency) shifts of the NO nitrogen resonance. The CN nitrogen shieldings show less pronounced low‐field (high‐frequency) shifts under the influence of electron acceptors. The signs and magnitudes of the observed effects are explained in terms of semi‐empirical molecular orbital calculations of the shieldings and molecular mechanics evaluations of strain energies. The overall picture of relationships between the NO and CN nitrogen shieldings and electron charge migration within the molecules concerned is in accord with that obtained in earlier studies of solvent‐induced effects on the nitrogen shieldings in alkyl cyanides and nitro compounds.
13C and 15N NMR study of substituted 1,2,4‐triazines
Authors: Kolehmainen Erkki , Šaman David , Pískala Alois , Masojídková Milena 
Published: May 2005

Abstract13C and 15N NMR spectra of eight substituted 1,2,4‐triazines were measured and assigned. The assignments of the 13C NMR spectra were based on the substituent chemical shifts and nJ(C,H) coupling constants. 15N NMR chemical shifts generally showing well separated ranges were assigned by the proton coupled 15N NMR spectra. 15N NMR chemical shifts of N‐4 in 3‐ and 5‐methoxy or ‐thiomethyl‐substituted 1,2,4‐triazines were found to be related significantly (confidence level >99%) with the π‐charge at N‐4 calculated by a semi‐empirical molecular orbital (AM1) procedure. For the 15N NMR chemical shifts of N‐1 and N‐2, no reliable correlations with the molecular electronic properties such as AM1 π‐charges and ionization potentials (—EHOMO) were found.
1H (300 MHz) and 13 C NMR spectral assignments for diisocyanoadociane
Authors: König Gabriele M. , Wright Antony D. 
Published: May 2005

AbstractComplete 1H and 13C NMR data are reported for the marine‐derived natural product diisocyanoadociane, based on COSY, NOESY, XHCO, HMQC, HMBC and INADEQUATE measurements. The 15N NMR data for this compound are also reported.
One‐ and two‐dimensional NMR study of resol phenol—formaldehyde prepolymer resins
Authors: Fisher Thomas H. , Chao Ping , Upton Cindy G. , Day Anthony J. 
Published: May 2005

AbstractA one‐ and two‐dimensional NMR study was performed on three commercial resol phenol—formaldehyde (PF) prepolymer resins. 1H, 13C, CSCM and DQF COSY NMR spectral data, in acetone‐d6, were obtained on each resin and on PF model compounds: phenol, five methylolphenols, four diphenylmethanes, two formals, two dibenzyl ethers and two dibenzylamines. Gated‐decoupled 13C experiments, using 2,4,6‐trimethylphenol as internal standard, were used to quantitate the major components present in each of the three resins. The major chemical differences of the three resins were noted. A DQF COSY method was developed that allowed the qualitative identification of most of the major phenolic components present in each of the PF resins.
Submicromole structure elucidation: Cryptolepicarboline—a novel dimeric alkaloid from Cryptolepis sanguinolenta
Authors: Sharaf Maged H. M. , Schiff Paul L. , Tackie Albert N. , Phoebe Charles H. , Howard Layne , Meyers Carol , Hadden Chad E. , Wrenn Susan K. , Davis Ann O. , Andrews C. Webster , Minick Doug , Johnson Robert L. , Shockcor John P. , Crouch Ronald C. , Martin Gary E. 
Published: May 2005

AbstractCryptolepis sanguinolenta (Lindl.) Schlechter (Asclepiadaceae), a shrub indigenous to West Africa, has been employed by traditional healers in the treatment of various fevers, including malaria. Column chromatography of the alkaloid fraction obtained from a defatted ethanolic extract of the roots of the plant afforded the previously characterized alkaloids cryptolepine, quindoline and cryptospirolepine. Continued extensive column chromatography, followed by preparative high‐performance liquid chromatography, resulted in the isolation of nine new alkaloids, including approximately 100 μg of a novel indoloquinoline‐β‐carboline dimeric alkaloid, cryptolepicarboline. The structure was elucidated through the use of a combination of spectroscopic techniques which included UV, Fourier transform, electron impact mass spectrometry, and 500 MHz NMR spectroscopy. NMR data included 1D 1H and 13C reference spectra, the latter recorded in 40 μl of DMSO‐d6 using a new Varian heteronuclear Nano‐probe and in 140 μl of DMSO‐d6 using a Nalorac carbon‐optimized microprobe. These 13C NMR spectra allow the first direct comparison of these two probe formats. Homonuclear 2D NMR data acquired included both COSY and ROESY spectra. The homonuclear 2D experiments were variously performed in both a homonuclear Nano‐probe and micro‐inverse detection probes. Heteronuclear shift correlation experiments included HMQC, HMBC and IDR (inverted direct response)‐HMQC‐TOCSY spectra, which were uniformly performed using a 500 MHz Nalorac micro inverse‐detection probe.
Computerized analysis of 2D INADEQUATE spectra to assign chemical shifts in aromatic compounds
Authors: Orendt Anita M. , Dunkel Reinhard , Horton W. James , Pugmire Ronald J. , Grant David M. 
Published: May 2005

