bluuebunny/crossref_metadata_2025_split huggingface dataset:
NMR studies in the heterocyclic series XXIV—1H, 13C and 15N study of 15N labelled indazoles
Authors: Fruchier Alain , Pellegrin Valdo , Schimpf Rémy , Elguero José 
Published: May 2005

AbstractThe 15N chemical shifts and 1H15N and 13C15N coupling constants of nine monolabelled indazoles were measured and assigned. The experimental values are discussed in terms of the indazolic and iso‐indazolic structures, and compared with literature data for other related heterocycles. All the results are consistent with an N‐1(H) tautomeric structure for indazole in DMSO‐d6.
29Si NMR spectra of methylphenylcyclotri‐and ‐tetrasilazanes
Authors: Lavrukhin B. D. , Astapov B. A. , Zhdanov A. A. , Engelhardt G. , Jancke H. 
Published: May 2005

Abstract29Si NMR spectra of various methylphenyl‐substituted cyclotri‐ and ‐tetrasilazanes, composed of different combinations of the unitsd= Me2SiNH,dph= MePhSiNH andd= Ph2SiNH, have been investigated. For most of the compounds having more than one asymmetric centre, the spectra of both the individual isomers and their mixtures have been studied, and the signals of the individual isomers have been assigned. The effect of a different arrangement of phenyl groups in the rings, and the influence of the stereochemistry of the isomers on the29Si chemical shifts in cyclotri‐ and ‐tetrasilazanes have been studied. The29Si chemical shifts in cyclotrisilazanes are additive and can be represented as the sum of increments corresponding to the number and positions of the phenyl groups in the rings. In these compounds, the spatial structure of the isomers does not exert any noticeable effect on the spectra. On the contrary, chemical shifts are not simply additive in cyclotetrasilazanes: a pronounced stereochemical dependence is apparent.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. NH proton exchange reactions of urea, thiourea, acetamide and thioacetamide
Authors: Chun Yu , Yavari Issa , Roberts John D. 
Published: May 2005

AbstractMeasurements are reported of NH exchange rates of urea, thiourea, acetamide and thioacetamide, using line‐shape analysis with natural‐abundance 15N NMR spectra. Base‐catalyzed NH‐proton exchange of thiourea is 30–40 times faster than for urea, while the corresponding acid‐catalyzed exchange is 150 times slower. The base‐catalyzed proton exchange for thioacetamide is about 1000 times faster than that of acetamide at 25°C, while the corresponding acid‐catalyzed exchange is some 260 times slower.
Application of the nuclear overhauser effect difference experiment: Assignment of the configuration of carboprostacyclin
Authors: Kotovych G. , Aarts G. H. M. 
Published: May 2005

AbstractNuclear Overhauser effect difference experiments, together with difference decoupling and inversion recovery measurements, have allowed the complete assignment of the proton magnetic resonance spectrum of carboprostacyclin. The nuclear Overhauser effect measurements prove the 5E configuration at C‐5 for carboprostacyclin. Protons H‐2,2*, H‐3,3*, and H‐4,4* are observed to be nonequivalent due to the asymmetric nature of this molecule.
Stereochemical aspects of proton chemical shifts. X—The slow exchange 1H NMR spectrum of cis‐transoid‐cis‐perhydroanthracene and of cis‐decalin
Authors: Tavernier D. , Anteunis M. J. O. 
Published: May 2005

AbstractThe slow exchange 360 MHz 1H NMR spectra of cis‐transoid‐cis‐perhydroanthracene and of cis‐decalin have been assigned. Shift increments due to the cis‐annelation of a tetramethylene bridge to cyclohexane are presented.
Assignment and analysis of the 500 MHz 1H NMR spectra of somatostatin and the acyclic precursor (S3,14‐Acm)‐somatostatin in dimethyl sulphoxide
Authors: Deleuze C. , Hull W. E. 
Published: May 2005

