bluuebunny/crossref_metadata_2025 huggingface dataset:
Variable temperature n.m.r. behaviour of 1,5‐benzodiazepinones and 1,5‐benzodiazepinthiones
Authors: Benassi Rois , Lazzeretti Paolo , Taddei Ferdinando , Nardi Dante , Tajana Alberto
Published: May 2005

The n.m.r. variable temperature behaviour of the 7‐membered ring in 1,3‐dihydro‐2H‐1,5‐benzodiazepin‐2‐one derivatives and in the corresponding 2‐thiones has been investigated. The results indicate that the ring inversion barrier is higher in the thiones and dependent on substituents bonded at N‐1. The activation parameters are obtained and discussed.
Hétérocycles contenant du phosphore: XXVIII—Etude par Résonance Magnétique Nucléaire et analyse conformationnelle de quelques oxazaphosphorinanes‐1,3,2 (II)
Authors: Roca Claude , Kraemer Raymond , Majoral Jean‐Pierre , Navech Jacques , Brault Jean François , Savignac Philippe
Published: May 2005

Les spectres de RMN du proton de quelques nouveaux oxazaphosphorinanes‐1,3,2 sont analysés. La stéréochimie et la conformation du cycle sont précisées. La valeur de l'enthalpie libre conformationnelle et de l'angle de torsion des liaisons C‐4C‐5 et C‐5C‐6 est calculée pour quelques uns de ces oxazaphosphorinanes‐1,3,2.
13C chemical shifts of some model olefins
Authors: Couperus P. A. , Clague A. D. H. , van Dongen J. P. C. M.
Published: May 2005

An extensive carbon‐13 nuclear magnetic resonance study of selected model olefins dissolved in deuteriochloroform has been carried out under standardized conditions. Assignments of the chemical shifts have been made. The influence of the nature of the solvent and the effect of changing the concentration of the solute have been investigated. The results are intended to provide a practical aid for the analysis of olefinic materials.
Diastéréotopies dans la série du benchrotrène
Authors: Tirouflet Jean , Besancon Jack , Mabon Francoise , Martin Maryvonne L.
Published: May 2005

L'analyse des spectres RMN 1H et 13C d'une série de benchrotrènes mono‐et disubstitués a permis de discuter l'influence des substituants et spécialement les diastéréotopies associées à plusieurs types de chiralité. La forme racémique (pseudosymétrique) et les deux formes meso (pseudoasymétriques) des glycols (OC)3CrC6H4(CHOHCH3)2 sont comparées. Les implications stéréochimiques des résultats sont examinées.
13C n.m.r. of organosulphur compounds: II—13C chemical shifts and conformational analysis of methyl substituted thiacyclohexanes
Authors: Barbarella Giovanna , Dembech Pasquale , Garbesi Anna , Fava Antonino
Published: May 2005

13C n.m.r. spectra of methyl substituted thianes and thianium cations have been determined. The magnitude of the 13C substituent effects of an equatorial methyl group or of a gem‐dimethyl grouping appear to depend in a systematic way on whether the carbon atom concerned is adjacent to, or removed from, the heteroatom. The shieldings are discussed in relation to the conformational properties of the thiane ring. Moreover, the average 13C substituent parameters obtained from conformationally biased systems are applied to potentially mobile systems to assess the position of the conformational equilibrium.
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

The 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

La 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

Substituent 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

The 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

The 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

The 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

Magnitudes 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

The 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

Total 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

The 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

Values 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

Die 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

13C 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

Aromatic 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

Durch 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

L'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

Tous 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

The 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

The 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

Empirical 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

The 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

1H‐, 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

Die 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

It 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

The 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

Proton, 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

13C 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

The 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

1H 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

The 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.
Carbon‐13 n.m.r. spectra of 2,3‐dimethylenebicyclo[2.2.1]heptanes and 2,3‐dimethylene‐7‐oxabicyclo[2.2.1]heptanes
Authors: Quarroz Daniel , Sonney Jean‐Marie , Chollet André , Florey André , Vogel Pierre
Published: May 2005

