bluuebunny/crossref_metadata_2025_split huggingface dataset:
100 MHz n.m.r. spectra and conformational analysis of some methyl and trimethyl derivatives of 1‐tetralone
Authors: Bergesen Knut , Cook Michael J. , Hock Teh Kim 
Published: May 2005

AbstractThe 100 MHz spectra of 2‐methyl‐, 4‐methyl‐, 4,5,8‐trimethyl‐ and 4,5,7‐trimethyl‐1‐tetralones have been analysed as 8‐spin systems using iterative computation. The monomethyl derivatives exist in inverting half‐chair conformations, the 2‐methyl group favouring the equatorial site and the 4‐methyl group showing equal preference for both axial and equatorial environments. The 5‐methyl substituent of the trimethyl derivatives constrains the 4‐methyl group to the axial site of rings which adopt non‐half‐chair conformations. The n.m.r. spectrum of 3‐methyl‐1‐tetralone is also discussed.
Utilisation des déplacements chimiques induits par les lanthanides dans l'analyse conformationnelle d'hétérocycles aromatiques β‐carbonylés
Authors: Gacel G. , Fournié‐Zaluski M. C. , Roques B. P. 
Published: May 2005

AbstractLa détermination des conformations préférentielles de formyl‐3 et acétyl‐3 furannes, thiophènes et pyrroles, ainsi que de quelques autres acyl‐3 furannes, a été effectuée par étude de la simulation des déplacements induits par les lanthanides. Les pourcentages conformationnels obtenus sont en accord avec ceux déterminés par d'autres méthodes RMN. Ceci montre que la complexation n'apporte aucun changement dans les rapports conformationnels et confirme ainsi la validité de la méthode dans l'analyse des aldéhydes et cétones hétéroaromatiques. Dans les trois hétérocycles étudiés, le groupement carbonyle montre une tr`s nette préférence pour la conformation XO trans dans le cas des aldéhydes, et un partage plus équilibré dans le cas des acétyles.
Stereochemical aspects of proton chemical shifts—IV: The cumulative nature of the geminal proton shift influenced by long chain substituents
Authors: Danneels Dirk , Anteunis Marc 
Published: May 2005

AbstractSubstituent shift effects on geminal protons are consistent with cumulative α‐, β‐ and γ‐effects of a long chain substituent, e.g. whereby not only the first, but also the subsequent β‐ and γ‐atoms of the sidechain should be taken into consideration. These shift contributions depend on rotational conformation in a way that lends itself to calculation where the necessary data are available. Therefore the shifts of the unsubstituted parent compound, the individual increment‐contributions of the β and γ groupings and the rotameric distribution must be known. This would enable, conversely, a semi‐quantitative prediction of one of these parameters if the others are accessible.
Complete assignment of the 13C n.m.r. spectrum of mutarotated D‐ribose by integration and specific deuteration
Authors: Breitmaier E. , Hollstein U. 
Published: May 2005

AbstractThe 13C n.m.r. spectrum of mutarotated D‐ribose is completely assigned by using 2‐ and 3‐deuterio‐D‐ribose as reference compounds. The signal intensities of the largely relaxed 13C n.m.r. spectrum are evaluated, and the equilibrium mixture of mutarotated D‐ribose is found to consist of 6·1% α‐furanose, 11·6% β‐furanose, 20·3% α‐pyranose and 62% β‐pyranose.
13C nuclear magnetic resonance studies on acetophenones: Barriers to internal rotation
Authors: Drakenberg Torbjörn , Sommer Jean M. , Jost Roland 
Published: May 2005

AbstractThe barrier to internal rotation in a series of p‐substituted acetophenones has been determined by means of low temperature carbon‐13 n.m.r. and total bandshape analysis, resulting in: ΔG = 5·4 ± 0·1 kcal mol−1 (22·4 ± 0·4 kJ mol−1) for the unsubstituted acetophenone. The substituent effects on the barrier are found to be the same as for the corresponding benzaldehydes. The barrier height is discussed in terms of contributions from resonance and steric effects.
Benzo‐ and indoloquinolizines: X—application of carbon‐13 n.m.r. to the stereochemistry of the 4b,5,6,7,8,8a,10,11,16,16b‐decahydrodibenz[f,h]indolo[2,3‐a]quinolizine isomers
Authors: Van Binst G. , Tourwé D. , De Cock E. 
Published: May 2005

