bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Townes and Dailey approach to the interpretation of NQR parameters in the light of non‐empirical calculations. Three‐membered rings
Authors: Balakina M. Yu. , Fominykh O. D. , Morozova I. D. , Osokin D. Ya. 
Published: May 2005

AbstractThe nuclear and electronic contributions to the EFG tensor components eqii at 14N, 17O, 33S and 35Cl nuclei in aziridine, methylaziridine, chloroaziridine, oxirane and thiirane were determined. The nuclear contributions were calculated within classical representations, while electronic contributions were calculated non‐empirically using a 6–31G* basis set within the framework of the LMO approach. On the basis of the analysis of the contributions to the EFG tensor components from definite bond and lone‐pair orbitals, the main concepts of the Townes and Dailey approach were tested.
1H and 13C NMR study of substituent effects in 2‐ and 3‐substituted diphenyl sulphides and sulphones and 4‐substituted 2′,6′‐dimethyldiphenyl sulphides
Authors: Perumal Subbu , Chandrasekaran Ramasubbu , Vijayabaskar Veerappan , Wilson David A. 
Published: May 2005

AbstractThe proton and carbon NMR spectra of nine 2‐substituted diphenyl sulphides (S‐2‐X), seven 3‐substituted diphenyl sulphides (S‐3‐X), nine 2‐substituted diphenyl sulphones (SO2‐2‐X), nine 3‐substituted diphenyl sulphones (SO2‐3‐X) and nine 4‐substituted‐2′,6′‐dimethyldiphenyl sulphides (Me2‐S‐4‐X) were obtained. Correlations of the 1H and 13C chemical shifts were made with benzene substituent‐induced chemical shifts (Lynch plots) and Hammett and dual‐substituent parameters and the results were compared with those of 4‐substituted diphenyl sulphides (S‐4‐X) and sulphones (SO2‐4‐X). The main conclusions are as follows: (i) the transmission of the substituent effects in substituted diphenyl sulphides decreases in the order S‐4‐X ≈︁ S‐2‐X > Me2‐S‐4‐X > S‐3‐X; (ii) the inductive effects are transmitted to a larger extent than the resonance effects to the unsubstituted ring in 3‐substituted diphenyl sulphides, while the reverse trend is observed in other substituted diphenyl sulphides; (iii) in 2‐methoxy‐, 2‐chloro‐, 2‐bromo‐ and 2‐nitrodiphenyl sulphides, an increase in the size of the substituent causes an upfield shift for H‐6 ascribable to the repulsion between the lone pairs of electrons on the sulphur and the substituent and its influence on the conformation; (iv) the diminished transmission of substituent effects to the remote rings in 4‐substituted 2′,6′‐dimethyldiphenyl sulphides is probably due to the orthogonal orientation of the rings; and (v) the signal due to the H‐6 of 2‐substituted diphenyl sulphones suffers a downfield shift with an increase in the size of the substituent, this being ascribable to the increasing steric interaction between the 2‐substituent and the sulphonyl oxygen and consequent changes in the conformation.
Solid‐state lead‐207 NMR of lead(II) nitrate: Localized heating effects at high magic angle spinning speeds
Authors: van Gorkom Leon C. M. , Hook James M. , Logan Michael B. , Hanna John V. , Wasylishen Roderick E. 
Published: May 2005

