bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon‐13 n.m.r. study of naturally occurring xanthones
Authors: Westerman Philip W. , Gunasekera Sarath P. , Uvais M. , Sultanbawa S. , Kazlauskas Rymantas
Published: May 2005

The 13C n.m.r. spectra of 36 naturally occurring xanthones are reported and all chemical shifts assigned. The shifts in substituted xanthones can be predicted from substituent effects evaluated for simple derivatives. The agreement between calculated and observed shifts decreases as the extent of substitution in the xanthone increases.
The carbon‐13 spectra of steroids on the way to ecdysone
Authors: Smith William B.
Published: May 2005

A combination of chemical shift reagent effects, partially relaxed spectra, and carbon T1 measurements have been used to assign the chemical shifts of the carbons in seven different steroids which have served as intermediates in a synthesis of the steroid moulting hormone ecdysone. The assignments of ergosterol have been completed. It has been shown that the T1's are consistent with the molecular structures.
A rotational barrier about the isopropyl to aryl bond in highly substituted sulphines
Authors: Tangerman Albert , Zwanenburg Binne
Published: May 2005

The rotational barriers in sulphines containing the substituents 2,6‐dimethyl‐3‐isopropyl‐4‐methoxyphenyl and 4,6‐dimethyl‐3‐isopropyl‐2‐methoxyphenyl are discussed. Particular attention is given to the occurrence of a barrier to rotation about the isopropyl to aryl bond. In both types of sulphines the isopropyl group is flanked by a methyl and a methoxy group. The isopropyl to aryl barrier could only be detected in the sulphines containing the second type of substituent where the o‐methoxy group experiences a buttressing effect from the CSO moiety.
Étude des Phénomènes de Redistribution dans les Systèmes BR3/BT3 avec T = –OCH3, –SCH3, –N(CH3)2
Authors: Costes Jean‐Pierre , Cros Gérard , Laurent Jean‐Pierre
Published: May 2005

L'étude des spectres de résonance nucléaire (1H, 11B) de différents mélanges BR3/BT3/ avec T = OCH3, SCH3 et N(CH3)2 met en évidence l'existence d'équilibres de redistribution entre les espèces BRnT3–n (n = 0, 1, 2, 3). II apparaǐt que, d'une façon générale, les espèces mixtes (n = 1 et 2) sont plus favorisées que ne le laisserait prévoir un modèle de redistribution au hasard. Les facteurs d'ordre stérique et électronique susceptibles d'intervenir dans ces réactions sont envisagés.
On the assignment of 13C resonances in unsymmetrical ortho‐disubstituted benzene rings. 13C N.m.r. spectrum of Piroxicam
Authors: Whipple Earl B.
Published: May 2005

Characteristic differences in multiplet hyperfine structure observed in coupled 13C n.m.r. spectra of symmetrical o‐disubstituted benzene rings are explained on general grounds. Contrary to earlier proposals, the observation of this effect in unsymmetrical systems is not a suitable basis for corresponding 13C n.m.r. assignments unless the proton spectrum has been sufficiently analyzed. The 13C spectrum of piroxicam, an antiinflammatory agent, is assigned and some interesting relaxation properties are noted.
1H n.m.r. study of the self‐association of acetone phenylhydrazone by hydrogen bonding
Authors: Stassinopoulou C. I. , Petrou J.
Published: May 2005

Proton magnetic resonance dilution studies of acetone phenylhydrazone were carried out in n‐heptane, carbon disulphide and hexachlorobutadiene solutions. Equilibrium constants and enthalpy values for the predominant self‐associated species are reported. Linear trimeric aggregates predominate in n‐heptane solutions. The monomeric units are associated by intermolecular hydrogen bonding of the NH proton to the iminic nitrogen. The enthalpy per hydrogen bond is 10.04 kJ (2.4 kcal). In carbon disulphide and hexachlorobutadiene solutions complexation of acetone phenylhydrazone with the solvent competes with self‐association.
Nuclear magnetic resonance of oriented molecules in lyotropic liquid crystalline media: p‐cresol
Authors: Long Robert C. , Goldstein J. H.
Published: May 2005

