bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H and 13C NMR study of 2‐aminothiazole urinary tract carcinogens
Authors: Davidson R. M. , Rice J. R. , Lakshmi V. M. , Zenser T. V. , Davis B. B. 
Published: May 2005

AbstractUsing 1H and 13C NMR, 13C‐labelled modifications of 2‐amino‐4‐(5‐nitro‐2‐furyl)thiazole (ANFT) and its N‐formyl analogue N‐[4‐(5‐nitro‐2‐furyl)‐2‐thiazolyl]formamide (FANFT), as well as the 5‐(S)‐substituted glutathione and N‐acetylcysteine conjugates of prostaglandin H synthase‐catalyzed peroxidative metabolism of ANFT were studied. 1H and 13C NMR chemical shifts, heteronuclear coupling constants, spin–lattice relaxation times (T1) and nuclear Overhauser enhancements (NOE) were obtained. Three‐bond coupling constants of the 13C‐labelled nucleus with the C‐5 protons of ANFT and FANFT were in close agreement but were absent in the conjugates owing to the 5‐substitution. Two‐bond coupling of the 13C‐labelled nucleus was observed with the amide proton of FANFT, but not with ANFT because of rapid exchange of the amine protons. Values of T1 were smaller in the conjugates than in FANFT or ANFT owing to their larger molecular weights. 1H spectra and NOEs provide further support for the prevalence of the 2‐aminothiazole tautomer over the 2‐iminothiazoline tautomer. Evidence is presented for a proton transfer of the C‐5 proton of ANFT, which proceeds over a time of the order of weeks in dimethyl sulphoxide and is autocatalytic. FANFT showed a different proton‐transfer reaction involving the amide proton, which occurs on a time scale of the order of days in dimethyl sulphoxide. The FANFT molecule revealed no evidence for transfer of its C‐5 proton, in contradistinction to ANFT. From a calculation of the percentage of the 13C relaxation due to the dipole–dipole mechanism, it can be concluded that for this class of sp2‐hybridized carbon (the C‐2 position of the 2‐aminothiazole system) a considerable portion of the relaxation is due to mechanisms other than dipolar.
Carbon‐13 chemical shift assignment of E‐stilbenyloxyalkanocarboxylic acids and their derivatives
Authors: Wyrzykiewicz Elżbieta , Grzesiak Jolanta , Prukała Wiesław 
Published: May 2005

AbstractThe 13C NMR spectra of 35 E‐stilbenols, E‐stilbenyloxyalkanocarboxylic acids and their esters and hydrazides have been calculated and fully assigned. The Ai empirical parameters of the p‐chlorostyryl, p‐bromostyryl, p‐alkoxycarbonylalkoxy, p‐carboxyalkoxy and p‐hydrazinecarbonylalkoxy groups have been calculated for use in the prediction of the chemical shifts of substituted benzenes and stilbenes.
Structure elucidation of an unexpected acylation product of dithranol: An application of improved heteronuclear two‐dimensional NOE spectroscopy
Authors: Bigler P. , Rychener M. , Séquin U. 
Published: May 2005

AbstractHeteronuclear NOEs have proved to be a valuable tool for the structure elucidation of an unexpected acylation product of dithranol. The application of a modified 2D HOESY pulse sequence with improved sensitivity is demonstrated.
Diastereoisomers with three neighbouring phenyl groups. XI—Hindered phenyl and formylmethylamino group rotations in 3‐(formylmethylamino)‐1,2,3‐triphenylpropyl chlorides
Authors: Dimitrov V. S. , Kurteva V. B. , Lyapova M. J. , Mikhova B. P. , Pojarlieff I. G. 
Published: May 2005