AbstractThe 500 MHz 1H NMR spectra of somatostatin and the precursor, di‐S3,14‐acetamidomethyl dihydrosomatostatin, in dimethyl sulphoxide solution have been assigned. Chemical shifts, coupling constants and NH shifts vs temperature coefficients are tabulated. The data are consistent with a stable β‐turn/β‐sheet conformation for the precurso, while somatostatin itself appears to be more conformationally mobile, with an average conformation significantly different from that in aqueous solution.
A carbon‐13 nuclear magnetic resonance spectral investigation of substituted triphenyl phosphates
Authors: Buchanan G. W. , Wightman R. H. , Malaiyandi M. 
Published: May 2005

Abstract13C NMR chemical shifts and 13C31P couplings are reported for triphenyl phosphate and 13 alkyl derivatives. In ortho‐alkylated materials, it is found that the upfield γ shielding effect is only operative when the carbon atom, situated γ to the exocyclic oxygen, bears at least one hydrogen. Conformational changes about the arylO bond can be monitored via the vicinal 31pOC13C couplings.
Proton, carbon‐13 and fluorine‐19 NMR studies of N‐alkyl‐8‐fluoroquinolinium halides: Relative signs of through‐space 1H19F and 13C19F coupling constants
Authors: Barfield M. , Walter S. R. , Clark K. A. , Gribble G. W. , Haden K. W. , Kelly W. J. , Le Houllier C. S. 
Published: May 2005

AbstractBecause of experimental and theoretical interest in long‐range 1H19F and 13C19F coupling constants between proximate atoms, a series of N‐alkylfluoroquinolinium compounds was synthesized and the NMR parameters were accurately measured. By means of spin tickling and selective population inversion difference spectroscopy, the 5J(HF) and 4J(CF), which are associated with the proximate fluorine and methyl groups, were shown to be of the same (positive) sign as the directly bonded 13C1H and vicinal 1H1H coupling constants. In N‐methyl‐8‐fluoroquinolinium iodide (1a) and chloride (1b) 5J(HF)=+8.8 and 4J(CF)=+16.3 Hz, and in N‐ethyl‐8‐fluoroquinolinium iodide 5J(HF)=+3.0, 6J(HF)=+1.5, 4J(CF)=(+)15.8 and 5J(CF)=±5.2 Hz. Calculated molecular orbital results, which were based on the INDO‐FPT method and a molecular geometry from the x‐ray diffraction data for 1b, were in reasonable agreement with the 4J(CF) values, but the 5J(HF) values were of the wrong sign and magnitude.
EPR study of the alimemazine cation radical
Authors: López‐Rupérez F. , Conesa J. C. , Soria J. 
Published: May 2005

AbstractThe EPR spectrum of alimemazine cation radicals (ALMZ+) in a perchlorate single crystal has been studied at 293 K. Since strong exchange interactions between the radicals did not allow the determination of the hyperfine splitting constants, the spectrum of an ALMZ+ solution, frozen at 77 K, was also studied. The results, checked by computer simulation, indicate orthorhombic symmetry of the g(2.0075, 2.0059, 2.0023) and hfs (A=3.6G; A=2.0G; A=15.6G) tensors.
17O and 14N spectroscopy of 17O‐labeled nucleic acid bases
Authors: Burgar Matija I. , Dhawan Devindra , Fiat Daniel 
Published: May 2005

AbstractOxygen‐17 and nitrogen‐14 nuclear magnetic resonance techniques have been utilized in studying liquid‐state hydrogen bonding interactions between nucleic acid bases and between the bases and solvent. The bases uracil and thymine have been labeled with 17O at positions 2 and 4, cytosine at position 2 and thymine riboside at position 4. The 17O chemical shift was found to be a sensitive structural probe and to provide information concerning the resonance forms that contribute to the total wave function. The chemical shift of the oxygen of thymine and uracil at position 2 was detected at a higher field than that of oxygen at position 4, presumably owing to an increased contribution of single bonded‐oxygen valence bond structures at position 2. The 17O and 14N chemical shifts of cytosine were found to be strongly pH dependent, and the results have been interpreted in terms of predominant cytosine resonance structures contributing to the aqueous cation and anion. The 17O line width of cytosine in aqueous solution indicates the presence of hydrogen bonded dimers between neutral and cationic forms.
Solvent‐induced isotope effects in NMR spectroscopy. A study of hydrogen bonding between the carbonyl group in chalcone and trifluoracetic acid (TFA‐d or TFA) in chloroform solution
Authors: Kozerski Lech 
Published: May 2005

