bluuebunny/crossref_metadata_2025_split huggingface dataset:
EPR and ENDOR study of chiral nitroxides
Authors: Stegmann Hartmut B. , Schaber Frank‐Martin , Schuler Paul , Scheffler Klaus 
Published: May 2005

AbstractRacemic and achiral alkyl aryl nitroxides were examined at various temperatures. The restricted rotation of the aminoxyl substituents was indicated both by the β‐proton coupling constants and by the inequivalence of the aromatic ortho protons. These results are interpreted by the presence of two different rotamers which may lead to two splitting constants for the β‐proton. The capability for inter‐ and intra‐molecular hydrogen bond formation in the nitroxides investigated was demonstrated. However, complexes consisting of chiral radicals and chiral auxiliaries do not show hyperfine structures which unambiguously indicate diastereomeric species. Therefore, hydrogen bonding between chiral molecules is not sufficient for chiral recognition if an alteration of the hyperconjugation angle does not occur. Simple steric interactions can result in the doubling of the β‐proton coupling constant, independently of diastereomeric complex formation.
31P NMR enantiomeric purity determination of free 1‐aminoalkylphosphonic acids via their diastereoisomeric Pd(II) complexes
Authors: Głowacki Zdzisław , Topolski Marek , Matczak‐Jon Ewa , Hoffmann Maria 
Published: May 2005

AbstractA convenient 31P NMR method for determining the enantiomeric excess of free 1‐aminoalkylphosphonic acids is presented. It was found by NMR that the interaction of PdII ions with 1‐aminophosphonate ligands (L) yields, in a non‐diastereoselective manner, diastereoisomeric chelate pairs (PdL2) observable in alkaline D2O solutions. The chelate complexes give two peaks in the 31P NMR spectra; one corresponds to the chiral species e (both ligands are R or S enantiomers) and the second to the meso forms (R and S ligands). The shapes of these peaks and the differences in the chemical shifts for the species (Δδ) depend on the temperature and the resonance frequency, typical for a dynamic process. Under the experimental conditions used (273–293 K and 40.48 or 121.5 MHz) Δδ values in the range 0.03–0.18 ppm were obseved. The separation of the 31P NMR signals of eight of the ten investigated racemic acids allowed the determination of the enantiomeric purity. The measured enantiomeric excess of an enantiomerically enriched sample of 1‐aminobenzylphosphonic acid (prepared by weighing) was in excellent agreement with the expected value.
Pseudolaric acid B: NMR assignments, conformational analysis and cytotoxicity
Authors: Hamburger Matthias O. , Shieh Hui‐Ling , Zhou Bing‐Nan , Pezzuto John M. , Cordell Geoffrey A. 
Published: May 2005

AbstractThe proton and carbon spectra for the fertility‐regulating agent, pseudolaric acid B (1), have been assigned using a combination of one‐ and two‐dimensional NMR spectroscopic techniques. NOE difference measurements revealed an unexpected conformation of the molecule, which could only be explained by a strained conformation of the six‐membered lactone ring. Molecular forcefield calculations confirmed the presence of a low‐energy conformer having the lactone ring in a half‐planar conformation. The solution conformation is closely related to the solid‐state conformation. Evaluation in a broad range of human cell lines established that 1 is a general cytotoxic agent.
29Si and 13C NMR spectra of alkenyl‐ and alkynyl‐trimethylsilanes
Authors: Al‐Hassan Mohammed I. , Al‐Najjar Ibrahim M. , Al‐Oraify Ibrahim M. 
Published: May 2005

Abstract29Si and 13C chemical shifts in substituted alkenyl‐ and alkynyl‐trimethylsilanes have been recorded and assigned. The 13C NMR study of R‐alkynyltrimethylsilanes gave new evidence for pπ‐dπ bonding or an equivalent interaction between the bonded carbon and silicon atoms. In addition, the 29Si and 13C NMR spectra of XC6H4SiMe3 [X = p‐CH3, p‐CH3O, m‐CH3O, H] were recorded, assigned and compared with those of the above‐mentioned compounds.
Single‐crystal electron‐spin resonance study of the 4‐phenyl‐1,2,3,5‐dithiadiazolyl radical
Authors: Lee F. L. , Preston K. F. , Williams A. J. , Sutcliffe L. H. , Banister A. J. , Wait S. T. 
Published: May 2005

