bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR assignments of brassinosteroids by two‐dimensional techniques
Authors: Ando Tetsu , Aburatani Masakazu , Koseki Nozomu , Asakawa Seiichi , Mouri Takehito , Abe Hiroshi 
Published: May 2005

Abstract1H NMR spectra of eight naturally occurring brassinosteroids, plant hormones with a steroid skeleton, and five synthetic analogues were analysed by COSY and long‐range COSY measurements. Based on the 1H resonances, the 13C signals were assigned by a combination of CH COSY and long‐range CH COSY spectra detecting 13C nuclei, or by HMQC and HMBC spectra detecting 1H nuclei. Although the steroids showed complex 1H signals around 1–2 ppm, the resonances for the two angular methyl groups and the other methyl groups in the side‐chain could be assigned unambiguously and used as a reference point for the other assignments. Strong correlation peaks between the methyl protons and carbons connected with the protons through two or three bonds were observed in the long‐range CH COSY or the HMBC spectra. These spectra provide valuable information for assigning the 13C NMR resonances of this class of compounds.
13C NMR spectroscopic study of diphenyl ether and 28 of its polychlorinated derivatives
Authors: Nevalainen Tapio , Kolehmainen Erkki , Säämänen Marja‐Leena , Kauppinen Reijo 
Published: May 2005

AbstractThe 13C NMR chemical shifts and coupling constants for diphenyl ether and 28 environmentally interesting polychlorinated diphenyl ethers were measured and analysed.
1H, 13C and 19F NMR spectral data for fifteen fluorinated steroids
Authors: Nelson Janis T. , Kurz Lilia J. 
Published: May 2005

AbstractAnalyses of the 1H, 13C and 19F NMR spectra of 15 mono‐, di‐, tri‐ or tetrafluoro‐substituted steroids were carried out by two‐dimensional 1H1H and 1H13C shift correlation experiments.
Assignment of the 1H and 13C NMR spectra of the C21 steroids 12‐β‐O‐acetyltenacigenin A and tenacigenin A by two‐dimensional NMR techniques and computer modeling
Authors: Luo Si‐Qi , Lin Long‐Ze , Cordell Geoffrey A. , Xue Liang , Johnson Michael E. 
Published: May 2005

AbstractStereochemical assignments of the C21 steroids 12‐β‐O‐acetyltenacigenin A and tenacigenin A were performed by use of two‐dimensional phase‐sensitive COSY, ROESY, 1H and 13C shift correlation spectroscopy (HETCOR and FLOCK), and ambiguous assignments were resolved through molecular modeling comparisons. This combination of techniques is applicable for the assignment of the highly overlapped 1H signals of these steroids.
13C and2H NMR studies of the molecular flexibility of phenylethylamine and amphetamine derivatives
Authors: Border Corinne L. , Craik David J. , Shehan B. Philip 
Published: May 2005

AbstractA series of phenylethylamine and amphetamine derivatives were synthesized in order to determine the nature of the internal and overall molecular dynamics in these systems.13C and2H NMR relaxation times were measured. For the latter measurements, compounds specifically deuteriated in the side‐chains were synthesized. The relaxation data were analysed via a computer model incorporating the spectral density function for axially symmetric anisotropic motion. The motion of these molecules was found to be substantially anisotropic, with rotation about the symmetry axis of the molecule being at least twice as fast as rotation normal to the symmetry axis. The results of more complex models of axially symmetric anisotropic molecular motion, involving internal rotation or conic diffusion of the side‐chains, were found to be sensitive to variation of the input data, but the correlation times for internal rotation of the ring—C‐β bond were longer than might have been expected. Similarly, owing to its flexibility, the effective correlation times of atoms in the side‐chain were found to be faster than those of the ring carbons, but did not always decrease along the side chain. Intermolecular interactions or aggregation states in CDCl3may reduce segmental motion of side‐chains. A particular feature of the current study is that it was demonstrated that deuteriation of the side‐chain gives a unique opportunity to determine independently side‐chain correlation times via the quadrupolar relaxation times of the2H nucleus, and to compare these results with those of the carbon atoms. These correlation times were found to be in very good agreement with those obtained from the13C data.
Principal component analysis of the 13C NMR shifts of norbornyl derivatives. II—tetracyclic dodecane derivatives
Authors: Tostes José Glauco Ribeiro , Seidl Peter Rudolf , Leal Kátia Zaccur , Bruns Roy Edward 
Published: May 2005

