bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exceptional resolution and new signals detected in the 13C NMR spectra of alkanes
Authors: Alemany Lawrence B. 
Published: May 2005

AbstractThe relative ease with which very high resolution 13C NMR spectra can now be obtained because of advances in NMR technology is shown. Spectra of four alkanes were obtained at 62.9 MHz with careful shimming, low‐power decoupling and a digital resolution of less than 0.1 Hz. Signals as little as 3 ppb apart can be clearly distinguished at this moderate field strength without resolution enhancement. Consequently, additional information can be obtained. For n‐hexadecane, six, not the usual five, signals are evident; the chemical shifts of C‐6, C‐7 and C‐8 are within 0.16 Hz (2.5 ppb) of each other and are not all the same. For 2‐methyltridecane, all 13 signals are visible; all the signals can be assigned with confidence except those for C‐7 and C‐8, which differ by only 4 ppb. For 7‐ methylhexadecane, all 17 signals are visible; many can be assigned to a specific carbon, including the signals for C‐3 and C‐14 (both of which are in CH3CH2CH2CH2CH2CH2— environments), which differ by only 37 ppb. For the two pairs of enantiomers of 2,6,10‐trimethyldodecane, all but one carbon give a pair of resonances; the two signals for C‐3 are only 2.9 ppb apart. The potential limitations on molecular size and field strength affecting line width are considered. The same solvent, concentration and temperature must be used if chemical shift data for different compounds are to be meaningfully compared in detail.
Two‐dimensional NMR analysis of selected benzazolo[3,2‐a]quinolinium salts
Authors: Cox Osvaldo , Prieto Jose A. , Rodriguez Margarita 
Published: May 2005

Abstract1H and 13C studies of selected benzazolo[3,2‐a]quinolinium salts were carried by two‐dimensional NMR methods. The assignments of the 1H resonances were made by 2D homonuclear shift correlation (COSY) and the 2D nuclear Overhauser effect (NOESY). Complete 13C chemical shift assignments were carried out by using DEPT and two‐dimensional heteronuclear correlation spectroscopy.
13C NMR of lapachol and some related naphthoquinones
Authors: Dawson Brian A. , Girard Michel , Kindack Daryl , Fillion Julie , Awang Dennis V. C. 
Published: May 2005

Abstract13C NMR chemical shift assignments for lapachol and nine related naphthoquinones have been measured and interpreted. Data, based on the results of a number of 1D and 2D experiments performed at 9.4 T, correct several previously reported assignments for some of these compounds.
Solution conformations of 1‐anilinonaphthalene‐8‐sulphonate
Authors: Mendz George L. , Vandenberg Robert J. , Easterbrook‐Smith Simon B. 
Published: May 2005

AbstractThe Conformations and dynamics of 1‐anilinonaphthalene‐8‐(ANS) in solutions of solvents with different polarities and hydrogen‐bonding properties were investigated by high‐resolution 1H and 13C NMR spectroscopy. Two‐dimensional correlated spectrocopy, tirations with paramagnetic ions and one‐dimensional spin‐decoupling techniques were employed t assign the spectra observed from both nuclei. Nuclear Overhauser effect data provided evidence that the fluorohore adopts compact conformations in the more pola solvents. 13C spin‐lattice relaxation times indicated that the benzene ring of ANS has a degree of internal mobility in the solutions of all the solvents studied. Measurement of Stokes shifts in different solvents that the special fluorescence properties of ANS in aqueous solutions arise from the proton donor character of the solvent rather than from its polarity or the conformational flexibility of the fluorophore.
Chiral hydroxymethyl groups: 1H NMR assignments of the prochiral C‐5′ protons of 2′‐deoxyribonucleosides
Authors: Kline Paul C. , Serianni Anthony S. 
Published: May 2005