AbstractSingle crystals of 4‐phenyl‐1,2,3,5‐dithiadiazolium trithiatriazinide magnified image, prepared by the reduction of S5N5+AlCl4− in SO2 with magnified image, contain a trace paramagnetic impurity which is shown by EPR spectroscopy to be the dithiadiazolyl free radical magnified image. The g and 14N hyperfine tensors of the radical were deduced from measurements made throughout three mutually orthogonal planes of crystallographically aligned specimens: g = (2.0011, 2.0075, 2.0197); 14N(2) = (37.1, 11.3, 3.4 MHz.). Within experimental error, the two nitrogen hyperfine interaction tensors are collinear and have their maximum principal value aligned parallel to gmin and perpendicular to the plane of the host cation. The results are interpreted in terms of a planar π‐radical which substitutes for the planar host cation, and which has considerable unpaired spin density in N(2px) atomic orbitals directed perpendicular to the heterocyclic ring.
13C NMR chemical shifts of the carbon atoms of the methoxymethyl group of di‐ortho‐substituted aromatic methoxymethyl ethers
Authors: Kaufman Teodoro S. , Sindelar Robert D. , Jürgens Alex R. 
Published: May 2005

AbstractComplete 13C spectral assignments of 28 aromatic methoxymethyl ethers bearing different substituents and substitution patterns were made. While meta‐, para‐ or mono‐ortho‐substitution did not significantly affect the 13C resonances of the carbon atoms of the methoxymethyl group, di‐ortho‐substitution produced the deshielding of both carbons. This effect was more pronounced on the methylene carbon atom.
Carbon‐13 NMR chemical shift assignment of neoflavonoids
Authors: Delle Monache Giuliano , Messana Irene , Botta Bruno , Gács‐Baitz Eszter 
Published: May 2005

AbstractThe 13C NMR resonances of some 5,7‐dihydroxy‐ and 5,7‐dimethoxy‐4‐arylcoumarins were assigned by two‐dimensional NMR experiments (HETCOR and LONG‐RANGE HETCOR) on some key compounds.
Natural abundance one‐bond 13C13C coupling constants and unambiguous assignments of 13C NMR chemical shifts of dithieno[b,d]pyridines; a multivariate data analysis
Authors: Gronowitz Salo , Hörnfeldt Anna‐Britta , Yang Youhua , Edlund Ulf , Eliasson Bertil , Johnels Dan 
Published: May 2005

AbstractThe one‐bond 13C13C coupling constants (1JCC) in all nine possible dithieno[b,d]pyridines were measured at natural isotope abundance by using the INADEQUATE pulse sequence technique. The unambiguous assignments of the 13C NMR shifts of these compounds are also reported. Assignments are based on proton decoupled 13C spectra, heteronuclear correlation spectra (HETCOR) and 1D‐INADEQUATE 13C NMR spectroscopy. The effect of the fusion pattern and the influence of the heteroatoms in the ring skeleton on the NMR parameters are discussed. By a multivariate principal components data analysis, it was shown that the magnitude of 1J(CC) of the pyridine subunit could be satisfactorily predicted from shift data, the azomethine CH coupling constant and MNDO bond orders. The last parameter gave only a minor contribution to the coupling variability.
Empirical computation of 13C NMR chemical shifts
Authors: Jaime Carlos 
Published: May 2005