AbstractSplittings, δi, were observed for each carbon atom, Ci, of chalcone in spectra obtained from coaxial 5 and 10 mm NMR sample tubes containing solutions equimolar in the concentration of the ketone and of TFA or TFA‐d as hydrogen‐bond donors, respectively. It was found that a linear expression, δi = (K–1)xHΔi+xDδi(D, H) relates these splittings, δi, induced by the isotopic substitution in a hydrogen bond, to the parameter Δi, denoting the change in chemical shift for each carbon site in complexed and free ketone, and δi(D, H), the solvent‐induced isotope effect in a complex. The origin of the phenomenon is briefly discussed. It is also shown that the secondary deuterium isotope effect can give the same information about the form of the potential energy well in the hydrogen‐bond as the primary H/D isotopte shifts.
Substituent parameters v. Lanthanide‐induced shifts in the interpretation of the 13C nuclear magnetic resonance spectrum of 5,5‐dimethyl‐2‐norbornanone
Authors: Yates Peter , Cong Dong Dao 
Published: May 2005

AbstractEarlier assignments of 13C NMR signals to C‐6 and C‐7 in 5,5‐dimethyl‐2‐norbornanone (1) based on lanthanide‐induced shifts are interchanged on the basis of studies of deuterium‐labeled derivatives of 1. The revised assignments are in accord with predictions based on substituent parameters.
A statistical study of the additivity of substituent effects on the 5J(HH) long‐range coupling constant of the formyl proton in substituted benzaldehydes
Authors: Kolehmainen E. , Knuutinen J. , Salovaara P. J. 
Published: May 2005

AbstractThe additivity of chloro and hydroxy substituent effects on the formyl proton spin‐spin coupling constants with the meta ring proton, 5J(HH), has been tested with 15 chlorinated benzaldehydes and hydroxybenzaldehydes by multiple linear regression analysis. No general additivity rule was detected with whole data. Using benzaldehyde as the reference substance, a good correlation was achieved for p‐hydroxybenzaldehydes. The same reference compound was not suitable for o‐hydroxy derivatives; a much better correlation was observed using o‐hydroxybenzaldehyde as a reference compound in the latter case.
Effect of the internal reference on ASIS correlations: 3—Intrinsic ASIS of formyl protons
Authors: Bertrán J. Fernández , Rodríguez M. 
Published: May 2005

AbstractThe intrinsic ASIS of formyl protons in p‐X‐benzaldehydes, dimethylformamide and diphenylformamide in a series of aromatic hydrocarbon solvents have been calculated. These values of Δ¯xα of the formyl protons present excellent correlations in aromatic hydrocarbon solvents, and are factorizable into solute and solvent factors Ux and Vα, respectively. The Ux values are linearly related to the value of σp of the substituent in the solute. The Vα values depend on the substitution pattern of the benzene ring of the solvent molecules.
31P nuclear magnetic resonance titrations: Simultaneous evaluation of all pH‐dependent resonance signals
Authors: Lachmann Heinrich , Schnackerz Klaus D. 
Published: May 2005

AbstractThe simultaneous evaluation of ali pH‐dependent resonance signals (or multiplets) of an NMR titration offers a substantially increased accuracy and significance. The number of linearly independent titration equilibria is determined by graphical matrix rank analysis. The chemical shifts of all pH‐dependent resonance lines are plotted against each other (chemical shift or CS diagrams) indicating whether a single or more titration equilibria are NMR spectrometrically observable and how far they overlap with each other. An iterative curve‐fitting program allowing the simultaneous evaluation of all (pH) curves is available, from which pK values and chemical shifts of all species can be calculated. The starting pK values for the iteration need only be estimated very approximately (accuracy ±1–2 units). The titration end‐points do not have to be experimentally accessible. The different methods for the simultaneous evaluation of all pH‐dependent NMR signals are exemplified in the 31P NMR titration of thiamine pyrophosphate. In this case either the observed resonance lines (two doublets in a broad band proton decoupled spectrum) or the calculated chemical shifts for this AB system can be evaluated. A titration of sodium pyrophosphate was performed and evaluated for comparison.
Carbon‐13 NMR data for 1‐ and 2‐naphthyltrimethylstannanes and 9‐phenanthryltrimethylstannane
Authors: Schaeffer C. D. , Lefferts J. L. , Zuckerman J. J. 
Published: May 2005