Abstract2′‐Deoxyadenosine, 2′‐deoxycytidine, 2′‐deoxyguanosine and 2′‐deoxyuridine were prepared with stereoselective deuteriation at C‐5′ and used to assign the prochiral C‐5′ protons in 300 MHz 1H NMR spectra obtained in 2H2O. In all cases, the more shielded C‐5′ proton was found to be the pro‐R proton. From these assignments, C‐4′–C‐5′ rotamer populations were determined using three previously published methods based on the spin couplings, 3J(H‐4′,H‐5′R) and 3J(H‐4′,H‐5′S), and the errors associated with these methods were assessed. The effects of base structure, furanose and N‐glycoside bond conformation on the relative populations of hydroxymethyl rotamers in nucleosides are discussed.
A novel approach for evaluating the NMR spectra of spinning solids: Application to the case of chemical exchange
Authors: Frydman Lucio , Frydman Benjamin 
Published: May 2005

AbstractAn approach is introduced that allows the evaluation of the effects of magic‐angle spinning (MAS) in the NMR spectra of inhomogeneously broadened spin‐1/2 nuclei. The method, which consists in replacing the time‐dependent MAS Hamiltonian by a set of three time‐independent Hamiltonians, is able to predict one of the main characteristics of the MAS experiment, namely the appearance of rotor echoes. Spectra were calculated using this approach and compared with 13C NMR spectra of model compounds, showing good agreement in the range of spinning rates normally used. A simple extension of the method also makes it useful for simulating some cases of variable‐angle spinning NMR. Although the approach is suitable for the evaluation of normal MAS NMR spectra, its main applications may be found in cases where the spin Hamiltonian is no longer self‐commuting. As an example, the method was employed for analysing the case of an exchange process between two equally populated chemically equivalent sites. Calculated spectra obtained in this way allowed the correct reproduction of the changes observed in the MAS NMR spectra of two compounds which are known to undergo reorientations in the solid state. Further possible applications of the approach are discussed.
13C and 31P solid‐state NMR studies of bis(dialkoxythiophosphoryl) disulfides
Authors: Chu Po‐Jen , Potrzebowski Marek J. 
Published: May 2005

AbstractThe principal elements of the chemical shift tensors for the phosphorus atoms in three bis(dialkoxythiophosphoryl) disulfides were determined from both static and magic angle spinning NMR spectra, using the intensities of the peaks in the spinning sidebands relative to those of the central band in the latter method. These studies show that it is possible to deduce a mode of molecular motion in the solid state by analysis of the shielding parameters. Variable‐temperature 13C and 31P CP MAS NMR of these samples from 190 to 320 K revealed a peculiar motion of the methoxy group and a rigid PSSP backbone for bis(dimethoxythiophosphoryl) disulfide. In addition, these studies confirmed that it is possible to distinguish the different x‐ray crystal structures from the solid‐state NMR experiment.
17O NMR study of steric hindrance in methoxylated flavones. Substitution on the phenyl ring and the heterocycle
Authors: Wallet Jean‐Claude , Gaydou Emile M. , Cung M. T. 
Published: May 2005

AbstractNatural abundance 17O NMR spectra were recorded for ten methoxyflavones and one flavonol. The chemical shifts are discussed in terms of steric and conformational changes. They are related to previously reported 13C NMR data.
Occurrence of β‐bends in bradykinin dissolved in DMSO‐d6
Authors: Mirmira Suman R. , Durani S. , Srivastava Sudha , Phadke Ratna S. 
Published: May 2005

AbstractThe conformation of the hormone bradykinin (Arg–Pro–Pro–Gly–Phe–Ser–Pro–Phe–Arg) in DMSO‐d6 was investigated using proton NMR spectroscopy at 500 MHz. Complete resonance assignments were made using 2D COSY and NOESY techniques. The chemical shifts, magnitudes of the 3JNH‐CαH couplings, temperature coefficient data on backbone NH protons and intramolecular NOEs were used to obtain information on the conformation. The nonapeptide assumes a rigid structure in DMSO‐d6. Based on the experimental results, a model is proposed using computer‐aided molecular graphics.
Carbon‐13 and nitrogen‐15 NMR spectra of some methanesulphonanilides
Authors: Wazeer Mohammed I. M. , Ali Sk. Asrof 
Published: May 2005

