bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR of substituted aryl carbenium ions: Continuous dependence of the ipso substituent shifts upon the carbenium character. Use of proportionality relationships for the evaluation of substituent–substituent interactions
Authors: Membrey François , Ancian Bernard , Doucet Jean‐Pierre 
Published: May 2005

Abstract13C substituent shifts in para‐substituted phenyl and 2‐phenylethenyl carbenium ions have been studied within the general model of para‐disubstituted benzenes XC6H4Y. Large variations are observed for the ipso shifts induced by the Y substituents (Y = NO2. … OCH3) depending upon the electron demand at the remote carbenium centre. A good representation of these substituent‐substituent interactions is obtained by a treatment derived from ‘proportionality relationships’, where the deviations from strict additivity are factorized into two terms characterizing, respectively, the influence of the fixed X group on the ring and the susceptibility of the incoming Y substituent. Continuity of the ipso shift variations in an extended range is demonstrated, without break‐off between neutral polarized systems or ions as the electronic influence of the fixed X group increases.
Carbon‐13 chemical shifts of some model carboxylic acids and esters
Authors: Couperus P. A. , Clague A. D. H. , van Dongen J. P. C. M. 
Published: May 2005

AbstractSelected model carboxylic acids and esters dissolved in deuteriochloroform have been studied by carbon‐13 nuclear magnetic resonance under standardized conditions. Assignments of the chemical shifts have been made for all samples, and the spin–lattice relaxation times and nuclear Overhauser effects measured for a few selected esters. The results are intended to provide a practical aid for the analysis of carboxylic acids and esters of a more complex nature (e.g. polymers, natural products, etc.).
The additivity of NMR carbon–carbon spin–spin coupling constants
Authors: Marshall James L. , Faehl Larry G. , Kattner Richard 
Published: May 2005

AbstractFluorene‐9‐13C, fluorenone‐9‐13C, acenaphthenone‐11‐13C, acenaphthenone‐12‐13C, 1‐methylcyclopentanol‐1‐13C and 1‐methylcyclopentene‐1‐13C were synthesized to obtain J(CC) values between the natural carbons and the labeled carbons. Each of these compounds possessed at least one asymmetric dual‐path coupling, i.e., coupling between the labeled carbon and another carbon via simultaneous two‐ and three‐bonded coupling paths. Model 13C‐labeled compounds were synthesized where necessary to give expected values of the constituent mono‐path couplings. Values of these dual‐path couplings (2+3)J suggested that the observed value is the (at least approximate) algebraic sum of the two constituent J values.
Comportement de Ligands Phosphorés Potentiellement Bidentates vis‐à‐vis de AlCl3 et de Al[OCH(CF3)2]3. Etude RMN (1H, 13C, 27Al, 31P)
Authors: Laussac Jean‐Pierre 
Published: May 2005

AbstractLes composés formés par le trichlorure d'aluminium et le tris(hexafluoroisopropoxy) aluminium avec cinq coordinats présentant deux centres donneurs potentiels (phosphore‐phosphore, phosphore‐arsenic) ont été préparés et caractérisés par analyse élémentaire et spectroscopie de RMN (1H, 13C, 27Al et 31P). Ces résultats permettent de préciser la nature des composés obtenus: dans tous les cas l'aluminium présente la coordinence quatre el les ligands agissent en tant que monodentate.
A dynamic nuclear magnetic resonance study of nitrogen inversion in N,N'‐dimethylimidazolidine
Authors: Anet Frank A. L. , Yavari Issa 
Published: May 2005

AbstractThe 251 MHz 1H and the natural‐abundance 63.1 MHz 13C NMR spectra of N,N'‐dimethylimidazolidine have been measured from −50 to −170°C. Below about −140°C. nitrogen inversion in the compound becomes slow on the NMR time scale and both the 1H and the 13C spectra indicate that it exists in solution as a mixture of cis and trans conformations having nearly the same energies. The free‐energy barrier (ΔG≠) for nitrogen inversion in N,N'‐dimethylimidazolidine is 6.4 kcal mol−1, a value which is 1.5 kcal mol−1 lower than that for N‐methylpyrrolidine.
14N and 13C NMR of tautomeric systems of mercapto‐ and amino‐pyridines
Authors: Stefaniak Lech 
Published: May 2005