AbstractAn equation correlating 13C NMR chemical shifts and the global van der Waals energy of the carbon atoms (rms deviation δ ≤ 2.6 ppm) in aliphatic hydrocarbons, alcohols and chlorinated derivatives was derived. Molecular mechanics calculations have been used to determine the global van der Waals energy.
Sign inversion of 1J(207Pb13C) coupling constants and correlations between 1J(207Pb13C) and 1J(119Sn13C) values for comparable lead and tin compounds
Authors: Wrackmeyer Bernd , Horchler Klaus 
Published: May 2005

AbstractRelative signs of 1J(207Pb13C) and 2J(207Pb1H) were determined for numerous methyllead derivatives by observing the 207Pb satellites in two‐dimensional (2D) 13C/1H heteroscalar correlated NMR spectra. The compounds studied include the species [R3Pb]Li (R = Me, 1a, Et 1b), Me3PbSiMe3 (2), [Me3PbBH3]Li, several alkenyltri‐methyllead compounds and some heterocyclics. Together with the linear correlation between 1J(207Pb13CMe) and 1J(119Sn13CMe) for the corresponding tin compounds, this enables the prediction of the absolute sign of 1J(207Pb13CMe). An analogous linear correlation 1J(207Pb13CC=)/1J(119Sn13CC=) exists which explains some apparently anomalous values reported in the literature, e.g. for [Ph3Pb]Li and for an intramolecular‐base‐stabilized plumbylene. The two coupling constants, 1J(207Pb13CMe), for the Me2Pb group in a 2,5‐dihydro‐1,2,5‐azoniaplumbaboratole are of opposite sign, giving the first example of this type of behaviour for any dimethyl element fragment. In the case of 2 the negative sign of 1J(207Pb29Si) [reduced coupling constant 1K(207Pb29Si) > 0] has been deduced from the tilt of the 207Pb satellites in the 2D 29Si/1H heteroscalar correlated NMR spectrum. A positive sign of 1J(207Pb11B) follows from the consistent trend observed for the reduced coupling constants 1K(M11B) and 1K(M13C) (M = 13C, 29Si, 119Sn, 207Pb) in the series of compounds [Me3MBH3]Li and Me4M, respectively.
Selective excitation of a single CSA side‐band family and a complementary experiment for discriminating CSA‐averaged resonances
Authors: Boudot D. , Canet D. , Tekely P. , Brondeau J. 
Published: May 2005

AbstractThe DANTE‐Z pulse train [(θ)x‐τ‐(θ)x‐τ]n (π/2) (Acq)±, applied to solid‐state samples in an asynchronous manner with respect to the rotor period of the magic‐angle spinning, is able to extract the spectrum of a single CSA (chemical shift anisotropy) side‐band family without any intensity alteration. The effects of such a selectivity sequence is described by means of a phenomenological approach. A related method, based on selective destruction of magnetization via T2 processes, is proposed for retaining only those resonances for which CSA effects are totally averaged out by magic‐angle sample spinning.
Deuterium isotope effects and bonding in carbonylvanadium complexes
Authors: Rehder Dieter , Hoch Martin , Jameson Cynthia J. 
Published: May 2005

AbstractThe effects of one‐bond and two‐bond 2H, 13CO and C18O isotope shifts on 51V shielding in various carbonyl–Cp–vanadium complexes (Cp = n5‐cyclopentadienyl) are reported and discussed with respect to the sensitivity of 51V shifts to bond extensions, and the rovibrationally averaged values of such bond extensions. These isotope effects provide some insight into the bonding situation in these complexes. It is shown that the rate‐determining step in the reaction between V(CO)6 and C5H5D, which leads to CpV(CO)4, is not subject to a kinetic isotope effect. The deuterium solvent isotope effects on 51V shielding in [V(CO)6]‐ and [VO4]3‐ are also investigated.
Tetrahedral, chelated, silver(I) diphosphine complexes. Rapid measurements of chemical shifts and couplings by two‐dimensional 31P–{109Ag} NMR spectroscopy
Authors: Berners‐Price Susan J. , Sadler Peter J. , Brevard Christian 
Published: May 2005