AbstractThe 13C and 15N NMR spectra of some ortho‐, meta‐ and para‐substituted methanesulphonanilides were recorded. Correlations of the 13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes were excellent and showed enhancement of the substituent effects at C‐1 (para to the substituent). The C‐1 chemical shifts were also examined by means of the dual substituent parameter (DSP) and DSP‐nonlinear resonance equations. The results indicate that the —NHSO2 Me moiety is a weak electron donor. The 15N chemical shifts of the para‐substituted compounds were analysed by means of DSP equations and the results compared with those of related compounds. Ortho‐substituted compounds indicate the high sensitivity of 15N chemical shifts towards steric compression. T1 and nuclear Overhauser enhancement data for the protonated carbons of methyl‐substituted compounds are given.
Assignment of proton and carbon‐13 spectra of a sucrose ester from tobacco by inverse detected two‐dimensional heteronuclear correlated NMR spectroscopy
Authors: Himmelsbach David S. , van Halbeek Herman , Arrendale Richard F. , Severson Ray F. 
Published: May 2005

AbstractThe complete assignment of the proton and carbon chemical shifts of 6‐O‐acetyl‐2,3,4‐tri‐O‐(3S‐methylpentanoyl)‐α‐D‐glucopyranosyl‐β‐D‐fructofuranoside, a naturally occurring flavor precursor of tobacco, is presented. These assignments were made by comparison of the spectra obtained from 1H‐detected heteronuclear multiple quantum coherence and 1H‐detected heteronuclear multiple‐bond connectivity two‐dimensional NMR experiments.
Conformational analysis of methyl phenyl sulphoxides containing fluorine substituents in the phenyl ring based on 1H, 13C and 17O NMR chemical shifts and long‐range nJ(HF) and nJ(CF) coupling constants
Authors: Benassi Rois , Folli Ugo , Iarossi Dario , Mucci Adele , Schenetti Luisa , Taddei Ferdinando 
Published: May 2005

AbstractThe preferred conformations of the methylsulphinyl group in a number of phenyl methyl sulphoxides substituted in the phenyl ring with one, two or three fluorine atoms have been studied by employing a multinuclear NMR approach. From the 1H, 13C and 17O chemical shifts of the methylsulphinyl group, and the torsional angles obtained either from MO calculations or experimental determinations for a number of the compounds, empirical correlations have been derived which enabled us to extract the preferred orientation of the SO bond or of the methyl group relative to the phenyl ring in all the molecules examined. For a limited number of the compounds, the structure of the preferred conformer is satisfactorily close to the solid‐state structure found in an independent study carried out with x‐ray diffraction. The twist of the SO bond relative to the phenyl ring changes as a function of the number of ortho substituents, being highest when two substituents are present. The lowest twist, torsional angle nearly zero, was found in ortho‐monosubstituted compounds and the SO bond is oriented towards the opposite side with respect to the substituent. Analyses were also carried out of the conformational dependence of long‐range nJ(HF) and nJ(CF) coupling constants, where the first nucleus in the parentheses refers to the methylsulphinyl group. The behaviour of these coupling constants as a function of internal rotation around the exocyclic CS bond was derived from semi‐empirical INDO MO FPT calculations, and scaled interpolating equations were derived in order to reproduce the experimental results. It thus emerges that 5J(HF), 4J(CF), 5J(CF) and 6J(CF) are conformationally dependent and show, experimentally, significant changes. These parameters can be usefully employed for the conformational analysis of methyl phenyl sulphoxides.
1H and 13C NMR study of the structure of pyrazoles, imidazoles and their benzo derivatives in sulphuric acid (azolium cations)
Authors: Elguero José , Jimeno María Luisa , Yranzo Gloria I. 
Published: May 2005