AbstractPrincipal component analysis is applied to the 13C NMR chemical shifts of 29 tetracyclic dodecane derivatives, the spectra of most of which have been recently assigned. These derivatives are subdivided into three classes: exo‐endo, exo–exo and endo–endo. Only the seven 13C shifts of one of the two norbornyl moieties of these derivatives are used in the construction of the data matrix, the other moiety being considered as a ring substituent. This data treatment allows these 29 systems to become a test system for a previously worked (through principal component analysis) standard or training set of 13C shifts of 55 substituted norbornanes. Only one two‐dimensional principal component projection is necessary for identifying the main structural effects in the chosen norbornyl moiety of the test system, highlighting trends in the 13C data of these test derivatives and confirming their recent 13C spectral assignments.
Interconversion of diastereomeric complexes involved in Rh(I)‐catalyzed asymmetric hydrogenation: A (31P, 31P) EXSY NMR study
Authors: Bircher Hansruedi , Bender Bruce R. , von Philipsborn Wolfgang 
Published: May 2005

AbstractRhodium(I) complexes containing chiral chelating diphosphines, e.g. R,R‐dipamp [(R,R)‐1,2‐bis(o‐methoxy‐phenylphenylphosphino)ethane] or S,S‐chiraphos [(2S,3S)‐bis(diphenylphosphino)butane] and a prochiral olefin, e.g. methyl (Z)‐α‐acetamidocinnamate (mac), form diastereomeric complexes which differ only in which enantiotopic face of the olefin is bound to rhodium and can be observed by 31P NMR. The interconversion of the two diastereomers has been observed with (31P,31P)‐{1H} 2D EXSY techniques for various mixing times, Tm, and in three different solvents (CD2Cl2, CD3OD and CD3COCD3). The results clearly demonstrate that both inter‐ and intramolecular ligand exchange processes are occurring, and that diastereomeric interconversion cannot proceed exclusively by complete mac dissociation followed by readdition to the opposite enantiotopic olefin face. The new results are consistent with previous DANTE NMR experiments. The differing results in CD2Cl2, CD3OD and CD3COCD3 solutions suggest the possibility of solvent involvement in the rate‐limiting step of ligand exchange. The 2D EXSY method appears to be the method of choice for elucidating the qualitative exchange pathway of this complex system.
Measurement of the paramagnetic intramolecular contribution to the spin–lattice relaxation time in a nitroxide‐labelled glucoside
Authors: Cinget Francis , Gagnaire Didier , Houdier Stephan , Vottéro Philippe J. A. 
Published: May 2005

AbstractDoubly labelled 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl‐4‐yl 2′,3′,4′,6′‐tetra‐O‐acetyl‐β‐D‐glucopyranoside, 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl‐4‐yl β‐D‐glucopyranoside and 1′,2′‐O‐[1‐(2,2,6,6,‐tetramethyl‐4‐oxy‐1‐oxylpiperidinyl)ethylidene]‐3′,4′,6′‐tri‐O‐acetyl‐α‐D‐glucopyranose (13C and NO⋅) were used as model compounds to study the paramagnetic intramolecular contribution (1/T1e)intra to the 13C longitudinal relaxation rate caused by the unpaired electron of the nitroxide radical. It is shown that measurement of (1/T1)intra is possible on the assumption that the electron–nucleus dipole–dipole interaction dominates the other terms contributing to 1/T1 in the case of paramagnetic substances, and by extrapolating the experimental value of 1/T1 to infinite dilution.
Studies of cis‐[PtCl2(PPh2nPr) (BzS{O}Bz)] by solid‐state CP/MAS 31P NMR spectroscopy, single‐crystal X‐ray diffraction and X‐ray powder diffraction: Investigation of a question concerning polymorphism versus space group ambiguity
Authors: Davies Julian A. , Dutremez Sylvain G. , Pinkerton A. Alan 
Published: May 2005

