bluuebunny/crossref_metadata_2025_split huggingface dataset:
Monitoring site‐specific natural hydrogen isotope fractionation using a novel phosphorus‐containing chiral discriminating reagent
Authors: Hägele Gerhard , Boisnière Bruno , Helie Isabelle , Rabiller Claude , Martin Gérard J. , Martin Maryvonne L. 
Published: May 2005

AbstractThe synthesis of a novel chiral discriminating reagent, the ester resulting from the reaction of L‐menthylphenylphosphoryl chloride with ethanol, is reported. This reagent, C, is aimed to differentiate the R and S monodeuterated enantiomers of ethanol, which constitutes an important isotopic probe for mechanistic studies and origin inference of natural products. The proportions of the two P‐epimeric structures, CA and CB, which compose reagent C are directly accessible by 31P NMR. Analysis of 1D and 2D NMR spectra and theoretical simulations enable the 1H and 13C chemical shifts of CA and CB to be determined. The chemical shift differences exhibited by the methylenic hydrogens of the ethoxy moiety in CA and CB are of the order of 0.3 ppm. These large differences can be mainly attributed to ring current effects. Such effects have been estimated using two different methods on the basis of model conformations of the two epimers, CA and CB, deduced from energy minimization in a quantum mechanical approach. The relative signs of the chemical shift differences δR(C)—δS(C) associated with the pro‐R and pro‐S positions in the CA and CB isomers cannot be determined from the proton spectrum. The ring current calculations suggest that δR(C)—δS(C) are of opposite signs in the two P‐epimers. This interpretation, and consequently the conformational analysis, are supported by the 2H NMR study of a chiral discriminating ester prepared from ethanol selectively enriched in deuterium in the pro‐R position by stereospecific exchange reactions involving the enzymatic pair alcohol dehydrogenase–diaphorase. The chiral discriminating reagent, C, was then used for determining the enantiomeric imbalance in ethanol samples obtained from biosynthesis under different conditions, and site‐specific fractionation factors were calculated.
Conformational analysis of cembrenenol: Application of 1H and 13C NMR spectroscopy and of computational methods
Authors: Bigler P. , Bircher H. R. , Müller C. , Gerber P. R. , Gubernator K. 
Published: May 2005

AbstractThe solution structure of the cyclic diterpene cembrenenol was investigated. A strategy for conformational analysis is proposed which is based on computational methods and experiments to determine the structure‐relevant NMR parameters. Computed and experimentally determined steady‐state NOEs were compared in a first step, which served to sort out a few probable conformers. The detailed analysis of homo‐ and hetero‐nuclear coupling information together with NOE data defining local geometries allowed, in a second step, the selection of the most probable conformation. The structure corresponds to the lowest energy structure proposed by computational methods alone. Its ring structure is in excellent agreement with the x‐ray ring structure of the closely related cembrenene.
NMR of terminal oxygen. 6—17O NMR of the SO ‘double bond’: Derivatives of arylsulphinic and arylsulphonic acids
Authors: Dahn Hans , Van Toan Vien , Ung‐Truong My‐Ngoc 
Published: May 2005

AbstractThe 17O NMR spectra of terminal oxygen atoms in esters, anions and amides of substituted arenesulphinic acids and in esters and amides of substituted arenesulphonic acids were measured. The signals of the terminal O appear close to those of the bridge O. Compared with carbonyl O, terminal SO shows (a) a lower sensitivity to the electronic influences of geminal groups, (b) only a low sensitivity to arene ring substituents and (c) small solvent effects. The difference between C‐ and S‐bound O is discussed in terms of π‐bond character. Dy3+ complexation occurs with the terminal O in methyl arenesulphinates.
Synthesis and steric structure of cis‐ and trans‐alicycle‐fused dihydrothiazepines
Authors: Sohár P. , Újszászy K. , Szabó J. , Simon L. , Talpas G. S. , Fodor L. , Bernáth G. 
Published: May 2005

