bluuebunny/crossref_metadata_2025_split huggingface dataset:
Unprecedented example of a 3J(13C,11B) through a CCNB linkage
Authors: Atchekzaï Jean , Bonnetot Bernard , Duplan Jean‐Claude , Fenet Bernard , Ferage Bernard , Mongeot Henri 
Published: May 2005

AbstractThe 13C NMR spectra of the tertiary amine‐boron trihalide adducts C6H5CH2N(CH3)2BX3 (X = Cl, Br, I) (I) and (C2H5)3NBCI, (2) show a long‐range 3J(13C,11B) coupling which was observed as an asymmetric quartet and measured as 2.2, 2.3 and 2.3 Hz for 1 (X = Cl, Br, I) and 1.1 Hz for 2.
Dynamic NMR study of the electronic state of heteroaromatics. V—Influence of the counter anion, ortho substituents and the ring heteroatom on the exocyclic C,N rotational barrier of pyrylium and thiopyrylium salts
Authors: Kleinpeter E. , Spitzner R. , Schroth W. 
Published: May 2005

AbstractThe 13C NMR spectra and variable‐temperature 1H NMR spectra of some NR2‐substituted pyrylium and thiopyrylium salts were studied, and the rotational barriers thus obtained about the exocyclic partial CN double bonds are discussed according to their dependence on the counter anion and other structural variations. The counter anion has a negligible influence on the barrier, but substituents on the ring can either strengthen electronically or weaken sterically the mesomerism of the NR2‐heteroaromatic system. The competition between these two effects is readily estimated from the rotational barriers obtained. The pyrylium salts display higher rotational barriers than the identically substituted thiopyrylium salts.
Determination of the pyrrolizidine alkaloids from Senecio jacobaea by 1H and 13C NMR spectroscopy
Authors: Pieters Luc A. C. , Van Zoelen Agnes M. , Vrieling Klaas , Vlietinck Arnold J. 
Published: May 2005

AbstractA method for the determination of the pyrrolizidine alkaloids from Senecio jacobaea (Compositae) by 1H and 13C NMR is presented. 1H NMR is a reliable method for the determination of the total alkaloid level. 13C NMR appears to be a suitable method for the determination of the individual alkaloids. The same techniques can also be applied to other plants containing pyrrolizidine alkaloids.
ESR evidence for the stereospecific spin trapping of 5‐alkyl‐5‐methyl‐1‐pyrroline N‐oxides
Authors: Zhang Yongkang , Xu Guangzhi 
Published: May 2005

AbstractThe ability of ten cyclic nitrones, 5‐alkyl‐5‐methyl‐1‐pyrroline N‐oxides, to trap a variety of short‐lived free radicals has been investigated using ESR spectroscopy. Stereospecific spin trapping by these nitrones has been demonstrated by comparison of the ESR spectra of their adducts with the ESR spectra of the corresponding 5‐alkyl‐5‐methyl‐1‐tetrahydropyrrolyl‐1‐oxyls. Phenyl radical trans addition to these nitrones has also been proved.
13C NMR of coumarins. III—Simple coumarins
Authors: Macias F. A. , Massanet G. M. , Rodríguez‐Luis F. , Salvá J. 
Published: May 2005

Abstract13C NMR data for several simple coumarins are reported. The γsyn effect of a 5‐methoxy substituent on the C‐4 chemical shift was observed and measured. The effects of an 8‐iodo substituent on the chemical shifts of the carbons of the coumarinic skeleton are discussed.
13C relaxation in cyclopentadienyliron dicarbonyl acyl compounds
Authors: Nance Lewis E. , Will H. J. , MacQueen D. Brent , Garrison J. Mark , Nicklaw Jeffrey M. 
Published: May 2005