AbstractSolid‐state Pb‐207 NMR spectra of lead(II) nitrate were found to be highly sensitive to variations in temperature. The Pb‐207 chemical shift exhibits a linear dependence on temperature with a positive slope of 0.70 ± 0.02 ppm K−1, i.e. increases in temperature cause a change in chemical shift to higher frequency. This slope is within experimental error of the value obtained from parallel experiments on the static solid, 0.72 ± 0.06 ppm K−1. At higher magic angle spinning (MAS) speeds and ambient probe temperature, the Pb‐207 signal splits into several components owing to localized heating effects. These effects are more pronounced in rotors made from partially stabilized zirconia than those made from silicon nitride and are attributed to the poorer thermoconductive properties of the zirconia ceramic. In the zirconia rotors, discrete thermal regions within the lead(II) nitrate sample were located and differ by 5 K at 12 kHz MAS speeds. The response of the Pb‐207 lead(II) nitrate signal to temperature variation suggests that it could be used for calibrating solid‐state NMR probes.
Determination of the molecular structure of s‐trioxane by NMR of partially oriented molecules
Authors: Esteban A. L. , Galache M. P. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of s‐trioxane partially oriented in three nematic solvents were analysed, and the measured dipolar coupling constants, corrected for harmonic vibrations and for correlated deformation, were used to obtain information about the rα structure of the molecule. It is concluded that the s‐trioxane molecule oscillates between two equivalent chair conformers and the methylene protons are tilted outwards from the threefold symmetry axis. The optimized values for the geometric parameters are 1.111 (2) Å for the CH bond length, 110.3 (3)° for the HCH bond angle and −2.1 (3)° for the methylene rocking coordinate.
NMR studies on the rhodium(I) chelates of two 2,3‐bis(O‐diphenylphosphino)‐β‐D‐glucopyranosides: Potent catalysts for enantioselective reactions
Authors: Michalik Manfred , Freier Thomas , Schwarze Manuela , Selke Rüdiger 
Published: May 2005

AbstractThe 1H, 13C and 31P NMR spectra of the 2,3‐bis(O‐diphenylphosphino)‐β‐D‐glucopyranoside rhodium(I) chelates 1 and 2 were recorded in CDCl3 solution and the spectral assignments were performed with 1D and 2D techniques. In both complexes the pyranoside ring has a chair conformation. For the seven‐membered chelate ring a twist‐boat conformation could be established for 1, whereas for 2 the expected twist‐chair conformation was found. The phenyl groups at the P atoms show unhindered rotation about the CphenylP bonds and the COD ligand seems to rotate about the RhCOD axis slowly on the NMR time‐scale.
Dynamic processes in solids: Three large‐amplitude processes revealed in a simple quaternary ammonium salt
Authors: Riddell Frank G. , Cameron Kenneth S. , Turnbull W. Bruce 
Published: May 2005

Abstract13C CP/MAS NMR spectra of trimethyl(3‐phenylpropyl)ammonium bromide show evidence of three independent rotational processes in the solid: methyl rotation, trimethylammonium rotation and phenyl rotation.
Long‐range 37Cl/35Cl and 81Br/79Br isotope shifts in the 19F NMR spectra of some substituted fluorobenzenes
Authors: Bernard Guy M. , Schurko Robert W. 
Published: May 2005

AbstractLong‐range isotope shifts, Δδ, due to 37Cl/35Cl and 81Br/79Br, in the 19F NMR spectra of some substituted benzenes are reported. The shifts appear to be invariant to solvent and are additive when the isotopes are in chemically equivalent positions relative to the fluorine site. The three‐bond isotope shift attributed to chlorine is approximately −1.60 ppb and that from bromine varies from −0.25 to −0.28 ppb. These shifts appear to be invariant to the substituent pattern. However, there is a large difference in the four‐bond shift for 2,6‐dichloro‐4‐fluorophenol (−0.16 ppb) and 2‐chloro‐6‐fluorocyanobenzene, (−0.55 ppb), suggesting that this isotope shift is mediated by the intervening group. In all cases, substitution by the heavier chlorine isotope resulted in increased shielding. The nearly equal natural abundance of 81Br and 79Br resulted in double peaks of approximately equal intensity. However, in almost all cases, the high‐field peak is of slightly lower intensity, suggesting that the sign of this isotope effect is also negative.
Conformational studies on B/C‐cis‐ and B/C‐trans‐morphinan derivatives
Authors: Szabó Zoltán , Marton János , Hosztafi Sándor 
Published: May 2005

AbstractAn unambiguous structural differentiation of B/C‐cis‐ and B/C‐trans‐morphinan derivatives (thebainone‐A and β‐thebainone‐A and their 7,8‐dihydro derivatives) is provided. The structures were confirmed by NOE difference spectroscopy and selective 2D J‐INEPT experiments. In addition, full a priori 1H and 13C NMR assignments of the isomeric pairs studied are presented.
Solution structures of the DP IV (CD26) inhibitor Val‐boroPro determined by NMR spectroscopy
Authors: Günther Ulrich L. , Sudmeier James L. , Coutts Simon J. , Snow Roger J. , Barton Randall W. , Bachovchin William W. 
Published: May 2005