Abstractβ‐Lactam‐condensed saturated thiaazabicycles underwent ring transformation to give a new type of alicycle‐fused 3‐phenyl‐2‐methoxycarbonyl‐4,5‐dihydro‐1,4‐thiazepine. Oxidation of the cis and trans cyclohexane derivatives with perbenzoic acid furnished sulphones. The configurations and conformations of the new compounds were confirmed by 1H and 13C NMR spectroscopy, making use of DR, DNOE, DEPT and 2D HSC measurements.
A simple procedure for the determination of the quadrupole interaction parameters and isotropic chemical shifts from magic angle spinning NMR spectra of half‐integer spin nuclei in solids
Authors: Engelhardt Günter , Koller Hubert 
Published: May 2005

AbstractA simple procedure is presented for the determination of the asymmetry parameter of the electric field gradient, the quadrupole coupling constant, the second‐order quadrupolar shift and the isotropic chemical shift of quadrupolar nuclei with half‐integer spin directly from the experimental magic angle spinning (MAS) NMR spectra of powder samples measured at a single magnetic field. General equations applicable to any half‐integer spin nucleus and the specific expressions for 23Na and 27 Al are given. The simple calculations can easily be performed with a pocket calculator and avoid any spectral simulation or lengthy computer work. The method was applied to a series of 23Na MAS NMR spectra of selected sodium compounds and the agreement of the results with those of computer simulations is demonstrated.
1H and 13C NMR study of some (E)‐3′‐and 4′substituted stilben‐4‐ols
Authors: Fisher Thomas H. , Schultz Tor P. 
Published: May 2005

AbstractA series of ten (E)‐stilben‐4‐ols, HOPhCHCHPhX, with X = H, 4′‐Cl, 4′‐F, 4′‐Me, 4′;‐OMe, 3′‐Me, 3′‐OMe, 3′‐OH, 3′‐F and 3′,4‐diOMe, were studied using one‐ and two‐dimensional NMR techniques. Interpretation of these spectra led to definitive assignments of all carbon and hydrogen chemical shifts. 1H chemical shift increments were quantitatively determined for the five substituents studied, and the para Ai value of the styryl group was found to be more deshielding than those recorded in previous reports.
NMR spectroscopy of hexa‐ and octahydropyrazino [1′, 2′ : 1,2]pyrido [3,4‐b]indoles and 15‐azayohimbanes
Authors: Valls Nativitat , Segarra Victor M. , Bonjoch Josep 
Published: May 2005

AbstractThe 1H (200 MHz) and 13C (50.3 MHz) NMR spectra of some hexa‐ and octahydropyrazino[1′, 2′ : 1,2]pyrido‐[3,4‐b]indoles (1–13), 15‐azayohimbanes (15–18), and related compounds (14, 19, 20) are reported. The data have been analyzed in terms of the preferred conformation (9–13, 15–20) and configuration (15–20).
NMR investigations of forskolin. Complete assignment of proton and carbon NMR spectra and conformational analysis
Authors: Kogler Herbert , Fehlhaber Hans‐Wolfram 
Published: May 2005

AbstractThe 1H‐ and 13C NMR spectra of forskolin have been re‐investigated. Assignments are based exclusively on unambiguous carbon–carbon and carbon‐proton correlations derived from two‐dimensional NMR spectra. Stereo‐specific differentiations were deduced from selective proton NOE measurements and the interpretation of vicinal and long‐range proton‐proton scalar couplings. The proton‐proton distances calculated from proton NOE effects fit best with a flattened boat‐like conformation of ring C, which is different from the conformation of forskolin in the solid state.
Chemical modifications of phenoxy resin. Synthesis and 1H NMR study of model compounds
Authors: Fdez‐Berridi Maria J. , Iruin Juan J. , de Ilarduya Antton Martinez , de Gauna Asun Ruiz , Valero Miguel 
Published: May 2005

AbstractThe hydroxy group of phenoxy resin has been modified by etherification and esterification. The 1H NMR spectra of these products show large differences in the splitting patterns of the methylene protons according to the chemical nature of the substituent groups. Model compounds for phenoxy resin and derivatives, as well as some other glycerol derivatives, have been synthesized in order to study in more detail the signals of the CH2 group. The 1H NMR spectra of these compounds show two types of splitting. In some cases both protons absorb clearly as a doublet through accidental equivalence, while in other cases they are magnetically non‐equivalent. This behaviour can be explained by non uniform conformer populations (JAX ≠ JBX) in some cases, but where JAX ≈︁ JBX it could not be explained without taking into account the molecular asymmetry.
1H NMR spectroscopy of cycloadducts of 1,5‐ and 1,6‐diazaphenanthrene phenacylides
Authors: Śliwa Wanda , Bachowska Barbara , Postawka Anna 
Published: May 2005