AbstractThe 31P CP/MAS NMR spectrum of cis‐[PtCl2(PPh2 nPr)(BzS{O}Bz)] was found to exhibit two central resonances with appropriate couplings to 195Pt, despite the fact that a single‐crystal x‐ray diffraction study indicated that the complex crystallized in the monoclinic space group P21/n with Z = 4, i.e. that there is only a single crystallographically unique phosphorus atom. The possibility that the 21 screw axis was absent (i.e. that the space group was actually Pn) was examined by a reinvestigation of the original x‐ray data, but no definitive evidence for the alternative space group could be obtained. An examination of a bulk sample of cis‐ [PtCl2(PPh2nPr)(BzS{O}Bz)] by x‐ray powder diffraction and comparison of the results with data from the single‐crystal x‐ray diffraction experiment revealed that the crystal selected for diffraction studies was a different polymorph from the bulk of the sample which was used for the 31P CP/MAS NMR measurements. X‐ray powder diffraction is thus shown to provide a valuable bridge between solid‐state CP/MAS NMR measurements and single‐crystal x‐ray diffraction data.
Effect of carbonyl substituents on the barrier to rotation in N‐ethyl‐N‐methylamides
Authors: Bonacorso Helio G. , Caro Miguel S. B. , Zanatta Nilo , Martins Marcos A. P. 
Published: May 2005

AbstractThe barriers to rotation about the C(O)N bond for 13 α‐alkyl‐ and α‐halo‐substituted N‐theyl‐N‐methylamides were determined by 1H NMR spectroscopy at coalescence temperature. Plots of Gibbs free energy (ΔG°) and Gibbs energy of activation (ΔG‡) values against Charton's electronic and steric parameters of the α‐carbonyl groups allows the conclusion that both the isomeric preference and the barrier to rotation about the C(O)N bond of the N‐ethyl‐N‐methylamides depend mainly on the steric effect of the α‐carbonyl group.
13C NMR spectra of a series of 2′,3′,4′‐trimethoxyflavones. Reinvestigation of signal assignment in 13C NMR spectra of flavones
Authors: Wallet J.‐C. , Gaydou E. M. 
Published: May 2005

Abstract13C NMR chemical shifts of a series of 2′,3′,4′‐trimethoxylated flavones are reported. The 13C NMR chemical shifts of 2′,3′, 4′‐trimethoxyflavone was reinvestigated by 2D NMR. It is shown that two signals which were assigned by the lanthanide shift reagent method in an earlier study must be reversed.
Explicit formulae for MQ‐filtered COSY of an arbitrary number of magnetically equivalent sets of spin‐1/2 nuclei
Authors: Shekar S. C. , Krishnan V. V. 
Published: May 2005

AbstractExpressions for the density matrix and the observable spectra are explicitly presented for multiple quantum (MQ) filtered correlation spectroscopy pertaining to weakly coupled spin‐½ nuclei. A feature of most general nature is preserved throughout the calculations, namely arbitrary number of magnetically equivalent sets, with no restriction on the number of spins contained in a given set. The equations have been encoded in a modular fashion into the code PQFCOSY in Fortran language for ease of computation.
Pair‐induced chemical shifts (pairwise corrections) and an additivity scheme for the estimation of aromatic 1H NMR shifts in polysubstituted benzenes with two or more vicinal substituents
Authors: Guy Robert G. 
Published: May 2005

AbstractThe aromatic 1H NMR shifts of ortho‐disubstituted benzenes were used to derive 285 pair‐induced chemical shifts (pairwise corrections) for vicinal pairs of the substituent set (F, Cl, Br, I, NH2, NHCOMe, NO2, OH, OMe, Me, CHO, COMe, CN, Ph). Using these parameters and a simple additivity scheme, 617 ring 1H shifts in polysubstituted benzenes with two or more vicinal substituents were reliably predicted with an average standard deviation of 0.08 ppm.
Conformational behaviour of some trifluoroenaminones by multinuclear magnetic resonance
Authors: Wöjcik Jacek , Domalewski Wojciech , Kamieńska‐Trela Krystyna , Stefaniak Lech , Vdovienko Siergiej I. , Gerus Igor. I. , Gorbunova Marina G. 
Published: May 2005