AbstractCarbon‐13NMR data recorded in the pulsed Fourier transform mode are re‐ ported for 1‐ and 2‐naphthyltrimethyl‐ stannanes and 9‐phenanthryltrimethyl‐ stannane. Assignments of ring carbon resonances are based on magnitudes of tin‐carbon spin‐spin coupling constants, substituent chemical shifts, spin‐lattice relaxation times and proton coupled spectra.
13C and 15N NMR spectra of 4‐substituted‐1‐dimethylphosphonopiperazines
Authors: Buchanan G. W. , Preusser S. H. 
Published: May 2005

Abstract13C and 15N NMR chemical shifts and 13C‐31P and 15N‐31P coupling contants are reported for a series of ten 4‐substituted‐1‐dimethylphosphonopiperazines.
13C and 15N spin–lattice relaxation and chemical shift studies of pentane‐2,4‐diamine
Authors: Yu Chin , Levy George C. 
Published: May 2005

Abstract13C and 15N NMR chemical shift and spin–lattice relaxation data have been measured for both meso‐ and racemic‐pentane‐2,4‐diamine. At high pH (12), relaxation is consistent with hindered rotation of the NH2 group due, in part, to the formation of intramolecular hydrogen bonds. At low pH (2), relaxation is consistent with relatively unhindered rotation of the NH3+ group. Rotational jump rates and barriers are reported, determined from the NT1 ratios between 15N and 13C nuclei. In all cases, the ratios for the racemic diastereomer are higher than those of the meso compounds; this is interpreted in terms of conformationally more stable intramolecular hydrogen bond formation in the meso compound. Chemical shifts for the diastereomeric amines show that 15N shifts move downfield on protonation along with methyl and methylene carbons, while the methine carbon resonances move upfield.
A 13C and 1H NMR study of the geometries of the 1,3‐dicyanoallyl anion: Thermal and photochemical interconversion
Authors: Boate D. R. , Hunter D. H. 
Published: May 2005

AbstractGlutacononitrile (1,3‐dicyanopropene) (2) was converted to its anion (1) by treatment with sodium hydride in tetrahydrofuran. Both 13C and 1 NMR showed that the sodium salt of 1 in THF existed in three slowly interconverting geometries (U, W and S). These geometries were present in similar amounts but the relative amounts of each proved to be concentration dependent. Irradiation of a 0.01 M solution of 1 at −80°C led to the conversion of a mixture of the U, W and S forms of 1 to only the W and S forms. Upon warming to 0°C equilibrium was re‐established with a half‐life of approximately 8 h.
Conformational investigations of cyclic dipeptides: Cyclo‐glycyl‐L‐methionyl, cyclo‐glycyl‐D,L‐norleucyl and cyclo‐glycyl‐D,L‐norvalyl
Authors: Siemion I. Z. , Picur B. 
Published: May 2005

AbstractThe E0 rotamer of c‐Gly‐Met has been found to be almost as equally populated as the F rotamer at low temperatures, whereas in c‐Gly‐D,L‐Nle and c‐Gly‐D,L‐Nvl the F rotamer predominates. The increase of the E0 rotamer population parallels the increase of the boat diketopiperazine (DKP) ring conformation, in which Med side‐chain occupies a pseudoaxial position. Thermodynamic parameters for DKP ring inversion and for conformational transitions in the side‐chains were experimentally determined for each cyclic dipeptide investigated.
The rα structures of propyne oriented in two different liquid crystals
Authors: Dombi G. , Diehl P. 
Published: May 2005