AbstractThe 1H NMR spectra of cycloadducts of 1,5‐ and 1,6‐diazaphenanthrene phenacylides with acrylonitrile, ethyl acrylate, dimethyl acetylenedicarboxylate (DMAD), maleic anhydride and ethyl maleate, and those of cycloadducts of 1,5‐ and 1,6‐diazaphenanthrenes with DMAD, are presented.
Carbon‐13 NMR studies of some di‐and tetra‐substituted anthracene‐9,10‐dione derivatives related to the anti‐cancer drug mitoxantrone
Authors: Blanz Joachim , Mewes Kersten , Beth Meike , Zeller Klaus‐Peter , Ehninger Gerhard 
Published: May 2005

AbstractCarbon‐13 NMR data of 18 di‐ and tetra‐substituted anthracene‐9,10‐dione derivatives related to the anticancer drug mitoxantrone.
1H and 13C NMR characterization of a new chiral porphyrin, meso‐Tetra(α, β, α, β‐o‐camphanylamidophenyl)porphyrin, and its rhodium(III) complex
Authors: Licoccia Silvia , Paci Maurizio , Tagliatesta Pietro , Paolesse Roberto , Antonaroli Simonetta , Boschi Tristano 
Published: May 2005

AbstractThe synthesis of a new chiral porphyrin, meso‐tetra(α, β, α, β‐o‐camphanylamidophenyl)porphyrin, and its Mn(III) and Rh(III) derivatives is reported. Complete resonance assignments of both the 1H and 13C spectra of the ligand has been achieved via homo‐ and hetero‐nuclear 2D NMR. Insertion of metal ions into the porphyrin ring was performed both in order to test the catalytic properties of the resulting complexes and to characterize the effect of of metal coordination on the spatial distribution of the bulky substituents. The Mn complex was then tested in catalytic chiral epoxidation reactions, giving low enantiomeric excesses (20%). The 2D NMR spectra of the Rh derivative indicate the existence of four molecular species generated by the interaction of the metal atom with the peripheral substituents of the porhyrin ring. In fact, a complex combination of axial coordination, together with the chirality of the camphanyl substituents, removed the symmetry of the porphyrin plane.
Studies of two‐dimensional 113Cd1H overhauser effect spectra
Authors: Yan Xin , Fan Jinsong , Xu Xiaolong , Wang Dehua , Nie Guojun , Qian Baogong 
Published: May 2005

AbstractThe two‐dimensional 113Cd1H Overhauser effect spectra of some cadmium compounds are reported. The results show that the two‐dimensional 113Cd1H Overhauser effect experiments can be used to investigate the intramolecular and intermolecular interactions and structures of cadium compounds.
Studies of tautomerism and protonation in 2‐aryl‐1H‐imidazo[1,2‐a]imidazole derivatives using 1H and 13C NMR
Authors: Liu Maili , Farrant R. Duncan , Glen Robert C. , Lindon John C. , Barraclough Paul , Smith Steven 
Published: May 2005

AbstractThe tautomerism and protonation of the putative inotropic 2‐(2′,4′‐dimethoxy)phenyl‐1H‐imidazo[1,2‐a]imidazole (2) has been studied in several solvents by comparing its 1H and 13C chemical shifts with those of its 1‐ and 7‐methyl derivatives 3 and 4, respectively, and acid salts. Tautomer and rotamer populations were also estimated from measurements of proton relaxation rates and NOE effects. Heterocycle 2 exists predominantly as the 1H‐tautomer in CDCl3, but as the 7H‐tautomer in DMSO‐d6 and methanol‐d4–D2O solutions. In CDCl3 solution, 2 appears to exist with the N‐1‐H and 2′‐OMe groups adjacent, but in DMSO‐d6 the conformation is the rotated form with N‐7‐H and H‐6′ adjacent; 3 exists as a mixture of rotamers in CDCl3 and in DMSO‐d6 whereas 4 is in the form with the N‐7‐Me and H‐6′ adjacent in both solvents. The observed conformational preferences have been compared with the results of semi‐empirical molecular orbital calculations and found to be in broad agreement. Protonation of 2 occurs mainly at N‐1 in DMSO‐d6 and at N‐7 in CDCl3, as expected from observed tautomeric ratios in the free base.
One‐bond 13C13C spin–spin coupling in cubanes
Authors: Axenrod T. , Liang B. , Bashir‐Hashemi A. , Dave P. R. 
Published: May 2005