AbstractL‐Val‐L‐boroPro, a potent DP IV (CD26) inhibitor, and its non‐inhibitory diastereomer L‐Val‐D‐boroPro, were studied by 1D 1H and 11H NMR and by 2D 1H NMR methods in aqueous solution. Complete 1D 1H NMR fine structures were computer analyzed to obtain the 1H chemical shifts and spin‐coupling constants. Dihedral angles were derived from coupling constants on the basis of the Altona equation (i.e. an improved Karplus equation). The structures and populations of proline ring conformations were determined with the aid of pseudo‐rotation analysis. Good agreement between the distances derived from NOESY data and dihedral angle‐constrained force‐field calculations was obtained. Structural analysis allowed the identification of the absolute stereochemistry of the α‐carbon of the proline residue, and showed that the active inhibitor is the diastereomer which is homochiral with L‐proline. L‐Val‐L‐boroPro exists largely in a single conformer, in contrast to L‐Val‐D‐boroPro, which adopts two proline conformations in a 2:1 ratio. Analysis of 1H and 11H NMR spectra proves that inactivation of the inhibitor at physiological pH results from a cyclization reaction in which the free N‐terminal nitrogen atom forms a covalent bond with the B atom.
Substituent‐induced chemical shifts of aromatic carbon centres in a series of non‐acetylated and peracetylated Para‐substituted aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides
Authors: Roy René , Tropper François D. , Williams Antony J. 
Published: May 2005

AbstractThe additive behaviour generally observed for the substituent‐induced chemical shifts (SCS) for disubstituted benzenes was examined for a series of aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides having a wide range of para substituents with varying possible electronic contributions. The SCS values associated with non‐acetylated and peracetylated glucoside rings in para‐substituted aryl 2‐N‐acetamido‐2‐deoxy‐β‐D‐glucopyranosides were calculated. The additive nature of SCS analysis for para‐substituted systems was shown to hold for the meta and para positions but the very small change in chemical shifts for the ortho positions precluded attempts at analysis of these data. The observation of a good correlation for the ipso carbons for the acetylated compounds compared with a poor correlation for the same site in the non‐acetylated compounds is not well understood.
Carbon‐13 NMR spectral assignments of some bicyclo[4.3.0]nonanone and bicyclo[4.4.0]decalone systems
Authors: Rao H. Surya Prakash , Reddy K. Subba 
Published: May 2005

AbstractCarbon‐13 NMR signal assignments of some bicyclo[4.3.0]nonan‐4‐ones (hydrindanones) and bicyclo[4.4.0]decal‐4‐ones are reported.
Sur les complexes formés par le trifluorure de bore avec les sulfoxydes, aminoxydes, phosphinoxydes et arsinoxyde: Aspects généraux des spectres de RMN (1H,11B,19F et31P)
Authors: Bravo R. , Durand M. , Laurent J.‐P. 
Published: May 2005

AbstractLes spectres de résonance magnétique nucléaire (1H,11B,19F et31P) des complexes RnMO·BF3formés par le trifluorure de bore et des sulfoxydes, aminoxydes, phosphinoxydes et arsinoxydes ont été obtenus. Les paramètres (déplacements et couplages) caractérisant ces spectres sont comparés à ceux de composés similaires renfermant également une liaison de coordination O·B.
Mise en evidence de la chiralité de l'édifice spirophosphoranique
Authors: Houalla D. , Sanchez M. , Wolf R. 
Published: May 2005

AbstractLa chiralité de l'édifice spirophosphoranique dans le mélange racémique 2a, 2ā, est décelée, en RMN, à l'aide d'inducteur de déplacement chimique optiquement actif.
Dynamic NMR: A single operational parameter approach for evaluation of lifetime in an uncoupled, equally populated AB system
Authors: Dimitrov Valentin S. 
Published: May 2005