The 13C n.m.r. spectra of 11 derivatives of 2,3‐dimethylenenorbornane, 1–11, of 5 derivatives of 2,3‐dimethylene‐7‐oxanorbornane, 12–16, and of 2,3,5,6‐tetramethylene‐7‐oxanorbornane (17) have been measured and the chemical shifts have been assigned. The effects of 1‐methyl, 5‐hydroxy, 5‐acetoxy, 5‐para‐bromobenzenesulphonyloxy and 5‐keto substituents on the olefinic carbons of the s‐cis‐butadiene group are compared with the same substituent effects reported for model compounds. Apparent linear correlations between the reciprocals of the V←N transition energies of the butadiene chromophores and the differences of the chemical shifts ΔδC between the quaternary and methylene olefinic carbons are found for the dienes 1–3, 12–14, butadiene and 2,3‐dimethylbutadiene. The ΔδC of the olefinic carbons of the tetraene 17 also falls on the correlation line if the average of the two absorption hands at 250 and 228 nm is taken for the V←N transition energy of this compound. The chemical shift of the carbon of the methano bridge H2C‐7 is almost insensitive to the presence of one or two methylene groups at C‐2,3, in contrast with the downfield shift of 10–14 ppm observed when an endocyclic double bond is introduced into the norbornane skeleton.
Isomérie Conformationnelle autour de la Liaison Carbone–Carbone dans les Sels de Propénylylidène Ammonium
Authors: Filleux‐Blanchard Marie‐Louise , Le Botlan Denis
Published: May 2005

L'étude par RMN protonique à des températures comprises entre −90 et 70 °C des sels de propenylylidène ammonium met en évidence la présence de deux conformères. L'examen des déplacements chimiques et constantes de couplage est an faveur d'une isomérie conformationnelle autour d'une liaison carbone–carbone, hypothèse corroborée par les résultats obtenus par spectrographie 13C. Les enthalpies libres d'activation sont données pour divers substituants.
13C, 13C coupling constants and 13C chemical shifts of aromatic carbonyl compounds. Effects of ortho‐ and peri‐interactions involving the carbonyl substituent
Authors: Hansen P. E. , Poulsen O. K. , Berg A.
Published: May 2005

Carbon‐13 n.m.r. data have been determined for a series of 26 aromatic carbonyl compounds including benzoyl, naphthoyl and pyrenoyl derivatives 13C labelled in the carbonyl group. Doubly labelled anthraquinone has also been included. The compounds investigated comprise non‐hindered molecules and molecules in which the carbonyl substituent is subject to ortho‐ or peri‐interactions affecting conjugation of the carbonyl group with the aromatic ring. The dependence of long range 13C,13C coupling constants involving the carbonyl carbon, in particular 2J and 3J, on steric conditions is discussed, as is the possibility of deciding on the orientation of the carbonyl bond. The following results have emerged. 2J(s‐t)>2J(s‐c) for ketones and aldehydes, and the reverse is valid for acids and acid derivatives. (s‐t and s‐c refer to the orientation of the CO group relative to the aromatic bond in question with respect to the connecting single bond). For ketones 3J(t,s‐c)<3J(t,s‐t), and both of these 3J(t) values decrease with increasing angle of twist, θ, about the single bond, whereas 3J(c,s‐c) increases with θ. For acids and acid derivatives no similar regularity was found. (The initial t and c refer to the geometry of the three‐bond coupling path). Generally it is found that 3J(t)>3J(c) and 3J(t)>2J, confirming earlier results. Theoretical calculations on a few model compounds are qualitatively in accordance with the experimental results. Some sign determinations for coupling constants are presented. A short discussion is given of substituent effects on chemical shifts. Observed trends are consistent with earlier results.
Benzo‐ and indoloquinolizines. XII—carbon‐13 n.m.r. study of the conformation of the 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9a H‐pyrido[1,2‐f]phenanthridine isomers
Authors: Van Binst G. , Laus G. , Tourwé D.
Published: May 2005

The influence of the configuration and the conformation on the 13C n.m.r. spectrum of 1,2,3,4,4a,6,7,8,9,13b‐decahydro‐9aH‐pyrido[1,2‐f] phenanthridine was investigated. These observations, coupled with the low temperature spectrum allowed us to confirm the trans‐syn‐cis as the preferred conformation for one of the four isomers. At −40°C, 2–3% of another conformer could be detected and identified as the cis‐anti‐cis‐2.
1H and 13C studies of alkenes, epoxides and cyclic thionocarbonates
Authors: Hevesi L. , Nagy J. B. , Krief A. , Derouane E. G.
Published: May 2005

