bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of heteronuclear dipolar powder patterns due only to directly bonded couplings
Authors: Nakai Toshihito , Terao Takehiko 
Published: May 2005

AbstractA method is proposed which allows a simple Pake doublet due only to the directly bonded CH pair to be obtained by measuring the local field at the position adjacent to a 13C nucleus under proton homonuclear decoupling. This approach allows precise determination of the CH distance even in compounds with high proton density.
13C and 19F nuclear magnetic resonance spectra of multisubstituted methanes
Authors: Takeuchi Yoshio , Itoh Noriaki , Koizumi Toru , Yamagami Chisako , Takeuchi Yoshito 
Published: May 2005

AbstractThe 13C and 19F (when appropriate) chemical shifts of a variety of di‐, tri‐ and tetrasubstituted methanes of the type CH2XCOOEt (I), CHXYCOOEt (II) and CXYZCOOEt (III), where the substituents X, Y and Z are F, Br, OEt, OPh, SEt, SPh and NO2, were determined. The prediction of the observed C‐α chemical shifts of I, II and III based on the simple additivity of substituent effects in monosubstituted methanes [MeX; SCS(IV)] is not satisfactory, although those of I are well correlated with SCS (IV). The C‐α chemical shifts of II and III can be correlated in terms of the multi‐parameter analysis of individual SCS (I), the difference between δ (CH2XCOOEt) and δ (CH3COOEt). The origin of the chemical shifts is discussed. The 19F chemical shifts of I, II and III were also satisfactorily analysed in terms of σI and σ.
Natural abundance 17O NMR spectra of thio analogues of chromanones, chromones, flavanones and flavones
Authors: Duddeck Helmut , Lévai Albert 
Published: May 2005

AbstractThe 17O NMR data of thio analogues of chromanones, chromones, flavanones and flavanones are compared with those of corresponding oxygen analogues. Substituent effects are discussed in terms of steric and electronic interactions and also the conformational behaviour of some substituents and the hetero ring.
Easy implementation of selective INADEQUATE and HCC relay experiments using heteronuclear chemical shift filtering
Authors: Kövér Katalin E. , Uhrin Dušan , Liptaj Tibor , Batta Gyula 
Published: May 2005

AbstractThe application of a chemical shift selective filter in 1D INADEQUATE and HCC relay experiments is proposed. It is demonstrated that highly selective filtering can be the equivalent of low‐power excitations. Applications to the selective detection of carbon–carbon connectivities are presented.
EPR study of pyrrolyl‐1‐oxyl and 3‐pyrrolinyl‐1‐oxyl radicals
Authors: Crayston Joe A. , Kakouris Costas , Walton John C. 
Published: May 2005

AbstractPyrrolyl‐1‐oxyl, 3‐phenylpyrrolyl‐1‐oxyl and a number of deuterium‐substituted derivatives were generated by hydrogen abstraction from the corresponding N‐hydroxypyrroles, and observed by EPR spectroscopy. They were all transient with lifetimes ≤ 10−2 s. The hyperfine splittings showed that unpaired spin was delocalized around the five‐membered ring with significant density at N‐1, C‐3 and C‐4, but very low density at C‐2 and C‐5. N‐Hydroxpyrrole and pyrrolyl‐1‐oxyl were studied by the semi‐empirical AM1 method, and the radical by the INDO method. The transient pyrrolinyl‐1‐oxyl was also generated from the corresponding N‐hydroxypyrroline and observed by EPR spectroscopy.
ESR and ENDOR study of 2,3‐dihydro‐1‐oxo‐1λ4,2,3,5‐thiatriazol‐3‐yl radicals
Authors: Neugebauer Franz A. 
Published: May 2005