AbstractT1 values for the protonated carbons of four acyl compounds, all possible combinations of methylpropanoyl and 2‐ethylbutanoyl groups with cyclopentadienyl‐ and methylcyclopentadienyl‐iron dicarbonyl, were determined at ambient temperature. Carbon‐13 T1 ratios for the acyl group relative to the ring system indicate relative differences in motion when obtained in the two solvents, CDCl3 and CD2Cl2. T1 values at −10°C, relative to 24°C, give further insight into motional modes. Carbon‐13 and proton NMR chemical shift values for all compounds and the NOE for one compound are reported.
Relationships between 1H, 13C and 17O NMR chemical shifts and H/D isotope effects on 13C and 17O nuclear shielding in intramolecular hydrogen‐bonded systems
Authors: Liepiņš E. , Petrova M. V. , Gudriniece E. , Pauliņš J. , Kuznetsov S. L. 
Published: May 2005

AbstractThe intramolecular Hbond strength in cis‐enolic forms of β‐diketones was investigated. The correlations between the 1H hydroxyl proton shieldings and the chemical shifts of the 13C and 17O nuclei involved in the chelate ring, and the H/D isotope shifts on the latter resonances, were determined. An increase in the hydrogen bond strength leads to increasing values of H/D isotopic shifts on the 17O resonances. The results obtained are compared with quantum chemical calculations and x‐ray measurements.
Dynamic nuclear magnetic resonance study of intramolecular processes in cyclohexanediaminetetraacetate–metal complexes
Authors: Ba Yong , Song Rui‐Fang , Qiu Zu‐Wen 
Published: May 2005

AbstractThe dynamic NMR (DNMR) of the intramolecular acetate scramblings that occur in Ca(II)‐, Sr(II)–, Ba(II)– and La(III)–cyclohexanediaminetetraacetate complexes has been studied. The working temperature range was extended to 430 K by using a sealed thick‐walled capillary sample tube and new DNMR phenomena were thus observed. Information on activation energy, enthalpy, entropy and the free energy of nitrogen inversion of the chelates was obtained by computer analysis.
Assignment of the 1H, 13C and 15N NMR spectra of methyl β‐D‐glucopyranoside tetranitrate, β‐cellobiose octanitrate and cellulose trinitrate by two‐dimensional homonuclear and heteronuclear 13C1H and 15NOC1H shift correlation spectroscopy
Authors: Axenrod T. , Liang B. , Bulusu S. 
Published: May 2005

AbstractThe unambiguous assignment of all the 1H, 13C and 15N resonance signals in methyl β‐D‐glucopyranoside tetra‐nitrate and β‐cellobiose octanitrate was made using homonuclear and heteronuclear 13C1H and 15NOC1H two‐dimensional shift correlation NMR experiments. Solvent‐induced shifts were used to confirm the 13C1H correlations in β‐cellobiose octanitrate. Based on these observations and selective decoupling experiments, the 15N resonance signals in cellulose trinitrate were tentatively assigned.
NMR study of three heteroyohimbine derivatives from Rauwolfia serpentina: Stereochemical aspects of the two isomers of reserpiline hydrochloride
Authors: De Bruyn André , Zhang Weiguo , Buděšinský Miloš 
Published: May 2005

Abstract1H NMR data for isoreserpiline and tetraphylline and 1H and 13C NMR data for reserpiline hydrochloride are presented. New insights into the 1H NMR coupling constants of the heteroyohimibines provide an easy means of assigning their configuration and conformation, allowing the elucidation of the stereochemical features of the two isomers of reserpiline hydrochloride.
Preparation and structure of cycloalkane‐condensed [1,3]thiazino[3,2‐a] pyrimidinones
Authors: Sohár Pál , Szöke‐Molnár Zsolt , Stájer Géza , Bernáth Gábor 
Published: May 2005

AbstractIsocyanate salts prepared from cis‐2‐amino‐1‐cyclopentane‐ and ‐hexane‐carboxylate and the corresponding trans‐cyclohexane and ‐cyclohexene derivates with KSCN were cyclized to cycloalkane/ene‐condensed 2‐thioxo‐4‐pyrimidinones, which were transformed to tricyclic 1,3‐thiazino[3,2‐a]pyrimidinones by addition of dimethyl acetylenedicarboxylate. The stereo structures of the new compounds were established by IR and 1H and 13C NMR spectroscopy, making use of the signal multiplicities in the proton‐coupled carbon spectra.
13C NMR studies of tautomerism in imidazo[4,5‐c]pyridines
Authors: Barraclough P. , Lindon J. C. , Nobbs M. S. , Williams J. M. 
Published: May 2005