AbstractUnusually high free energies of activation for the rotation of phenyl groups, 12.1 and 11.1 kcal mol−1, are observed in the (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers of 3‐(formylmethylamino)‐1,2,3‐triphenylpropyl chloride, and for the rotation of the formylmethylamino group (11.7 kcal mol−1) in the Z rotamer of the former isomer. These high barriers can be related to the interdependence of the rotation of such large planar groups in the strongly biased preferred conformations. The barriers for rotation of the formyl group are in the usual range (22.5 and 20.6 kcal mol−1) for (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers, respectively.
Phosphorus—nitrogen compounds. Part 57—variable‐temperature phosphorus‐31 nuclear magnetic resonance spectroscopy of some phenyl‐substituted cyclotriphosphosphazatrienes
Authors: Deutsch W. Francis , Parkes Harold G. , Shaw Robert A. 
Published: May 2005

AbstractThe temperature dependence of the 31P NMR spectra of N3P3Cl6, phenyl‐substituted cyclotriphosphazatrienes, N3P3PhnCl6‐n (n = 2, 4, 6), and a series of derivaties, N3P3Ph2[X(CH2)n Y]Cl2 (where X = Y = O, NH, n = 2, 3, 4; X = Y = NMe, n = 2, 3; X = NH, Y = NMe, n = 3), of gem‐N3P3Ph2Cl4 was studied. Differential changes in chemical shift as a function of temperature were observed between different 31P nuclei. In a number of cases second‐order effects could be greatly reduced through a change in temperature. The temperature dependence of the 31P shift was found to differ with solvent, for example when CDCl3 replaced CD2Cl2.
ENDOR and triple resonance studies of 1,4‐dihydro‐1,2,4‐benzotriazinyl radicals and 1,4‐dihydro‐1,2,4‐benzotriazine radical cations
Authors: Neugebauer Franz A. , Rimmler Gösta 
Published: May 2005

AbstractESR, ENDOR and triple resonance studies of 1,4‐dihydro‐1,3‐diphenyl‐ (1a) and 3‐tert‐butyl‐1,4‐dihydro‐1‐phenyl‐1,2,4‐benzotriazinyl (2a) and of the corresponding radical cation 3a (2a protonated at N‐4) yielded the magnitude and the sign of almost all of the 1H and 14N hyperfine coupling (HFC) constants. Their assignment was performed using various 2H labelled and/or methyl substituted derivatives. Both radical groups show major hyperfine coupling to the three 14N nuclei. In the uncharged species 1a and 2a, the spin density at N‐4 apparently directs the 1H HFC pattern in the 1,2,4‐benzotriazinyl component, a(H‐5) and a(H‐7) being larger than a(H‐6) and a(H‐8). In the radical cation, on the other hand, N‐1, with an unusually large splitting of 9.9 G, is the position of highest spin density which determines the 1H HFC pattern, a(H‐6) and a(H‐8) being larger than a(H‐7).
Configurational assignment of β‐fluoro‐β‐phenylamines using 1H and 19F NMR
Authors: Hamman Sylvain , Benaïssa Tahar , Béguin Claude G. 
Published: May 2005

AbstractThe 1H and 19F NMR parameters [δH‐α, δH‐β, δF, 3J(HH) and 3J(FH)] of β‐fluoro‐β‐phenylamines of the two series PhCHFCH2NR1R2 and PhCHFCH(R)‐NR1R2 in CDCl3 (amine form) and in CD3OD (protonated amine form) and those of the corresponding β‐hydroxy‐β‐phenylamines were measured. It is shown that for the protonated amines the predominant conformation is that in which the ammonium group is antiperiplanar to the phenyl group, especially for tertiary amines. Assignment of the diastereoisomers of the PhCHFCHRNR1R2 series can be made with the NMR parameters of the protonated amines: high (low) 3J(HH) values, low (high) 3J(FH) values, 19F chemical shifts to high (low) frequency are those for the threo (erythro) isomers.
Complete structural assignment in a series of thieno[3,4‐b]quinoxalines by means of 2D NMR
Authors: Legendre Lucien , Mahuteau Jacqueline , Miocque Marcel , Vierfond Jean‐Michel 
Published: May 2005