AbstractThe 1H spectra with natural abundance 13C satellites of propyne partially oriented in the liquid crystals ZLI 1167 and Merck Phase IV were analysed and molecular structures determined from the direct couplings corrected for harmonic vibrations. The resulting internuclear distance ratios and angles agree with microwave data and the solvent effects are small, i.e. of the order of 1% and 0.5° in the methyl group, and 2% in the acetylenic moiety.
A proton spin–lattice relaxation rate and nuclear Overhauser effect investigation of the stereochemistry of some 1‐aryl derivatives of 1,2‐dihydro‐s‐triazines
Authors: Peiris Sriyawathie , Colebrook Lawrence D. 
Published: May 2005

AbstractProton spin–lattice relaxation rates (R1 values) have been measured, at 400 MHz, for a number of 2‐methyl‐ and 2,2‐dimethyl‐substituted 4,6‐diamino‐1‐aryl‐1,2‐dihydro‐S‐triazines. These compounds have high barriers to internal rotation about the aryl CN bond, and exist in solution as mixtures of enantiomeric or diastereomeric rotational isomers. Diastereotopically related 2‐methyl groups in enantiomeric rotamers, and 2‐methyl and 2‐methine protons in diastereomeric rotamers, typically have different relaxation rates. In favourable circumstances this information may be used to identify the individual rotamers. Unequivocal direct identification of rotamers may be obtained from nuclear Overhauser effect difference spectra.
Unusual deuterium isotope effects in 13C NMR spectra of trans‐stilbene
Authors: Meić Ziatko , Vikić‐topić Dražen , Güsten Hans 
Published: May 2005

AbstractA detailed analysis of the 13C NMR spectra of trans‐stilbene and ten deuteriated trans‐stilbenes has been undertaken. Some unusual deuterium isotope effects on carbon–hydrogen spin–spin coupling constants could not be explained by the ordinary primary and secondary isotope effects. The positive and negative changes of nJ(CH) were interpreted in terms of a steric effect, the vibrational influence of the CD bond and the para‐effect induced by deuterium. In this respect, deuterium behaves as a real substituent with electronic properties different from those of hydrogen. The deuterium isotope effects on 13C NMR chemical shifts and carbon–deuterium coupling constants have also been determined.
Quaternary suppression via difference spectroscopy for 13C CP/MAR of organic solids: Application to a phenylazonaphthol
Authors: Harris Robin K. , Jonsen Paul , Packer Kenneth J. 
Published: May 2005

AbstractA pulse sequence for obtaining solid‐state NMR spectra of proton‐bearing 13C nuclei only, based on a difference method, is proposed. As an example, spectra of the dyestuff CI Pigment Red 57:1 [monohydrated calcium salt of 1‐(2‐sulpho‐4‐methylphenylazo)‐2‐hydroxnaphthyalene 3‐carboxylic acid] are illustrated. The difference method reveals a peak which is otherwise severely overlapped by others. Its presence is confirmed by higher field spectra. The results show that the dyestuff is present as the keto‐hydrazo tautomer.
Carbon‐13 chemical shift assignment of E‐Hydroxyazastilbenes
Authors: Wyrzykiewicz Elżbieta , Lpucha Andrzej , Sylwestrzak Urszula 
Published: May 2005

AbstractThe 13C NMR spectra of nine isomeric E‐hydroxyazastilbenes (E‐hydroxystyrylpyridines) have been fully assigned. The Ai and AiK empirical parameters of o‐(m or p‐)hydroxystyryl and 2‐(3‐ or 4‐)vinylpyridyl groups for the prediction, of chemical shifts of substituted styrylpyridines were calculated.
13C NMR spectral data for some N,N‐dialkylbenzylamines and their cyclopalladated complexes
Authors: Barr Neal , Dyke Stanley F. , Frost R. L. W. 
Published: May 2005

Abstract13C NMR data for some N,N‐dialkylbenzylamines and their chloro‐(N,N‐dialkylbenzylamine‐6,C,N)‐tri‐phenylphosphinepalladium(II) complexes are presented and simple shift parameters defined.
Multinuclear NMR spectra of (CH3)3SnCH2M(CH3)3 (MSn, Ge, Si, C) and some halogenated derivatives
Authors: Hawker Darryl W. , Wells Peter R. 
Published: May 2005