Proton‐proton distance ratios and order parameters for partially oriented p‐cresol in a lyotropic mesophase derived from potassium laurate are obtained. The order parameters are the largest yet found for an ordered solute in a nematic‐like lyotropic system. The dipolar couplings and structural data were independent of the rotational potential from 0–200 cal mol−1.
Etude Conformationnelle par Résonance Magnétique Nucléaire Protonique des Dérivés de la O‐Isopropylidène‐2′,3′ Adénosine
Authors: Gaudemer Alain , Nief François , Pontikis Renée , Zylber Jean
Published: May 2005

Les états conformationnels de plusieurs dérivés de la O‐isopropylidène‐2′3′ adénosine différante par la nature des substituants en C‐5′, C‐8 et N‐6 ont été déterminés à partir des données de RMN du proton, δ,3J et de mesures d'effet nucléaire Overhauser. Les variations conformationnelles observées résultent d'interactions spécifiques entre la partie sucre et la base purique et, d'autre part, d'autre part, d'effets de solvants.
NMR‐daten substituierter 1,2‐diphospholane sowie des 1,5‐diphosphabicyclo[3.3.0]octans und seiner p‐derivate
Authors: Issleib K. , Thorausch P. , Meyer H.
Published: May 2005

Anhand von 13C‐ und 31P‐Spektren wird die Struktur 1‐ sowie 2‐substituierter 1,2‐Diphospholane, des 1,5‐Diphosphabicyclo[3.3.0]octans und dessen P‐Derivate ermittelt. Die 31P‐chemischen Verschiebungen zeigen für letztere eine zusätzliche sterisch bedingte Wechselwrikung der Phosphoratome. Sämtliche Verbindungen sind innerhalb der NMR‐spektroskopischen Nachweisgrenze sterisch einheitlich.
Carbon‐13 n.m.r. investigation of 2‐arylaminothiazolines and analogous thiazines, thiazepines and their amides
Authors: Sohár P. , Fehér G. , Toldy L.
Published: May 2005

The 13C n.m.r. spectra of 2‐arylaminothiazoline, ‐thiazine and ‐thiazepine derivatives, and also those of some N‐substituted isomeric pairs were recorded and assigned. The structure of the individual isomers, which as a result of contradictory spectroscopic data had earlier been ambiguous, was established. In addition, the tautomeric structure of some N‐unsubstituted compounds was determined.
Carbon‐13 NMR studies. 73—carbon‐13 spectra of several 10‐methyl‐trans‐decalins. Further definition of the deshielding antiperiplanar γ effect
Authors: Ayer W. A. , Browne L. M. , Fung S. , Stothers J. B.
Published: May 2005

The 13C spectra of a series of 21 10‐methyl‐trans‐decalins have been recorded to explore in greater detail the deshielding antiperiplanar γ effects found earlier in a few of these derivatives. From the data for the series complete assignments for each compound were obtained, permitting an analysis of the shielding effects of the methyl and hydroxyl groups.
Natural‐abundance lithium‐6 NMR spin–lattice relaxation in some simple organolithium compounds
Authors: Wehrli F. W.
Published: May 2005

6Li, 7Li and 13C spin–lattice relaxation and NOE data are reported for methyllithium, butyllithium and phenyllithium with 6Li T1 values found in the order of tens of seconds and their relaxation 2–3 orders of magnitude less efficient than that for 7Li. The data indicate that 6Li is substantially relaxed by the intramolecular 6Li–1H mechanism, whereas both quadrupolar and 6Li–7Li dipolar relaxation are minor processes. The non‐linearity of the Arrhenius curve for Me6Li is compatible with a small spin–rotation contribution. Since 6Li in solution behaves essentially as a spin‐1/2 nucleus, it represents, in spite of its lower magnetic moment and overall sensitivity, an attractive alternative to 7Li NMR.
Carbon‐13 NMR studies of twenty‐four methyl‐substituted morpholines
Authors: Nilsson Bertil , Hernestam Sven
Published: May 2005