AbstractDehydrogenation of 2,5‐dihydro‐1,2,3,5‐thiatriazole 1‐oxides with thermally formed bis(4‐methylphenyl)aminyl generated 2,3‐dihydro‐1‐oxo‐1λ4,2,3,5‐thiatriazol‐3‐yl radicals. ESR, ENDOR and triple resonance studies in combination with 15N labelling yielded the magnitude and assignment of all 1H and 14N hyperfine coupling (HFC) constants. The radicals have a basic five‐π‐electron amidrazon‐2‐yl structure with the highest spin density at N‐2.
Apramycin: Complete 1H and 13C NMR assignments and study of the solution conformation by ROESY measurements
Authors: Szilágyi László , Puzstahelyi Zita Sz. 
Published: May 2005

AbstractComplete and self‐consistent assignments have been achieved, through the concerted use of various 2D techniques, for the 1H and 13C NMR spectra of the free base and protonated forms, respectively, of apramycin (1) in D2O solution. It is shown that J‐relayed dipolar (or J/R) and coherent transfer (HOHAHA) processes in ROESY experiments can hardly be eliminated with spin systems such as that studied here. True ROE cross‐peaks can, nevertheless, be identified by varying the experimental conditions. The solution conformation of 1 has been characterized based on the ROESY data, proton‐proton coupling constants and 13C T1 measurements. The 4‐aminoglucose unit appears to be locked together with the octodiose fragment in a conformation satisfying the requirements of the exo‐anomeric effects around the C‐1"OC‐8′ bond; the 2‐deoxystreptamine unit, on the other hand, enjoys more rotational freedom around the respective glycosidic bond. The undistorted chair conformations of all six‐membered rings in 1, and the overall conformation of the molecule, are totally independent of the pH, i.e. the protonation state of the molecule.
Compounds with bridgehead nitrogen 68—NMR spectra and stereochemistry of perhydropyrido [1,2‐c] [1,3]oxazines
Authors: Crabb Trevor A. , Ingate Simon T. , Nevell Thomas G. 
Published: May 2005

AbstractLow‐temperature 13C NMR spectroscopy shows perhydropyrido [1,2‐c] [1,3]oxazine to adopt a conformational equilibrium in CD2Cl2–CFCl3 solution containing 98% trans fused conformer in equilibrium with 2% O‐outside‐cis fused conformer at 203 K. A similar equilibrium position is adopted by the trans‐(H‐4,H‐4a)‐4‐methylperhydropyrido[1,2‐c][1,3]oxazine, whereas the C‐4 epimer adopts exclusively the trans fused conformation.
119Sn NMR characterization of the series of complex [Pt(SnClxBry)5]3− Anions (x + y = 3) extracted into chloroform using a liquid anion exchanger
Authors: Koch Klaus R. 
Published: May 2005

AbstractIn the presence of excess SnCl2 or SnBr2, 119Sn NMR spectroscopy shows that the complex anions [Pt(SnCl3)5]3− or [Pt(SnBr3)5]3− are exclusively extracted into chloroform containing methyltrioctylammonium chloride or bromide. Significantly, in the presence of even small amounts of chloride ion, halogen scrambling of the [Pt(SnBr3)5]3− complex anion occurs, resulting in a distribution of the [Pt(SnClxBry)5]3− species, all possible isomers of which can be observed in this solvent system at room temperature.
Solvent‐induced variations in nitrogen NMR shieldings of tert‐butyl isocyanide as a probe for solvent polarizability–polarity
Authors: Witanowski Michal , Sicinska Wanda , Webb Graham A. 
Published: May 2005

AbstractThe nitrogen NMR shielding of tert‐butyl isocyanide (1) is shown to be a sensitive probe of solvent polarizability–polarity, since the shielding is demonstrated to be unresponsive to hydrogen bonding effects between 1 and the solvent. The direction of solvent effects observed is explained in terms of the solvaton model, used within the INDO/S–SOS framework. A comparison is made with solvent‐induced nitrogen shielding variations of the corresponding isomeric covalent cyanides.
Nuclear spin relaxation in proteins and models at low temperature
Authors: Marshall Eric A. , Bryant Robert G. 
Published: May 2005