AbstractThe carbon‐13 n.m.r. spectra of three isomers of 4b, 5,6,7,8,8a,10,11,16,16b‐decahydrodibenz[f,h]indolo[2,3‐a]quinolizine were interpreted with the aid of the 1,2,3,4,4a,5,6,10b‐octahydro‐6‐phenylphenanthridines and the 2‐phenylcylohexylamines. The configuration and the conformation of these compounds can be determined from the chemical shift values.
13C13C coupling constants in derivatives of trans‐stilbene and tetraphenylethylene. Determination of relative signs II
Authors: Hansen P. E. , Poulsen O. K. , Berg A. 
Published: May 2005

AbstractMagnitudes and signs of 13C13C coupling constants in compounds of the type Ph13CR1R213CR1R2Ph have been determined and the results are discussed in a broader context. Two types of coupling constants, J(C‐i, C‐α) and J(C‐i, C‐β), between aromatic carbon atoms and the benzylic carbons, probably with different coupling mechanisms, are considered. Whereas 2J(C‐2, C‐α) are always found positive, 2J(C‐1, C‐β) in the present compounds are found to be negative or about zero. 3J(C‐3, C‐α) has the same sign as 2J(C‐2, C‐α). A 4J and a 5J were observed in trans‐stilbene.
13C magnetic resonance studies of reduced proaporphine alkaloids
Authors: Ricca Giuliana Severini , Casagrande Cesare 
Published: May 2005

AbstractThe natural abundance 13C magnetic resonance spectra of reduced proaporphines are reported, with complete assignments based on peak multiplicity and empirical calculations of chemical shifts. The chemical shift values of C‐8, C‐12 and C‐7 are found to be strongly diagnostic of the spiro carbon configuration.
N.m.r. studies of a rate process in a bridged biphenyl: Resolution of a discrepancy between n.m.r. and polarimetric kinetic data
Authors: Carter Robert E. , Dahlqvist Kjell‐Ivar , Berntsson Peder 
Published: May 2005

AbstractTotal bandshape analysis of the temperature‐dependent n.m.r. spectrum of the bridge methylene protons in 6,6‐dicarbethoxy‐1,2,3,4‐dibenzcyclohepta‐1,3‐diene has been carried out to yield the following activation parameters: ΔG = 60.96 ± 0.17 kJmol−1 (14.57 ± 0.04 kcal mol−1), ΔH‡ = 47.3 ± 0.8 kJ mol−1 (11.3 ± 0.2 kcal mol−1) and ΔS‡ = −45.6 ± 3.3 J mol−1 K−1 (−10.9 ± 0.8 cal mol−1 K−1). A value of ΔG‡ in agreement with the above may be obtained from a bandshape analysis (at a suitable temperature) of the spectrum of the methylene protons in the carbethoxy groups. In our opinion, the rate process described by these activation parameters must be the configurational inversion of the biphenyl system, and thus the polarimetric data on this compound reported by Iffland and Siegel [J. Am. Chem. Soc. 80, 1947 (1958); half‐life of 80 min at room temperature] are seriously called to question, as previously noted by Sutherland and Ramsay [Tetrahedron 21, 3401 (1965)]. We have attempted unsuccessfully to repeat the polarimetric work, and have been able to show by means of thin‐layer chromatography in the cold, mass spectral analysis and polarimetry that an optically active impurity (as yet unidentified) is the most probable cause of the discrepancy.
The n.m.r. of paramagnetic complexes of vanadyl acetylacetonate with organic phosphites and hydroperoxides
Authors: Pobedimskii D. G. , Nasybullin Sh. A. , Kirpichnikov P. A. , Svitych R. B. , Yablonskii O. P. , Buchachenko A. L. 
Published: May 2005