1H and 13C chemical shift data are presented and discussed for a number of di‐ and tri‐alkyl substituted alkenes, epoxides and thionocarbonates. The completely stereospecific interconversion of these compounds, together with the n.m.r. data, allows a straightforward and quantitative stereochemical analysis. For 1H n.m.r., the most useful intermediates proved to be the thionocarbonates. The differential shieldings between cis and trans isomers are tentatively explained in terms of the conformational change of the 5‐membered thionocarbonate ring. In 13C n.m.r., either series can be useful to distinguish between stereoisomers. The conclusions stemming from the 13C n.m.r. results complement the 1H n.m.r. studies.
Conformational study of phosphoserine in aqueous solutions. II—1H n.m.r. results
Authors: Pogliani L. , Ziessow D. , Krüger Ch.
Published: May 2005

The 270 MHz n.m.r. spectra of phosphoserine (PSer) have been measured and completely analysed for seven pD values. The resulting vicinal coupling constants 3J(HαHβ) and 3J(PHβ) are used to discuss the conformations of PSer with respect to the (Hα)CαCβ(O) and (Cα)CβO(P) bond axes. The all‐trans conformer predominates for all pD values, with its fractional population being minimal at pD values close to neutrality. The CβO bond rotamer populations agree reasonably well with those obtained from 13C investigations.
1H and 31P n.m.r. spectra of the arylsulphonylamides of some chiral or prochiral organophosphoric acids
Authors: Barabás A. , Popescu R. , Mureşan V. , Almási L.
Published: May 2005

1H and 31P n.m.r. spectra recorded for arylsulphonylamides of several organophosphoric acids confirmed the expected molecular formulae. Geminal methylenic protons of the arylsulphonylamides of diethylthiophosphinic acid, of ethoxyethanethiophosphonic acid, of ethoxycyclohexanephosphonic acid, of ethoxybenzenethiophosphonic acid and the tautomeric N‐methylated or S(or O)‐methylated derivatives are diastereotopic, showing different chemical shifts and different coupling constants to neighbouring nuclei.
The structure of 1,2‐dithioles studied by 13C n.m.r. spectroscopy
Authors: Frandsen Erik G. , Jacobsen Jens P.
Published: May 2005

The charge separation between the dithiole ring and oxygen in 3‐(1′,2′‐dithiole‐3′‐ylidene)‐6‐methyl‐2,3‐dihydropyran‐2,4‐diones and 3‐(1′,2′‐dithiole‐3′‐ylidene)‐2,3‐dihydrobenzo[b] pyran‐2,4‐diones has been determined by 13C and 19F n.m.r. spectroscopy. By both methods it is found that these compounds are relatively polar. A correlation is established between the 13C chemical shift of some carbon atoms and the S2p binding energies measured by e.s.c.a. in the 1,2‐dithiole derivatives. This correlation shows that these 13C shifts depend on the positive charge taken by the 1,2‐dithiole ring and can then constitute a convenient evaluation of this charge.
Equation de Karplus et l'Hybridation du Carbone. Correlation de la Constante de Couplage Vicinale 3J(Hi, Hj) et la Somme de Constantes de Couplages 1J(C, H)
Authors: Jankowski K.
Published: May 2005

L'hybridation de carbone affecte la constante de couplage vicinale 1H1H. La constante de couplage directe 13C1H a été utilisée pour faire la corrélation de l'équation du type Karplus. Le terme correctif de cette équation a été proposé.
Carbon‐13{1H} Off‐Resonance Rauschentkopplung
Authors: Roth Klaus
Published: May 2005

Die 13C{1H} Off‐Resonance Rauschentkopplung (ORND) kann nicht nur zur Identifizierung von Signalen quartärer Kohlenstoffatome herangezogen werden: scharfe Signale für sekundäre Kohlenstoffatome treten auf, wenn die beiden direkt gebundenen Protonen chemisch äquivalent sind. Bei chemisch nichtäquivalenten Protonen steht die Linienbreite des 13C‐Signals mit der Differenz der chemischen Verschiebungen beider Protonen im linearen Zusammenhang. Die ORND‐Entkopplungstechnik wird an einigen Beispielen demonstriert.
Calculation of some fluorine nuclear screening constants
Authors: Ebraheem K. A. K. , Webb G. A.
Published: May 2005