Abstract13C NMR spectra were obtained using cross‐polarization methods at temperatures near 5 K to examine the magnetization transfer spin dynamics and the practicality of routinely making low‐temperature measurements as a means for gaining sensitivity. The magnetization transfer rate between protons and carbon was generally found to be more rapid at 5 K than at room temperature, and the proton and carbon relaxation times in the rotating frame were considerably longer. Both conspire to improve the sensitivity of the cross‐polarization experiment. The limiting factor in the ease of executing the experiment rapidly is the value for the proton spin–lattice relaxation time, which in samples with few methyl groups may become much longer than is common at higher temperatures. However, when the methyl group concentration is high, the proton spin–lattice relaxation rate at 5 K may be in the range of seconds, making the low‐temperature experiment a highly sensitive and practical opportunity.
Carbon‐13 nuclear magnetic resonance. Study of 2‐halopicolines, their N‐oxides and 2‐halo‐4‐nitropicoline N‐oxides
Authors: Puszko Aniela 
Published: May 2005

AbstractThe 13C NMR spectra of 2‐halopicolines, 2‐halopicoline N‐oxides and 2‐halo‐4‐nitropicoline N‐oxides were recorded and their chemical shifts assigned. The influence of the electronic properties of the substituents on the direction of the chemical shifts is discussed.
Investigation of phase‐sensitive 13C‐detected 13C1H shift correlation sequences with partial and full 1H1H decoupling and partial spectral editing
Authors: Carpenter Katharine A. , Reynolds William F. 
Published: May 2005

AbstractSeveral different versions of the 13C‐detected 13C1H shift correlation sequence in phase sensitive mode with partial and full 1H1H decoupling are described and evaluated. As expected, they show sensitivity advantages over their absolute value analogues. Further, it is possible partially to edit the 2D spectra since CH2 peaks are inverted relative to CH and CH3 peaks.
NMR and theoretical investigation of dicylopentadiene derivatives
Authors: Bakke Jan M. , Brænden Jon Erik , Krane Jostein 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of endo‐tricyclo[5.2.1.02,6]deoane (1‐H), endo‐tricyclo[5.2.1.02,6]decan‐2‐ol (1‐OH) and 2‐endo‐tricyclo[5.2.1.02,6]decanyl acetate (1‐OAc) were assigned by the use of 1H1H, 1H13C and 13C13C correlation spectra. The substituent chemical shifts were similar to those observed for the analogous norbornane derivatives.2 The flip angle of the five‐membered ring and the conformational composition were estimated from the vicinal 1H1H coupling constants. The results were compared with those from molecular mechanics calculations (MMPMI) and semi‐empirical molecular orbital calculations (MNDO). The geometries obtained from the NMR data were close to those from the MMPMI calculations, and the calculated and observed energy differences were within ± 2 kJ mol−1 of each other. The endo conformation of the five‐membered ring was found to be most stable for both 1‐OH and 1‐OAc. The MNDO calculation indicated a close to planar five‐membered ring to be the most stable. This result could not be accommodated with the NMR data.
13C, 15N, 29Si and 31P NMR study of N‐trimethylsilylaminophosphorus compounds: Sign determination of coupling constants and application of Hahn‐echo extended pulse sequences
Authors: Wrackmeyer Bernd , Kupče Ēriks , Kehr Gerald , Schiller Jürgen 
Published: May 2005

