bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereochemistry of the B/C ring junction in 3‐benzylidenebenzo[a] quinolizidines
Authors: Hajpál I. , Scheiber P. , Nádor K. 
Published: May 2005

AbstractA trans B/C ring junction has been found to exist in 3‐benzylidinebenzo[a]quinolizidines. 1H NMR analysis of partially deuteriated compounds showed that the signals at 4.0‐4.2 ppm should be assigned to the H‐4‐exo proton.
Two‐dimensional 1H and 13C‐NMR spectra of 5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene, its precursor and metabolite
Authors: Lyčka Antonin , Jirman Josef , Nobilis Milan , Kvasničková Eva , Hais Ivo M. 
Published: May 2005

AbstractThe 1H and 13C chemical shifts in 5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene (1) and 5‐hydroxy‐7‐oxo‐7H‐benzo[c]fluorene (2) were assigned using H,H‐COSY, H,C‐COSY and selective INEPT spectra. It was found that the main phenolic metabolite of 1 and its hydrochloride corresponds to 9‐hydroxy‐5‐(2‐dimethylaminoethoxy)‐7‐oxo‐7H‐benzo[c]fluorene (3).
Solution structure of porphyrin aggregates determined by 1H NMR ring current shifts. I. Heterodimers of oppositely charged porphyrins
Authors: Hofstra U. , Koehorst R. B. M. , Schaafsma T. J. 
Published: May 2005

AbstractThe solution structures of dimers consisting of negatively charged Zn[tetra(4‐carboxyphenyl)porphyrin], ZnTPPC, with positively charged Zn[tetra(4‐N‐methylpyridyl)porphyrin], ZnTMPyP, and with H2[tetra(4‐N‐methylpyridyl)porphyrin], H2TMPyP, were determined by 1H NMR ring current shifts. The conformation is not affected by the presence of the metal in the centre of the TMPyP monomer. The dimers have a cofacial conformation with a plane‐to‐plane separation of 3.1 Å and an in‐plane translation of 4.2 Å along the aryl—aryl axis.
Use of 13C1H coupling constants for the investigation of azide—tetrazole tautomerism in aromatic nitrogen heterocycles. Detection of ditetrazolo [1,5‐a: 1′,5′‐c:] pyrimidine
Authors: Denisov Aleksei Yu. , Krivopalov Viktor P. , Mamatyuk Viktor I. , Mamaev Vladimir P. 
Published: May 2005

AbstractThe proton‐coupled 13C NMR and 1H NMR spectra of azidobenzene, tetrazolo[1,5‐a]pyridine, 2‐azidopyrimidine and tetrazolo[1,5‐a]pyrimidine in different solvents have been analysed, and criteria for using the NMR spectral parameters (especially the 13C‐1H coupling constants) for tautomeric structure determination have been elaborated. The efficiency of these criteria has been demonstrated in studies of azide‐‐tetrazole equilibria in 2,4‐ and 4,6‐diazidopyrimidines. The ditetrazolo tautomeric form of 2,4‐diazidopyrimidine has been found in polar solvents.
Carbon‐13 and proton two‐dimensional NMR study of diterpenoids of Coleus forskohlii
Authors: Prakash Om , Roy Raja , Tandon J. S. , Dhar M. M. 
Published: May 2005

AbstractThe stereochemical assignments of coleonol‐B (1), coleonol‐D (2) and coleosol (3) were accomplished by 2D 1H1H (COSY), 1H13C (hetero COSY), NOE difference NMR spectroscopic, stereospecific coupling constant and selective heteronuclear spin decoupling studies. The complete 13C chemical shift assignments of 2, 3 and coleol (4) were made for the first time. The earlier 1H chemical shift assignments were corrected and the stereostructure of coleonol‐D was reassigned.
Improvement in the evaluation of quantitative data in FT NMR spectroscopy by the convolution difference resolution enhancement (CDRE) technique
Authors: Kupka Teobald , Dziȩgielewski Jan Olgierd 
Published: May 2005