AbstractThe structure of pyrrolo ([4,5‐b]‐1′,2′,3′,4′‐tetrahydroquinoxaline) [1,2,3‐Im]‐ 1 ‐ methyl ‐ 3 ‐ propyl ‐ 1, 3, 3a, 4, 9, 9a ‐ hexahydrothieno[3,4‐b]quinoxaline 2,2‐dioxide, isolated in the course of a study on a series of thieno[3,4,‐b]quinoxalines, was assigned on the basis of a spectral 1H‐13C correlated inverse chemical shift experiment.
ESR spectroscopy of the 4,5‐bis(methoxycarbonyl)‐1,3,2‐dithiazol‐2‐yl radical labelled with sulphur‐33 and nitrogen‐15
Authors: Preston Keith F. , Sandall John P. B. , Sutcliffe Leslie H. 
Published: May 2005

AbstractA derivative of the 1,3,2‐dithiazol‐2‐yl radical was labelled with 33S in order to evaluate the p spin densities on the sulphur atoms. This information is required to provide a full description of the SOMO which, in turn, aids the understanding of the structure of the radical dimers. An unexpected result is that the two sulphur atoms are non‐equivalent in the solid state. Calculations suggest that this is due to out‐of‐plane twisting of the substituent groups. Comparison of the ESR parameters of the bis(methoxycarbonyl) derivative with other members of the 1,3,2‐dithiazol‐2‐yl group of radicals (including the parent radical) shows that it is a good model for the whole group.
Application of cyclodextrins to chiral analysis by 1H NMR spectroscopy
Authors: Casy A. F. , Mercer A. D. 
Published: May 2005

AbstractThe influence of inclusion complex formation between cyclodextrins (chiefly the β‐polymer) and a variety of chiral antihistaminic and analgesic agents on the 1H NMR features of both guest and host partners is reported. In many cases equivalent protons of antipodes give resonances which differ in chemical shift after inclusion, and the potential value of the data to chiral analysis and to elucidation of the structures of the inclusion complexes is demonstrated.
Two‐dimensional NMR spectroscopy of connected transitions by linear combination of flip angle dependent cosy: An alternative scheme for E.COSY
Authors: Chandrasekhar K. , Kumar Anil 
Published: May 2005

AbstractAn alternative pulse scheme which simplifies and improves the recently proposed P.E.COSY experiment is suggested for the retention of connected or unconnected transitions in a coupled spin system. An important feature of the proposed pulse scheme is the improved phase characteristics of the diagonal peaks. A comparison of various experiments designed for this purpose, namely COSY‐45, E.COSY, P.E.COSY and the present scheme (A.E.COSY), is also presented. The suppression of unconnected transitions and the measurement of scalar coupling constants and their relative signs are illustrated from A.E.COSY spectra of 2,3‐dibromopropionic acid and 2‐(2‐thienyl)pyridine.
Application of 1H/13C inversely correlated NMR spectroscopy to the determination of the stereochemistry of a polysubstituted [2.2]paracyclophane
Authors: Fischer Rüdiger E. , Dabrowski Janusz , Ejchart Andrzej , Staab Heinz A. 
Published: May 2005

AbstractThe relative orientation of substituents in the opposite rings of one of the isomeric 4,7‐Dichloro‐5,8,12,15‐tetramethoxy‐13,6‐bis[4‐(2‐methoxycarbonylphenyl) butyl][2.2]paracyclophanes was determined by establishing by NOE their orientation relative to the bridge protons, which thus served as ‘space‐spy nuclei’. The mutual orientation of these bridge protons was ascertained by the analysis of their coupling constants, obtained from a phasesensitive COSY spectrum. The 1H and 13C resonances were assigned with the aid of 1H COSY and 1H/13C inversely correlated spectra.
Improvement of 2D NMR spectra by matching symmetry‐related spectral features
Authors: Neidig K.‐P. , Kalbitzer H. R. 
Published: May 2005