AbstractA detailed analysis of the 13C NMR spectra of the 1‐N‐ and 3‐N‐methyl derivatives of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine, utilizing long‐range couplings and 2D 1H13C correlation experiments, has led to an unambiguous assignment of all carbons. Comparison of these definitive assignments of C‐3a and C‐7a, in particular, with those of the tautomers of 1H‐2‐(2,4‐dimethoxyphenyl)imidazo[4,5‐c]pyridine has permitted confirmation of the predominance of the 1H‐tautomer for the latter. In addition, previous conflicting assignments for 1H‐imidazo[4,5‐c]pyridine and its 3‐N‐methyl derivative are now resolved. Revision of these assignments leads to the conclusion that the 1H‐tautomer of 1H‐imidazo[4,5‐c]pyridine is predominant.
1H and 13C NMR assignments for lanostan‐3β‐ol derivatives: Revised assignments for lanosterol
Authors: Emmons Gary T. , Wilson William K. , Schroepfer Jr George J. 
Published: May 2005

Abstract1H and 13C NMR assignments are presented for 30 oxygenated lanostane derivatives, including lanosterol, dihy‐drolanosterol, 7‐ketolanosterol, agnosterol, 24,25‐epoxylanosterol, 8α,9α‐epoxylanostan‐3β‐ol, three 15‐oxygenated derivatives of lanost‐7‐en‐3β‐ol, lanostane‐3β,7α‐diol, lanostane‐3β,9α‐diol and their acetates. These assignments, which were largely determined by a combination of DEPT, one‐boad and long‐range 13C1H chemical shift correlation and lanthanide‐induced shift experiments, are not dependent on previously reported assignments, several of which were found to be incorrect. 1H and 13C acetylation shifts for lanostan‐3β‐ols were sufficiently invariant among the sterols studied that they were useful for assigning carbons in rings A and B. The acetylation shifts reported for lanostan‐3β‐ols were extended and partially revised.
Solvent effect on the 13C and 15N NMR chemical shifts and rotational barriers in N,1N1‐dimethyl‐and N,1N1‐hexamethylene‐N2 ‐phenylformamidines
Authors: Wawer Iwona 
Published: May 2005

AbstractSolvent‐induced 13C NMR chemical shifts of N1,N1‐dimethyl‐N2‐phenylformamidine can be correlated with the acceptor number of solvents, AN, and also with the π* and α parameters of Kamlet and Taft. No correlation was found for the height of the rotational barrier around the CN1 bond. The self‐association of formamidine and the influence of polar, aprotic solvents cause an increase in ΔG1 of approximately 1 kJ mol−1 whereas, contrary to expectations, the ΔG1 values found in hydrogen‐bonding solvents are smaller than in cyclohexane. The barrier, however, increases with the strength of the hydrogen bond and on protonation. Downfield shifts of the N1 and upfield shifts of the N2 signals were observed in the 15N NMR spectra of formamidine when the strength of the hydrogen bond with the solvent increased.
Isotope effects on the 13C NMR chemical shifts of 5‐substituted indoles: Evidence for electron density dependence on the hydrogen (deuterium) atom
Authors: Morales‐Ríos M. S. , Del Río R. E. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe dependence of the deuterium/hydrogen NMR isotope effects on 13C chemical shift (DHIECS) values on the electron density at the hydrogen (deuterium) atom in a series of para‐like substituted indoles with a partially deuterated NH site, measured as 0.83 M solutions in DMSO‐d6, is established on the basis of a series of correlations relating the isotope shifts with Hammett‐type í parameters, 1H(NH) chemical shifts, 15N chemical shifts and group electronegativity. The sensitivity of the nΔ isotope effects appears to be connected closely with electron redistribution at the 5‐substituent of the carbon atom under consideration.
13C NMR assignment of protonated carbons in d‐type porphyrins
Authors: Timkovich Russell , Bondoc Laureano L. 
Published: May 2005