AbstractA computerized analysis of a single 2D INADEQUATE spectra assigns all of the 13C chemical shifts in fairly complex aromatic systems. Without the aid of the computer this information is often difficult, if not impossible, to retrieve owing to overlap of the signals in the double quantum dimension. In addition, the use of the computerized analysis allows for the interpretation of INADEQUATE spectra with much lower signal‐to‐noise ratios than are practical if the analysis were to be done visually. Finally, narrowing the spectral window to a subset of the entire spectrum and the companion advantages are demonstrated. The assignments of the aromatic chemical shifts in 2‐methoxydibenzofuran, 6‐methylchrysene, 1‐decylpyrene, and 7‐methylbenzo[a]pyrene illustrate the power of automated pattern recognition methods while supplying previously unavailable chemical shift assignments on these complex fused polycyclic aromatic systems.
Two‐dimensional nutation echo 75As NQR spectroscopy in antiferroelectric NH4H2AsO4 using the maximum entropy method
Authors: Kątowski P. , Maćkowiak M. 
Published: May 2005

AbstractWith a view to developing efficient methodologies for the evaluation of the asymmetry parameter of the electric field gradient (EFG) tensor from polycrystalline specimens, an alternative approach which involves two‐dimensional spin‐echo NQR data processing by the maximum entropy method (MEM) is presented. The superiority of MEM over the traditional fast Fourier transform (FFT) method is demonstrated by the analysis of two‐dimensional NQR data obtained using the modified pulse sequence. The method has been successfully applied to the determination of the EFG tensor at the 75As site in the antiferroelectric phase of polycrystalline ammonium dihydrogenarsenate (ADA), where conventional nutation spectroscopy fails owing to the large NQR linewidth.
NMR assignments and absolute stereochemistry of two guaianolide sesquiterpenes from Tanacetum densume subsp. amani
Authors: Ulubelen Ayhan , Gören Nezhun , Jiang Tian‐Yi , Scott Lincoln , Tianasoa‐Ramomojy Manoelson , Snyder John M. K. 
Published: May 2005

AbstractThe guaianolide sesquiterpene pyrethroidinin (1) and the corresponding ketone parishin A (2) wee isolated from Tanacetum densum subsp. amani (Asteraceae). The absolute stereochemistry of 1 was established as (1R, 3R, 6S, 7S, 10R) on the basis of the differential shielfing in the 1H NMR spectra of the (−)‐ and (+)‐O‐methylmandelate esters. The structure, including absolute stereochemistry, of 2 was confirmed by oxidation of 1 whit Jones' reagent.
Complete assignments of the 1H and 13C NMR spectra of some fluoro‐substituted chromenes
Authors: Barberis Claude , Campredon Myléne , Lokshin Vladimir , Giusti Gérard , Faure Robert 
Published: May 2005

AbstractThe total assignment of the 1H and 13C NMR spectra of four fluoro‐substituted chromenes was deduced from the concerted application of homonuclear correlation (COSY), 1H‐detected one‐bond heteronuclear multiple quantum coherence (HMQC) and long‐range (two and three bonds) heteronuclear multiple bond connectivity (HMBC) experiments.
Struktur‐Reaktivitätsuntersuchungen mit heterosubstituierten Nitrilen—VII:13C‐, 14N‐ und 19F‐NMR‐Spektroskopische Untersuchungen an Verbindungen vom Typ ArXCN
Authors: Radeglia R. , Storek W. , Engelhardt G. , Ritschl F. , Lippmaa E. , Pehk T. , Mägi M. , Martin D. 
Published: May 2005

AbstractAn aromatischen Nitrilverbindungen der allgemeinen Struktur para‐YC6H4XCN mit X = O, S, Se und N(CH3) wurden die 13C‐NMR‐ sowie für X = O die 14N‐NMR‐und für Y = F die 19F‐NMR‐chemischen Verschiebungen bestimmt. Die Meßergebnisse wurden in Zusammenhang mit der elektronischen Struktur der Moleküle (Substituentenkonstanten, π‐Elektronendichten in PPP‐Näherung) diskutiert.
Chemical polarisation of 15N and 13C nuclei in diazo coupling reactions
Authors: Lippmaa E. , Pehk T. , Saluvere T. , Mägi M. 
Published: May 2005