AbstractPractical guidelines for obtaining the optimum results in quantitative FT NMR spectroscopy through the use of the convolution difference resolution enhancement (CDRE) method are given. Use of the optimum parameter set diminishes the errors in the integral intensity and the line position measurements caused by poorly resolved signals.
Deuterium‐induced NMR isotope shifts for13C resonance frequencies of norbornane. Quantitative data for the dihedral angle dependence of vicinal shifts
Authors: Aydin Rafet , Frankmölle Walter , Schmalz Dietmar , Günther Harald 
Published: May 2005

AbstractThe complete set of deuterium‐induced intrinsic13C NMR isotope shifts,nΔ(13C), for norbornane have been determined from the isotopomeric monodeuteriated systems, and the results are discussed with respect to structure. No correlation is found between1Δ values and thescharacter of the CD bond hybrid. For vicinal isotope effects, however, a quantitative correlation with the dihedral angles of the intervening13C‐CCD bond fragment can be formulated: |3Δ(13C) | (ppb) = 2.2 + [7.3 × 10−3(ϕ −117.8)2]Negative3Δ values are found for bonding pathways in the five‐membered ring partial structure with anantiarrangement of the CCCD bond fragment.
Complete carbon‐13 and proton NMR assignments for two mesogenic series containing cyclohexyl rings
Authors: Frech Cheryl Baldwin , Fung B. M. , Schadt Martin 
Published: May 2005

AbstractComplete 13C and 1H spectral assignments for two series of liquid crystals in CDCl3 solution were made. The 4‐(trans‐4‐alkylcyclohexyl)benzonitriles had propyl‐to pentyl‐substituted alkyl chains, whereas the 4‐(trans‐4‐alkenylcyclohexyl)benzonitriles had varying positions of the alkenyl bond. 13C and 1H chemical shifts and 13C1H scalar coupling constants are reported.
Temperature dependence of NMR secondary references for D2O and (CD3)2SO solutions
Authors: Hoffman R. E. , Davies D. B. 
Published: May 2005

AbstractChemical shifts of secondary references for D2O and (CD3)2SO solutions were measured as a function of temperature. The 1H and 13C chemical shifts of dioxane, sodium 4,4‐dimethyl‐4‐silapentanesulphonate, HOD, tetramethylammonium chloride and sodium 3‐(trimethylsilyl)propionate‐d4 in D2O solution were measured relative to external TMS and the chemical shifts of (CD3)2SO and H2O were measured in (CD3)2SO solution relative to internal TMS. For accurate comparison of chemical shifts it is necessary to take into account the sample temperature and, therefore, the temperature dependences of 1H and 13C chemical shifts of a number of secondary references have been determined accurately and fitted to a parabola or straight line, as appropriate.
Restricted rotation in sterically hindered dichalcogenides. A dynamic NMR study
Authors: Pinto B. Mario , Leung Ronald Y. N. , Sharma R. Dev 
Published: May 2005

AbstractThe rotational barriers in bis(2,4,6‐tri‐tert‐butlphenyl) diselenide and ditelluride have been investigated by total line‐shape analysis of variable‐temperature 1H NMR spectra in CFCI3CD2Cl2 (85:15). The free energies of activation, ΔG, for the diselenide and ditelluride were determined to be 49.4 ± 0.6 and 39.2 ± 0.2 kJ mol−1, respectively. The difference is attributed to the dominance of steric effects in the transition state for rotation.
Practicalities and applications of reverse heteronuclear shift correlation: Porphyrin and polysaccharide examples
Authors: Cavanagh John , Hunter Christopher A. , Jones David N. M. , Keeler James , Sanders Jeremy K. M. 
Published: May 2005

AbstractThe practical aspects of proton‐detected heteronuclear shift correlation spectroscopy are described in detail, with emphasis on the precautions necessary to obtain efficient suppression of signals from protons that are not coupled to 13C. The experiment has been used to assign the quaternary carbon signals of a porphyrin and to resolve the proton spectrum of the K3 serotype polysaccharide.
Improvement of relayed—NOESY type experiments by implantation of spin‐lock sequences
Authors: Kessler H. , Gemmecker G. , Haase B. , Steuernagel S. 
Published: May 2005