AbstractThe 13C resonances for all protonated carbons have been observed and assigned for the free base esters derived from the following natural products: heme d, the prosthetic group of the bacterial cytochrome oxidase cytochrome d; heme d1, the prosthetic group of the dissimilatory nitrite reductase cytochrome cd1; and a stable form of sulfheme, the chemically modified prosthetic group from the degradation product of myoglobin known as sul‐fmyoglobin. These partially saturated porphyrins have in common that a heteroatom or atoms has added to a pyrrolic carbon. 13C NMR spectra were obtained on limited amounts of naturally derived samples by proton‐detected heteronuclear correlation spectroscopy.
Accuracy of molecular dynamics obtained by T1ρ measurements on the microsecond time scale in solution
Authors: Wang Yu‐Sen , Ikuta Satoshi 
Published: May 2005

AbstractMeasurements of T1ρ were performed for well characterized systems in which the number and population of exchange sites are known. These systems include the chair‐to‐chair isomerization of cyclohexane‐d11, a two‐site exchange model with equal population, and the cis‐trans isomerization of methyl nitrite, a general two‐site exchange model. The kinetic parameters obtained by T1ρ measurements were compared with other published results, and the predicted and observed chemical shift difference between the two sites at low temperature were more rigorously compared. These comparisons showed that measurements of T1ρ in solution provide a convenient probe of the molecular dynamics in solution on the microsecond time scale.
Use of an internal reference in 13C chemical shift measurements
Authors: de Kowalewski D. G. , de Los Santos C. , Marceca E. 
Published: May 2005

AbstractThe use of the nominal value of the chemical shift of the solvent to calibrate the spectrometer in 13C NMR spectroscopy was found to introduce errors due to the effect which the solute has on the solvent. In addition, hexamethyldisiloxane (HM) is proposed as an internal standard; owing to its high boiling point it is easier to manipulate than tetramethylsilane (TMS) and it is therefore possible to prepare solutions of known concentrations. In order to convert the data obtained with this standard to the TMS scale, the chemical shift of HM was determined in 16 solvents using cyclohexane as external standard in a spherical cell (5% w/w concentration of HM) as a function of the solvent factor g2. Comparing these results with a similar plot obtained previously for TMS by other workers, it is possible to convert one type of data to the other by a simple linear expression.
Side‐band analysis in variable‐angle sample‐spinning (VASS) NMR for the central transition of quadrupolar nuclei (half‐integer spin)
Authors: Amoureux J. P. , Fernandez C. , Lefebvre F. 
Published: May 2005

AbstractVariable‐angle sample‐spinning (VASS) NMR was investigated for the case of limited rotation speed of the spinner. Side‐band intensities and line‐shapes for the central transition of half‐integer quadrupolar spin nuclei were calculated as a function of the parameter \documentclass{article}\pagestyle{empty}\begin{document}$ X = \frac{1}{4}[I(I + 1) - \frac{3}{4}]v_{\rm Q} ^2 (1 + \eta ^2 /3)/v_{\rm L} v_{\rm R}$\end{document}. It is shown that complex sideband patterns can be analysed using a very fast computational program.
13C relaxation and anisotropic molecular reorientation in liquid dibromomethane
Authors: Nance Lewis E. , Nealey Marty R. , Rodriguez A. A. 
Published: May 2005