AbstractN‐Trimethylsilylaminophosphorus compounds containing phosphorus in different oxidation states [P(III) and P(V)] and with different coordination numbers (2, 3 or 4) were studied by 13C, 14N, 29Si and 31P NMR, using a variety of one‐ and two‐dimensional (2D) techniques, including Hahn‐echo extended (HEED) pulse sequences. These techniques were demonstrated by the determination of the signs of all coupling constants involving the 1H, 13C, 15N, 29Si and 31P nuclei in bis(trimethylsilyl)aminodimethylphosphane (1). Appropriate experiments, including inverse 2D 1H{15N} correlations, were performed for the other compounds in order to determine the signs of the coupling constants. A geometric dependence of 2J(31P, N, 29Si) was proved for bis(trimethylsilyl)amino(tert‐butyl)chlorophosphane (2c), where large negative 2J(31P,29Si) and a small positive 2J(31P,29Si) values, indicate syn and anti orientations, respectively, of the NSi bond relative to the phosphorus lone pair of electrons. The HEED pulse sequences allow the rapid determination of isotope‐induced shifts, 1δ15/14N(31P), as shown for 1, derivatives of 1 and 2c.
NMR study of some anthraquinones from rhubarb
Authors: Danielsen Knut , Aksnes Dagfinn W. , Francis George W. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of the anthraquinones physcion, emodin, chrysophanol, aloe‐emodin and rhein were assigned. The previously preferred assignments for C‐2 and C‐4 in physcion were reversed. The NOE technique was used for the assignment of the 1H signals and SEFT and/or heteronuclear decoupling for 13C resonances.
Substituent effects on the 13C NMR spectra of ethyl cis‐ and trans‐2‐(p‐substituted‐phenyl)‐1‐cyclopanecarboxylates
Authors: Kusuyama Yoshiaki , Tokami Kenjiro 
Published: May 2005

Abstract13C NMR spectra were measured for a series of ethyl cis‐ and trans‐2‐(p‐substituted ‐ phenyl) ‐ 1 ‐ cyclopropanecarboxylates. The effects of the para substituents and the geometry on the chemical shifts are discussed.
Total assignment of the 1H and 13C spectra of peridinin
Authors: McLean Stewart , Reynolds William F. , John Lisa M. D. , Tinto Winston F. 
Published: May 2005

AbstractComplete 1H and 13C spectral assignments are reported for peridinin, the major dinoflagellate carotenoid responsible for ‘red tides’ in the ocean. These assignments were made with the aid of HETCOR, FLOCK and COSY 2D spectra and NOE difference spectra.
Improved strategy for sequence‐specific 13C NMR assignments in [d(CGTACGTACG)]2
Authors: Wang Ke Yu , Heffron Gregory J. , Bishop Karl D. , Levy George C. , Garbesi Anna M. , Tondelli Luisa , Medley James H. , Borer Philip N. 
Published: May 2005

Abstract13C resonances of [d(CGTACGTACG)]2 were assigned by heteronuclear multiple quantum coherence and longrange heteronuclear multiple coherence. The maximum likelihood method was used for the sugar regions of the HMQC spectrum, which made it possible to assign unambiguously all the C‐2′ carbons and some of the C‐5′ carbons.
Reorientational dynamics and internal mobility of [Lys8]‐vasopressins by analysis of 13C, 15N and 1H NMR relaxation
Authors: Zieger G. , Sterk H. 
Published: May 2005

AbstractThe dynamic behaviour of [Lys8]‐vasopressin derivatives, especially of N‐Gly‐Gly‐Gly‐[Lys8]‐vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from 13C spin–lattice relaxation times, T1, spin–spin relaxation times, T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co‐workers and the ‘model‐free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108–109 s−1, we observe a faster mobility of the order of 109–1010 s−1 in addition to slow dynamic contributions. The latter can be associated by means of T1, measurements with a motion involving the SS linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from 13C relaxation were corroborated by 15N T1 measurements, performed at the 15N natural abundance level by an INEPT–reverse INEPT method, and by 15N NOE investigations.
Solvent effects on the 1H1H, 1H19F and 19F19F coupling constants of fluorobenzene and 1,2‐difluorobenzene
Authors: Suntioinen Sirpa , Laatikainen Reino 
Published: May 2005