AbstractChemical polarisation of nitrogen and carbon nuclei in the decomposition and diazo coupling reactions of benzenediazonium fluoborate has been investigated. If homo‐ and heterolytic processes run in parallel in a multistage reaction sequence, then the nuclear polarisation created in a free‐radical reaction can be nearly quantitatively carried over to products of rapid ionic reactions such as azo dyes.
CIDNP as the proof of a radical mechanism of the reactions of Grignard reagents with diazonium salts
Authors: Savin V. I. , Temyachev I. D. , Kitaev Yu. P. 
Published: May 2005

AbstractThe PMR spectrum recorded during the reaction of tert‐butylmagnesium chloride with p‐chlorophenyl diazonium tetrafluoborate shows the CIDNP effect in the spectra of the the reaction products. Enhanced absorption and emission (the multiplet effect) has been observed for the protons of the vinyl group of isobutylene and the methyl protons of isobutane. The reaction of these diazonium salts with benzylmagnesium chloride results in only one polarised product, chlorobenzene. Such a polarisation proves the radical mechanism of the reaction which started with one‐electron transfer from the Grignard reagent to the diazonium salt.
Configurational assignments in some dihydrobenzo[c]thiophenes by NMR solvent effects. Correlation of the relative chemical shifts of α‐methyl groups with sulphoxide stereochemistry
Authors: Sataty Ishai 
Published: May 2005

AbstractThe configuration of isomeric 3,3‐dimethyl‐1‐phenyl‐1,3‐dihydrobenzo[c]thiophene 2‐oxides was assigned on the basis of selective benzene‐ and TFA‐induced NMR shifts. The same method was employed for assigning the α‐methyl resonances of these sulphoxides. Examination of NMR data for a variety of cyclic sulphoxides revealed that in CCl4 or CDCl3 solution, α‐hydrogen cis to SO often resonates at higher magnetic field, while α‐methyl group cis to SO characteristically resonates at lower field, than the same hydrogen or methyl group trans to SO, respectively.
Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation de la monofluoroacétone
Authors: Courtieu J. , Gounelle Y. 
Published: May 2005

AbstractLes spectres RMN des monochloro‐, monobromo‐ et monofluoroacétone orientées dans une phase nématique ont été interprétés et les constantes de couplage dipolaire mesurées. La barrière s'opposant à la libre rotation du groupement CH2F a été étudiée pour le composé fluoré à l'aide de différentes hypothèses. En utilisant une répartition de Boltzmann pour peupler les différentes conformations du groupement CH2F, et une fonction potentielle de la forme V(θ) = Σn Vn(1 – cos n θ)/2, on obtient un bon accord avec les résultats d'infra‐rouge pour V1 = 250 ± 50 cal.mol−1, V2 = 1650 ± 100 cal.mol−1, V3 = −1000 ± 100 cal.mol−1.
Carbon‐13 magnetic resonance spectra of quaternary ammonium salts derived from enamino ketones
Authors: Dabrowski Janusz , Kamieńska‐Trela Krystyna , Kozerski Lech 
Published: May 2005

Abstract13C magnetic resonance spectra of nine quaternary ammonium salts of the general formula R1C1(O)C2HC3HNR34Cl (where R1, R4 = alkyl) were obtained and compared with those of the parent amino compounds. The chemical shift differences between these two classes of compounds are qualitatively accounted for by π‐electron density changes. Steric effects and hyperconjugation of the alkyl substituents are also discussed.
Chemical shift nonequivalence of sulfinates: Structural, solvent and temperature effects
Authors: Norton Richard V. , Douglass Irwin B. 
Published: May 2005

AbstractThe structural, solvent and temperature effects on the PMR spectra of several alkyl alkanesulfinates and arenesulfinates are discussed. A low order intrinsic nonequivalence was observed in substituents alpha to the sulfinate sulfur atom, the nonequivalence being significantly less than in sulfoxides, and solvent and temperature dependent. Nonequivalence of diastereotopic substituents on the ester oxygen exceeded nonequivalence in similar sulfoxides and is largely insensitive to temperatures from 25° to 120°C. Benzene complexes with sulfinates greatly enhancing the proton nonequivalence of alpha substituents apparently by causing a further shielding of the already more shielded nonequivalent protons.
Application of the temperature dependence of vicinal spin‐spin coupling constants to the investigation of the configuration of substituents in saturated 5‐membered rings
Authors: Filippova T. M. , Lavrukhin B. D. , Shmyrev I. K. 
Published: May 2005