Carbon‐13 NMR spectra of all the isomers of monomethyl‐, 2,3‐, 2,5‐, 2,6‐, 3,5‐dimethyl‐, 2,3,5‐, 2,3,6‐trimethyl‐ and 2,3,5,6‐tetramethylmorpholine have been obtained at both ambient (25 °C) and low temperature (∼ −100 to −120 °C). The ring carbon shifts appear to be additive with respect to the position of the methyl groups. A good correlation between predicted and experimental shift values was obtained (r = 0.9989). The values were used in an attempt to assign, conformationally, the ‘all cis’ isomer 2,3,5,6‐tetramethylmorpholine, which from 1HNMR spin–spin coupling studies has been unsuccessful. Methyl carbon shifts to high field were found for axially oriented carbons. The extracted ‘steric shift’ values for such carbons were compared to their corresponding proton shift data.
The calculation of 2J(HH) couplings in benzyl groups
Authors: Abraham R. J. , Bakke J. M.
Published: May 2005

The results of FPT/INDO theory together with the observed 2J(HH) coupling in benzyl groups (Ph · CH2X) leads to a simple equation 2J(HH) = A+B cos θ+C cos 2θ where θ is the C.C.C.X dihedral angle, and X = C,H. The extension to other X substituents can be obtained from additivity rules.
Application of artificial intelligence for chemical inference. XXV. A computer program for automated empirical 13C NMR rule formation
Authors: Mitchell Tom M. , Schwenzer Gretchen M.
Published: May 2005

A computer program which generates empirical rules associating 13C NMR shifts with local structural environments is described. The program uses a heuristic method to search for common structural features for those carbon atoms exhibiting similar shifts. Rules have been generated by our program from a combined set of acyclic amine and paraffin data. Examples of these rules are presented, and their performance as a tool for structure elucidation is examined.
Some self‐consistent perturbation calculations of 15N13C coupling constants
Authors: Khin Tun , Webb G. A.
Published: May 2005

Self‐consistent perturbation calculations within the INDO framework are reported for 63 15N13C coupling constants. Examples are presented for which each of the contact, orbital and dipolar terms provides the dominant contribution to the observed coupling constant. In general, good agreement with the experimental data is obtained when the integral products SN2(O)SC2(O) and 〈r−3〉N〈r−3〉C take the values 14.480 au−6 and 2.446 au−6 for 1J(15N13C), and the corresponding values of 10.444 au−6 and 17.664 au−6 for 1J(15N13C). All 19 of the 1J(15N13C) couplings considered are predicted to have a negative sign.
Bulky alkyls and amides of main group 5 elements II. Rotational barriers in phosphorus compounds containing bulky groups
Authors: Goldwhite Harold , Power Philip P.
Published: May 2005

The group [(CH3)3Si]2CH is effectively bulkier than the (CH3)3C group in inhibiting rotation about the PC bond in R2PCI compounds. In phosphonamidous chlorides, RP(CI)NR2′, increasing the bulk of the groups at nitrogen, e.g., from CH3 to (CH3)2CH to (CH3)3Si, increases the rotational barriers about the PN bond; however, changing R from (CH3)3C to [(CH3)3Si]2CH increases the barrier, which is a reversal of the trend earlier observed. It is suggested that these very bulky silylated groups represent limiting cases of steric interference.
A carbon‐13 nuclear magnetic resonance spectral data base and search system
Authors: Dalrymple D. L. , Wilkins C. L. , Milne G. W. A. , Heller S. R.
Published: May 2005

A data base containing approximately 4000 13C nuclear magnetic resonance spectra has been assembled. The spectra have been evaluated and all the corresponding compounds have been registered by the Chemical Abstracts Service (CAS). The data base is available to the international scientific community on magnetic tape or microfiche and is also the basis of a search system operating upon an international computer network.
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

13C 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

Selected 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.).
13C13C coupling constants of cyclobutane derivatives
Authors: Stöcker Michael , Klessinger Martin
Published: May 2005

Five 13C‐labelled cyclobutane derivatives were synthesized and the couplings involving the labelled carbon were determined.
The additivity of NMR carbon–carbon spin–spin coupling constants
Authors: Marshall James L. , Faehl Larry G. , Kattner Richard
Published: May 2005