AbstractThe structures of 4‐N‐methylamino and 4‐N,N‐dimethylamino‐1,1,1‐trifluorobut‐3‐en‐2‐one (1, 2) were solved by means of an analysis of 1H, 1H and 1H, 13C coupling constants. NOE measurements, 13C, 1H heteronuclear correlation and selective decoupling. The spectra of 1 are strongly solvent dependent. Variable‐temperature experiments indicated that in these compounds the double bond character of the CN bond is fairly pronounced and that the p‐electrons from the nitrogen atom are engaged in the conjugated π‐electron system. 14N, 15N, 17O and 19F chemical shifts for 1 are reported.
Reorientational dynamics and internal mobility of the mixed agonist‐antagonist opioid narcotic cyclazocine by 13C NMR relaxation times
Authors: Carbone Domenica , Grassi Antonio , Pappalardo Giuseppe C. , Radics Lajos 
Published: May 2005

AbstractThe motional behaviour of the mixed agonist‐antagonist opioid narcotic cyclazocine (2‐cyclopropylmethyl‐2′‐hydroxy‐5,9‐dimethyl‐6,7‐benzomorphan) as a cationic species (CLZH +) was analysed by 13C NMR spin–lattice relaxation times (T1). Both AM1 and MM2 theoretical calculations were performed to predict the preferred conformations and torsional energetics of CLZH+ in the vapour phase. The analysis of the experimental T1 data (in aqueous solution) was performed by using an analytical model to describe the overall and internal motions of the molecule. The best fit of the relaxation times allowed the detection, in the liquid phase, of effective solute‐solvent interactions and the fully anisotropic diffusive process of the molecule. The motional parameters obtained indicated an increased retational anisotropy of CLZH+ on passing from the gas phase to the solution state. Different activation energies arising from separate solvation effects were found for the motion of the 10‐Me and 11‐Me groups. The fitted energies and transition energies matrix relative to the internal motion of the N‐cyclopropylmethyl group indicated that the preferred conformational states are not isolated and that the overall and internal motions are of the same order of magnitude.
Diazo compounds stabilized, by keto and/or sulphonyl groups. A comparative study by 17O NMR spectroscopy
Authors: Cerioni Giovanni , Culeddu Nicola , Saba Antonio 
Published: May 2005

AbstractComparison of the 17O NMR chemical shifts for the keto and the sulphonyl group when stabilizing the carbanionic centre of aliphatic diazo compounds allowed the exclusion for the sulphonyl group, a stabilizing effect through resonance.
13C NMR data for abieta‐7,13‐diene diterpenoids
Authors: Feliciano A. San , del Corral J. M. Miguel , Gordaliza M. , Salinero M. A. 
Published: May 2005

Abstract13C NMR data for several abieta‐7,13‐diene diterpenoids are reported. The most significant effects caused by the change in the stereochemistry at C‐4 and other structural modifications are discussed.
NMR studies on conformational and N‐configurational interconversion in 3‐methyl derivatives of the non‐narcotic analgesic drug nefopam
Authors: Glaser Robert , Blumenfeld Jeanine , Geresh Shimona 
Published: May 2005