AbstractThe 109Ag NMR spectrum of [Ag(Ph2PCHCHPPh2)2]NO3, a complex with antimicrobial and antitumour activity, was obtained using a retro‐INEPT two‐dimensional 31P–{109Ag} pulse sequence. This allowed the measurement of the 31P and 109Ag chemical shifts and the 1J(109Ag,31P) coupling constant in a single 2 h experiment and offered a considerable signal‐to‐noise gain compared with 109Ag–{31P} INEPT measurements.
Assignment of 13C NMR spectra of multisubstituted aromatic compounds using a combination of extended DEPT and COLOC illustrated through the total assignment of SR2640
Authors: Rastrup‐Andersen Niels , Aagaard Grethe 
Published: May 2005

AbstractThe combination of Extended DEPT and COLOC was found to be a good alternative to the more time‐ and sample‐consuming INADEQUATE technique for assigning the 13C NMR spectra of multi‐substituted aromatic compounds. The use of the method is illustrated by spectra of the leukotriene D4/E4 antagonist SR2640 {2‐[3′‐(2″‐quinolylmethoxy)phenyl]aminobenzoic acid} as the potassium salt. Total assignments of the 1H and 13C NMR spectra are given.
Complete 13C and 1H NMR assignments for a series of aromatic C‐ring derivatives of dehydroabietic acid
Authors: Jurgens Alex R. , McChesney James D. 
Published: May 2005

AbstractComplete 13C and 1H NMR spectral assignments for a series of derivatives of the naturally occurring C‐ring aromatic diterpene resin acid dehydroabietic acid have been made. The use of a combination of 1D and 2D NMR techniques allowed mostly unambiguous assignments of all 13C resonances. 1H resonances were also assigned.
Substituent effects on the 13C NMR chemical shifts of 1‐hydroxyalkylphosphonic acids
Authors: Glowacki Zdzisław , Hoffmann Maria 
Published: May 2005

Abstract13C chemical shifts and 31P,13C coupling constants are reported for nine 1‐hydroxyalkylphosphonic and two additional phosphonic acids. The α‐substituent‐induced chemical shifts (α‐SCS) of the phosphonate group were calculated and their non‐additivity was observed. Good linear correlations exist between the chemical shifts and also between the α‐SCS parameters of 1‐hydroxyalkylphosphonic acids and the respective values of analogously constituted 1‐aminoalkylphosphonic acids.
13C NMR chemical shifts and substituent effects transmission in 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes
Authors: Gandhi R. P. , Ishar M. P. S. , Kumar Sudhir 
Published: May 2005

Abstract13C NMR chemical shifts were determined for all carbons in a number of 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes [aryl = C6H5, C6H4CH3‐p, C6H4F‐p, C6H4Cl‐p, C6H4Br‐p, C6H4CN‐p, C6H4NO2‐p, C6H4OCH3‐p, C6H3(OCH3)2‐m, p and α‐furyl]. Substituent chemical shift (Δδ13C) values for C‐1, C‐3, C‐4, C‐5, C‐6, C‐1′, C‐2′, C‐3′ and C‐4′,8′ were correlated with various Hammett parameters by singleparameter analysis. The correlations revealed that the substituent effects are transmitted across three π‐bonds in conjugation with the aryl ring. Dual‐substituent‐parameter treatment of the substituent chemical shifts revealed that resonance plays a major role in the substituent effect transmission. Hammett parameters were also derived for the α‐furyl substituent.
13C NMR of coumarins. IV—Furanocoumarins
Authors: Macias F. A. , Massanet G. M. , Rodriguez‐Luis F. , Salvá J. 
Published: May 2005

Abstract13C NMR data for several linear furanocoumarins are reported. The β, γsyn and δ effects of a 5‐oxygenated function on the coumarinic skeleton were measured. A spectroscopic criterion for distinguishing between C‐5 and C‐8 oxygenated, between C‐5 oxygenated, C‐8 alkylated and C‐5 alkylated, C‐8 oxygenated linear furanocoumarins and between C‐5 oxygenated linear or angular furanocoumarins is proposed.
NMR spectroscopic identification of (1S, 4R, 6R)‐ and (1S, 4R, 6S)‐1,3,3‐trimethyl‐2‐oxo‐6‐(2‐oxopropyl)bicyclo[2.2.2]octane, key intermediates towards the total synthesis of (+)‐norpatchoulenol
Authors: Liu Hsing‐Jang , Ralitsch Milan 
Published: May 2005