The 19F screening constants and their anisotropies have been calculated for 50 fluorine molecular environments. The calculations have been performed within a framework in which gauge‐dependent atomic orbitals are used in the molecular orbital description. Calculations employing both INDO and CNDO/S standard parameterizations are reported. The molecules considered include simple binary fluorides and fluorocarbons. Both sets of calculations provide reasonable accounts of the 19F screening data for the binary fluorides. The presence of electric field effects in the aliphatic fluorocarbons are not accounted for by the present calculations. In the conjugated fluorocarbons the gross 19F chemical shift trend is reproduced except for ortho fluorines where electric field contributions are significant. The most highly screened component of σ is calculated to lie along the CF bond of various fluorobenzenes but perpendicular to the plane of 4,4′‐difluorobiphenyl, in agreement with experiment.
I. Etude de l'Influence de la Nature et de l'Orientation d'un Substituant sur les Constantes de Couplage en Série Tertiobutyl‐4 Cyclohexanonique par RMN à Haut Champ
Authors: Grenier‐Loustalot M. F. , Lectard A. , Lichanot A. , Metras F.
Published: May 2005

Nous avons enregistré les spectres RMN 1H de six α‐halogéno tertiobutyl‐4 cyclohexanones (composés 2 à 7) afin d'examiner les variations des constantes de couplage (2J, 3J, 4J) en fonction de la nature, la position, l'orientation et le nombre de substituants (CO, Cl, tBu). Les résultats observés sont interprétés en termes de déformations géométriques ou d'effets de substituants.
Bandshape analysis with internal resolution standard. Barriers to internal rotation in 3,5‐dimethyl‐4‐(N,N‐dimethylthio‐carbamoyl)pyrazoles
Authors: Berg U. , Karlsson S. , Sandström J.
Published: May 2005

The barriers to rotation of the dimethylamino group in a series of 4‐N,N‐dimethylthiocarbamoylpyrazoles have been determined by the 1H n.m.r. technique. For one of the compounds the rate constants have been determined over a temperature interval of 113 degrees by monitoring the exchange rate in the fast and slow exchange regions by the intensity of the resonances of the exchanging protons relative to an internal reference signal, and in the intermediate region by the conventional complete bandshape technique. The entropy and enthalpy of activation have been calculated, and the values obtained by the intensity method are in reasonable agreement with those obtained by the complete bandshape analysis. For the other compounds the usual coalescence approximation has been used. The thiocarbamoylpyrazoles were prepared by reaction between N,N‐dimethyl‐α,α‐diacetylthioacetamide and the appropriate hydrazines.
Unterscheidung enantiotoper/diastereotoper Protonen und regioselektive Spinentkopplung in metallorganischen Komplexen mit Hilfe von Shiftreagenzien
Authors: Kläui Wolfgang , Neukomm Heinrich
Published: May 2005

Dimethylphosphonat HP(O)(OCH3)2 und die Dimethylphosphonat‐Komplexe [(C5H5)MX{P(O)(OCH3)2}{P(OCH3)3}] (M = Co, Rh; X = I; CH3), [(C3H5) Co{P(O)(OCH3)2}2{P(OH)(OCH3)2}] und [(C5H5)Ni{P(O) (OCH3)2}{P(OCH3)3}] werden 1H‐NMR spektroskopisch untersucht. Es wird gezeigt, dass sich die enantiomeren Formen von [(C5H5)MX{P(O)(OCH3)2}{P(OCH)3)}] in Gegenwart des chiralen Shiftreagens Eu(tfc)3 getrennt beobachten lassen. Man findet einen starken Einfluss des Substituenten X auf die Unterscheidbarkeit der diastereotopen Phosphonat‐Methoxylgruppen in [(C5H5)MX{P(O)(OCH3)2}{P(OCH3)3}]. Die enantiotopen Phosphonat‐Methoxylgruppen in HP(O)(OCH3)2 werden durch Wechselwirkung mit Eu (tfc)3 unterscheidbar. Die gleichen Gruppen in [(C5H5)Ni{P(O)(OCH3)2}{P(OCH3)3}] werden durch Zugabe von Eu(tfc)3 von 31P entkoppelt. Der entkoppelt. Der komplex [(C5H5)Co{P(O)(OCH3)2}2P(OH)(OCH3)2}] reagiert als Chelatligand mit Eu(tfc)3 unter Freisetzung von tfcH.
N.m.r. studies of the keto–enol tautomerism of acylthioacetamides
Authors: Klose G. , Ludwig E. , Uhlemann E.
Published: May 2005