AbstractNitrogen chemical shifts are shown to provide a means of estimating equilibrium compositions of tautomeric systems of mercapto‐ and amino‐derivatives of pyridine. Carbon chemical shifts can afford only qualitative information about such equilibria.
13C NMR spectroscopy of natural substances: IV—13C NMR studies of trachylobane diterpenes: Complete carbon assignment
Authors: Arnone A. , Mondelli R. , St Pyrek J. 
Published: May 2005

AbstractThe diterpene trachylobane and a series of derivatives have been completely analysed by FT 13C NMR spectroscopy. All 13C frequencies for trachylobanol have been unambiguously assigned by experimental techniques, i.e. by proton single‐frequency selective decoupling and shift reagent experiments. Shift calculations have been performed for the parent compound by using known methods. The results are discussed in comparison with the experimental data. Satisfactory agreement between predicted and experimental values has been obtained.
Carbon‐13 NMR spectra of ericaceous toxins
Authors: Ohta Tomihisa , Hikino Hiroshi 
Published: May 2005

AbstractAssignments of the 13C NMR resonances for the toxic diterpenoids of ericaceous plants have been made. The data have proved to be a useful tool for the structural examination of the congeners. For example, the structure of asebotoxin‐VII to which a 6‐O‐acyl moiety had previously been assigned has now been revised to contain a 7‐O‐acyl group.
Carbon‐13 NMR spectra of saturated heterocycles: VIII—tetrahydrofurans and 1,3‐dioxolanes
Authors: Eliel Ernest L. , Rao V. Satyanarayana , Pietrusiewicz K. Michal 
Published: May 2005

AbstractThe 13C NMR spectra of 17 methyl‐ and ethyl‐substituted tetrahydrofurans and 58 alkyl‐ and aryl‐ substituted 1,3‐dioxolanes are reported. For the cases in which substituents recur, additive substituent parameters are calculated and compared with similar parameters in cyclopentanes and in 6‐membered rings. Considering the conformational flexibility of 5‐membered ring systems, additivity of the parameters is surprisingly good.
Carbon‐13 NMR Studies: 82. Carbon‐13 spectra of several 10‐methyl‐cis‐decalins. Conformational preferences of some cis‐decalin derivatives
Authors: Browne L. M. , Klinck R. E. , Stothers J. B. 
Published: May 2005

AbstractThe 13C spectra of a series of 21 cis‐decalins, 17 of which bear 10‐methyl substituents, have been recorded to examine geometrical and conformational effects on the 13C shieldings. Although the data for a few of the simpler examples have been reported, these compounds were examined to obtain results for a common medium and temperature. All of the derivatives are conformationally mobile and their spectra were examined as a function of temperature to obtain shieldings representative of the slow exchange limit. The examples include compounds which populate both available chair‐chair conformations equally, some which exhibit a preference for one of these conformations and some which exist essentially in a single conformation. The data for the latter group combined with the observed temperature dependencies and results for other decalin systems led to specific assignments for each carbon. The internal consistency of the entire body of data offers strong support for these assignments. The conformational preferences observed for a number of decalones and Δ3‐10‐methyldecalin derivatives are discussed.
Eine neue Methode zur Temperaturbestimmung in Kernresonanzspektrometern
Authors: Friebolin H. , Schilling G. , Pohl L. 
Published: May 2005

AbstractMit Hilfe des Klärpunktes von Flüssigkristallen kann im Kernresonanzspektrometer die Probentemperatur sehr exakt bestimmt werden. Das Verfahren ist für 1H‐ und 13C‐NMR‐Messungen geeignet und um den Faktor 5 genauer als die bisher bekannten. Bei 1H‐Messungen liegt der Fehler bei ±0,2°C, bei 13C‐NMR‐ Messungen bei ±0,3°C. Folgende Untersuchungen wurden durchgeführt: überprüfung der Ethylenglykol‐Eichgeraden, Eichung der Skala von NMR‐Temperatur‐Regelgeräten, Bestimmung des Temperaturgradienten in NMR‐Proben, Abhängigkeit der Probentemperatur vom Luftstrom und Beeinflussung der Probentemperatur durch Breitband‐ und Off‐Resonanz‐Entkopplung.
1H, 13C and 77Se NMR spectra of substituted selenoanisoles
Authors: Kalabin G. A. , Kushnarev D. F. , Bzesovsky V. M. , Tschmutova G. A. 
Published: May 2005