AbstractSeveral Relayed—NOESY type pulse sequences are discussed which use spin‐lock periods for one or both of the two transfer steps. The use of such experiments for the sequence analysis of peptides is shown. The requirements for a successful application of special data processing techniques are explained. Even in conformationally rigid peptides where these conditions are no longer fulfilled, the 2D techniques described represent a sensitive and reliable method for the sequential assignment of the spin systems.
Application of natural abundance 2H NMR. Simultaneous measurement of primary and secondary kinetic deuterium isotope effects
Authors: Zhang Ben‐Li 
Published: May 2005

AbstractInternal and external reference methods are introduced for the study of kinetic deuterium isotope effects (KDIEs) by natural abundance 2H NMR. These methods take account of both inter‐ and intra‐molecular competive reactions of fully protonated and naturally monodeuteriated molecules of the substrate in the reaction. Specifically deuteriated compounds are not necessary using these methods. These techniques have further advantages over other methods; for example, primary and secondary KDIEs of different types can be measured simultaneously. The methodology is summarized and examples of its application are presented.
Triazoles. XIV—15N NMR study of substituted 5‐amino‐1,2,4‐triazoles
Authors: Orendt Anita M. , Michl Josef , Reiter József 
Published: May 2005

Abstract15N NMR chemical shifts were measured for a series of substituted 5‐amino‐1,2,4‐triazoles. The assignment of isomeric structures agrees with earlier results obtained with the use of proton‐coupled 13C NMR.
1H and13C spectra of fluorine‐containing polycyclic aromatic hydrocarbons.1H19F and13C19F coupling across bay regions
Authors: Sardella D. J. , Boger E. 
Published: May 2005

AbstractThe1H and13C NMR spectra of several fluorine‐substituted polycyclic aromatic hydrocarbons in which fluorine projects into a bay region were studied. Both protons and carbons of the sterically opposed CH bond show anomalously large F‐induced shifts and couplings to fluorine. The magnitudes of the couplings (particularly the four‐bond CF couplings which average 26 Hz) indicate a large through‐space contribution due to direct overlap between fluorine and CH bond orbitals, whereas the F‐induced shifts seem more likely to stem from diamagnetic anisotropy rather than F‐induced CH bond polarization.
High‐resolution solid‐state 119Sn and 207Pb NMR study of organotin and organolead chalcogenides: Observation of J‐coupling in solids
Authors: Harris Robin K. , Sebald Angelika 
Published: May 2005

AbstractHigh‐power decoupling, cross‐polarization and magic‐angle spinning techniques were used to obtain high‐resolution 119Sn NMR spectra of six organotin chalcogenides. In addition, the 207Pb spectrum of bis(triphenyllead)sulphide was obtained. The data were compared with the results of NMR measurements in solution and are discussed in relation to crystallographic considerations. Satellite resonances allow some metal‐metal coupling constants to be determined. The existence of intramolecular crystallographic inequivalence makes this feasible even for (Ph3Pb)2S. Use of a rotation‐synchronized Carr‐Purcell‐Meiboom‐Gill pulse sequence improves the ability to measure such coupling constants, as is demonstrated for (Me2SnS)3.
Carbon‐13 NMR studies of acridine derivatives. Part VII.—13C chemical shifts of some substituted 9‐acridanones and 9‐thioacridanones
Authors: Faure R. , Galy J. P. , N'Gadi L. , Barbe J. 
Published: May 2005

Abstract13C NMR data are presented for 31 variously substituted derivatives of 9‐acridanone and 15 derivatives of 9‐thioacridanone. Unexpected shifts are explained in terms of hydrrgen bonding or tautomeric equilibria.
13C NMR structural analysis of a series of tricarbony(diene)iron complexes
Authors: Rodriguez J. , Brun P. , Zahra J. P. , Waegell B. 
Published: May 2005