AbstractHigh‐field NMR studies of (1S, 4R, 6R)‐ and (1S, 4R, 6S)‐1,3,3‐trimethyl‐2‐oxo‐6‐(2‐oxopropyl)bicyclo[2.2.2]octane were carried out by one‐ and two‐dimensional methods. The stereochemical aspects of these molecules were studied through the application of the nuclear Overhauser effect and stereospecific coupling constants. Unambiguous 1H and 13C chemical shift assignments have been made on the basis of two‐dimensional homonuclear (1H–1H) and heteronuclear (1H–13C) correlation spectroscopy, APT, INAPT and broad‐band proton decoupling experiments.
Dependence of 13C NMR methoxy substituent chemical shift values on π‐bond orders of fused aromatic compounds
Authors: Joseph‐Nathan Pedro , García‐Martínez Cirilo , Morales‐Ríos Martha S. 
Published: May 2005

AbstractThe substituent chemical shift values induced by the methoxy group at the two ortho positions of aromatic compounds which include naphthalenes, quinolines, indoles, coumarins, flavones and benzofurans were linearly correlated with π‐bond orders, affording the equation Δδortho(13C) = ‐98.68Pπ + 50.38 (correlation coefficient = 0.929; root mean square error = 1.95 ppm) when 40 pairs of values are considered. Elimination of six points corresponding to ring‐junction quaternary carbons improves the correlation coefficient to 0.961 (root mean square error = 1.4 ppm) for the equation Δδortho(13C) = ‐126.85Pπ + 69.66.
Sulphur‐33 and oxygen‐17 NMR studies of sulpholane in acetic acid and related solvents
Authors: Ali Ahmed A. M. , Harris Robin K. , Belton Peter S. 
Published: May 2005

AbstractSulphur‐33 NMR spectra were obtained for sulpholane in acetic acid, trifluoroacetic acid, methyl acetate and methyl trifluoroacetate over the entire solution range and at a variety of temperatures. Oxygen‐17 NMR spectra were recorded for both components of each solution. The line width and chemical shift data are discussed in terms of molecular interactions and viscosity variations. Some variable‐temperature measurements are included, as are some values of 13C spin‐lattice relaxation times. It is concluded that there is an interaction, probably protonation, between sulpholane and trifluoroacetic acid, although occurring to only a small extent, which is not shown by the other solutions. The 33S and 17O line widths of sulpholane are peculiarly sensitive to the interaction.
15N and 13C NMR study of acylated hydrazines. The instability of trifluoroacethydrazide in the solid state
Authors: Fritz Hans , Kristinsson Haukur , Mollenkopf Max , Winkler Tammo 
Published: May 2005

AbstractTrifluoroacethydrazide is unstable even in the solid state with respect to hydrazonium N,N′‐ditrifluoroacetyl hydrazinate, as shown by 15N and 13C NMR spectroscopy. The 1H, 13C and 15N NMR data and rotamer distributions of formyl‐, acet‐ and trifluoroacet‐hydrazide and of N,N′‐diformyl‐, N,N′‐diacetyl‐ and N,N′‐ditrifluoroacetyl‐hydrazine are reported and compared with the results of earlier investigations. A conformational dependence is observed for 1J(NH) and 2J(NH) in the formylhydrazides and of 1J(NH), 2J(NH) 3J(NH) in the N,N′‐diformylhydrazines. The conformational dependence of 2J(CH) in formamide, reported in the literature, however, could not be confirmed.
NMR spectra of the porphyrins. 38—Conformational analysis of azacycloheptane and azacyclooctane using a novel cobalt(III) porphyrin shift reagent
Authors: Abraham Raymond J. , Medforth Craig J. 
Published: May 2005