AbstractThe vanadium IV ion in vanadyl acetylacetonate (VIV) forms labile paramagnetic complexes with organic phosphites in the first coordination sphere. The enthalpy of complex formation between VIV and triphenyl phosphite was 2.6 kcal mol−1. Complex formation enthalpies ΔH and the activation energies E of ligand (hydroperoxide) escape from the metal ion sphere were determined from the temperature dependence of paramagnetic broadening of the n.m.r. lines of hydroperoxides in the presence of vanadyl acetylacetonate. At low temperatures the phosphite sharply weakens the bond between the metal ion and hydroperoxide in the second coordination sphere (ΔH decreases fivefold). Taken in excess, phosphite displaces the hydroperoxide molecules from the coordination sphere of the VIV ion and thus blocks it. The observed n.m.r. characteristics of the paramagnetic complexes explain, on the model level, the kinetic regularities of the reaction of hydroperoxides with phosphite catalysed by transient metal ions.
Vicinal 13CH coupling through olefinic double bonds
Authors: Douglas Alan W. 
Published: May 2005

AbstractValues of long range 13CH coupling through the double bond in a number of isopropenyl compounds are reported. There is evidence that substituent dependence of 3J(CH) is not related linearly to that of HH couplings in vinyl compounds. The ratio of 3J(CH) to 3J(HH) in analogous pairs of compounds appears to increase with decreasing substituent polarity and increasing steric bulk.
NMR‐Untersuchungen an Dicyclopentadienderivaten: III—Stereochemische Zuordnung von überbrückten endo‐Dicyclopentadienderivaten und deren Wagner‐Meerwein‐Umlagerungs‐produkten mit Hilfe der NMR‐Spektroskopie
Authors: Kleinpeter E. , Kühn H. , Mühlstädt M. 
Published: May 2005

AbstractDie 1H‐NMR‐Spektren einer Reihe substituierter Oxa‐ bzw. Azatetracycloundecane werden aufgezeigt und an ausgewählten Beispielen mit Hilfe von Spin‐Spin‐Entkopplung und Eu(fod)3—paramagnetischen Verschiebungsversuchen eingehend analysiert. Aus den mit angeführten 13C‐NMR‐Spektren werden die einzelnen C‐Resonanzen unter Verwendung bekannter Substituenteneffekte und paramagnetischer Signal‐verschiebungen zugeordnet. Die paramagnetischen Verschiebungswerte ΔEu werden hinsichtlich ihrer Kontakt‐ und Pseudokontaktbeiträge diskutiert.
Carbon‐13 spin–lattice relaxation times as a probe for the study of electron donor–acceptor complexes
Authors: Blackburn Barry J. , Friesen Kenneth J. 
Published: May 2005

Abstract13C spin–lattice relaxation times (T1's) are reported for C‐3 of 2‐methylindole (methyl,3‐13C2) as a function of the concentration of added 1,3,5‐trinitrobenzene at 35°C in 1,2‐dichloroethane. The observed decreases in T1, with increasing concentrations of 1,3,5‐trinitrobenzene, are interpreted in terms of longer time‐averaged correlation times which result from (a) the formation of increasing amounts of electron donor–acceptor complex and (b) increases in viscosity. An equation is derived which makes it possible to obtain estimates of the equilibrium constant for complex formation, and the spin–lattice relaxation time of the complex, from the observed T1's and viscosity measurements. From the data obtained, values of 6.4 × 10−12 and 14.1 × 10−12 s rad−1 were calculated for the effective correlation times (at 35°C and 0.686 centipoise) and 0.21 and 0.28 nm for the effective radii of free and complexed donor respectively.
The origin of aromatic solvent‐induced shifts in 19F n.m.r.
Authors: Takada Kanako , Nakagawa Naoya , Nikki Kunio , Kimura Hiroshi 
Published: May 2005

AbstractAromatic solvent‐induced shifts (ASIS) in 19F n.m.r. spectra of several organic fluoro compounds have been determined in several solvents. 19F n.m.r. signals of unsaturated fluoro compounds in C6F6 and C6H6 show excess high field shifts corresponding to the term σc (solvent shift caused by chemical interactions). The mechanism of this shift is discussed in connection with the presence of an F‐π interaction. A thermal study also supports this idea.
Benzofurobenzthiazole: VI—1H‐ und 13C‐NMR‐Spektren von 2‐Aminobenzofuro[2,3‐f] benzthiazol und 2‐Aminobenzofuro[2,3‐e]benzthiazol im Vergleich mit Dibenzofuran und 2‐Aminobenzthiazol
Authors: Florea Stelian , Kimpenhaus Wolfgang , Fărcăşan Valer 
Published: May 2005