AbstractAlthough dibromomethane is a simple molecule, little work has been directed toward the analysis of its reorien‐tational motion. This is surprising, since two components of its inertia tensor are nearly degenerate and may, in principle, be treated as a quasi‐symmetric top. The 13C spin–lattice relaxation times and nuclear Overhauser enhancements were measured at various temperatures in the liquid phase. Field‐dependent measurements indicated the presence of the scalar relaxation mechanism. Calculated rotational diffusion constants were found to be in reasonable agreement with values predicted by the J‐diffusion model of inertially controlled reorientation. The results show that scalar coupling of the second kind is an important mechanism for 13C spin–lattice relaxation in this molecule. The data further indicates that dibromomethane may indeed be exhibiting quasi‐symmetric top behavior of this phase.
Method for evaluating the reliability of distances and rotational correlation times deduced from 2D 1H NMR NOESY experiments
Authors: Genest D. , Simorre J. P. 
Published: May 2005

AbstractAn experimental method is proposed which selects from all the inter‐proton distances r determined from two‐dimensional NMR NOESY experiments, those which do not depend on the internal motions of the molecule under investigation. Only these distances are quantitatively reliable for modelling purposes, owing to (1/r6) averaging and the possible correlation between r and the orientation of two protons as a consequence of the molecular Brownian internal dynamics. All the other distances must be used only qualitatively. Two examples of the application of this method to the lipopeptide stendomycin are given.
Carbon‐13 spin–lattice relaxation study on molecular dynamics of some penta‐ and tricarbonylchromium complexes
Authors: Gryff‐Keller Adam , Szczeciński Przemyslaw , Koziel Hanna 
Published: May 2005

AbstractCarbon‐13 spin–lattice relaxation times were measured for some penta‐ and tricarbonylchromium complexes of organic ligands. The chemical shift anisotropy of the carbonyl carbons was estimated to be ca. 500 ppm. The contributions of dipole–dipole and chemical shift anisotropy mechanisms to the overall relaxation were evaluated and used to determine the reorientational parameters for the ligand and carbonylchromium moieties. It seems that the internal rotation rate about the ligand—chromium bond is governed mainly by intermolecular interactions.
Dynamics at the active site of N,N‐bis(2‐fluorophenyl)carbamoyl‐α‐chymotrypsin
Authors: Kairi M. , Gerig J. T. 
Published: May 2005

AbstractN,N‐Bis(2‐fluorophenyl)carbamoyl chloride inactivates the serine protease α‐chymotrypsin by stoichiometric carbamoylation, presumably at the active site serine‐195 residue. At sample temperatures above 25°C fluorine NMR spectra of this enzyme derivative reveal the presence of conformations which are interchanged by processes that have ΔG of about 70 kJ mol−1 as estimated by two independent methods. Fluorine NMR spectra of the protein dissolved in 8 M urea were characterized by shift and relaxation parameters which suggest an unfolded state for the protein but with interconversion kinetics similar to those of the native structure. At sample temperatures below 25°C a second kinetic process becomes apparent in the spectra of both the native and denatured protein, although it was not possible to quantitate the rate of this process. These spectral changes are discussed in terms of the likely conformational properties of the N,N‐bis(2‐fluorophenyl) group attached to the native enzyme and are shown to be consistent with one of the 2‐fluorophenyl rings having a high barrier to rotation, and thus rotating slowly, while the other rotates rapidly. Both rings rotate rapidly in the denatured protein. A form of the modified enzyme which had fluorine NMR characteristics similar to those of the denatured enzyme yet was fairly soluble in 0.05 M sodium chloride solution was detected in samples after extended heating; formation of this species was not readily reversible. Spin‐lattice relaxation times (T1) and 19F{1H} NOE data for the native and denatured modified enzymes are reported.
Two‐path spin–spin coupling in tetrastannacyclohexanes
Authors: Mitchell Terence N. , Faust Rüdiger , Fabisch Bodo , Wickenkamp Roland 
Published: May 2005

AbstractTin‐119 NMR data are presented for thirteen 1,2,4,5‐tetrastannacyclohexanes. The one‐bond tin‐tin coupling constant shows a monotonic decrease with increasing methyl substitution at the ring carbon atoms. In a series of compounds the two‐path couplings 2+4J(SnSn) and 3+3J(SnSn) can be assigned and interpreted on the basis of a sign change for the former coupling. Values of 4J(SnSn) for substituted 2,3,5,6‐tetrastannaheptanes suggest that the magnitude of the four‐bond component of 2+4J(SnSn) in the stannacycles can be considerable.
Study of the self‐association of methylated pyrimidines in aqueous solutions by 1H NMR chemical shifts
Authors: Aradi Ferenc 
Published: May 2005