AbstractThe 1H and 19F NMR spectra of fluorobenzene and 1,2‐difluorobenzene were measured in several pure solvents and in binary solvent mixtures to study the solvent dependence of 1H19F and 19F19F coupling constants. The solvents are distinctly divided into two groups on the basis of their hydrogen bonding properties. Most the coupling constants increase with increasing polarity of the solvent within both groups. The 3J(F,H) and 4J(F,H) coupling constants are typically increased by 4‐7% when the solvent is changed from cyclohexane to acetone. For the 5J(F,H) coupling of fluorobenzene the change is as large as 70%.
Carbon‐13 NMR chemical shift substituent effects 8—3‐monosubstituted 2‐methylpropenes
Authors: Rittner Roberto , Braibante Mara E. F. 
Published: May 2005

Abstract13C NMR chemical shifts for some 3‐heterosubstituted 2‐methylpropenes are reported. The α‐methylene chemical shifts show excellent linear correlations with the corresponding data for some substituted carbonyl compounds (propanones, methyl acetates and N,N‐diethylacetamides). Their estimated intramolecular interaction shifts are indicative of electronic interactions between the heteroatom and the ethylenic double bond. The sp2 carbon shifts calculated by Dorman et al.'s method, taking a proposed set of βσ and βπ parameters, are in close agreement with the experimental values. Neither the α‐methylene nor the olefinic carbon chemical shifts correlate well with the usual electronic and steric parameters of the substituents.
Stereochemistry of crown ethers. V.—solution structure and complexational behaviour of dibenzo crown ethers
Authors: Stoss S. , Schroth W. , Kleinpeter E. 
Published: May 2005

AbstractThe preferred conformations and the complexing behaviour of 16‐ and 17‐membered dibenzo crown ethers were studied by means of both NMR spectroscopy and molecular mechanical calculations. Conclusions could be drawn about the stoichiometry and stability of the alkali metal ion corand complexes. The spin–lattice relaxation times of the crown ether carbon atoms and the relevant complexes are discussed with respect to the intramolecular flexibility of these species. The intramolecular reorientations detected are reduced considerably in the alkali metal ion complexes. In the preferred conformers of corands 2, 3 and 6, the molecular mechanical calculations prove that the phenyl rings are positioned in a chair conformation at a twist to each other. The same phenyl rings in the crown ethers 1, 4 and 5 are in a boat conformation. These conformations seem to be important for the optimum complexation of the alkali cations.
195Pt NMR study of (η5‐cyclopentadienyl)trialkylplatinum(IV) complexes
Authors: Boardman Larry D. , Newmark Richard A. 
Published: May 2005

Abstract195Pt NMR data are reported for a series of (η5‐cyclopentadienyl)trialkylplatinum(IV) complexes. Chemical shift differences are rationalized primarily on the basis of substituent electronic properties. Changes in solvent produce relatively modest changes in chemical shift, and the dependence of the chemical shift on temperature and concentration is sufficiently strong to warrant control of these variables for comparative measurements. An improved synthesis of [IPtMe3]4 is also described.
1H NMR and 19F NMR chemical shifts of fluorinated retinals, Schiff bases and protonated Schiff bases
Authors: Colmenares Leticia U. , Liu Robert S. H. 
Published: May 2005

AbstractFluorine‐induced shifts of neighbouring protons were studied by comparing the 1H NMR data of 20 fluorinated retinal isomers and their non‐fluorinated counterparts. Concurrent 19F NMR data of various isomers, analysed with respect to those of the all‐trans fluorinated isomers, showed an interactive effect between the γ‐protons and F. Successful application of the observed trends in 1H NMR and 19F NMR chemical shifts to retinylidene Schiff bases and protonated Schiff bases demonstrates their importance as practical aids in assigning configuration and predicting relative 1H NMR and 19F NMR resonances.
Spectroscopic analysis of 3β‐acetoxy‐8‐hydroxy‐8,11‐epoxy‐8,9‐seco‐6,11‐cyclolanostane‐7,9‐dione
Authors: Fujiwara Fred Y. , Rehder Vera G. , Marsaioli Anita J. 
Published: May 2005