AbstractTwo different N‐configurations and two different eight‐membered ring conformations were found in the diastereomeric crystalline (1R,3S)/(1S,3R)‐ and (1S,3R)/(1S,3S)‐3‐methylnefopam hydrochloride salts. 1H and 13C NMR spectroscopy showed that both crystalline epimers undergo N‐configurational and eight‐membered ring conformational equilibria on dissolution in a solvent (e.g. CD2Cl2). Observation of N‐H proton vicinal coupling in both the solution‐state major and minor species for each epimer signifies slow exchange limit kinetic regimes for N‐configurational interconversion via a prototropic shift‐nitrogen inversion. Since previous studies have shown 2,5‐benzoxazocine ring inversion to be unfavourable, the finding of weighted time‐average vicinal coupling constants for the OCH(CH3)CH2NH(CH3)CH2 moiety is interpreted in terms of a fast exchange limit (and in some cases fast magnetic site exchange broadening) kinetic regime for eight‐membered ring conformational change. For each C‐3 epimer; a quantitative estimation was made for the 2n = 4 solution‐state diastereomeric forms resulting from the two stereogenic elements of N‐configuration and ring conformation. Comparisons were made with the parent nefopam hydrochloride, N‐desmethylnefopam hydrochloride metabolite and the nefopam methiodide quaternary ammonium salt.
Inverse‐detected two‐dimensional NMR experiments on a system undergoing chemical exchange near coalescence
Authors: Robinson Valerie J. , Bain Alex D. 
Published: May 2005

AbstractIn systems undergoing intermediate chemical exchange, observation of carbon NMR signals by standard onedimensional methods is often hampered by severe line broadening accompanied by reduced sensitivity. In contrast, the HMQC inverse‐detected heteronuclear chemical shift correlated experiment detects the 13C satellites of the proton lines. If the proton exchange is fast, the width of the satellites is independent of the intramolecular carbon exchange, and hence the carbons are more efficiently detected. The carbon spectrum of 1‐tert‐butoxycarbonyl‐N‐tert‐butyloctahydro‐1H‐indole‐2‐carboxamide serves to demonstrate this phenomenon. Carbons severely broadened in the 1D experiment appear largely unaffected when detected in the HMQC experiment. A straightforward explanation for this observation is presented together with a preliminary discussion of the carbon (F1) line widths in the HMQC spectra of exchanging systems.
NMR studies on natural all‐trans‐(9′Z,11′Z)‐(3R,3′S,5′R,6′R)‐pyrrhoxanthin, an acetylenic C37‐skeletal nor‐carotenoid butenolide
Authors: Englert Gerhard , Aakermann Torunn , Liaaen‐Jensen Synnøve 
Published: May 2005

AbstractAll‐trans‐(9′Z,11′Z)‐(3R,3′S,5′R,6′R)‐Pyrrhoxanthin was isolated from a natural bloom of dinoflagellates (mainly Ceratium spp.) and submitted to detailed 1H NMR and 13C NMR analysis, including homonuclear COSY (2D), ROESY (1D and 2D), TOCSY (1D) and 1H‐detected one‐bond and multiple‐bond 1H, 13C COSY. All chemical shifts and coupling constants in the 1H NMR spectrum and all carbons in the 13C NMR spectrum were assigned. The result is consistent with the structure, previously deduced, including relative configuration. A recently proposed variant of the ROESY pulse sequence, called T‐ROESY, claimed to suppress undesired TOCSY transfer, provided excellent results free of TOCSY artifacts caused by coherent magnetization transfer via J coupling pathways independent of the choice of the position of the carrier frequency.
Multinuclear 195Pt and 15N magnetic resonance spectroscopic studies of the reaction of K[PtCl3(NH3)] with KI and amines
Authors: Qu Y. , Farrell N. , Valsecchi M. , de Greco L. , Spinelli S. 
Published: May 2005

AbstractReaction of the platinum complex K[PtCl3(NH3)] with NH3 or NH2(CH2)nNH2 in the presence of I− gives the mixed chloroiodoamine complexes cis‐[PtCl3(NH3)2] and [{cis‐Pt(Cl)3(I)(NH3)2}2μNH2(CH2)nNH2], respectively. These findings prompted an examination of the nature of the reaction of K[PtCl3(NH3)] with I− in detail. Rapid displacement of two chlorides to give the trans‐[Pt(I)2Cl(NH3)]− anion is observed with a subsequent slow displacement of the third chloride to give the [PtI3(NH3)]− anion. Concomitant with the formation of the triiodo anion, dimerization occurs, giving the iodo‐bridged compound [PtI2(NH3)]2. Correlation of δ(195Pt) and δ(15N) chemical shifts and 1J(195Pt,15N) coupling constants was made with literature values, allowing a complete set of data for the series [PtXn(NH3)4 − n](2 − n)+ with systematic variation of X (Cl,I) to be presented.
1H and 13C NMR studies of E/Z 2‐hydroxyindolenines
Authors: Morales‐Ríos Martha S. , Bucio M. Alvina , Joseph‐Nathan Pedro 
Published: May 2005