AbstractTwo simple formulae involving only one variable are presented for the simple and rapid estimation of the mean lifetime (τ) of exchange in uncoupled, paripartite AB systems. These formulae are shown to provide τ values comparable to those obtained from total line‐shape analysis.
NMR spectrum of 1‐chloronaphthalene orientated in the nematic phase
Authors: Diehl P. , Vogt J. 
Published: May 2005

AbstractThe NMR spectrum of 1‐chloronaphthalene has been studied in the nematic phase of N‐(p′‐ethoxybenzylidene)‐p‐n‐butylaniline. Ratios of interproton distances have been derived.
Determination of the erythro and threo configuration of the two diastereoisomeric 2‐amino‐3‐mercaptobutyric acids by NMR spectroscopy of derived thiazolidines
Authors: Toppet S. , Claes P. , Hoogmartens J. 
Published: May 2005

AbstractA study of the 1H and 13C NMR spectra of the N‐formyl‐2,2,5‐trimethyl‐4‐carboxythiazolidines and the N‐formyl‐4‐carboxy‐5‐methylthiazolidines derived from the two diastereoisomeric 2‐amino‐3‐mercapto‐DL‐butyric acids, permits unambiguous assignment of the erythro and threo configuration of these amino acids. The spectra of the N‐formylthiazolidines, recorded in DMSO‐d6 solution, reveal the presence of two conformational isomers with a low rate of interconversion. The geometry around the carbon–nitrogen bond and correlated conformations of the 5‐membered ring in both forms are discussed.
Temperature dependent NMR spectra of oxazepines, thiazepines, oxazocines and thiazocines
Authors: Puar Mohindar S. , Yale Harry L. , Cohen Allen I. 
Published: May 2005

AbstractThe temperature dependence of several 7‐membered 5‐substituted‐5,11‐dihydrodibenz[b,e] [1,4]oxazepines (Z = O) and thiazepines (Z = S), as well as of 8‐membered 12‐substituted ‐6,11‐dihydro‐12H‐dibenz[b,f] [1,4]oxazocines (Z = O) and thiazocines (Z = S), has been studied by NMR spectroscopy. The average ΔF* (kcal/mol) values at coalescence temperatures are 14·0 (M = CHO), 18·2 (M = COCH3) for oxazepines, 17·3 (M = CHO), >21 (COCH3) for thiazepines, and 13·0 for oxazocines and 13·3 for thiazocines, respectively. These data show that replacement of oxygen by a sulfur atom raises the barrier height of ring inversion, but that this effect is greater with the 7‐membered than with 8‐membered heterocycles. Thus the 8‐membered rings have a greater degree of flexibility than do the 7‐membered ones. With the oxazepines and the thiazepines, it was also possible to measure the thermodynamics (ΔF*, ΔH* and ΔS*) of the hindered rotation around the NCO bond by studying the temperature dependence of the formyl and acetyl proton resonances. The results suggest that the processes of conformational inversion and hindered rotation in the same molecule are independent of each other. The rate of hindered rotation is slower than the rate of conformational inversion. The conformational preferences of the compounds are also discussed.
NMR spectra of 1,3‐butadienes: VII—the conformation of 2,4‐dimethyl‐2,4‐pentadiene
Authors: Cunliffe A. V. , Harris R. K. 
Published: May 2005

AbstractProton magnetic resonance spectra of 2,4‐dimethyl‐2,4‐pentadiene have been examined for a number of solution conditions and (for a CF2Cl2 solution) over a range of temperatures. Coupling constants for the ethylenic protons were obtained from double resonance (methyl decoupled) spectra. Further double resonance experiments established the sign of 4Jc. It is found that 4Jc = −1·20 Hz and [4Jt] = 0·18 Hz. It is concluded that the compound exists in a single nonplanar conformation with an average dihedral angle (from the s‐cis form) ϕ = 50° ± 15°. Some long range coupling constants involving the methyl group were found to be appreciable in spite of the lack of planarity of the diene chain.
On the NMR spectrum of 1,3‐oxathiane‐3‐oxide: A contrast between the conformational preference of the sulphinyl oxygen in 1,3‐oxathiane‐3‐oxide and in 1,3‐dithiane‐1‐oxides
Authors: Bergesen Knut , Cook Michael J. , Tonge Alan P. 
Published: May 2005