Acetylthioacetamides exist as different keto and enol isomers in chloroform solutions. The keto form with intramolecular hydrogen bonding between the NH and the carbonyl group is the dominant keto isomer. On the other hand the enol forms with intramolecular hydrogen bonding between the OH and the thioketo group are the dominant enol isomers in the temperature range 60°C to −60°C. The thermodynamic data of the keto‐enol equilibria were obtained by measuring the intensities of appropriate high resolution proton signals as a function of temperature. At low temperatures all lines characteristic of the enol forms are doubled in the N‐phenyl‐substituted derivatives because the rotation of the NHC6H5 group around the CN bond becomes slow and the chemical shifts characteristic of the E and Z isomers are different. We estimated approximate thermodynamic data of the E/Z equilibrium in some of the compounds. The changes of the line shape as well as the chemical shifts as a function of temperature indicate the presence of various additional exchange processes. In order to obtain further information we performed curve fittings of the chemical shifts of one acetylthioacetanilide and of a series of monothio‐β‐diketones (studied in another paper) assuming a fast two site exchange process. On the basis of the results obtained a reaction scheme for N‐substituted acylthioacetanilides in solution is proposed.
A case of negative homoallylic coupling constants: 3‐cyclopentenone
Authors: Lemarié B. , Ripoll J. L.
Published: May 2005

The 1H n.m.r. spectrum of 3‐cyclopentenone has been analysed and all (except the geminal) HH couplings obtained with their signs. The results are compared (i) with those obtained previously for the derivatives of cyclopentene and (ii) with those calculated by CNDO/2 and INDO finite perturbation methods. The coupling constants are discussed in order to define the factors contributing to the couplings.
13C19F spin–spin coupling in some monofluoro‐substituted polycyclic aromatic hydrocarbons
Authors: Hansen P. E. , Berg A. , Jakobsen H. J. , Manzara A. P. , Michl J.
Published: May 2005

The determination and complete assignment of the 13C19F coupling constants and 13C chemical shifts for 15 monofluoro derivatives of nine polycyclic aromatic hydrocarbons are reported. Fluorine substitutent effects on the 13C chemical shifts are given and their regular behaviour, making comparisons between different compounds possible, is discussed. The numerical values of the 13C19F long range coupling constants are found, with a few exceptions, to decrease in an alternating manner along the periphery of the molecules. In several cases the signs of the coupling constants have been determined. It appears that the signs alternate, but additional evidence is required. The magnitudes of different types of coupling constants are discussed in terms of steric and electronic effects. CNDO/2 and INDO calculations of the 13C19F coupling constants in the fluoronaphthalenes have been performed using the ‘sum‐over‐states’ method with the aim of examining the orbital and spin–dipole contributions to the various couplings.
N.m.r. characterization of functional groups: 5—on the nature of olefinic end groups in polyisobutylenes
Authors: Manatt Stanley L. , Ingham John D. , Miller Joseph A.
Published: May 2005

Proton n.m.r. signals for two types of olefinic end groups, ‐CH2C(CH3)CH2 (δ4.68 and δ4.87) and ‐CHC(CH3)2 (δ5.21), have been observed in high molecular weight polyisobutylenes. Comparable amounts of both these end groups exist in commercial and laboratory prepared samples of polyisobutylenes contrary to previous reports that the former group is by far predominant. That different catalysts produce different relative concentrations of these end groups is demonstrated. Evidence for the presence of a third type of unsaturation from the ‐CH2C(CH2)CH2‐ structure is discussed.
Etude en RMN du carbone 13 de dicoumarols substitués
Authors: Convert Odile , Deville Catherine , Godfroid Jean‐Jacques
Published: May 2005