AbstractEndocyclic one‐bond 13C13C spin–spin coupling constants in a series of cubane derivatives were recorded. The values measured using the INADEQUATE pulse sequence were found to be insensitive to the nature of the substituent, fall in a narrow range (27–30 Hz) and are comparable to values reported for similar cyclobutane derivatives.
Two‐dimensional NMR and 13C spin—lattice relaxation study of methyl fluorene‐3‐carboxylate
Authors: Pissas D. , Dais Photis , Sauriol Francoise 
Published: May 2005

Abstract13C nuclear magnetic relaxation rates were measured as a function of temperature for methyl fluorene‐3‐carboxylate and used to describe the dynamics of this molecule. The easiest reorientation is about the x principal diffusion axis, which is situated close to that inertial principal axis corresponding to the smallest moment of inertia. The reorientation of this planar asymmetric rotor is found to be anisotropic about the in‐plane x and y axes, as expected from unequal moments of inertia. The reorientation about the out‐of‐plane axis z is faster at the lowest temperature measured and it becomes comparable to the in‐plane motion at the remaining temperatures, showing decreased frictional forces for rotation in the molecular plane. Total assignment of the 1H and 13C NMR spectra of the fluorene derivative was achieved by employing 1D and 2D NMR techniques.
Yttrium(III) oxoisopropoxide: A new synthetic route and reinvestigation of the 1H, 13C and 89Y NMR of Y5(μ5‐O)(μ3‐OiPr)4(μ2‐OiPr)4(O iPr)5
Authors: Page Catherine J. , Sur Sandip K. , Lonergan Mark C. , Parashar Gyanendra K. 
Published: May 2005

AbstractYttrium(III) oxoisopropoxide, Y5O(OiPr)13, was synthesized via a new synthetic route and characterized by mass spectrometry and multinuclear magnetic resonance spectroscopic techniques. Extensive 1H, 13C and 89Y NMR studies with full assignments are reported.
13C NMR spectra of some 3‐substituted cycloalkanespirohydantoins and their 4‐hydroxy derivatives
Authors: Pedregal C. , Espada M. , Albert J. , Cruz E. , Virgili A. 
Published: May 2005

Abstract13C NMR data for 21 cycloalkanespiro‐hydantoin derivatives, substituted at position 3, are reported and compared with those for the corresponding 4‐hydroxy derivatives.
Platinum‐phosphine cluster chemistry: New potentials from 195Pt‐31P{1H} triple‐resonance spectroscopy
Authors: Rüegger Heinz , Moskau Detlef 
Published: May 2005

AbstractPlatinum‐phosphorus heteronuclear multiple‐quantum coherence spectroscopy has been employed for the characterization of platinum‐phosphine cluster compounds. Rules are developed for the interpretation of these spectra, whose appearance depends on the chosen pulse‐sequence, phase‐cycling and whether direct or remote platinum‐phosphorus coupling constants have been selected. Spectral editing according to the different isotopomers (with respect to 195Pt) is possible when complete evolution of multiple‐quantum coherence is allowed. This method offers a substantial advantage in the characterization of larger cluster compounds.
EPR investigation of the second sphere coordination of [Cr(CN)5(NO)]3− with protonated polyethyleneimine
Authors: Chandramouli G. V. R. , Schläpfer C. W. , von Zelewsky A. 
Published: May 2005