AbstractDurch Cyclisierung von 3‐Dibenzofurylthioharnstoff unter Bedingungen der Hungershoff‐Reaktion entsteht ein Isomers, das die lineare Struktur 1 besitzt. Zur Entscheidung dienten die 1H‐NMR‐ und 13C‐NMR‐Spektren der zwei isomeren Aminobenzofurobenzothiazole (1 und 3), aufgenommen bei 220 MHz, 60 MHz und 22,62 MHz. Die magnetischen Parameter ergaben sich teils durch Spektreninterpretation nach den der der Regeln ersten Ordnung, teils durch Spektrensimulation mit Hilfe von LAOCOON 3; eine Zuordnung der Resonanzen gelang durch den Vergleich der chemischen Verschiebungen und Kopplungskonstanten mit denen der Stammkörper Dibenzofuran (4a) und 2‐Aminobenzthiazol (5c). Soweit die Zuordnungen der Stammkörper selbst unbekannt waren oder allein durch Analogieschluß erfolgten, sind sie durch experimentelle Kriterien bestimmt worden, wie durch Deuterium‐Substitution oder durch Untersuchung der Veränderungen der chemischen Verschiebungen bei Derivatisierung.
Etude par RMN 1H des effets de solvant sur les déplacements chimiques et les couplages vincinaux des benzothiénopyridines
Authors: Roques B. P. , Prange T. , Oberlin R. 
Published: May 2005

AbstractL'étude des interactions solvant/soluté des quatre benzothiénopyridines isomères a été entreprise par RMN 1H. Le calcul des spectres au second ordre permet de révèler: (i) dans l'acétone une orientation préférentielle des molécules de solvant au niveau du cycle pyridinique; (ii) une forte variation des couplages de la partie benzénique en fonction de la nature du solvant; (iii) une interaction préférentielle du cycle pyridinique dans les complexes de collision du benzène. Ces résultats peuvent ětre transposés aux interactions hétérocycles azotés/bases appariées de l'ADN (intercalation).
Interactions intramoléculaires. XXVII—Etudes structurales en série bicyclo[4.1.0]heptanique (effets d'anisotropie sur les déplacements chimiques du proton; constantes de couplage et équilibres conformationnels)
Authors: Pizzala Louis , Bodot Hubert , Fruchier Alain 
Published: May 2005

AbstractTous les paramètres RMN sont déterminés pour les dérivés suivants du diméthyl‐1,6 bicyclo[4.1.0]heptane: diméthoxycarbonyl‐3,4 (3 diastéréoisomères), méthoxycarbonyl‐3 (d4‐2,2,5,5) cis et trans, méthyl‐3 méthoxycarbonyl‐3 cis et trans; les triméthyl‐1,5,5 bicyclo[4.1.0]heptanols‐3 cis et trans ont été également étudiés. Les divers déplacements chimiques sont corrélés grǎce à un ensemble d'incréments déterminés empiriquement. Les équilibres conformationnels sont précisés à partir des constantes de couplage vicinales; les enthalpies libres conformationnelles du groupement COOCH3 sont évaluées; le rǒle des interactions gauches est considéré.
Carbon‐13 n.m.r. spectra of saturated heterocycles. Part VII—Thianium Salts
Authors: Willer Rodney L. , Eliel Ernest L. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of 53 thianium, S‐methylthianium, S‐alkylthianium and S‐methyl‐1‐thiadecalinium salts, most of them substituted with methyl groups in the ring, have been recorded. The chemical shifts of the ring carbons in these thianium and S‐methylthianium salts and the S‐methyls in the S‐methylthianium salts have been analyzed in terms of additive parameters of the methyl substituents which are compared to those previously determined for the parent thianes. Comparison is also made with other charged species.
19F n.m.r. spectrum of hexafluoroquinazoline long‐range inter‐ring FF coupling constants
Authors: Matthews R. S. 
Published: May 2005

