bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 and phosphorus‐31 NMR spectroscopy of phenoxychlorocyclotriphosphazenes, N3P3Cl6‐n(OC6H5)n
Authors: Reuben Jacques 
Published: May 2005

AbstractThe 31P and 13C NMR spectra of all twelve phenoxychlorocyclotriphosphazenes of general formula N3P3Cl6‐n(OC6H5)n (n = 1‐6) were assigned in detail. With samples abundant in one homolog, but with a disparity between geometrical isomers, the signals due to the cis and trans isomers of N3P3Cl4(OC6H5)2 and N3P3Cl2(OC6H5)4 were also assigned. The 31P chemical shifts and coupling constants correlate linearly with the level of substitution, n. The 13C NMR spectra exhibit complex multiplets for the ipso‐ and ortho‐carbons. It is shown that each of these is the X part of one of the spin systems XAM2, XAA′M, XAA2′, XAB2 and XAA′B. The 13C chemical shifts of the ipso‐ and para‐carbons also exhibit correlations with n. The 13C‐31P coupling constants, both 2J(POC) and 3J(POCC), are larger for the PCl(OC6H5) than for the P(OC6H5)2 moieties.
13C NMR spectra of eudesmanolides. II. Eudesman‐12,8‐olides
Authors: Marco J. A. , Carda M. 
Published: May 2005

AbstractThe 13C NMR spectra of 20 natural and synthetic eudesmanolides, including the naturally occurring sesquiterpene factones 1‐deoxy‐8‐epiivangustin, yomogin, 1‐deoxyivangustin and isoalloalantolactone, and of nine related eudesmane derivatives have been measured and interpreted. Substitutent effects are briefly discussed.
13C NMR chemical shift substituent effects. 4–α‐monosubstituted acetones
Authors: Rittner Roberto , Vanin José A. , Wladislaw Blanka 
Published: May 2005

Abstract13C NMR chemical shifts for some α‐heterosubstituted acetones were recorded. The carbonyl carbon shieldings are discussed in the light of the substituent electronic effects and were also empirically estimated by Tanaka et al.'s equation. An approximate linear relationship was observed between the 13C and 17O chemical shifts. A nonadditivity of substituent chemical shifts was observed for the α‐methylene carbon, and attributed to intramolecular interactions between the α‐heteroatom and the carbonyl group.
Configuration of cross‐conjugated caroten‐20‐als: 2D NMR study on four isomers of renierapurpurin‐20‐al
Authors: Englert Gerhard , Glinz Ernst , Liaaen‐Jensen Synnøve 
Published: May 2005

AbstractThe 400 MHz 1H NMR spectra of four cis isomers of synthetic renierapurpurin‐20‐al (χ,χ‐caroten‐20‐al) were completely assigned by application of two‐dimensional proton‐proton chemical shift correlated spectroscopy (2D COSY) with high digital resolution of ca 0.4 Hz per point by acquisition of only the olefinic part of the spectra. Connectivities to the methyl and aldehyde protons absorbing outside the measured range were also obtained owing to the folding of their cross‐peaks along the F1 axis. Nuclear Overhauser difference experiments and consideration of chemical shift changes were applied to derive unequivocally the 13‐cis (13E), 7,13‐di‐cis (7Z), 13,7′‐di‐cis (7′Z) and 13,9′‐di‐cis (9′Z) configuration of the isomers. The 1H‐detected one‐bond 1J(CH) and long‐range 2,3J(CH) multiple quantum coherence heterocorrelated 2D spectra of 1.2 mg of the main 13‐cis isomer were acquired and the 13C signals partly assigned. The structural consequences with respect to other cross‐conjugated caroten‐20‐als are discussed.
1H, 2H, 19F, 14N ENDOR and TRIPLE resonance investigations of substituted flavin radicals in their different protonation states
Authors: Weilbacher E. , Helle N. , Elsner M. , Kurreck H. , Müller F. , Allendoerfer R. D. 
Published: May 2005