Les spectres de RMN en 13C des dicoumarols substitués sur le carbone du pont sont interprétés dans le but d'obtenir des informations structurales pour des relations structure‐activité quantitatives. Les résultats sont en accord avec ceux obtenus en RMN du 1H: ces dicoumarols présentent une double rotation restreinte autour des liaisons du pont.
Détermination du Site de Protonation de l'Azido‐2 thiazole et du Thiazolo[2,3‐e]tétrazole à Partir de la Largeur des Raies des Signaux Protoniques
Authors: Faure R. , Galy J.‐P. , Vincent E.‐J. , Elguero J.
Published: May 2005

Les signaux des protons fixés sur un atome de carbone en α d'un azote pyridinique en série thiazole et en γ en série thiazolo[2,3‐e]tétrazolique sont élargis à cause de la présence d'atomes d'azote 14N; cet élargissement disparait par irradiation, par refroidissement et en milieu acide (dans ce cas, cela permet la détermination du site de protonation des deux molécules).
Concerning carbon‐13 n.m.r. spectroscopy of 5β‐hydroxylated phytoecdysones
Authors: Krepinsky J. , Findlay J. A. , Danieli B. , Palmisano G. , Beynon P. , Murakami S.
Published: May 2005

The 13C n.m.r. spectra of the 5β‐hydroxylated phytoecdysones polypodine B, muristerone A and kaladasterone are presented and briefly discussed together with the spectrum of makisterone A. Comparisons with previously reported spectra of ecdysone, ecdysterone and poststerone are made and allow a correction for the C‐20/C‐24 assignment for ecdysone.
A general purpose n.m.r. microcell system suitable for volatile, air sensitive and toxic samples
Authors: Al‐Rawi Jassim M. A. , Bloxsidge James P.
Published: May 2005

A microcell system that is convenient to fill and which can be evacuated and/or filled with gas or vapour has been developed for handling tritiated n.m.r. samples and has subsequently proved to have a more general application. A 3 mm tube, after the removal of a 5 mm filling extension, is sleeved into a 5 mm n.m.r. tube or used directly in a reduced diameter probe.
Calculation of the nitrogen screening constants of some N‐heterocycles
Authors: Ebraheem K. A. K. , Webb G. A. , Witanowski M.
Published: May 2005

Absolute nitrogen screening constants and chemical shifts of some N‐heterocycles are calculated within the CNDO/S level of approximation to Pople's model. Satisfactory agreement between calculated and observed nitrogen chemical shifts is obtained in most cases. The application of the results to the study of tautomeric equilibria is discussed. ‘Pyridine‐type’ nitrogen chemical shifts are dominated by n → π* transitions together with significant contributions from π → σ* and σ → π* transitions whereas the latter two are the dominant ones for ‘pyrrole‐type’ nitrogen nuclei.
1H and 13C n.m.r. study of butatriene‐bis‐tricarbonyliron complexes. Assignment of geometric orientation by comparative J(CCCH) values
Authors: Victor Rae , Ringel Israel
Published: May 2005

A number of substituted butatriene‐bis‐tricarbonyliron complexes have been studied by 13C and 1H n.m.r. spectroscopy. Long range coupling values, J(CCCH), have confirmed chemical shift results that methyl and phenyl groups assume opposite orientations at the coordinated double bonds with the methyl group preferentially trans to carbon and the phenyl group preferentially trans to iron.
The proton spectrum including 13C‐satellites of π‐benzenechromium tricarbonyl in a nematic solvent
Authors: Diehl P. , Kunwar A. C.
Published: May 2005

The proton spectrum of π‐benzenechromium tricarbonyl with 13C‐satellites due to ring‐ and carbonyl‐carbons at natural abundance has been investigated in a nematic solvent. The structural data are found to be in agreement with those from electron and neutron diffraction measurements. The proton–proton indirect coupling constants have also been determined.
Time‐dependence of the polarized intensity ratio in CIDNP investigations
Authors: Kende Imre
Published: May 2005

The time‐dependence of the polarized intensity ratio within a product molecule has been studied by a kinetic method. The kinetic analysis of polarized product formation shows that considerable changes in CIDNP ratios occur during the reaction but characteristic curves can be obtained under different experimental conditions. A method is proposed to evaluate the relative enhancement coefficients on the basis of these characteristic curves, and to obtain information on the kinetics of the reaction.