AbstractThe 13C NMR spectra of two series of substituted tricarbonyl(cyclohexadiene)iron complexes and of subsitituted tricarbonyl(vinylcyclohexene)iron complexes were recorded; 1‐ and 2‐substituted complexes can be distinguished by chemical shift comparison with parent compound.
Experimental and theoretical study of the methoxy group conformational effect on 13C chemical shifts in ortho‐substituted anisoles
Authors: Biekofsky Rodolfo R. , Pomilio Alicia B. , Econteras Ruben H. , de Kowalewski Dora G. , Facelli Julio C. 
Published: May 2005

AbstractAromatic 13C chemical shifts are reported for a number of ortho‐substituted anisoles. Quantitative determination of the substituent chemical shift (SCS) effects of the methoxy group with a fixed coplanar conformation on aryl carbon nuclei was achieved using experimental and theoretical methods. The experimental values were compared with those calculated through the use of the additivity, and a systematic departure from additivity was found for carbon nuclei in ortho positions. Ortho‐SCSs were found to be non‐equivalent, and the ortho effect on the carbon cis to the fixed methoxy moiety was more shielding than in anisole. The IGLO (Individual Gauge for Localized Orbitals) method was used to calculate the SCSs. Experimental and theoretical trends obtained for the influence of the side‐chain conformations on chemical shifts are in very good agreement with each other, and with recent results obtained by solid‐state NMR.
Analysis of the carbon and proton NMR spectra of 2‐arylthiophenes and related heterocycles
Authors: Del Mazza Dario , Reinecke Manfred G. , Smith William B. 
Published: May 2005

AbstractComplete proton and carbon NMR assignments were made for five 2‐(2‐X‐phenyl)thiophenes (X = NH2, NO2, COOH, Br), four 2,5‐diphenylheterocycles (thiophene, furan and N‐methyl‐ and N‐phenylpyrrole) and N‐phenylpyrrole using HETCOR, COSY, XCORFE and, in one case, NOESY 2D NMR techniques. In the first set of compounds a good correlation was found between the chemical shifts of certain carbon atoms and σp and/or the Q‐parameter. In the second series the expected correlation with the aromatic character of the heterocycle was observed primarily with the furan compound, where the heterocyclic ring strongly increases the electron density of the phenyl rings.
1H and 13C dynamic NMR study of the E, Z isomers of vinylogous diamides. Effect of conjugation and electrostatic and steric repulsion on the C(O)N rotation barriers and low‐temperature conformation
Authors: Szalontai Gábor , Sándor Péter , Bangerter Felix , Kollár László 
Published: May 2005

AbstractA 1H dynamic NMR study was carried out on N,N‐diethylmethacrylamide (1a), N,N,N′,N′‐tetraethylitaconamide (2), N,N,N′,N′‐tetraethylcitraconamide (3) and N,N,N′,N′‐tetraethylmesaconamide (4) over a wide temperature interval. Amide rotational barriers were determined from the coalescence temperatures. In 3 a second dynamic process was observed below 240 K, which made the geminal methylene protons non‐equivalent. The phenomenon is interpreted in terms of a non‐planar conformation caused by electrostatic and/or steric repulsion of the amide carbonyls. Homonuclear NOE experiments revealed an s‐cis, s‐cis′ conformation for the compounds studied.
1H and 13C NMR study of the interaction of formaldehyde on adenine and its derivatives
Authors: Le Botlan D. J. 
Published: May 2005

AbstractIt has previously been shown that formaldehyde causes the formation of hydroxymethylated derivatives with nucleobases, but these were identified after separation of the reaction products; such handling might destroy labile derivatives or remove products present in small proportions. This work is based on a study of the reactivity of formaldehyde on adenine, adenosine and adenosine monophosphate in the reaction medium. It demonstrates the high reactivity of the N‐9 site of adenine, the reactivity of the hydroxymethyl at the C‐5′ of the ribose and brings to light such new derivatives as N‐9‐CH2OCH2OH and N‐6‐CH2OCH2OH. Further, the order of appearance of different derivatives and their approximate determination were achieved.
NMR study of substituent effects in 4‐substituted and 4,4′‐disubstituted diphenyl sulphoxides and sulphones
Authors: Chandrasekaran R. , Perumal S. , Wilson D. A. 
Published: May 2005