AbstractThe 1H NMR spectra of E/Z 2‐hydroxyindolenines are reported in both CDCl3 and DMSO‐d6 solvents. The data suggest a preferred conformation of the heterocyclic ring, which is slightly distorted from planarity, in agreement with the x‐ray crystallographic data of one of the isomers. The 13C NMR spectra for the Z‐hydroxyindolenines are also described. Substituent effects on E/Z isomerism about the exocyclic CC bond are discussed.
Residual dipolar splittings in, 13C MAS NMR arising from interactions with chlorine nuclei
Authors: Harris Robin K. , Sünnetçioǧlu M. Maral , Cameron Kenneth S. , Riddell Frank G. 
Published: May 2005

AbstractResidual dipolar splittings in 13C cross‐polarization magic‐angle spinning spectra arising from coupling to chlorine nuclei are reported for the three chloroacetanilide isomers, using several spectrometers. At medium to high magnetic field doublets are seen for CCl carbon resonances. Perturbation theory explains the appearance of the spectra qualitatively but is inadequate quantitatively.
Full assignments of proton and carbon signals of picrasidine‐G by 1D and 2D NMR methods
Authors: Liu Jian , Davidson R. Stephen , Howarth Oliver W. 
Published: May 2005

AbstractThe alkaloid picrasidine‐G was isolated from Picrasma quassioides. This alkaloid has previously been reported as a new natural product, but its 13C NMR signals still remain unassigned and some ambiguities remains in the proton assignments. Analysis of the 1H and 13C NMR spectra and 1 D NOE and 2D NMR spectra led to the unambiguous assignment of the 1H and 13C signals of picrasidine‐G.
1H nuclear magnetic resonance studies of the reaction of iron(III) porphyrin cation radical with aryl Grignard reagents
Authors: Chmielewski Piotr J. , Latos‐grażyński Lechoslaw , Rachlewicz Krystyna 
Published: May 2005

AbstractAddition of aryl Grignard reagents to an iron(III) tetraphenylporphyrin π cation radical, [(TPP⋅)FeIIICl] (SbCl6), in dichloromethane solution at 202 K yields a mixture of σ‐phenyl iron(IV) tetraphenylporphyrin, [(TPP)FeIV(Ph)] (SbCl6), and σ‐phenyl iron(III) tetraphenylporphyrin, (TPP)FeIIICl. A σ‐phenyliron(III) complex is also formed by nucleophilic addition to the tetraphenylporphyrin macrocycle accompanied by σ‐phenyl axial coordination. The complexes formed were identified by 1H NMR spectroscopy. A new route for generating σ‐aryl iron(IV) porphyrin species from the iron(III) porphyrin π cation radical was established. The characteristic 1H NMR pattern of the low‐spin iron(III) porphyrin ring modified species reflects its Cs symmetry and includes four upfield‐shifted pyrrole resonances (2.31, −10.40, 20.39 and −20.87 ppm, 202 K) accompanied by a set of σ‐phenyl resonances (ortho, −188.4; p‐H, −102.5; p‐CH3 for σ‐p‐tolyl, 162.3 ppm). Analysis of the paramagnetic shifts of the σ‐phenyl (σ‐p‐tolyl) ligand of the new species indicates a high π spin density consistent with the electronic structure of low‐spin iron(III) and the contribution of a σ‐delocalization mechanism via donation from a filled σ‐phenyl orbital to an empty dz2; orbital. The formation of a low‐spin σ‐phenyliron(III) isoporphyrin or low‐spin σ‐phenyl N‐arylporphyrin is considered. The meso substitution can be accounted for by a mechanism which emphasizes the radical nature of the reaction substrate and involves the formation of σ‐transient forms.