AbstractA novel NMR shift reagent, cobalt(III) meso‐tetraphenylporphyrin (CoTPP) was used to determine the conformations of azacycloheptane and azacyclooctane ligands complexed to the metalloporphyrin. Using the observed ring current shifts and a previously calibrated ring current model, the best agreement between the observed and calculated ring current shifts for azacycloheptane was obtained for a chair conformation, in agreement with previous theoretical and experimental studies on the conformational stability of seven‐membered rings. The ring current shifts for azacyclooctane are best interpreted in terms of a mixture of many conformations. These results suggest that CoTPP may be useful as a probe of other conformationally mobile ligands.
Assignment of C‐2 and C‐4 of zearalenones
Authors: Pathre S. V. , Khadikar P. V. , Mirocha C. J. 
Published: May 2005

AbstractAssignments of the hydroxylated aromatic carbons C‐2 and C‐4 of zearalenone and its derivatives are reported. The C‐2 carbon is more deshielded than C‐4 for zearalenones in which the C‐2 hydroxy group is intramolecularly hydrogen‐bonded to the C‐12 lactone carbonyl.
Use of long‐range 1H, 13C correlation experiments (COLOC) for the assignment of the 13C NMR spectrum of chloroquine and related 4‐aminoquinoline compounds
Authors: Moreau S. , Veignie E. 
Published: May 2005

AbstractThe 13C NMR spectra of chloroquine and related 4‐aminoquinolines have been completely assigned by the use of 1H‐13C correlation sequences based on direct and long‐range J(CH) coupling constants in conjunction with DEPT.
1H and 13C NMR aromatic solvent‐induced shifts of n‐alkanes
Authors: Nikki Kunio 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of a series of n‐alkanes (C5‐C32) were measured in CCl4, CDCl3, C6D6, C6H5Cl and C6D5CD3 and the aromatic solvent‐induced shifts (ASIS) are discussed. The chemical shifts of the inner methylene protons show a steady downfield shift as the carbon number of the n‐alkane increases, while the shifts of the methyl protons are smaller than those of the inner methylene protons in aromatic solvents. The ASIS of the outer carbons are larger than those of the inner carbons up to the sixth carbon from the end. The ASIS of the sixth and further inner carbons of the short chains are larger than those of the long chains. These results suggest that n‐alkanes have a folded structure in aromatic solvents and that the degree of folding increases with increasing chain length.
Intrinsic deuterium isotope effects of deuteriated tert‐butyl groups on the 13C NMR spectra of aromatic compounds
Authors: Balzer Hartmut H. , Berger Stefan 
Published: May 2005

AbstractThe 3Δ‐deuterium isotope effects of partially and fully deuteriated tert‐butyl groups on the 13C NMR spectra of tert‐butylbenzene and derivatives are discussed in detail. It is shown that they correlate with the chemical shift of C‐1 of the aromatic ring. It has been demonstrated that when deuterium is replaced with some other substituents, the SCS values of these substituents show a parallel behaviour to the deuterium isotope effects. It is concluded that, for the compounds studied, deuterium isotope effects and substituent chemical shifts can be described on a common basis.
Two‐dimensional INADEQUATE 13C NMR studies of maleopimaric acid, the diels–alder adduct of levopimaric acid and maleic anhydride, and of abietic acid
Authors: Kruk C. , de Vries N. K. , van der Velden G. 
Published: May 2005

AbstractTwo‐dimensional INADEQUATE 13C NMR was used to establish firmly the carbon‐carbon connectivities present in abietic acid and maleopimaric acid, i.e. the adduct of levopimaric acid and maleic anhydride. This information leads to unambiguous assignments for the 20 and 24 carbon resonances of abietic acid and maleopimaric acid, respectively. Proton‐carbon chemical shift correlation and NOE experiments further revealed the three‐dimensional structure of maleopimaric acid.