AbstractThe NMR spectra of two imidazoles, benzimidazole, four pyrazoles and three indazoles were recorded in 98% sulphuric acid, and the 1H, 13C, 1H–1H and 1H–13C spectral parameters of the corresponding azolium ions were obtained. The 1H N‐H chemical shifts and the 1H and 13C couplings with the NH proton are discussed. All 3J(1H1H) and 4J(1H1H) coupling constants have values between 1.5 and 3.0 Hz. All 2J(1H13C) and 3J(1H13C) values are about 6 Hz, with the exception of couplings involving C‐4 in imidazolium ions [2J(C‐4,H‐5) ≈ 12 Hz, 3J(C‐4,H‐1) ≈ 3 Hz].
Configurational assignment in N‐acetylneuraminic acid and analogues via the geminal C,H coupling constants
Authors: Prytulla S. , Lambert J. , Lauterwein J. , Klessinger M. , Thiem J. 
Published: May 2005

AbstractHigh field 1H and 13C NMR spectra were recorded of N‐acetylneuraminic acid, its methyl ester and its per‐O‐acetylated methyl ester. The sign and the magnitudes of the geminal coupling constants between the H‐3 protons and the C‐2 quaternary anomeric carbon were determined by heteronuclear 2D‐experiments. The C‐2,H‐3ax coupling in the α anomers (−8 Hz) was significantly more negative than that in the β anomers (−3 to −4 Hz). Therefore, the determination of 2J(C‐2,H‐3ax) offers a unique criterion for anomeric assignment in sialic acid ketosides. The geminal coupling constants are discussed in terms of the number and orientation of the oxygen substituents. Due to their 3‐deoxy function adjacent to the quaternary anomeric centre, sialic acids give novel contributions to the correlation of carbon‐proton coupling constants with molecular geometries in carbohydrates.
Synthesis, 1H, 13C and 31P NMR spectral studies of novel 2‐aryloxy/cyclicamino‐ 3‐(4‐methylphenyl)‐ 1H‐ naphth[ 1,2‐e] [1,3,2] oxazaphosphorine 2‐oxides/sulphides and 13C NMR data for some 4‐substituted‐dinaphtho dioxaphosphepin 4‐oxides/sulphides
Authors: Raju C. Naga , Naidu M. S. R. , John E. O. , Reddy M. C. 
Published: May 2005

AbstractThe syntheses, 1H, 13C and 31P NMR chemical shifts and 13C‐31P coupling constants of 2‐aryloxy/cyclicamino‐2,3‐dihydro ‐3‐ (4‐methylphenyl) ‐1H ‐ naphth [1,2‐e] [1,3,2]oxazaphosphorine 2‐oxides/sulphides and the 13C NMR data for 4‐substituted ‐ dinaphtho [2,1 ‐d:1′,2′‐f] [1,3,2] dioxaphosphepin 4‐oxides/sulphides are reported.
A two‐dimensional NMR strategy for the complete 1H chemical shift assignment of extended proton spin systems in triterpenoids
Authors: Loganathan Duraikkannu , Trivedi Girish K. , Chary K. V. R. 
Published: May 2005

AbstractAn assignment strategy that utilizes one‐dimensional lanthanide‐induced methyl proton shifts, reported 13C NMR data of model compounds and two‐dimensional 1H and 13C shift correlated spectroscopy, homonuclear proton chemical shift correlated spectroscopy and nuclear Overhauser enhancement spectroscopy methods was demonstrated to be effective for the complete 1H chemical shift assignments of extended proton spin‐systems in a triterpenoid viz., 3‐keto‐urs‐12‐en‐24‐oic acid methyl ester. Complete 13C chemical shift assignments have also been accomplished.
Determination of enantiomeric purity from solid‐state 31P MAS NMR of organophosphorus compounds
Authors: Andersen Knut Vendelboe , Bildsøe Henrik , Jakobsen Hans Jorgen 
Published: May 2005