AbstractA variety of isotopically labelled and/or substituted flavins have been converted into their corresponding radical states. Cation and neutral radicals were generated chemically and anion radicals were obtained electrochemically. By performing ENDOR and TRIPLE resonance experiments, complete sets of hyperfine coupling constants including their signs were accessible. The hyperfine data allowed (a) identification of the radical state present, (b) information to be obtained about the preferred conformational arrangements of the substituents and (c) conclusions to be drawn about the influences of the substituents on the spin density distributions of the different radical states.
Heteronuclear directed site‐selective NOESY spectroscopy by polarization transfer or multiple quantum filtering
Authors: Volk A. , Mispelter J. , Dimicoli J. L. , Papamichael E. , Sakarellos C. 
Published: May 2005

AbstractTwo methods are examined which allow a NOESY experiment to be performed involving only a specific site of the molecule labelled by a heteronucleus. They involve the merging of a classical phase‐sensitive NOESY experiment with either an INEPT sequence, which transfers 1H magnetization to a coupled heteronucles, or a multiple quantum filtering sequence which allows the selection of only the 1H resonances which are coupled to the heteronucles. The two methods are first compared on two small molecules, non‐labelled alanine and [U‐13C]alanine, particularly with respect to the signal‐to‐noise ratio. An example of the application of these methods on a 25000 molecular weight protein system (elastase‐peptide complex) is also given. The limitations of the methods, in particular in terms of T2, are discussed.
A 13C study of hydroxymethyl derivatives of five‐membered ring heterocycles
Authors: Katritzky Alan R. , Law Kam Wah 
Published: May 2005

AbstractThe 13C spectra of the hydroxymethyl derivatives of pyrrole, furan, 5,5‐dimethylhydantoin, imidazole, thiophene, pyrazole, and phenol have been studied and assigned. The substituent parameters for the hydroxymethyl group in pyrrole, thiophene, furan, and imidazole were determined.
Complete 1H and 13C spectroscopic assignments for the antibiotic novobiocin and NOE evidence for multiple conformations
Authors: Pearce C. M. , Sanders Jeremy K. M. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of the antibiotic novobiocin have been fully assigned by a combination of homonuclear and heteronuclear two‐dimensional techniques. One‐dimensional NOE difference spectra provide evidence for multiple conformations of the carbohydrate moiety with respect to the coumarin group. Mobile parts of the molecule gave positive NOEs whereas all other parts gave negative NOEs.
Proton and carbon‐13 NMR study ofN‐(β‐benzoylethyl)‐β‐alanine ethyl esters and their hydrochlorides
Authors: Avrsa Maria Chiara , Ferlazzo Alida , Giannetto Placido 
Published: May 2005

Abstract1H and13C NMR chemical shifts and coupling constants ofN‐(β‐benzoylethyl)‐β‐alanine ethyl esters and their hydrochlorides are reported; the assignments of the13C resonances are based on chemical shift arguments, analysis of the splittings and comparison with model compounds.
Stereochemical analysis and complete 1H/13C NMR chemical shift assignments of matrine. Application of NOE and two‐dimensional NMR techniques
Authors: Gonnella Nina C. , Chen Jen 
Published: May 2005

AbstractThe stereochemical and structural analysis of matrine was carried out using nuclear magnetic resonance spectroscopy. Several methods, including 13C1H two‐dimensional shift correlation spectroscopy, 1H1H two‐dimensional correlated spectroscopy and measurements of vicinal 1H1H coupling constants were used for chemical shift assignments and configurational analysis. Nuclear Overhauser effect difference spectroscopy was used to establish the sterochemistry. This investigation demonstrates the power of two‐dimensional NMR techniques and the nuclear Overhauser effect (NOE) in the structural determination of natural products.
13C NMR chemical shift trends and conformational changes in alkali metal cation complexes of a series of naphthalene crown ethers
Authors: Johnson Mark R. , Colburn Christopher A. , Ganion Susan J. , Son Byungki , Mosbo John A. , Sousa Lynn R. 
Published: May 2005