AbstractThe 1H, 13C and 77Se chemical shifts and the 1J[C(Me)H(Me)], 1.2J(SeC) and 2J(SeH) coupling constants in 14 para‐ or meta‐substituted selenoanisoles, RC6H4SeCH3, have been measured and the dependence of these parameters on the electronic effects of the substituent R is discussed. A significant (up to 6 ppm) deviation from additivity of the substituent influence on the shielding of the 13C ring carbons has been found.
Restricted rotation involving the tetrahedral carbon: XXIII—comparison of barriers to rotation of 9‐(2‐isopropylphenyl) fluorene obtained by 1H DNMR, 13C DNMR, double resonance and kinetic measurements
Authors: Nakamura Mikio , Kihara Hiroshi , Nakamura Nobuo , Oki Michinori 
Published: May 2005

AbstractRates of rotation about the C‐9‐C‐ar bond of 9‐(2‐isopropylphenyl) fluorene were measured by 1H DNMR, 13C DNMR, double resonance, and a kinetic method. The kinetic data obtained by these methods were critically examined. The DNMR methods afforded satisfactory results if rate data obtained by total line shape analyses of complicated signals with couplings were used, and those derived from simple patterns were abandoned. Agreement among the data yielded by the four different methods was excellent, provided that the data which might contain dubiously large errors were excluded.
13C NMR spectra of some 1‐, 3‐ and 4‐monosubstituted and disubstituted isoquinolines
Authors: van Veldhuizen A. , van Dijk M. , Sanders Georgine M. 
Published: May 2005

AbstractChemical shifts and substituent chemical shift (SCS) effects are reported for 21 monosubstituted iso‐quinolines, carrying a halogeno, amino, piperidino or ethoxy group in position 1, 3 or 4. In some cases, assignments of 13C resonances were based on the spectra of the corresponding 5‐deutero derivatives. For the fluoroisoquinolines some 13CF coupling constants are given. The 13C NMR spectra of 15 disubstituted isoquinolines were measured; with a few exceptions, mainly the 3,4‐ and 1,4‐disubstituted isoquinolines, the chemical shifts agreed well with those calculated by addition of the SCS effects.
Use of silver trifluoroacetate together with lanthanide shift reagents for simplification of1H NMR spectra of aromatic hydrocarbons
Authors: Da̧mbska Anna , Janowski Andrzej 
Published: May 2005

AbstractThe equimolar mixtures of typical lanthanide shift reagents such as Eu(fod)3, Pr(fod)3or Yb(fod)3with silver trifluoroacetate, previously used to induce paramagnetic shifts in the1H NMR spectra of alkenes, have been successfully applied to simple aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylenes. In benzene andp‐xylene the signals of all the aromatic protons are shifted identically. In other substituted benzenes the magnitude of the induced shift depends on the distance between the proton and the substituents. In addition, the different behaviour of the signals of the methyl groups inmeta‐andpara‐xylene on the addition of the complex shift reagent allows the quantitative analysis of the two xylenes in their mixtures.
A note on the calculations of spin–spin coupling constants involving carbon
Authors: Khin Tun , Webb G. A. 
Published: May 2005

AbstractSum‐over‐states perturbation and self‐consistent perturbation calculations of nJ(CC) using standard INDO parameters are discussed. Calculated values of 1J(OC) for acetone are reported. In general it seems that the sum‐over‐states calculations are the more reliable. The importance of including non‐contact contributions in the calculation of couplings between carbon and nuclei with larger values of 〈r−3〉 is stressed.
13C NMR spectra of alkyl‐ and phenylpyrazines and their N‐oxides
Authors: Matsuo M. , Matsumoto S. , Kurihara T. , Akita Y. , Watanabe T. , Ohta A. 
Published: May 2005