AbstractThe second sphere coordination of protonated, branched polyethleneimine (PEI) with [Cr(CN)5(NO)]3− (CPN) was studied by EPR spectroscopy. The interaction between the CPN complex ion and protonated PEI is reported as a function of pH. Simulation of the spectra indicated that ca. 98% of the CPN is bound to the polymer at pH ≈︁ 7. The tumbling rate of this species was determined by simulation as 1/τc = 1 × 10−8 s−1. The binding of CPN by PEI was influenced by the addition of other salts. Exchange interaction between Cu2+ and CPN was observed on the simultaneous binding of these two paramagnetic species to PEI. The pH dependence of the exchange was measured. At an intermediate pH range (7–9), CPN binds in the second and Cu2+ in the first sphere. The exchange interaction increases with the ‘loading’ of the polymer with the two paramagnetic species. Based on these results, a model is proposed for the species in solution.
15N NMR study of the linkage isomerism of pentaammine(glycinato)rhodium(III)
Authors: Appleton Trevor G. , Cox Matthew R. 
Published: May 2005

AbstractRefluxing a solution of [Rh(NH3)5(gly‐O)]2+ at pH 10 produces [Rh(NH3)5(gly‐N)]2+ (glyH = glycine, +NH3CH2CO2−). 15N NMR spectra of reaction mixtures obtained with either 14N or 15N isotopes present in the ammine or glycinate ligands are consistent only with the O‐ to N‐isomerization reaction being intramolecular. The analogous β‐alaninate complex does not isomerize under similar conditions.
Inverse two‐dimensional 31P, 103Rh{1H}NMR of cationic rhodium(I) complexes containing chelating diphosphines
Authors: Ernsting J. M. , Elsevier C. J. , De Lange W. G. J. , Timmer K. 
Published: May 2005

AbstractA series of new and known Rh(I) complexes [Rh(R2P(CH2)nPR2)2]Y and [Rh(diene)(R2P(CH2)nPR2)]Y (R = Me, Et, Ph, C6F5, C6H4CF3; Y = Cl, ClO4, PF4, BF4, OSO2CF3; diene = norbornadiene, cyclooctadiene) were prepared and their 103Rh NMR spectra were recorded on a 100‐MHz spectrometer by using inverse two‐dimensional 31P, 103Rh{1H} NMR. This technique provides quick access to 103Rh NMR data (2–8 h for ca. 0.1 M samples) when dealing with Rh‐phosphine complexes. The 103Rh NMR data are discussed. All δ(103Rh) of the cationic Rh(I) complexes appear at the lower frequency end of the Rh(I) range, i.e. between −1350 and + 200 ppm, which is in agreement with the fact that the Rh shift is determined by σp and with a large ΔE in square‐planar d8 complexes. The relative change in ΔE between complexes is not large and the changes in paramagnetic shift for these complexes are essentially determined by their relative σ‐donor capacities. δ(103Rh) shows an inverse correlation with δ(31P), which was rationalized by invoking the chelate ring size containing the Rh centre and the bidentate phosphine ligands.
1H and 13C NMR spectra, 13C NMR relaxation times and molecular modelling studies of the narcotic agonist–antagonist α‐( − )‐N‐propynylnormetazocine
Authors: Amato Maria E. , Grassi Antonio , Pappalardo Giuseppe C. , Machytka Daisy , Radics Lajos 
Published: May 2005

AbstractThe analysis of high‐frequency 1H and 13C NMR spectra and both 1H1H homonuclear and 1H13C heteronuclear chemical shift correlation experiments indicate that N‐propynlnormetazocine (NPMH+) is configurationally heterogeneous in solution, with the N‐equatorial isomer being more populated than the N‐axial isomer. The experimental proton–proton coupling constants measured for both diastereoisomers were in agreement with the calculated values for a chair conformation of the piperidine ring. AM1 and MM2 theoretical calculations both indicated the chair conformation as that preferred by the piperidine ring, and the N‐equatorial isomer as being energetically favoured with respect to the N‐axial form. The best fit of the 13C T1 relaxation time data and the related motional analysis of NPMH+ was carried out using the anisotropic model of reorientation with superimposed internal motion. The results showed an increase of the rotational anisotropy of the molecule on passing from the gas phase to the solution state.
Solid‐state 2H NMR study of the dynamics of the methoxy groups in perdeuteriated bis(dimethoxythiophosphoryl) disulphide
Authors: Potrzebowski Marek J. 
Published: May 2005