Fluorene‐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

Les 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

The 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

Nitrogen 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

The 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

Assignments 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

The 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

The 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

Mit 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

The 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

Rates 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

Chemical 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

The 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

Sum‐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

The 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

The 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

The 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

Assignment 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

Carbon‐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).
Determination of the enantiomeric purity of α‐tocopherol by 13C NMR spectroscopy
Authors: Bremser Wolfgang , Vogel Friedrich G. M.
Published: May 2005

High field high resolution 13C NMR spectroscopy allows the quantitative determination of a mixture of the four diastereomers in racemic α‐tocopherol.
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

Carbon‐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

The 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

In 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

The 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

The 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

The 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

13C 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

A 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

In 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

The 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

The 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

15N 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.
Carbon‐13 NMR spectral studies on some labdane diterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Biswas Swapna , Gupta Chitra Das , Basak Ajoy , Barua A. K.
Published: May 2005

Carbon‐13 NMR signal assignments of the labdane diterpenoids andrographolide and 14‐deoxyandrographolide, along with their acetates, and isodeoxyandrographolide have been made. This study indicates that the C‐6 and C‐11 resonance assignments of isovirescenol‐B, made earlier, should be interchanged.
Carbon‐13 spin–lattice relaxation in some polyfluoroaromatic compounds
Authors: Hamza M'Hamed Ali , Serratrice Guy , Delpuech Jean‐Jacques
Published: May 2005

Carbon‐13 chemical shifts, spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T1 values for the para‐carbon of monosubstituted fluorobenzenes is clearly shorter than the T1 values for the ortho‐ and meta‐carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C2 in‐plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.
Improved methods for assignment of multiplicity in 13C NMR spectroscopy with application to the analysis of mixtures
Authors: Cookson David J. , Smith Brian E.
Published: May 2005

Improved methods for the assignment of resonance multiplicity in 13C NMR spectra are described. Assignments are achieved either by direct observation of resonance intensity modulations resulting from gated spin echo (GASPE) experiments, or from the derivation of ‘selected multiplet’ spectra containing only C, CH, CH2 or CH3 carbon resonances. The methods are time‐efficient and, by comparison with the single frequency off‐resonance decoupling assignment technique, show improved spectral resolution. Chemical mixtures are used to illustrate the procedures. Possible application to materials deriving from fossil fuel sources is considered.
Linear and angular annelation effects on the 13C NMR spectra of tricyclic aromatic ketones. 1—annelated indanones
Authors: Buchanan G. W. , Isabelle M. E. , Wightman R. H.
Published: May 2005

Carbon‐13 NMR chemical shifts are reported for nine tricyclic aromatic ketones formally derived from indanone. The influences of remote ring size, as well as linear, angular exo and angular endo ketone orientation are examined. Results are compared with available 1H NMR data. For indanone itself, based on selective 1H decoupling experiments, a recently reported CIDNP derived 13C signal assignment is shown to be in error.
The tetramethylammonium ion (TMA+) versus the hydronium ion (H3O+) as internal reference for 1H NMR measurements in superacid media. Solute–solvent interactions
Authors: Rimmelin Paul , Schwartz Sylvie , Sommer Jean
Published: May 2005

It is shown that the chemical shift of the generally utilized internal reference for 1H NMR measurements in superacid media, namely, tetramethylammonium bromide, which is normally fixed at 3.10 ppm from external TMS, changes with the composition of the acid mixture (HF or HSO3F:SbF5). This is attributed to solute–solvent interactions. The use of both the tetramethylammonium ion or the hydronium ion as internal references is discussed, as the hydronium ion appears to be only slightly influenced by these interactions.
Conformational analysis by 13C spin–lattice relaxation times. Evidence for an intramolecular CH …︁ N hydrogen‐bond in a 4H‐1,2,4‐triazole derivative
Authors: Houssin Raymond , Hénichart Jean‐Pierre
Published: May 2005

The modification of the 13C spin–lattice relaxation time values for the C atoms in the side‐chain of 4‐(morpholinoethyl)‐1,2,4‐triazole has been found to be characteristic of the structure variation caused by different solvents, and evidence for the formation of an intramolecular hydrogen bonding in an apolar medium has been provided.
13C NMR spectra of natural products. 1—guaianolides
Authors: Da Silva Antonio J. R. , Garcia Marcos , Baker Paul M. , Rabi Jaime A.
Published: May 2005