AbstractThe 13C chemical shifts of 37 pyrazines, including their N‐oxides, are reported. Substituent effects of methyl, phenyl and N‐oxide groups on the chemical shifts were examined. To comprehend these effects, the chemical shifts were compared with charge densities calculated by the CNDO/2 method and a good correlation was obtained. 13C, 1H coupling constants of some pyrazines were also determined and assigned. These data enable us to assign the 13C NMR spectra of substituted pyrazines and to understand the effects of N‐oxidation on the pyrazine nuclei.
Carbon‐13 NMR spectra of methylated cyclobutanes and ethyl cyclobutane‐carboxylates
Authors: Eliel Ernest L. , Michal Pietrusiewicz K. 
Published: May 2005

AbstractThe 13C NMR spectra of cyclobutane and seven methylated homologs and of ethyl cyclobutanecarboxylate and five isomeric diethyl cyclobutanedicarboxylates are reported and substituent parameters for methyl groups in methylcyclobutanes are calculated. Of note is a sizeable and nearly configuration‐independent upfield shifting γ‐effect.
Trifluoroacetic anhydride. A convenient NMR solvent for carbohydrates. 270 MHz 1H NMR studies of 2‐acetamido‐2‐deoxyhexoses
Authors: Ranganathan M. , Balaram P. 
Published: May 2005

AbstractThe use of trifluoroacetic anhydride as an NMR solvent for sugars has been explored. Dissolution of carbohydrates in this solvent is accompanied by trifluoroacetylation at the hydroxyl groups. Esterification results in downfield shifts of the sugar protons yielding very well resolved 1H NMR spectra. The use of trifluoroacetic anhydride in the analysis of complex systems is exemplified.
NMR studies in the heterocyclic series. XX—a carbon‐13 NMR study of the structures of N‐hydroxybenzotriazole and its acylated derivatives
Authors: Fruchier Alain , Elguero José , Hegarty Anthony F. , McCarthy Daniel G. 
Published: May 2005

AbstractAssignment of the carbon resonances in nine derivatives of N‐hydroxybenzotriazole has been carried out. The 13C NMR method enables tautomeric N‐hydroxy and N‐oxide and isomeric O‐ and N‐acyl structures to be identified. In DMSO, the predominant tautomer of N‐hydroxybenzotriazole was found to be the N‐hydroxy form. The structure of the benzoate and methyl and phenyl carbonate esters were likewise established, but for the two latter compounds, hydrolysis of the equilibrating O‐ and N‐acyl isomers imposed some limitations on the usefulness of the technique.
Carbon‐13 NMR spectra of kauranoid diterpenes
Authors: Patra A. , Mitra A. K. , Mitra S. R. , Kirtaniya C. L. , Adityachaudhury N. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of a number of (−)‐ent‐kauranoids have been studied. An unambiguous selfconsistent assignment of resonances has been made by considering the changes in chemical shifts produced by the change of substituent(s).
Studies in tertiary amine oxides part II—carbon‐13 nuclear magnetic resonance spectra of selected acetylenic amines, their N‐oxides and the Meisenheimer rearrangement products
Authors: Al‐Iraqi Mohammed A. , Al‐Rawi Jasim M. A. , Khuthier Abdul‐Hussain 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts and 1J(CH), 2J(CH) and 3J(CH) coupling constants of selected saturated nitrogen heterocyclic molecules containing the acetylenic moiety have been determined. These NMR parameters have also been determined for the corresponding N‐oxides and the Meisenheimer rearrangement products, the O‐allenylhydroxylamines. The effect of the N‐oxidation on the chemical shifts of the ring and the acetylenic carbon atoms is discussed.
The relationship between 19F substituent chemical shifts and electron densities: meta‐ and para‐substituted benzoyl fluorides
Authors: Brownlee Robert T. C. , Craik David J. 
Published: May 2005