AbstractPhosphorus‐31 Magic‐Angle Spinning (MAS) NMR is shown to be an extremely useful and accurate method for the determination of the enantiomeric purity for chiral organophosphorus compounds. 31P and 13C chemical shielding tensors in racemic and enantiomeric crystals of organophosphorus compounds vary because of different crystal symmetries. This implies that solid‐state 31P (13C) MAS spectra of an enantiomerically impure sample reveal separate signals from the racemic and enantiomer crystallites. Simple integration (or deconvolution) of the MAS NMR signals can thus be used to determine the enantiomeric purity of the sample. For organophosphorus compounds the application of this technique to 31P MAS NMR is of particular interest due to the high sensitivity and large shielding anisotropy of the 31P nucleus.
Aluminium‐27 MAS NMR of Al2Ge2O7 and LaAlGe2O7: Two pentacoordinated aluminium environments
Authors: Massiot Dominique , Kahn‐Harari Andrée , Michel Daniel , Muller Dirk , Taulelle Francis 
Published: May 2005

AbstractCharacterization by 27Al MAS NMR of two pentacoordinated environments of aluminium has been carried out in different fields and at different spinning speeds for Al2Ge2O7 and LaAlGe2O7. Complete simulations of the spectra have been performed, including computation of the individual shape and intensity of each spinning side band, which lead to the determination of both the quadrupolar interaction parameters and isotropic chemical shifts, and enable the detection of impurities in the material. The parameters determined are:
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Kinetics of skeletal rearrangement of H2FeP[CH2CH2CH2P(CH3)2]3 by an inversion–transfer–recovery NMR method
Authors: Field Leslie D. , Bampos Nick , Messerle Barbara A. 
Published: May 2005

AbstractThe iron dihydride FeH2(PP3) [PP3 = P(CH2CH2CH2PMe2)3] is fluctional, with the terminal co‐ordinated phos‐phine groups undergoing intramolecular exchange in addition to the iron‐bound hydrides. The exchange kinetics of the metal‐bound hydrides was examined using a magnetization inversion–transfer–recovery method, and the activation energy was ca. 64 kJ mol−1 at 260 K. The effect of spin–spin coupling on the magnetization transfer was examined.
Application of 2D EXSY NMR spectroscopy to the study of the dynamic behaviour of aroylcyanoketene‐S,S‐dimethylacetals
Authors: Fischer G. , Kleinpeter E. 
Published: May 2005

AbstractThe applicability of 2D EXSY NMR spectroscopy for studying quantitatively the dynamic behaviour in three aroylcyanoketene‐S, S‐dimethylacetals was tested by means of 1H NMR spectroscopy. It can be concluded that the method is a reasonable qualitative supplement to complete line‐shape analysis.
77Se, 13C and 1H NMR spectra of phenylselenenylcycloalkanes, ‐cycloalkenes and some of their selenoxides and 125Te NMR of a tellurium analogue
Authors: Duddeck Helmut , Wagner Petra , Biallaß Armin 
Published: May 2005

AbstractThe 77Se, 13C and 1H NMR spectra of 46 mostly new compounds with phenylselenenyl groups attached to carbocycles and of three new corresponding selenoxides and the 125Te NMR of phenyltellurenylcyclohexane are reported. Substituent effects on the chemical shifts of these nuclei are compiled and discussed in terms of the configuration and conformation. Low‐temperature NMR spectra of some cyclohexane derivatives allowed the evaluation of thermodynamic data, such as A values of the PhSe, PhSe(O) and PhTe groups.
13C NMR study of derivatives of dibenzobarrelene, anthraquinone and anthracene
Authors: Sieckmann Ralf 
Published: May 2005