AbstractChemical shift and scalar coupling constant information has been obtained from the 1H, 13C, 29Si and 119Sn NMR spectra of a series of compounds (CH3)3SnCH2M(CH3)3, where M = Sn, Ge, Si or C and with one or two CH3(Sn) groups replaced by Cl, Br or I. The (CH3)3M and (CH3)3MCH2 groups appear to have opposite substituent effects on chemical shifts.
Aromatic chemical shifts in ar‐hydroxy‐ and ‐methoxy‐substituted indole alkaloids; reference data and substituent‐induced chemical shifts for ten different chromophoric groups
Authors: Verpoorte R. , van Beek T. A. , Riegman R. L. M. , Hylands P. J. , Bisset N. G. 
Published: May 2005

AbstractOn the basis of available 13C NMR spectral data for indole alkaloids, substituent‐induced chemical shifts have been calculated for various types of ar‐hydroxy‐ and ‐methoxy‐substituted indole alkaloids.
Investigation of intracellular phosphate pools of the green alga Chlorella using 31P nuclear magnetic resonance
Authors: Sianoudis J. , Mayer A. , Leibfritz D. 
Published: May 2005

Abstract31P NMR measurements were performed in order to study the intracellular phosphate pools of the green alga Chlorella fusca. Cells of asynchronous cultures contain a large pool of polyphosphates, whereas the amount of polyphosphates in cells of synchronous cultures depends on the state of differentiation. The assignment of extracellular and intracellular inorganic orthophosphate is achieved by changing the pH, whereas the intracellular compartmentation of inorganic orthophosphates and sugar phosphates is shown during irradiation of the cells with light within the NMR spectrometer.
Multinuclear magnetic resonance study of organomercury fulminates. The structure of mercury fulminate in solution
Authors: De Sarlo Francesco , Brandi Alberto , Fabrizi Lino , Guarna Antonio , Niccolai Neri 
Published: May 2005

Abstract1H, 13C, 14N and 199Hg NMR data were obtained for organomercury fulminates, RHgCNO (R  Me, Ph, CNO). The relatively slow relaxation processes effective for the quadrupolar nitrogen muclei of these compounds allow the detection of 199Hg14N scalar coupling constants. This feature is ascribed to the presence of low electric field gradients around the 14N nucleus, owing to the presence of the mercury atom. In mercury fulminate, the 199Hg nucleus appears to be coupled with two equivalent 14N nuclei, thus indicating the existence of a covalent structure Hg(CNO)2 in solution.
Theoretical additivity in multipath 13C, 1H coupling constants
Authors: Contreras R. H. , Scuseria G. E. 
Published: May 2005

AbstractDifferent path contributions to the Fermi contact term of carbon‐hydrogen coupling constants in several bicycloalkanes were calculated using the ‘inner projections of the polarization propagator’ (IPPP) approach. The ground‐state wave functions were calculated at the INDO level of approximation. Three and four‐bond contributions to the couplings, and the through‐space transmission via the rear lobes of the CX (X  H, F) bonds attached to the bridgehead carbon atoms, were calculated. The additivity of these contributions compared with the total INDO couplings is good. Similar paths in different molecules give dissimilar contributions to the couplings.
Compounds with bridgehead nitrogen. 48—stereochemistry of the 5‐methylperhydropyrido[3,2,1‐i,j][3,1]‐benzoxazines
Authors: Crabb Trevor A. , Jupp Philip A. , Turner Christopher H. 
Published: May 2005

AbstractSix of the eight possible diastereoisomeric 5‐methylperhydropyrido[3,2,1‐i,j][3,1]benzoxazines have been synthesized, and the utility of the C‐3 methylene proton NMR parameters [J(3ax3eq) and Δ3ax3eq] in the assignment of configurations has been demonstrated.
Conformational study of methyl esters of some aliphatic erythro‐ and threo‐dichlorocarboxylic acids
Authors: Pitkänen Maija 
Published: May 2005

AbstractThe average conformations of methyl esters of some aliphatic erythro‐ and threo‐dichlorocarboxylic acids in dilute carbon tetrachloride solutions have been determined from the vicinal proton–proton coupling constants and 1H NMR shifts. The 13C shift differences between the erythro and threo forms are compared and discussed with regard to the differences in the average conformations.