AbstractTemperature dependence of cis‐ and trans‐vicinal spin‐spin coupling constants of substituted cyclic 5‐membered compounds is discussed. The temperature dependence of trans‐vicinal coupling constants is shown to be essentially stronger than that of cis‐vicinal coupling constants if the energies of the conformers corresponding to potential energy curve minima are different. The temperature dependence of 33 vicinal spin‐spin coupling constants has been studied for di‐ and trisubstituted thiophanes with a known configuration of substituents. Experimentally determined changes of trans‐vicinal coupling constants with temperature are markedly larger than those for cis‐vicinal coupling constants, whose values, in most cases, are practically temperature independent. Differences in the temperature dependence of cis and trans‐vicinal spin‐spin coupling constants can be applied for the determination of the configuration of substituents in saturated 5‐membered rings.
13C chemical shifts of monosubstituted adamantanes
Authors: Maciel Gary E. , Dorn Harry C. , Greene Robert L. , Kleschick William A. , Peterson Max R. , Wahl George H. 
Published: May 2005

Abstract13C chemical shifts are reported for adamantane, nine 1‐substituted adamantanes and nine 2‐substituted adamantanes. The substituents are F, Cl, Br, I, NH2, OH, CH2, CN and CO2H. The assignments and results are discussed in terms of chemical shift patterns.
The NMR spectra and conformations of cyclic compounds: IX—conformational studies of bicyclo(3,1,0)hexane derivatives by 13C NMR
Authors: Abraham Raymond J. , Holden Collette M. , Loftus Philip , Whittaker David 
Published: May 2005

AbstractThe 13C spectra of α‐thujene (1), isothujone (2), (−)isothujol (3), (+)neoisothujol (4), sabinol (5), dihydroumbellulone (6) and umbellulone (7) and the alcohol acetates are recorded and assigned. The C‐6 chemical shift may be used in conjunction with the steric shift mechanism as a conformational probe in these molecules. The results obtained indicate that isothujol, neoisothujol, isothujone and dihydroumbellulone adopt boat‐like conformations whilst sabinol has a much flatter conformation. Conjugation of the isolated double bond of α‐thujene and the carbonyl group of dihydroumbellulone with the cyclopropane ring has virtually no effect on the 13C shifts, but those of umbellulone itself are anomalous, indicating conjugation of the α,β unsaturated ketone system with the cyclopropyl ring.
The 1H NMR spectra of p‐substituted phenyl 2‐chloro‐2‐fluoroethyl sulphides
Authors: Takahashi Kensuke , Akasaka Takeshi , Kondo Shuji , Tsuda Kazuichi 
Published: May 2005

AbstractThe 60 MHz 1H NMR spectra of p‐substituted phenyl 2‐chloro‐2‐fluoroethyl sulphides have shown characteristic patterns; in the ABC portion of an ABCX spin system (X = 19F) of the compounds, one of the subspectra shows an ABC pattern and the other apparently an AB2 pattern. These spectral patterns have been analysed and the 1H NMR data obtained are discussed briefly.
Hétérocycles contenant du phosphore. XXII—Etude par RMP de dérivés de l'oxazaphospholane‐1,3,2: II—Analyse des spectres de composés monosubstitués en 5 ou disubstitués en 4 et 5.
Authors: Devillers Jean , Cornus Martine , Roussel Jean , Navech Jacques , Burgada Ramon 
Published: May 2005

AbstractL'influence de différents facteurs (température, nature et concentration du solvant) ou l'utilisation de différentes techniques de double irradiation (par exemple, tickling ou INDOR) est mise à profit pour analyser le spectre de RMP de toute une série de dérivés de l'oxazaphospholane‐1,3,2 possédant soit un substituant sur le carbone en 5, soit deux substituants sur les carbones en 4 et 5.
Etude du couplage 2J(N15H) en série hétérocyclique. Application à la détermination des constantes d'équilibres prototropiques rapides
Authors: Maquestiau A. , Van Haverbeke Y. , Muller R. N. 
Published: May 2005

AbstractLa comparasion des constantes de couplage 2J(N15H3) présentées par la (N15)‐4‐phénylisoxazoline‐5‐one (2) et par deux de ses formes fixes, la (N15)‐2‐méthyl‐4‐phénylisoxazoline‐5‐one (3) et le (N15)‐4‐phényl‐5‐méthoxyisoxazole (4), indique une participation élevée de structure énolique (et/ou ionique) dans les milieux basiques.
NMR spectroscopic study of rotation around CC and CN bonds in diene δ‐aminocarbonyl compounds
Authors: Prokof'ev E. P. , Krasnaya Zh. A. , Kucherov V. F. 
Published: May 2005

AbstractA relatively fast rotation around the α,β carbon–carbon double bond at the equilibrium of geometrical isomers and a comparatively slow rotation around the carbon‐nitrogen single bond in compounds of the type

(X1, X2 are electron‐attracting substituents) were detected and investigated by the NMR technique. The relationships between the free energies of activation for these rotational processes and the character of the substituents, the number of double bonds, solvents and concentration were studied.