AbstractThe 100 MHz spectrum of 1,3‐oxathiane‐3‐oxide is reported. Parameters obtained from first order analyses are interpreted in terms of an absence of a conformational preference of the SO bond at 38°C, but an axial preference at low temperatures. The behaviour contrasts with that found previously in the 1,3‐dithiane‐1‐oxide series.
Hindered rotation about the amido NC bond and the tautomeric equilibrium in N,N‐dimethylacetoacetamide
Authors: Hobson R. F. , Reeves L. W. , Shaddick R. C. 
Published: May 2005

AbstractThe molecule N,N‐dimethylacetoacetamide, which is subject to a keto–enol equilibrium process in solution, also exhibits hindered rotation about the amido NC bond. The hindered rotation rates have been studied by lineshape fit methods of the nuclear magnetic resonance spectra. In spite of some overlap of the keto and enol N‐methyl proton signals, the simultaneous measurement of the two distinct energy barriers in the two forms is possible as well as a determination of the keto–enol equilibrium. The differences in free energy of activation between keto and enol forms for the rotation barrier can be related to the conjugation energy of the NC π system with the enolic hydrogen bonded ring. Appeal to the model compound acetylacetone reveals a consistent set of energies for the keto and enol forms in the ground and transition states for internal rotation. The opportunity has been taken to reexamine and compare the keto–enol system ethylacetoacetate. Long range, solvent, concentration and temperature sensitive scalar couplings 4J(HH) between the enolic –OH and the adjacent methyl group in acetoacetic ester have not hitherto been reported.
Hétérocycles contenant du phosphore. XXIII—Etude par RMP de dérivés de l'oxazaphospholane‐1,3,2: III—Interprétation des résultats. Tentative d'analyse conformationnelle
Authors: Devillers Jean , Cornus Martine , Navech Jacques 
Published: May 2005

AbstractMoyennant certaines hypothèses, il est possible de déterminer la conformation au niveau du fragment C4C5 des différents dérivés de l'oxazaphospholane‐1,3,2 dont les paramètres de RMP ont été préalablement calculés.
Nuclear magnetic resonance spectra of pyrido‐ and azapyridocyanines
Authors: Leubner Ingo H. 
Published: May 2005

AbstractThe nuclear magnetic resonace spectra of six pyridocyanines, four azapyridocyanines, one monoquaternized 2,4′‐dipyridylamine and two dipyridylamines were measured and fully analyzed. The spectra of the 2,2′‐pyrido‐ and azapyridocyanines support previously published results that these dyes exist in the all‐trans form and not in the mono‐cis form, as stated by others. Strong evidence was obtained that N,N′‐ethylene‐2,2′‐pyridocyanine is twisted. The spectra of dyes with p‐connected pyridine rings indicate that these nuclei may rotate around the bond between the meso group and the p‐position. Relative chemical shifts in the spectra of the homologous pyrido‐ and azapyridocyanines can be explained by electronic effects rather than by magnetic anisotropy of the aza group or changes in ring currents.
Utilisation de la RMN a champs forts dans la série du norbornène: triméthylsilyl‐endo‐3 bicyclo (2.2.1) heptène‐5
Authors: Gassend R. , Limouzin Y. , Maire J. C. 
Published: May 2005

AbstractLa RMN à 250 et à 300 MHz combinée à des expériences de double irradiation de type classique ou INDOR a été utilisée pour établir sans ambiguité la structure endo d'un triméthylsilyl‐3 norbornène‐5. Les déplacements chimiques et les constantes de couplage ont été très exactement déterminés, des couplages à longue distance n'obéissant pas à la ‘règle du W’ ont été mis en évidence.
Ring strain effects: VI—benzocyclobutadienoquinone radical anion
Authors: Rieke Reuben D. , Westmoreland David G. , Rieke Loretta I. 
Published: May 2005