AbstractA novel algorithm based on a two‐dimensional feature match is presented which compares the local features of the region containing a data point with the characteristics of the symmetry‐related area. The proposed method results in a very effective suppression of artifacts and t1 noise ridges, equal to the quality obtained by conventional spectral symmetrization. It is superior to conventional techniques because peak shapes are less distorted, it does not create spurious peaks (at the crossing of ridges), does not remove real cross‐peaks when the symmetry‐related cross‐peak is very weak and retains some of the global spectral asymmetry as important information for computerized evaluation procedures.
Computer‐aided evaluation of two‐dimensional multiple‐quantum, carbon shift correlation
Authors: Egli Huldrych 
Published: May 2005

AbstractA computer program for the automated interpretation and data evaluation of two‐dimensional multiple‐quantum, carbon shift correlations is presented. The program handles the assignment of CH, CH2 and CH3 groups and diastereotopic CHAHB groups. The correlated chemical shifts for carbons and protons are listed in the computergenerated output table, together with a value for the multiple‐quantum splittings and signal intensities. Examples are given which demonstrate that the program produces lists of correlated chemical shifts for carbons and protons, together with the group assignment for solutions of pure compounds and for more demanding cases. Emphasis is paid on possible misinterpretations, and ways to overcome the problem by user interaction are shown.
Radicals induced by illumination of a mixture of unsaturated fatty acids with ultraviolet light at 77 K
Authors: Melø Thor B. , Mahmoud Gharib S. 
Published: May 2005

AbstractElectron paramagnetic resonance has been used to identify the radicals produced by photoirradiation of a mixture of polyunsaturated fatty acids in ethanol. One solvent and one solute radical were formed during irradiation under anaerobic conditions at 77 K. The radicals were formed in hydrogen transfer reactions belonging to Type I photosensitization processes, and were produced from the same photosensitizer. The yield of the solvent radical varied linearly with the mixing ratio of the fatty acids in ethanol whereas the solute radical, as expected, varied with the concentration of the solute to the second power. The solute radical decayed by secondary thermal reactions at 77 K into a third radical with no hyperfine interaction structure. When oxygen was present in the sample the superoxide radical or, possibly, a peroxy radical was also produced. At 77 K the effect of the antioxidant spermine was to increase the yield of radical formation by preventing the recombinations of solvated electrons with the ionized sensitizer. Spermine is hence acting as an electron scavenger in this system. These results indicated that photoirradiation will cause radical formation by hydrogen transfer reactions and hence contribute to initiation processes in the oxidation of polyunsaturated fatty acids, and that spermine is not operative as an antioxidant in the initiation phase of the total oxidation.
15N‐13C spin coupling as a probe of electronic structure in benzenediazonium ions: INDO—SOS—MO calculations and steric inhibition of resonance
Authors: Axenrod T. , Huang X. H. , Tufaro D. , Watnick C. , Webb G. A. 
Published: May 2005

AbstractThe magnitude of 1J(15N13C) in para‐substituted benzenediazonium ions has been used to assess the importance of the several resonance forms contributing to the ground state of the ion. From a comparison of values observed in 4‐nitro‐ and 4‐dimethylamino‐benzenediazonium ions and their respective 3,5‐dimethyl derivatives, it is concluded that diazo‐type structures are important only with strong electron‐releasing substituents in the aromatic ring. INDO–SOS–MO calculations indicate that the large and negative Fermi contact term dominates this interaction.
Determination of the stereochemistry of isoxazolidinium salts by nuclear Overhauser effect difference spectroscopy
Authors: Liguori A. , Ottanà R. , Romeo G. , Rotondo E. , Sindona G. , Uccella N. 
Published: May 2005

AbstractThe configurations of some isoxazolidinium salts have been determined by nuclear Overhauser effect difference spectroscopy (NOEDS). The stereochemical findings give a good explanation of the different reactivities experienced in the five‐membered ring‐opening process as a function of the steric requirement of the system.
Complete spectral assignments of cevadine and veratridine by 2D NMR techniques
Authors: Krishnamurthy V. V. , Casida John E. 
Published: May 2005