AbstractSpectroscopic analysis of a lanostane derivative, which was synthesized with a view to its application as an intermediate in chiral building block syntheses, is presented together with the conformational analysis of a secolanostane‐7‐8‐9,11‐tetraone.
1H and 13C NMR studies of the proton transfer in complexes of substituted phenols with trimethylamine N‐oxide
Authors: Brycki Bogumil , Brzezinski Bogumil , Zundel Georg , Keil Thomas 
Published: May 2005

AbstractSubstituted phenol–trimethylamine N‐oxide (TMAO) systems were studied. The 1H chemical shift of the hydrogen‐bonded proton first increases with decreasing pKa of the phenols and, after a sharp maximum, it then decreases. Thus, the shielding of the hydrogen‐bonded proton by the O atom of the phenol first decreases, and this proton is most deshielded in the 3,4‐dinitronphenol–TMAO system. With a further decrease in the pKa of the phenol this proton becomes shielded again by the O atom of the TMAO molecule. This behaviour of the 1H NMR signal is in very good agreement with the changes in the shape of the proton potential obtained from IR spectra. In the case of the strongest hydrogen bond, in the 3,4‐dinitrophenol‐TMAO system, the 13C signals are considerably broadened, probably owing to the long lifetime of this bond. Δ14 Values were calculated from the 13C NMR signals, which should also reflect the changes in the nature of the phenol—TMAO hydrogen bonds. A small difference is obtained between the results obtained from the 13C and 1H NMR spectra. This difference is caused by the effects of the substituents on the 13C NMR signals, which are not taken into account in the calculation of the Δ14 values.
15N NMR, 1H NOE difference spectroscopy and conformation of N‐(o‐aminophenyl)‐N′‐alkylureas
Authors: Jean‐Claude Bertrand J. , Just George 
Published: May 2005

AbstractThe 15N NMR spectra of five N‐(o‐aminophenyl)‐N′ substituted ureas and their hydrochloride salts were recorded in DMSO. N‐1 was more shielded in these ureas than in N‐phenyl‐N′‐methylurea. The shifts of N‐3 varied with the substituents. Proton exchanges at N‐3 were observed when the spectra of the hydrochloride salts were recorded. The preferential trans‐trans orientation of the protons with respect to the carbonyl in the ureido group was confirmed by NOE difference spectroscopy. In the solid, the conformation of N(o‐aminophenyl)‐N′‐methylurea, which was determined by x‐ray diffraction, was found to be similar to the suggested conformation in solution; the 15N shifts of this compound in the solid state were determined by 15N cross‐polarization magic angle spinning NMR.
High‐field 1H and 13C NMR spectra of synthetic protostane derivatives: Total assignment by 2D NMR
Authors: Paryzek Zdzislaw , Martynow Jacek , Shimo Tetsuro 
Published: May 2005

AbstractTriterpenes with the protostane skeleton, which are available from biomimetic rearrangements of lanostane derivatives, were analysed by one‐ and two‐dimensional high‐field 1H and 13C NMR spectroscopy. Complete assignments of the proton and carbon signals of 11α‐acetoxy‐3β‐benzoyloxy‐5α.9β‐protost‐13(17)‐ene (4) and of 11α‐acetoxy‐31‐nor‐5α,9β‐protost‐13(17)‐en‐3‐one (5) are presented. The assignments were largely determined using substituent chemical shift and conformational effects and by a combination of DEPT, 1H‐‐1H COSY, 1H‐‐13C HETCOR and XCORFE spectra. Nuclear Overhauser effect and lanthanide‐induced shift experiments were also useful for assignments. The results confirm the structure of 4 proposed previously on the basis of the low‐resolution spectra, and provide evidence for the structure of the new fusidane 5. The effect of methyl substitution at the 4β‐position on the 13C chemical shifts is briefly discussed. The assignment of the sp2 carbon atom signals reported for diacholest‐13(17)‐enes is revised on the basis of the XCORFE experiments.