AbstractThe self‐association of pyrimidine and its methylated derivatives was studied by measuring the concentration‐dependent changes in proton chemical shifts in deuterium oxide at 35°C. The data were analysed by a dimer model with two parameters. The equilibrium constants give an increasing tendency for self‐association within the series pyrimidine (0.091 ° 0.006 l mol−1) < 5‐methylpyrimidine (0.165 ° 0.006 l mol−1) ≈ 4‐methylpyrimidine (0.183 ± 0.005 l mol−1) < 4,6‐dimethylpyrimidine (0.410 ± 0.011 l mol−1), and the values of the dimer shifts suggest a stacking‐like arrangement for the associated molecules.
13C NMR study on linderones and lucidones
Authors: Ng Soon , Lee Hiok‐Huang , Bennett Graham J. 
Published: May 2005

AbstractThe 13C NMR spectra of linderone (1), lucidone (2), methyllinderone (3), methyllucidone (4), demethyllinderone (7), dihydrolinderone (8) and 2‐(1‐hydroxyethylidene)‐4‐methylcyclopent‐4‐ene‐1,3‐dione (9) are reported. The 1H chemical shift data for 1–4 are also reported. Geometric isomers exist in 4, while external tautomers exist in all the other compounds (except 3) through strong intramolecular hydrogen bonding. With the aid of deuterium isotope effects (in 1 and 2), C‐H coupling constants and nuclear Overhauser effects, the 13C NMR spectra are assigned to the external tautomers and the geometric isomers.
Anthraquinone sulphonate as a general‐purpose shift reagent for the NMR analysis of cyclodextrins
Authors: Djedaïni Florence , Perly Bruno 
Published: May 2005

AbstractThe potential use of sodium anthraquinone 2‐sulphonate (ASANA) as a general‐purpose shift reagent for cyclodextrins is reported. It is demonstrated that completely resolved proton NMR spectra are obtained on inclusion of the host in the cavity of β‐and y‐cyclodextrins. The inclusion complexes have been characterized in terms of stoichiometry and association constants.
Nitrogen‐15 NMR, 2D NMR and ESCA characterization of a new stable 6a‐thia(SIV)‐1,6‐diazapentalene
Authors: Weber Lutz , Szargan Rüdiger , Schulze Bärbel , Mühlstädt Manfred 
Published: May 2005

AbstractReaction of 2‐methyl‐3‐thiocyanatocrotonaldehyde with aniline hydrochloride and subsequent addition of dicyclohexylamine afforded a new 6a‐thia(SIV)‐1,6‐diazapentalene. The presence of the NSN bond was verified through the N 1s and S 2p binding energies and the nitrogen‐nitrogen coupling constant in the doubly 15N‐labelled compound, prepared by using [15N]aniline hydrochloride.
Compounds with bridgehead nitrogen. 63—NMR spectra and stereochemistry of perhydropyrido[3,2,1‐j,k][3,1]benzoxazepines
Authors: Crabb Trevor A. , Fallah Asadollah 
Published: May 2005

AbstractThe configurations and conformations of diastereoisomeric 1‐(decahydroquinolin‐8‐yl)butan‐2‐ols and of perhydropyrido[3,2,1‐j,k][3,1]benzoxazepines resulting from ring closure of these compounds with formaldehyde have been assigned by 1H and 13C NMR spectroscopy.
47/49Ti NMR of some titanium compounds
Authors: Berger S. , Bock W. , Marth C. F. , Raguse B. , Reetz M. T. 
Published: May 2005

AbstractThe results of 47/49Ti NMR measurements on 21 organotitanium compounds are reported. A signal could be detected for only about half of the compounds measured. Methyltitanium trichloride is highly deshielded compared with TiCl4.