Abstract13C NMR studies of alkali metal cation complexation by six related crown ethers are described. The crown ethers (and ions studied) were 2,3‐naphtho‐20‐crown‐6 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐17‐crown‐5 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐14‐crown‐4 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐21‐crown‐6 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐18‐crown‐5 (Na+, K+, Rb+, Cs+) and 1,5‐naphtho‐22‐crown‐6 (K+, Rb+, Cs+). For each crown ethercation combination, 13C NMR spectra were obtained for a number of different ion concentrations in CD3OD. Data were analysed by a non‐linear least‐squares treatment to give complexation constants and chemical shifts that would result at the limit of complete 1:1 complexation. Analyses of the limiting chemical shifts for a number of carbons indicate regular, cation‐dependent trends (for Cs+ through Na+). Deviations from these trends are interpreted as reflecting differences in conformations of crown ether–cation complexes. Conformational differences between cation complexes that occur near the point of naphthalene attachment cause deviations from the trend in the aromatic carbon chemical shifts, while conformational differences further from the naphthalene cause trend deviations only in the crown ether carbon chemical shifts.
Accurate exchange rate constants from valley‐to‐peak intensity ratios of a two‐site system with equal populations
Authors: Perrin Charles L. 
Published: May 2005

AbstractThe valley‐to‐peak ratio of a 1:1 doublet undergoing chemical exchange can be calculated from the line shape equation. Numerical analysis provides a table that permits the evaluation of the rate constant from that ratio. This method is exact, without the approximations of previous equations that suffer from systematic errors. Statistical analysis shows how the experimental error depends on the rate constant and how to weight rate constants of unequal reliability for least‐squares analysis. From the tabulated errors it is possible to recognize conditions to optimize the evaluation of rate constants, so that it is realistic to obtain them with a precision of ± 1–2%.
31P nuclear magnetic resonance spectroscopy of the phosphorylated tetrapeptide GlyGlyAspAla
Authors: Schlemmer Heinz , Sontheimer Gerhard M. , Kalbitzer Hans Robert 
Published: May 2005

AbstractThe model peptide glycylglycylaspartylalanine was phosphorylated in the NMR sample tube and characterized by 31P NMR spectroscopy. The pKa2 value of the acyl phosphate group in glycylglycyl(β‐aspartyl phosphate)alanine was determined to be 4.6 and the chemical shift was −6.45 ppm at low pH (1.5) and −1.27 ppm at high pH (8.0).
Deuterium isotope effects as a conformational probe in cyclic and acyclic ketones
Authors: Berger Stefan , Diehl Bernd W. K. 
Published: May 2005

AbstractCyclic ketones from cyclobutanone to cyclohexadecanone were labelled with deuterium in the α‐position. The deuterium isotope effect on the 13C NMR spectra was measured and in some cases was indicative of perturbation of conformational equilibrium. Similar effects were observed with acyclic ketones. The results were confirmed by temperature‐dependent measurements and molecular mechanics calculations.
Magnetic properties in terms of localized quantities. VIII—Azines and azoles
Authors: Schindler Michael 
Published: May 2005

AbstractSecond‐order magnetic properties, i.e. magnetic susceptibility and chemical shift tensors, of some five‐ and six‐ membered heterocycles containing nitrogen were calculated by means of the IGLO method. The molecules studied were the azoles pyrrole, pyrazole, imidazole, 1,2,3‐triazole, 1,2,4‐triazole, and 1H‐ and 2H‐tetrazole, together with the corresponding N‐methyl‐substituted compounds, the azines pyridazine, pyrimidine, pyrazine, s‐triazine, 1,2,3‐triazine, s‐tetrazine, pyridine and borazine.Confirming previous investigations, good agreement was found between calculation and experiment. Only the calculated NMR shifts of nitrogen atoms that are involved in NN multiple bonds are too paramagnetic (deshielded). This effect (probably due to the neglect of electron correlation) is much less pronounced for the partial NN double bonds in aromatic rings than for genuine NN multiple bonds studied previously.
13C NMR investigations of phenol–triethylamine complexes: Ion pair–molecular complex tautomerism
Authors: Ilczyszyn Marek , Ratajczak Henryk , Skowronek Krzysztof 
Published: May 2005