AbstractThe long‐range CH correlation NMR experiment (with decoupling of modulation of intensities due to one‐bond couplings during refocusing) and the double quantum coherence correlation spectroscopy (DQCOSY) experiment were used, together with the standard one‐bond CH correlation and COSY spectra, for complete 13C and 1H spectral peak assignments of veratrine (a 2:1 mixture of cevadine and veratridine). The long‐range CH correlation experiment determined the long‐range CH connectivity network, thus indirectly providing carbon–carbon connectivity. The DQCOSY experiment proved to be a complementary technique to the standard COSY experiment in unraveling and/or confirming proton–proton connectivities in this highly crowded proton spectrum.
Scalar 13C, 1H and 13C, 19F spin—spin couplings between carbonyl carbons and aromatic protons (or fluorine) in (η6‐arene)tricarbonylchromium complexes
Authors: Szeczeciński Przemyslaw , Gryff‐Keller Adam 
Published: May 2005

AbstractSpin–spin coupling between carbonyl carbons and aromatic protons (or fluorine atoms) in several (η6‐arene)tricarbonylchromium complexes has been observed for the first time. The values of the coupling constants are of the order of 0.6 Hz for protons and 2 Hz for fluroine, and seem to depend on the electron‐donating properties of the aromatic substituent.
Computer predictions of 13C spectra. II—Alcohols and ketones
Authors: Bastard J. , Bernassau J. M. , Bertranne M. , Maia E. R. 
Published: May 2005

AbstractA methodology is described which allows the rationalization of the 13C chemical shifts of a variety of compounds including alkanes, alcohols and ketones. The geometries of 250 rigid compounds were computed by the MM2 force field. Multiple linear regression analysis was used to model the 13C shifts from topological, geometric and energetic parameters. Among these parameters, the most important were those corresponding to interatomic distances, hybridization state of the quaternary carbons and energetic parameters. The final result is a rationalization of the 13C chemical shifts with an average RMS error of 1.25 ppm.
Determination of ligand lifetimes in the Ni(glycerol)+ complex by proton NMR spin—lattice relaxation time measurements
Authors: Larsson Tomas , Kowalewski Jozef 
Published: May 2005

AbstractThe activation enthalphy and entropy for ligand exchange in the weak complex Ni(glycerol +) were estimated by variable‐temperature proton spin–lattice relaxation time measurements at 9.4 and 6.3 T on a 0.044 molal solution of NiCl2 in glycerol. A description of the dynamic process in terms of a simple two‐site exchange model yields ΔH≠ = 18.4 ± 1 kJ mol−1 and ΔS≠ = −114 ± 3 J mol−1 K−1.
Conformational analysis. 15—Lanthanide‐induced shift investigation of 2‐exo‐norborneol using tailored models of lanthanide complexation
Authors: Abraham Raymond J. , Rowan A. E. 
Published: May 2005

AbstractThe complete assignment of the proton chemical shifts for 2‐exo‐norboreol was obtained from a COSY experiment at 250 MHz. Using these assignments the conformation of this molecule in solution was studied using the lanthanide‐induced shift technique, applying a new three‐site lanthanide complexation model (LIRAS4) reflecting the coordination geometry at the hydroxyl oxygen atom.The substrate geometry which was found to give the best correlation between the calculated and observed shifts was not in agreement with the optimized geometry calculated using ab initio methods, the CCO angle being optimized as 108° in the former compared with 110.80° in the latter. The lanthanide complex geometry found indicated that one of the sites (trans to H‐2n) was occupied by the hydroxyl proton with the shift reagent bound to two other sites. This was supported by the increase in the vicinal J(HCOH) coupling observed on addition of the shift reagent. This LIRAS4 solution was then refined using a more complex model, HARDER, which treats each site as being independent of each other. The final two‐site solution obtained reflects the symmetry about the binding site in this molecule, and gave an excellent correlation between the observed and calculated shifts (Rx = 2.594, RR = 3.20 Å, PhiR = 105°, PsiR = 130°, RL = 3.00 Å, PhiL = 130°. PsiL = 130°).
High‐field aluminium‐27 nuclear magnetic resonance investigations of sodium aluminate solutions
Authors: Akitt J. W. , Gessner W. , Weinberger M. 
Published: May 2005