The 13C NMR spectra of 18 guaianolides have been measured and the chemical shifts assigned. The compounds investigated include the naturally occurring eremanthin (1), dehydrocostus lactone, eregoyazin, eregoyazidin and other semisynthetic lactones derived from 1. Qualitative analysis of the data suggests that the predominant conformation in almost all compounds so far studied is a distorted chair‐like form.
13C NMR spectra of natural products. 2—eudesmanolides
Authors: da Silva Antonio J. R. , Garcia Marcos , Baker Paul M. , Rabi Jaime A.
Published: May 2005

The 13C NMR spectra of eight eudesmanolides have been measured and the chemical shifts assigned. Among the compounds studied are the naturally occurring α‐cyclocostunolide, santamarin, arbsculin A and reynosin.
Investigation of benzimidazoles: II—the influence of substituents and solvents on the 1H and 13C NMR chemical shifts of 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates
Authors: Larina L. I. , Vakul'skaya T. I. , Filatov A. V. , Istomin B. I. , Shibanova E. F. , Lopyrev V. A. , Voronkov M. G.
Published: May 2005

The influence of substituents on 1H and 13C NMR chemical shifts of 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates in different solvents has been investigated. It has been shown that the transmission of the electronic effects of the substituents in benzimidazoles and their quaternary salts are almost the same. The nature of the solvent influences only the intensity of the transmission of the electronic effects of substituents in 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates.
13C NMR and ESR spectroscopic investigations on tert‐butyl‐substituted cyclopentadienones
Authors: Kalinowski Hans‐Otto , Franz Lothar H. , Maier Günther
Published: May 2005

13C NMR spectra of 11 di‐, tri‐ and tetra‐tert‐butyl‐substituted cyclopentadienones are discussed with respect to charge distribution and substituent effects. The chemical shifts of the unsubstituted cyclopentadienone, calculated from substituent increments, are in good agreement with published CNDO calculations and can be rationalized by the inductive effect of the carbonyl group. In addition, the ESR signals shown by some of the cyclopentadienones are described, and possible reasons for their appearance are discussed.
The effect of phosphorylation of the histidyl residue in the tetrapeptide Gly‐Gly‐His‐Ala. Changes of chemical shift and pK values in 1H‐ and 31P‐NMR spectra
Authors: Kalbitzer Hans Robert , Rösch Paul
Published: May 2005

Phosphorylation of the tetrapeptide Gly‐Gly‐His‐Ala by phosphoamidate provides a model peptide for proteins which, in the course of their reaction, bind a phosphoryl group to an imidazole ring. 31P‐ and 1H‐NMR data, including chemical shift and pK values, for this peptide and its three phospho‐derivatives are presented. These data show that it is possible, by NMR studies, to decide whether or not a peptide or a protein is phosphorylated at the N‐1 or at the N‐3 position of an imidazole ring, and how this information can be achieved.
13C NMR study of psilostachyinolides from some ambrosia species
Authors: Borges‐del‐Castillo J. , Manresa‐Ferrero M. T. , Rodríguez‐Luis F. , Vázquez‐Bueno P. , Joseph‐Nathan P.
Published: May 2005

13C NMR data are presented for the psilostachyinolides, psilostachyin C, psilostachyin, canambrin, psilostachyin B, altamisin, paulitin and isopaulitin, obtained from Ambrosia cumanensis H.B.K., Ambrosia psilostachya D.C. and Ambrosia canescens (Gray).
Carbon‐13 NMR parameters of phenyltin halogenides and phenyltin chalcogenides
Authors: Mathiasch B.
Published: May 2005

The 13C NMR shift parameters and couplings to tin are reported for nine phenyltin halogenides and seven phenyltin chalcogenides, as well as the T1 results for Ph2SnTe. A pronounced linear dependence of all coupling constants on the para‐carbon shift is discussed.
13C NMR spectra of 1‐stearoyl‐2‐linoleyl‐sn‐glycero‐3‐phosphorylcholine and 1‐stearoyl‐2‐arachidonoyl‐sn‐glycero‐3‐phosphorylcholine in CDCl3 solution and in sonicated dispersions in 2H2O
Authors: Santarén Juan F. , Rico M. , Guilleme J. , Ribera A.
Published: May 2005