AbstractThe 19F substituent chemical shifts (SCS) of meta‐ and para‐benzoyl fluorides are found to correlate well with substituent parameters using the dual substituent parameter (DSP) equation, indicating that they reflect electronic perturbations induced by the substituent. The direction of the SCS values is such that donating substituents cause upfield shifts whilst acceptors cause downfield shifts. STO‐3G calculations indicate that substituents induce only very small changes in π‐electron density about the fluorine atom, but that these changes correlate reasonably well with the observed SCS values. For the para series, the slope of the relationship between δq and 19F SCS is 5000 ppm/electron, indicating the great sensitivity of the flourine atom to small changes in electron density.
Automated analysis of high‐resolution NMR spectra III—the nematic phase spectra of three allyl halides
Authors: Stephenson David S. , Binsch Gerhard 
Published: May 2005

AbstractIn recent publications we have described a novel method of analysis for high‐resolution NMR spectra of compounds in isotropic solution which differs from conventional procedures in that it exploits the full information content of a spectrum and does not require assignments of energy levels or transitions. We now present a further development of this technique which also makes it applicable to the NMR spectra of molecules partially oriented in liquid crystal solvents. Illustrative applications are reported for the nematic phase spectra of allyl fluoride, allyl chloride and allyl bromide. The results are discussed in terms of various theoretical models of the interplay between the internal and overall rotations of the conformationally mobile solutes.
13C and 77Se NMR of some selenium and thiophene derivatives. 1J, 2J and 3J SeSe coupling constants
Authors: Granger Pierre , Chpelle Stella , Paulmier Claude 
Published: May 2005

AbstractThe results of 13C and (when pertinent) 77Se NMR spectra of thiopene and selenophene derivatives containing exocyclic selenium atoms are presented. The 77Se spectra show an interaction between nitro or carbonyl groups and selenium when they are ortho to each other. The measurement of 1J(SeSe), 2J(SeSe) and 3J(SeSe) has been attempted on disymmetric diselenides; only 1J(SeSe) can be measured and values are very low, generally below 20 Hz. Other coupling cannot be observed and are smaller than the line width, which is 2 Hz. No theoretical interpretation can be advanced at present.
13C NMR spectra of diazastilbenes. I—trans‐styryldiazines
Authors: Erb Hans‐Peter , Bluhm Thorsten 
Published: May 2005

AbstractThe 13C NMR spectra of all trans‐styryldiazines, methyldiazines and trans‐styrylpyridines have been fully assigned. Empirical shift increments were obtained for the chemical shifts of the carbon atoms; these are discussed in the light of theoretical considerations.
Photolysis of 2,6 di‐tert‐butyl‐4‐tert‐butylperoxy‐4‐methyl‐2,5‐cyclohexadienone
Authors: Pilaǎ J. , Kovářová J. , Pospíšil J. 
Published: May 2005

AbstractThe photolysis of a heptane solution of 2,6‐di‐tert‐butyl‐4‐tert‐butylperoxy‐4‐methyl‐ 2,5‐cyclohexadienone (1) with light of 360–480 nm in the presence of 2,6‐di‐tert‐butyl‐4‐methylphenol or 2,4,6‐tri‐tert‐butylphenol gives rise to their corresponding phenoxyls in a reaction with thetert‐butoxyl arising in the photolysis. Direct evidence of the formation oft‐BuO.by the photolysis of 1 was provided by the ESR characterization of spin‐adducts of this radical with nitrosobenzene and nitrosodurene. Evidence of the photolysis of the peroxide bond in 1 is important for the mechanism of reaction of phenolic chain‐breaking antioxidants.
13C NMR Spectra of some diterpenes of Premna latifolia Roxb
Authors: Rao C. H. Bheemasankara , Vijayakumar E. K. S. 
Published: May 2005

Abstract13C NMR data are presented for premnolal (13‐formyl‐11,14‐dihydroxypodocarpa‐8,11,13‐triene), the tetraacetate of nellionol (6α,11,14,16‐tetra‐O‐acetylabieta‐8,11,13‐trien‐7‐one), 11‐ketosandaracopimar‐15‐en‐8β‐ol, sandaracopimar‐15‐en‐1β, 8β‐diol and its l‐keto derivative, and sandaracopimaran‐1β,8β,12β‐triol, obtained from Premna latifolia Roxb.
Dynamic 13C NMR study of the cyclohexane ring in spirocyclohexanes
Authors: Iratçabal Pierre , Grenier‐Loustalot Marie‐Florence , Lichanot Albert , Metras Franck 
Published: May 2005