AbstractThe tautomeric equilibria in phenol–triethylamine complexes have been quantitatively investigated. A method of calculation of thermodynamic parameters based on reproducing the temperature dependences of 13C chemical shifts is described. The results are in agreement with UV and IR predictions for similar complexes. The chemical shifts characterizing molecular forms of the complexes depend on the type of phenol derivative.
Configurations and conformations of some methyl‐substituted 2,4‐dioxabicyclo[3.3.1]nonanes
Authors: Mattinen Jorma , Pihlaja Kalevi , Czombos Jószef , Bartók Mihály 
Published: May 2005

AbstractThree dimethyl‐ and one trimethyl‐2,4‐dioxabicyclo[3.3.1]nonanes were prepared and their configurations and conformations were determined by means of multinuclear high‐field NMR spectroscopy. Even at 400 MHz the proton spectra were so degenerate that several 2D experiments and, also, deuterium NMR had to be used to make the spectral analysis possible. 13C and 17O NMR spectra are also reported. The information obtained shows that two of the dimethyl derivatives are in boat–chair conformations with 3α9syn and 3α6α configurations, whereas the third dimethyl and the trimethyl derivative exist in chair–chair conformations with 3β9syn and 3β9syn9anti configurations.
Carbon‐13 NMR relaxation studies of gluconate and manganese—gluconate interactions
Authors: Coffin David B. , Carper W. Robert 
Published: May 2005

AbstractThe effect of temperature on the spin–lattice (R1) and spin–spin (R2) 13C relaxation rates of gluconate and manganese (II)–gluconate interactions was determined in D2O. An R2 vs T−1 minimum was observed for gluconate similar to that observed in solid‐liquid phase transitions. Nuclear Overhauser enhancement factors indicated predominately dipolar relaxation mechanisms for all atoms except the carbonyl carbon. Activation energies and chemical shifts indicated a molecular reorientation involving the carbonyl carbon which resulted in changes in solvation effects. Addition of manganese(II) to gluconate in D2O resulted in an observed minimum in the R1 vs T−1 plots for all carbon atoms except the carbonyl species. The activation energies further supported the concept of changes in solvent‐manganese‐gluconate interactions produced by variations in intramolecular structure.
1H and 13C NMR study of hindered rotation in N1,N1‐dimethyl‐N2‐substituted phenylacetamidines
Authors: Wawer Iwona 
Published: May 2005

AbstractBarriers to rotation about the partial double CN1 bond were determined from line shape analysis of 1H and 13C dynamic NMR spectra of N1,N1‐dimethyl‐N2‐substituted phenylacetamidines with twelve different substituents on the phenyl ring. The values of ΔG are 51.2–58.7 kJ mol−1 and the correlation with Hammett's σ values indicates an important contribution from the substituent effects to the barrier height. The decrease of the rotational barrier of approximately 10 kJ mol−1 in acetamidines in comparison with the respective formamidines is probably mainly due to a steric interaction of the CCH3 group with aromatic protons; this leads to non‐planarity and a decrease of the conjugation of the aromatic ring with the acetamidine moiety.
Carbon‐13 to nitrogen‐14 coupling constants in some heterocyclic cations containing quaternary nitrogen atoms
Authors: Taylor Michael J. , Calvert David J. , Hobbis Catherine M. 
Published: May 2005

AbstractSpin–spin coupling between 14N and 13C nuclei is observed in NMR spectra of some quaternary ammonium compounds, including a series of heterocyclic cations. 1J values are in the range 2.2–4.2 Hz. Instances of coupling through two and three bonds are also reported and these are correlated with 13C chemical shift data for the structures concerned.
Carbon‐13 NMR spectra of 1,6‐bis derivatives of hexa‐2,4‐diynes
Authors: Majumdar K. C. , De R. N. , Sen B. K. , Banerji A. , Mitra A. K. 
Published: May 2005