Two mixed‐acid lecithins: 1‐stearoyl‐2‐linoleyl‐sn‐glycero‐3‐phosphorylcholine (SLL) and 1‐stearoyl‐2‐arachidonoyl‐sn‐glycero‐3‐phosphorylcholine (SAL) have been synthesized by phospholipase A2 digestion of 1,2‐distearoyl‐sn‐glycero‐3‐phosphorylcholine (DSL), followed by reacylation of the lysolecithin with the desired fatty acid anhydride. 13C (25.2 MHz) NMR spectra of SLL and SAL in CDCl3 solution and in sonicated dispersions in 2H2O have been obtained. Complete spectral assignments are reported for the two molecules in both systems. 13C nuclear spin‐lattice relaxation times (T1) of SLL and SAL in sonicated aqueous dispersions have also been measured. Relaxation rate profiles as a function of the chain segment position are in general agreement with those recently obtained from 2H NMR for similar systems.
Characterization of organic substrates bound to cross‐linked polystyrenes by 13C NMR spectroscopy
Authors: Jones Alan J. , Leznoff Clifford C. , Svirskaya Polina I.
Published: May 2005

The 13C NMR spectra of a wide variety of organic substrates bound to 2% cross‐linked polystyrenes may be obtained routinely, provided the resins can be sufficiently swollen. The 13C chemical shifts of polymer‐bound trityl alcohol, polymer‐bound monotrityl ethers of the symmertrical diols HO (CH2)nOH (n=2, 4, 6, 7, 9 and 10), and some related intermediates in the solid phase synthesis of insect pheromones are presented. 13C shift additivity correlations, differing little from those in free trityl ethers, are drawn.
Structure elucidation with lanthanide‐induced shifts. 13—A critical evaluation of methods for obtaining bound shifts and association constants
Authors: Raber Douglas J. , Hardee Linda E.
Published: May 2005

The use of lanthanide‐induced shifts for rigorous structure analysis requires accurate values corresponding to only one of the complexes that can be formed. A combination of computational and experimental studies have been carried out to evaluate several commonly used procedures for obtaining bound shifts. The results indicate that only two of these methods afford values which are reliably related to the actual bound shifts. In addition, both methods afford values for the association constant. Guidelines are suggested which allow a chemist to anticipate when each methods can be successfully employed.
Polar substituent effects on 13C NMR spectra in ethyl cis‐2‐substituted cyclopropane carboxylates
Authors: Kusuyama Yoshiaki , Inoshita Satoru , Okada Ginjiro , Yanagi Minoru , Tokami Kenjiro , Fuchu Hiroshi , Tsuno Yuho , Mishima Masaaki
Published: May 2005

13C FT NMR spectra of ethyl cis‐2‐substituted cyclopropanecarboxylates were obtained in chloroform‐d and the chemical shifts were compared with those of the corresponding trans isomers. In most cases, the resonances for the ring carbons and the carbonyl group carbon appeared further upfield than those of the trans isomers, and were found to be useful for distinguishing the stereoisomeric 1,2‐disubstituted cyclopropanes.
13C NMR of camphene and α‐pinene: Revised assignments
Authors: Offermann Werner
Published: May 2005

The 13NMR signals of camphene (1) and α‐pinene (2) are reassigned unequivocally. J(CH) values of 1, 2, bornene, norbornene and norbornadiene are reported.
The rα structure of benzonitrile, determined by NMR of the oriented molecule
Authors: Diehl P. , Amrein J. , Veracini C. A.
Published: May 2005

The indirect and direct proton–proton, proton–carbon and proton–nitrogen coupling constants of benzonitrile have been measured from proton spectra with natural abundance satellites, and also from proton and 15N spectra of the molecule enriched in 13C or 15N at the cyano group, both in isotropic as well as in oriented solvents. The rα structure of the entire molecule has subsequently been determined.