AbstractThe proton and carbon NMR spectra of nine 4‐X‐diphenyl sulphoxides, seven 4‐X‐4′‐NO2‐diphenyl sulphoxides, eight 4,4′‐X2‐diphenyl sulphoxides, eight 4‐X‐diphenyl sulphones, seven 4‐X‐4′‐NO2‐diphenyl sulphones and eight 4,4′‐X2‐diphenyl sulphones have been obtained. Correlation of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes (Lynch plots) does not show the enhancement of substituent effect at C‐1 (para to the substituent) that was a feature of the corresponding sulphides studied earlier. Dual substituent parameter (DSP) correlations of the 13C chemical shifts with σ1/σR0 are excellent for carbons meta (C‐2,6) and para (C‐1) to the substituent. The trends for the series sulphides, sulphoxides, sulphones, where a decreasing response to the change of substituent is the general observation, are discussed. Changes of molecular conformation may also influence the transmission of electronic effects to the ring not carrying the variable substituent X.
NMR spectra and conformational analysis of substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives
Authors: Malik Farnaz , Hassan Mashooda , Rosenbaum Doris , Duddeck Helmut 
Published: May 2005

AbstractAn investigation of the molecular dynamics of substituted 1,3,4,5‐tetrahydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives revealed that these molecules adopt cycloheptadiene‐like boat conformations. There is an equilibrium between the quasi‐axial and the quasi‐equatorial conformer in which the quasi‐axial conformer is predominant. The difference in their conformational energies is less than 1 kcal mol−1. The most important factor influencing the energy barrier between the conformers is the presence of a substituent other than hydrogen at N‐1. Our findings disprove earlier reports by other workers.
Quantitative small molecule NOESY. A practical guide for derivation of cross‐relaxation rates and internuclear distances
Authors: Andersen Niels H. , Eaton Hugh L. , Lai Xiaonian 
Published: May 2005

AbstractThe pure absorption 2D NOE experiment can provide small molecule cross‐relaxation rate data suitable for quantitative conformational analysis even when the data are collected in a time‐saving manner using preparatory delays (PD) far short of the recommended values of 3–5 times T1. In our experience, the relative NOE intensities and cross‐relaxation rates are most readily extracted from cross‐relaxation spectra which are sums of adjacent rows (or columns) of the 2D data matrix. Intensity anomalies associated with t1 streaks can be removed by plotting cross‐relaxation difference spectra. PD truncation produces significant deviations from diagonal symmetry which must be accounted for in the data analysis. The influence of PD truncation on apparent auto‐peak decay rates and cross‐/auto‐peak intensity ratios is examined in both real and simulated spectra in order to develop appropriate quantitation strategies. These strategies, when applied to NOESY data for aqueous prostaglandin (PG) F2 α and a PG analog in organic media, yield cross‐relaxation rates that are within experimental error of those calculated from structural models or determined by more time‐consuming 1D NOE methods.
13C and 1H NMR investigations of quinic acid derivatives: Complete spectral assignment and elucidation of preferred conformations
Authors: Flores‐Parra Angelina , Gutiérrez‐Avella Dora Marina , Contreras Rosalinda , Khuong‐Huu Françoise 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 23 quinic acid derivatives are reported. The complete assignment of the 1H NMR spectra using selective proton decoupling experiments allowed the conformation of the six membered ring to be established from vicinal coupling constants and the calculation of dihedral angles. The 13C spectral assignments were made by consideration of substituent effects and comparison within the series. In some cases the similarities in chemical shifts did not allow unambiguous assignments; the chemical shifts were then calculated from empirical parameters.
Quantitative evaluation of electronic effects of the 1‐tetrazolyl group from1H and13C NMR data for substituted 1‐phenyltetrazoles
Authors: Karavai Vladimir P. , Gaponik Pavel N. , Ivashkevich Oleg A. 
Published: May 2005