Abstract13C NMR data for 1,6‐bis derivatives of hexa‐2,4‐diynes are reported. Introduction of a sulphone or sulphoxide moiety at C‐1, C‐6 in place of sulphide, ether or amino groups caused a 6–7 ppm upfield shift (β effect) for the C‐2, C‐5 carbons and a 3–4 ppm downfield shift (y effect) for the C‐3, C‐4 carbons.
Stereochemical factors determining the effects of glycosylation on the 13C chemical shifts in carbohydrates
Authors: Shashkov Alexander S. , Lipkind Grigory M. , Knirel Yuriy A. , Kochetkov Nikolay K. 
Published: May 2005

AbstractBasic stereochemical factors have been revealed which affect the 13C chemical shifts in glycosides with a chiral cyclohexane‐type aglycone and in disaccharides with a pyranosidic aglycone. The effects of glycosylation depend on the configuration of the anomeric centre of the glycosylating sugar residue (glycone) and on the relative absolute configuration of the glycone and aglycone. When at least one of the carbons of the aglycone, adjacent to the glycosylated carbon, bears an equatorial proton, this dependence is well accounted for by a strengthening or weakening of the spatial interaction between the protons of the glycone and aglycone, caused by a change in the conformation around the glycosidic linkage. Regularities in the glycosylation effects for disaccharides are generalized for various modes of substitution and different general configurations of the pyranosidic aglycones. Simple rules have been formulated for the prediction of the magnitudes of the glycosylation effects which can be used for the determination of some unknown structural elements in glycosides and disaccharides, in particular the absolute configuration of one of the constituent sugars.
Compounds with bridgehead nitrogen. 57—NMR spectra and stereochemistry of protonated perhydrooxazolo [3,4‐a]pyridines, perhydropyrido[1,2‐c] [1,3] oxazine and perhydropyrido[1,2‐c] [1,3]oxazepine
Authors: Crabb Trevor A. , Trethewey Andrew N. 
Published: May 2005

AbstractProtonation of perhydrooxazolo[3,4‐a]pyridine, perhydropyrido[1,2‐c][1,3]oxazine and perhydropyrido[1,2‐c][1,3]oxazepine by hydrogen chloride gas in diethyl ether gave mixtures of trans‐ and cis‐fused hydrochlorides containing 28, 75 and 79% of the trans‐fused salts, respectively, which compare with free base equilibria containing 68, 90 and 74% trans‐fused conformers. The cis‐fused salts from perhydrooxazolo[3,4‐a]pyridine existed in solution (CDCI3, 298 K) as an equilibrium containing 55% O‐inside cis‐ and 17% O‐outside cis‐fused conformers. Similar mixtures, but with smaller percentages of cis‐fused salts, were formed in D2ODCI.
Pseudohalogen chemistry. IX—Substituent constants (Z) for the isothiocyanato group in the estimation of the chemical shifts of vinyl protons inα,β‐unsaturated isothiocyanates
Authors: Guy Robert G. 
Published: May 2005

AbstractSubstituent constants for the isothiocyanato group (Z 0.92, Z 0.01 and Z −0.22) were derived by an additivity procedure, and shown to reproduce the chemical shifts of vinyl protons in a wide variety of α,β‐unsaturated isothiocyanates with an accuracy of ±0.30 ppm in 92% of the cases studied. Deviations are discussed in terms of the steric and field effects of the substituents involved.
Structural studies on some mesoionic compounds using nitrogen NMR
Authors: Jazwinski J. , Stefaniak L. , Webb G. A. 
Published: May 2005