AbstractElectron paramagnetic resonance studies were carried out on the radical anion of 4‐deuterobenzocyclobutadienoquinone. The hyperfine coupling constants which had been assigned previously were found to be in error. The effects of the strained 4‐membered ring on the spin density distribution are discussed.
Solvent effects on the proton magnetic resonance spectra of thio‐ and dithio‐oxamides
Authors: Lepoivre J. A. , Desseyn H. O. , Alderweireldt F. C. 
Published: May 2005

AbstractThe chemical shifts of the N‐methyl signals for a number of thio‐oxamide and oxamide derivatives are unambiguously determined in the solvents chloroform, carbon tetrachloride, benzene, chlorobenzene, o‐dichlorobenzene and nitrobenzene. The ASIS effect is discussed. The temperature dependence of the absolute shift and of the relative shift differences of both methyl groups of the N,N‐dimethyl derivatives are studied.
NMR studies of sulphur heterocycles. II—substituent effects in the thieno[2,3‐b] [1]benzothiophene and thieno[3,2‐b] [1]benzothiophene systems
Authors: Ewing D. F. , Gregory D. N. , Scrowston R. M. 
Published: May 2005

AbstractSubstituent chemical shifts for the title systems have been determined at infinite dilution in CDCl3 from a study of 40 derivatives. An excellent correlation is found between the ortho effect of substituents in the thiophene ring and the corresponding effects in thiophene itself, indicating negligible perturbation by the fused rings. Long range effects of 2‐ and 3‐substituents on the 5‐ and 6‐protons are electronic in origin, but cannot be interpreted in terms of simple resonance theory. These long range effects correlate linearly with σp°. An O, S‐cis conformation for the formyl group in 2‐formyl‐thieno[2,3‐6][1]benzothiophene is adduced on the basis of chemical shifts.
Analysis of fine splittings in the fourier transform 1H magnetic resonance spectra of some 15N labeled borazine derivatives
Authors: Turbini Laura J. , Porter Richard F. 
Published: May 2005

AbstractProton NMR spectra are reported for 15N enriched borazine and a series of 15N enriched derivatives: N‐methyl‐borazine, N,N′‐dimethylborazine and a new photochemical product, 1‐methyl‐2‐aminoborazine. Chemical shifts for the ring (15NH) protons have been measured. Using a Fourier transform spectrometer, fine structure in the 15NH doublet is resolved. Ortho and meta ring proton and three‐bond 15N to H coupling constants have been determined. Substituent effects on chemical shifts and coupling constants for borazine derivatives are compared with those for analogous benzene derivatives.
A theoretical study of nuclear spin coupling constants and hyperfine coupling constants of se‐heterocyclics
Authors: Galasso V. , Bigotto A. 
Published: May 2005

AbstractMO calculations based on the finite perturbation theory in the INDO approximation have been carried out on selenophene, eighteen of its monosubstituted derivatives and benzo (b)selenophene. The calculated nuclear spin coupling constants satisfactorily reproduce signs, magnitudes, internal orders and some trends of the experimental values. Comparison of different ZDO calculations provides information on the relative importance of σ and π pathways for the various coupling constants in selenophene and benzo(b)selenophene. Unrestricted Hartree‐Fock calculations at the INDO level have been performed on the radical anions of dibenzoselenophene and 2,1,3‐benzoselenadiazole, the phenoselenazine radical cation, the phenoselenazine neutral radical and the phenoselenazine nitroxide. The isotropic hyperfine coupling constants have been found to be generally in satisfactory agreement with experiment.
Systèmes aromatiques à 10 électrons π dérivés de l'aza‐3a pentalène. IX—etude par RMN de l'équilibre azide/tetrazole dans le cas du tetrazolo [5,1‐b] benzothiazole
Authors: Faure R. , Galy J. P. , Giusti G. , Vincent E. J. , Elguero J. 
Published: May 2005

AbstractNous avons observé l'équilibre azide‐tétrazole dans le cas du tétrazolo [5,1‐b] benzothiazole par résonance magnétique nucléaire du proton à 250 MHz, en solution dans le deutériochloroforme. L'analyse des spectres a permis la détermination des déplacements chimiques et des constantes de couplage des deux formes tautomères.