AbstractCarbon‐13 chemical shifts of 22 derivatives of dibenzobarrelene, anthraquinone and anthracene are reported, each of which includes a symmetrical ortho‐benzene moiety. The assignment of the chemical shifts of the aromatic carbons of these derivatives was achieved by correlation with the corresponding 13C chemical shifts of ortho‐disubstituted benzenes.
Complete 1H and 13C NMR assignments of tallysomycin s10b by modern two‐dimensional NMR techniques
Authors: Freyder Catherine P. , Marzilli Luigi G. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of tallysomycin s10b (TLM), a third‐generation analog of bleomycin, were completely assigned through the use of two‐dimensional NMR experiments (NOESY, HOHAHA, HMQC, HMBC) in D2O at pH 2.5 and 6.8 (uncorrected values). Significant differences in the resonances for the β‐aminoalanine, β‐hydroxyhistidine and pyrimidinylpropionamide residues were observed owing to the protonation/deprotonation of these moieties. The assignments for TLM at pH 6.8 were compared with the latest 2D NMR‐based assignments of bleomycin A2 (BLM A2) at pH 6.7. In general the agreement was excellent, in view of the size and complexity of these anticancer antibiotics. Of the several differences found, most can be attributed to the different substitution patterns in the variable regions of the larger TLM and the BLM A2. Both drugs have similar structures in the region of protonation. For this invariant region of the molecules, comparison of the TLM 13C data at pH 2.5 with the 1D BLM A2 13C data at low pH revealed that protonation induced similar changes in chemical shift for the corresponding signals in the two drugs. It is particularly noteworthy that the glucose and mannose 13C signals shift in a very similar manner for both drugs. Since the protonation shifts of the signals of these two sugars are much too large to be attributed to inductive effects, it is highly likely that both drugs, despite the structural differences in the variable region, undergo the same conformationl changes of the gulose and mannose moieties. These chemical shift similarities at both low and high pH confirm the validity of the assignments made independently on these two large drug molecules. The few differences between the two most recent 13C assignments of BLM A2, which are based on modern 2D NMR methods, can be resolved using the TLM assignments.
Computer‐assisted studies of structure–property relationships using graph invariants
Authors: Miyashita Yoshikatsu , Ohsako Hiroyuki , Okuyama Tohru , Sasaki Shin‐Ichi , Randić Milan 
Published: May 2005

AbstractThe correlation between molecular path numbers and chemical shift sums found previously in smaller alkanes is extended to larger alkanes. Using data on alkanes with 2–31 carbon atoms a satisfactory regression equation (R = 0.999 and S = 7.5 is derived based on a single molecular descriptor. The simple combination of elementary path numbers, M = P0 + P1+P2 − P3, apparently adequately represents both the size of molecules and the molecular shape, i.e. variations in properties among isomers.
Comparison of rotational‐echo double‐resonance and double‐cross‐polarization NMR for detection of weak heteronuclear dipolar coupling in solids
Authors: Christensen Allyson M. , Schaefer Jacob , Kramer Karl J. 
Published: May 2005

AbstractInsect exoskeleton, multiply labeled with 13C and 15N, was examined by rotational‐echo double‐resonance (REDOR) and double‐cross‐polarization (DCP) magic‐angle spinning 13C NMR. Low levels of incorporation of label make the analysis of these samples a practical test of the relative advantages of REDOR and DCP for the detection of weak, heteronuclear dipolar coupling between rare spins in solids. The sensitivity of REDOR for the detection of directly bonded 13C–15N pairs is an order of magnitude greater than that of DCP when neither label is involved in homonuclear dipolar coupling of strength comparable to the spinning frequency. However, if either of the 13C or 15N labels undergoes homonuclear spin flips, DCP gains in relative sensitivity and is easier to use for spin counting than REDOR.
13C nuclear magnetic resonance studies of pyrazolo[α]‐9(10H)‐acridinones
Authors: Boyer G. , Galy J. P. , Faure R. , Elguero J. , Barbe J. 
Published: May 2005

Abstract13C NMR chemical shifts of six pyrazolo[a]‐9(10H)‐acridinones are reported; they were assigned on the basis of multiplicities, carbon–proton coupling constants, selective proton decoupling experiments and comparison with related substances.
The radical anion of (E)‐azobenzene revisited
Authors: Buser Urs , Ess Caspar H. , Gerson Fabian 
Published: May 2005

AbstractThe radical anion of (E)‐azobenzene, generated from the neutral compound by reaction with potassium mirror in an ethereal solvent, has been fully characterized by its hyperfine data with the use of ESR, ENDOR and TRIPLE‐resonance spectroscopy. Assignments of coupling constants to protons in the individual positions are based on comparison with the spectra of the radical anions of 4,4′‐dideuterio and 2,2′‐dimethyl derivatives. Effects of 14N hyperfine anisotropy on ESR spectra and of association with the counter ion K+ are briefly discussed.