AbstractThe 27Al chemical shift, line widths and intensities have been measured for a series of sodium aluminate solutions with a range of sodium and aluminium concentrations. The aluminium is present entirely as the anion [Al(OH)4]− in all but the most concentrated solutions, where intensity is lost owing to the formation of species with very broad lines. The viscosities of the solutions were also measured and it was shown that these accounted to a great extent for the observed changes in line width, so that the unusually wide lines seen in the most concentrated solutions cannot be said to arise from dimeric species.
Identification of C‐glycopyranosides and C‐glycofuranosides by 13C NMR and 1H NMR. Complete assignment of their spectral data using carbon–proton chemical shift correlation spectroscopy
Authors: Wright Brian , Hughes Leslie R. , Qureshi Sheila S. , Davidson Alan H. 
Published: May 2005

AbstractC‐Glycopyranosides and C‐glycofuranosides were identified using 13C and 1H chemical shift and coupling constant data. Full assignments for all α‐ and β‐anomers were made possible by recourse to carbon–proton chemical shift correlation spectroscopy. Greater steric shielding effects were observed on the carbon atoms in cis‐1,2‐substituted compounds compared with their trans counterparts. Consistent proton chemical shift differences were also noted in that the anomeric protons resonate at lower field in all cis‐1,2‐isomers.
Suppression of uninformative peaks in two‐dimensional relayed‐NOESY spectra
Authors: Cavanagh John , Titman Jeremy J. , Keeler James 
Published: May 2005

AbstractTwo‐dimensional relayed‐NOESY spectra are of utility in assigning connectivities in crowded spectra. A modified version of this pulse sequence is described which removes uniformative diagonal peaks and one other type of unwanted peak. The resulting spectra are less crowded and can be interpreted more easily.
The γ‐butyrolactone ring puckering
Authors: Galache M. P. , Garcés P. , Esteban A. L. , Diez E. , Guilleme J. 
Published: May 2005

AbstractThe 60 and 100 MHz 1H NMR spectra of γ‐butyrolactone were analysed in detail. The best set of coupling values (Hz ± 0.03) is 3J = 7.86, 3J = 6.27, 3J = 9.52, 3J = 6.86, 4J + 4J = −0.18, 2JA − 2JB = 3.89 and 2JB − 2JC = 4.86 (A, B and C refer to α, β and γ protons, with respect to the ring oxygen, and c and t mean the same and opposite side of the ring, respectively). The 3J values support the conclusion that the molecule is interconverting between two equivalent conformations of near envelope type with the β‐carbon out of the mean plane defined by the fragment COCOC.
Rotational dynamics of flexible‐chain molecules. 13C NMR relaxation study of hydrocarbon chains attached to a heavy anchor
Authors: Dais Photis 
Published: May 2005

Abstract13C spin‐lattice relaxation times (T1) were measured for resolved carbons in flexible‐chain molecules consisting of a hydrocarbon chain attached to benzophenone at the para position. Effective correlation times, teff, were determined from T1 data and used to discuss the motional features of these molecules as a function of chain length, chain unsaturation and type of linkage by which the chain is attached to the benzophenone moiety. Of particular interest is the finding that the overall motion and chain mobility are greatly affected by the introduction of an unsaturated bond in the chain, depending on its configuration and location in the hydrocarbon tail.
1H NMR studies on alkyl‐substituted, 2,3‐ and 3,4‐annulated tetrahydro‐thiophenes
Authors: Kiesewetter Rene , Anklam Elke , Margaretha Paul 
Published: May 2005

Abstract1H NMR chemical shifts and coupling constants allow the configurational and conformational analysis of both the (rigid) annulated and the (non‐rigid but conformationally homogeneous) alkyl‐substituted 2,3‐ and 3,4‐tetrahydrothiophenes.