AbstractThe1H and13C NMR spectra of severalmeta‐ andpara‐substituted 1‐phenyltetrazoles have been recorded, and the observed chemical shifts used for (i) the evaluation of σp, σm, σI, σRand σR°, the Hammett and Taft values of the 1‐tetrazoyl group, and (ii) the transmission of the electronic effects of themetaandparasubstituents on the phenyl ring to the tetrazole carbon and hydrogen atoms.
NMR spectroscopy of paramagnetic complexes. Part 36—2/1H NMR of paramagnetic metallocenes: Primary and secondary isotope effects and signal narrowing
Authors: Hebendanz Nikolaus , Köhler Frank H. , Scherbaum Franz , Schlesinger Björn 
Published: May 2005

Abstract1H and 2H NMR spectra were recorded for the paramagnetic metallocenes Cp2M (M = V, Cr, Mn, Co, Ni). For Cp2V, Cp2Cr, Cp2Mn and Cp2Ni, a signal narrowing factor of 36–37 is observed on going from Cp2M‐h10 to Cp2M‐d10, which is close to simple theoretical predictions. Additional quadrupolar relaxation leads to a factor of 27 for cobaltocene. The enhanced resolution of the 2H NMR spectra makes it possible to observe isotopomeric cobaltocenes with signals showing a secondary isotope shift of 0.71 ppm. In Cp2 Co‐d9 and ‐d8, the residual 1H atoms lead to a splitting of the 2H NMR signals, which is traced to the lifting of an orbital degeneracy due to the perturbation of the ligand π‐system by the lighter isotope. Primary isotope shifts of 2.33, 1.24, and 1.45 ppm are found for the pairs Cp2Mn‐d10/h10, Cp2Co‐d10/h10 and Cp2Ni‐d10/h10. They reflect a change in the electron spin distribution after complete deuteriation.
Study of hydrolytic kinetics of the hexachlorostannate anion by two‐dimensional 119Sn exchange spectroscopy
Authors: Mao Xi‐An , You Xiao‐Zeng , Dai An‐Bang 
Published: May 2005

AbstractTwo‐dimensional 119Sn exchange spectroscopy was applied to study the hydrolytic kinetics of the hexachloro‐stannate anion, SnCl62−. Two 119Sn exchange spectra for SnCl4 · 5H2O solutions with various HCl concentrations are presented. Magnetization exchanges, which are related to the hydrolysis processes, occur in the SnCl62− hydrolysis series. The exchange rate constants, the hydrolysis rate constants and the hydrolysis equilibrium constants were evaluated.
13C NMR studies of insulin. Part I—Spectral assignments
Authors: Craik David J. , Higgins Kerry A. , Hall Jon G. , Andrews Peter R. 
Published: May 2005

AbstractNatural abundance 75 MHz 13C NMR spectral assignments are reported for bovine and porcine zinc insulin in solution. A large number of protein resonances are well resolved, and approximately 80% of these have been assigned to either residue types or to specific sites within the protein. Assignment techniques included consideration of free amino acid or peptide shifts pH studies and comparison of sequence and spectral differences between bovine and porcine insulin, in addition to the use of NMR relaxation times. The DEPT spectral editing technique was also found to be particularly valuable as an assignment aid. This technique allows subspectra containing only CH, CH2 or CH3 carbon types to be generated. The method also produces signal enhancement relative to broad band decoupled 13C NMR spectra of large proteins which generally have reduced nuclear Overhauser enhancements.
Complete 1H and 13C NMR spectral assignment of venturicidin A by 2D NMR spectroscopy
Authors: Gogoll Adolf , Tanner David 
Published: May 2005

AbstractAfter correlation of the majority of signals by COSY and one‐bond heteronuclear correlation, the complete assignment of the 1H and 13C NMR spectra of the macrolide antibiotic venturicidin A required the application of long‐range CH coupling information. This was accessible by the COLOC‐S and selective INEPT experiments, and the sensitivity of these experiments is discussed. Steric information was obtained from a NOESY spectrum, and the solution structure compared with that in the crystal.