AbstractThe 19F n.m.r. spectrum of hexafluoroquinazoline has been analyzed giving the signs and magnitudes of all but two of the coupling constants, and supporting the analyses of the 19F n.m.r. spectra of heptafluoroquinoline and heptafluoroisoquinoline. Long range FF inter‐ring coupling constants are a guide for assessing π‐electron delocalization pathways. In addition, nitrogen in the β position enhances the distant F‐5, F‐7 meta‐coupling constant, implying a π‐contribution to J(FF)meta. A rationalization of changes in peri‐coupling constants is also presented. The observed changes appear to be the sum of two effects: (i) ring contraction by the insertion of shorter CN bonds into the aromatic ring and (ii) a secondary effect which is dependent on the existence of a β‐nitrogen, adjacent to the peri nuclei.
13C n.m.r. chemical shifts in aliphatic alcohols and the γ‐shift caused by hydroxyl and methyl groups
Authors: Ejchart Andrzej 
Published: May 2005

AbstractEmpirical correlations for the prediction of the chemical shifts of the carbon atoms in aliphatic alcohols are presented. Structural and conformational effects contributing to the 13C chemical shifts of γ‐carbons are discussed.
Carbon‐13 n.m.r. studies. Part 66—13C spectra of several methyl, hydroxymethyl and carboxylic acid derivatives of bicyclo[2.2.1]heptane and bicyclo[2.2.2]octane
Authors: Brouwer H. , Stothers J. B. , Tan C. T. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of a series of 52 substituted norbornanes, norbornenes, bicyclo[2.2.2]octanes and ‐octenes have been recorded to examine the stereochemical effects of closely neighboring substituents on the carbon shieldings of these well‐defined molecular frameworks. These moderately rigid skeletons permit detailed examination of a variety of orientations of substituents and, in this study, attention has been focused on a series of vicinally substituted systems. The substituents include methyl, hydroxymethyl and carboxylic acid groups for comparison with earlier data for several bicyclic alcohols and hydrocarbons, from which conclusions regarding the conformational preferences of the hydroxyl group may be drawn. The deviations of the observed shieldings from those predicted by simple additivity follow definite patterns which should be useful for stereochemical assignments in related systems.
Anisole, acetophenone and benzoic acid methyl ester oriented in a nematic phase: Structure and internal motion
Authors: Diehl P. , Huber H. , Kunwar A. C. , Reinhold M. 
Published: May 2005

Abstract1H‐, 1H{2D}‐, 2D‐ and 2D{1H}‐N.m.r.‐spectra were used in an investigation of the partially oriented molecules anisole, acetophenone and benzoic acid methyl ester. The phenyl ring geometries were found to deviate slightly from the regular hexagon. For anisole and acetophenone the measured couplings indicate a structure with the substituent group in the plane of the ring and one of the methyl protons pointing away from it. It is not possible, however, to draw further conclusions on the depths and shapes of the potentials hindering the internal motions. For benzoic acid methyl ester the measurements indicate that the dominant conformer is the one with the OCH3 axis approximately parallel to the effective molecular C2‐symmetry axis.Semiempirical MO calculations were found to provide reasonable molecular structures but no information on the potentials.
Selektive Verbreiterung von 1H‐NMR Restsignalen deuterierter Lösungsmittel
Authors: Roth Klaus 
Published: May 2005

AbstractDie Anwendung der 1H{2H} Off‐Resonance Rauschentkopplung führt in den 1H‐NMR‐Spektren nicht vollständig deuterierter Verbindungen zu einer selektiven Verbreiterung der Protonenrestsignale, sofern diese durch H/D Kopplungen aufgespalten sind. Diese Entkopplungstechnik ermöglicht den einfachen Nachweis von Signalen, die von Lösungsmittelrestsignalen verdeckt sind, wie am Beispiel von Gemischen aus Aceton und Aceton‐d6 gezeigt wird. Typische Geräteparameter zur experimentellen Durchführung dieser Doppelresonanztechnik werden angegeben.
3J(HH)Pμ,ν correlation for planar 7‐membered cyclic π‐systems—structural effects on 3J(HH)
Authors: Günther Harald , Schmickler Hans , Günther Maria‐Eugenia , Cremer Dieter 
Published: May 2005