Abstract1H, 13C, 14N and 15N NMR data are reported for two 1,2,3,4‐oxatriazolium‐5‐thiolates and for two 1,2,3,4‐thiatriazolium‐5‐olates. It is demonstrated that nitrogen NMR is the most sensitive technique for determining the structures of these mesoionic compounds; of particular significance is the N‐2 chemical shift, which distinguishes between the presences of either oxygen or sulphur in position 1. Cyclic structures are confirmed for these compounds on the basis of the nitrogen chemical shifts.
13C1H shift correlation with full 1H1H decoupling. II—Further significant improvements in resolution and sensitivity
Authors: Reynolds William F. , McLean Stewart , Perpick‐Dumont Marion , Enríquez Raúl G. 
Published: May 2005

AbstractIn previous work a modified COLOC sequence combined with a selective BIRD pulse which allows one to obtain one‐bond 13C1H shift‐correlated spectra with full 1H1H decoupling and good (ca 15 Hz)f1 resolution, in addition to improved sensitivity over earlier sequences measured under the same conditions, was developed. In this paper it is demonstrated that a further modification of this sequence to allow the pair of 1H and 13C 180° pulses to traverse the entire fixed evolution period allows excellent (ca 7–8 Hz) f1 resolution plus a further increase in sensitivity (in the same time) of almost √2. Factors contributing to the sensitivity advantages relative to other sequences were examined. Whereas some artifacts are noted for tightly coupled CH2 groups, these may actually aid in the accurate determination of very small chemical shift differences. The precision of measurement of 1H chemical shifts is ca 1 Hz.
Relaxation of platinum‐195 in tetracyanoplatinate(II) and hexacyanoplatinate(IV) in aqueous solutions
Authors: Wasylishen Roderick E. , Britten James F. 
Published: May 2005

AbstractThe mechanism of 195Pt spin–lattice relaxation in aqueous solutions of Pt(CN)− and − has been elucidated from variable‐temperature T1 measurements at 4.70 and 8.48 T. For Pt(CN)− both the chemical shielding anisotropy and spin rotation mechanisms are important; for Pt(CN)− the spin rotation mechanism completely dominates. The value of Δσ obtained for Pt(CN)− is 2350 ppm, which is in excellent agreement with the value previously measured for the tetracyanoplatinate(II) ion in a variety of salts in the solid state.
Determination of the 18‐α/18‐β configuration of pentacyclic triterpenes. A multivariate data‐analytical approach
Authors: Grahn Hans , Masino Charles J. , Nordén Bo , Edlund Ulf 
Published: May 2005

AbstractIt is shown that by using a multivariate statistical approach the analysis of the 13C chemical shifts of variously substituted 18‐α/18‐β pentacyclic triterpenes can be significantly simplified. By examination of the components that result from a principal components data analysis, it is possible to separate configurational information from substituent induced changes. New structures can be predicted from the obtained model. The present approach minimizes the risk from incorrect assignments, or other errors, which are associated with large data tables.
13C NMR spectra of substituted carbazoles and azacarbazoles (β‐carbolines)
Authors: Erra‐Balsells Rosa 
Published: May 2005

Abstract13C NMR spectra of a series of derivatives of carbazole and azacarbazole (norharmane or 9H‐Pyrido [3,4‐b]indole) are reported. The dependence of 1H and 13C shieldings on molecular geometry is discussed briefly.
1H and 13C NMR spectral studies of some biquinoline derivatives and a re‐investigation of the reaction of quinoline with sodium
Authors: Osborne Alan G. , Green Richard , Sadler Ian H. , Reed David 
Published: May 2005

AbstractThe 360 MHz 1H and 15 MHz 13C NMR spectra of 2, 2′‐biquinoline, 2,3′‐biquinoline and 6,6′‐dimethyl‐2,3′‐biquinoline are presented and assigned. The diamagnetic anisotropic effect of the neighbouring aromatic ring (Dc) and the electrostatic field effect of the nitrogen lone pair (DN) result in characteristic deshielding effects in the 1H NMR spectra of these compounds. The characteristic chemical shift differences (ΔH and Δc) between nuclei at the corresponding position but on different rings is proposed as an additional assignment aid for the 1H and 13C NMR spectra of unsymmetric biaryls and biheteroaryls. The reaction of quinoline and of 6‐methylquinoline with sodium gives the 2,3′‐biquinoline.