AbstractA dynamic study of spirocyclohexanes was carried out using low‐temperature 13C nuclear magnetic resonance spectroscopy. The variations of the energy barrier to inversion of the cyclohexane ring are interpreted in terms of the electronegativity of the heteroatoms of the spiro substituent.
High resolution 13C NMR spectroscopy V—structure dependence of the 13C, H coupling constants in aceheptylene, azulene and 5‐azaazulene
Authors: Braun S. , Kinkeldei J. , Walther L. 
Published: May 2005

AbstractIn order to study the structure dependence of the 13C,H coupling constants in polycyclic conjugated π electron systems with 5‐and 7‐membered rings, the 1H coupled 13C NMR spectra of aceheptylene, azulene and 5‐azaazulene have been analysed. The results are discussed, including published data of monocyclic reference compounds, and are compared to theoretical values calculated by the FPT‐INDO method. It is shown that, first, the geminal 13C,H couplings in the unsaturated 5‐membered carbocycles are predominantly dependent on CC bond lengths. Second, the vicinal 13C,H coupling constants in 5‐ as well as in 7‐membered unsaturated carbocyclic rings can be linearly related to the lengths of the central CC bonds. Third, the vicinal inter‐ring couplings show a large variation and give information on ring junction, thus being of special value in structure determination and are governed mainly by the bond angles. Fourth, the calculated 13C,H couplings across one and two bonds are totally useless for practical purposes; those across three bonds, however, at least reflect the experimental trends.
A dynamic nuclear magnetic resonance spectroscopic study of conformational properties of 1,3‐dioxepane and 4,4,7,7‐tetramethyl‐1,3‐dioxepane
Authors: Yavari Issa 
Published: May 2005

AbstractThe 251 MHz 1H and the natural abundance 63.1 MHz 13C NMR spectra of 1,3‐dioxepane (1) and 4,4,7,7‐tetramethyl‐1,3‐dioxepane (2) have been investigated over the temperature range of 5 to −180 °C. While the spectra of 1 show no dynamic NMR effect, compound 2 exists in solution as a 1:1 mixture of a symmetrical (C2) twist‐chair and its mirror image conformation. The free energy barrier for the conformational racemization of 2 is 43 kJ mol−1 (10.3 kcal mol−1). Interconversion paths between various conformations of 2 are discussed. Compound 1 is suggested to have a symmetrical (C2) twist‐chair conformation which is rapidly pseudorotating via a chair conformation to achieve a time averaged symmetry of C2v, even at −180 °C.
The protonation of ortho‐methoxy‐ and hydroxy‐benzaldehydes in FSO3HSbF5SO2 solution
Authors: Kotkowska‐Machnik Zofia , Zakrzewski Janusz 
Published: May 2005

AbstractThe protonation of o‐methoxy‐ and o‐hydroxy‐benzaldehydes in FSO3HSbF5SO2 solution was investigated by 1H NMR spectroscopy. The formation of the Z‐carbonyl protonated molecule is explained by intramolecular hydrogen bonding.
15N NMR study of azo‐hydrazone tautomerism of 15N‐labelled azo dyestuffs
Authors: Lyčka Antonín , Šnobl Dobroslav , Macháček Vladimír , Večeřa Miroslav 
Published: May 2005

Abstract15N chemical shifts of 3‐methyl‐1‐phenylpyrazole‐4,5‐dione 4‐phenylhydrazone (1), 4‐hydroxyazobenzene (2), 2‐hydroxy‐5‐tert‐butylazobenzene (3) and 1‐phenylazo‐2‐naphthol (4), monolabelled with 15N at α‐(compounds prepared from 15N‐aniline) and β‐positions (compounds prepared from Na15NO2), have been measured and the temperature dependence of these chemical shifts followed between 240 and 360 K. For 4, representing a mixture of the azo and hydrazone forms, the hydrazone content has been calculated from the 15N chemical shifts of both nitrogen atoms at various temperatures. The two calculations gave identical results.