AbstractIt is shown that sterically unperturbed vicinal HH coupling constants in planar 7‐membered π‐systems correlate linearly with the HMO π‐bond order: 3J(HH) = 20.91Pμ,ν–3.85 (r.m.s. error 0.26 Hz, correlation coefficient =0.988). Systematic deviations from this relationship which most probably originate from valence angle changes are found for fused π‐systems containing rings of different size. Model calculations using the CNDO/2 method as well as finite perturbation theory and INDO wave functions support the experimental findings. An improvement of existing 3J(HH)Pμ,ν correlations for planar 6‐membered rings is possible if CNDO/2 π‐bond orders are used instead of HMO or PPP‐SCF data.
Identification by e.s.r. spectroscopy of pentyloxyphenylnitroxyl and diphenylnitroxyl radicals during the reaction of aniline and pentyl nitrite
Authors: Paton R. Michael , Weber Rudolf U. 
Published: May 2005

AbstractThe e.s.r. signal observed during the reaction of aniline and pentyl nitrite in benzene is shown to be due not to phenyldiazoxyl (PhNNO·), as previously reported, but to a mixture of pentyloxyphenylnitroxyl and diphenylnitroxyl radicals, this assignment being made with the aid of deuterium labelling and on the basis of their observed hyperfine coupling constants and g values.
The axial/equatorial preference of the diphenylphosphino group bonded to the phosphorus of a 2‐oxo‐1,3,2‐dioxaphosphorinanyl ring
Authors: Okruszek Andrzej , Stec Wojciech J. , Harris Robin K. 
Published: May 2005

AbstractProton, 13C and 31P n.m.r. spectra of the diastereoisomeric 2‐diphenylphosphino‐2‐oxo‐4‐methyl‐1,3,2‐dioxaphosphorinans indicate that the diphenylphosphino group is essentially axial for the trans isomer, whereas it is predominantly equatorial in the case of the cis isomer.
Conformational study of phosphoserine in aqueous solution. I—13C n.m.r. results
Authors: Pogliani L. , Ziessow D. , Krüger Ch. 
Published: May 2005

Abstract13C chemical shifts and coupling constants of phosphoserine in aqueous solutions were studied as a function of pH values. Carboxyl and α‐amino titration shifts agree with those observed in amino acids. The analysis of the coupling constants indicates that for rotation about the (C)CO(P) axis the trans conformer predominates for all pH values. The fractional population of the gauche conformer reaches a maximum at pH=8.
A 13C n.m.r. study of the charge‐transfer complexes between o‐chloranil and some aromatic electron donors
Authors: Prins I. , Verhoeven J. W. , De Boer T. H. J. 
Published: May 2005

AbstractThe 13C n.m.r. spectra of complexes between o‐chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the 13C n.m.r. signals for the acceptor (o‐chloranil), but for signals from the 13C nuclei in the donors both diamagnetic and paramagnetic shifts are found.These phenomena are thought to be the result of competing anisotropy and charge‐migration effects. Charge migration in o‐chloranil complexes appears to be more important than in corresponding 1,3,5‐trinitrobenzene complexes.
The structure of α‐(1,2‐dithiole‐3‐ylidene) ketones and α‐(1,2‐dithiole‐3‐ylidene) aldehydes studied by means of n.m.r. spectroscopy
Authors: Pedersen Carl Th. , Frandsen Erik G. , Schaumburg Kjeld 
Published: May 2005

Abstract1H and 13C n.m.r. studies of a series of twelve 1,2‐dithiole‐3‐ylidene ketones and aldehydes have shown that the geometry of the carbon backbone is the same as found in 1,6,6aλ4‐trithiapentalenes. No evidence has been found which favours a bicyclic structure for the system. A linear correlation of observed 13C chemical shifts with calculated charge densities is found to be valid. The observations are in agreement with a structure which is a hybrid between a true ketonic structure and a true mesoionic structure.By using the difference in the 13C chemical shifts of ortho and meta carbon atoms in substituent phenyl groups it is possible to qualify the degree of coplanarity of the phenyl groups with the backbone of the molecule.
Linear dependence of 1J13C, 199Hg) and 2J(1H, C,199Hg) for dibenzylmercury in various solvents
Authors: Petrosyan Valery S. , Roberts John D. 
Published: May 2005

AbstractThe 1J(13C, 199Hg) spin–spin coupling constants have been studied for dibenzylmercury in various solvents. A linear correlation was found between 1J(13C, 199Hg) and the 2J(1H, C, 199Hg) constants obtained earlier for the same solutions.