Abstract2H solid‐state NMR was employed to study the statio and dynamic properties of perdeuteriated bis(dimethoxythiophosphoryl) disulphide. It was found that sample preparation has a significant influence on the line shapes of the broad‐line solid‐state spectra. It was concluded from inversion–recovery experiments that the methyl groups are in the fast exchange regime, τc < 10−s s. The three‐site jump model, with reorientation of the methyl group about a C3 symmetry, was assumed as the best explanation of the T1 anisotropy. The apparent activation energy calculated from an Arrhenius plot was found to be 5.35 kJ mol−1.
Carbon‐13 NMR spectra of some 2‐ ethylthio‐4′‐substituted acetophenones and their mono‐ and di‐oxygenated derivatives
Authors: Olivato Paulo Roberto , Bonfada Élida , Rittner Roberto 
Published: May 2005

AbstractThe 13C NMR signals for some 2‐ethylthio‐, 2‐ethylsulphinyl‐ and 2‐ethylsulphonyl‐4′‐substituted acetophenones were assigned. The carbonyl carbons exhibit a progressive upfield shift on going from the ketosulphides to the ketosulphoxides and to the ketosulphones. The α‐methylene carbons fro the three classes of compounds are shielded by almost the same amount in relation to the corresponding calculated values. The chemical shifts of the aromatic ring carbons are in close agreement with those calculated using substituent chemical shifts.
1H and 13C high‐resolution NMR analysis of a siloxane polymer with phenyl benzoate side‐chains
Authors: Findeisen M. , Roth H. 
Published: May 2005

AbstractThe peaks have been assigned in the 1H NMR spectrum (250 MHz) and in the 13C NMR spectrum in solution of polysiloxane with phenyl benzoate side‐chains.
19F, 14N and 15N NMR spectroscopic studies on triazadienyl fluoride, N3F
Authors: Schatte Gabriele , Willner Helge , Willert‐Porada Monika 
Published: May 2005

AbstractThe results of 19F, 14N and 15N NMR measurements for all 14N/15N isotopomers of N3F in CD2Cl2 solution are reported. Substantial deshielding for the N‐α and N‐γ atoms, relative to other covalent azides XN3 (X  Cl, H, CF3, etc.), is observed. The coupling constants also indicate unusual bonding in N3F. 1J(15N‐α, F) and 3J(15N‐γ, F) are similar (58.2 and 58.6 Hz, respectively), very small for a 1J(15NF) but very large for a 3J(15NF) value. The observed value of 26.5 Hz for 1J(15N‐α 15N‐β) is the largest, and 2J(15N‐α 15N‐γ) (5.3 Hz) is the first reported coupling constant for an azide. The unusual N3F NMR data are discussed in terms of calculated atomic charges and the influence of the paramagnetic term which dominates the chemical shifts. This term expresses the deshielding due to the circulation of electrons in the magnetic field between the HOMOs and the LUMOs.
Magnetic field‐dependent nuclear spin–spin coupling
Authors: Raynes William Thomas , Stevens Sarah Jane 
Published: May 2005

AbstractAs the magnetic fields used in NMR spectrometers become greater, it is expected that a field dependence of nuclear spin–spin coupling will be observed. A part of this, which would be independent of temperature, is due to the contributions of higher terms in the Hamiltonian of the molecule in the external magnetic field and the two nuclear spin operators. Perturbation theory at second, third and fourth order is used to extract the general features of these higher order terms. Contributions are due (a) to diamagnetic and paramagnetic terms of each of the four familiar parts of the spin coupling— Fermi contact, spin–dipolar, and orbital paramagnetic and orbital diamagnetic, and (b) to cross‐terms determined by operators for the diamagnetic and paramagnetic shielding at the two coupled nuclei. Explicit expressions are presented for the more important contributions. It is estimated for strongly magnetic nuclei in large molecules that the coupling varies as 0.5 × 10−5 B2 Hz, so that a field of about 14 T should produce a change in the coupling of 0.001 Hz. These are, respectively, the field used in high‐field NMR spectrometers and the upper limit of precision in the measurement of spin–spin coupling constants at the present time.