bluuebunny/crossref_metadata_2025 huggingface dataset:
The conformation and configurational assignment of 6,7‐disubstituted 2‐oxabicyclo[3.3.0]octan‐3‐ones
Authors: De Clercq P. , Samson M. G.
Published: May 2005

The conformational behaviour of 6‐alkyl‐3‐oxo‐2‐oxabicyclo[3.3.0]octan‐7‐ols and some derivatives possessing the configurations a (6‐endo‐7‐exo), b (6‐endo‐7‐endo) and c (6‐exo‐7‐endo) is discussed. It is shown that an easy configurational assignment is possible between these three series.
19F spectra—structure correlations of fluorinated quaternary phosphonium salts
Authors: Van Hamme Michael J. , Burton Donald J. , Greenlimb Peter E.
Published: May 2005

The 19F NMR chemical shifts and geminal FCP and FCH coupling constants are reported for a number of fluorinated quaternary phosphonium salts of the type \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm R}_3 \mathop {\rm P}\limits^ \oplus {\rm CFXY}]{\rm Z}^ \ominus $\end{document}, where generally R = alkyl or aryl; X, Y = hydrogen or halogen and Z = halogen. Spectral parameters remain relatively unaffected upon variance of R, Z−, and/or solvent, except when R is a bulky alkyl group. Linear relationships accurately describe the correlation between the summation of the electronegativities of X and Y, or simply of Y if X = F, and the 19F NMR chemical shift and geminal FCP coupling constant; geminal FCH coupling constants show no such dependence. These relationships are of demonstrated analytical value, particularly for the purpose of spectral prediction.
Etude en RMN du 13C des Effets de Substituant sur les Déplacements Chimiques du Carbone dans les Méthyl Tétrahydrofurannes
Authors: Accary Armand , Huet Jean , Infarnet Yves , Duplan Jean Claude
Published: May 2005

Les spectres de RMN du 13C de quelques méthyltétrahydrofurannes ont été enregistrés et analysés. Les effets du groupement méthyle sur les atomes de carbone du cycle sont interprétés en fonction de l'encombrement stérique et de l'équilibre conformationnel.
A dynamic NMR study of Z, E‐isomerization in solutions of indolyl‐substituted α‐nitroacrylates
Authors: Bakhmutov V. I. , Burmistrov V. A. , Babievsky K. K. , Kochetkov K. A. , Kvasov B. A. , Belikov V. M. , Fedin E. I.
Published: May 2005

Fast Z, E‐isomerization of α‐nitro‐β‐indolylacrylates in polar solvents has been studied by dynamic 1H NMR spectroscopy. With indolylnitroacrylates having no substituents at the ring nitrogen atom, isomerization proceeds via intermediate formation of a mesomeric anion and ionization of the N–H bond as the rate determining step. For methyl‐substituted indolylnitroacrylates, no general isomerization mechanism can be suggested, and isomerization pathways depend on the structures of isomerizing species.
The torsional barrier in aromatic carbonyl compounds. V. Carbon‐13 DNMR study of stable protonated p‐substituted acetophenones
Authors: Barthelemy Jean‐François , Jost Roland , Sommer Jean
Published: May 2005

The barrier to internal rotation around the phenyl–carbonyl bond in a series of stable protonated p‐substituted acetophenones has been determined by means of low temperature 13C NMR and total bandshape analysis resulting in a value of ΔG = 48.1 kJ mol−1 for the unsubstituted protonated compound. The energy results and the 13C chemical shifts are in good agreement with the quasi‐planarity of the ground state in p‐substituted protonated acetophenones. The barrier heights are discussed in terms of contributions from steric and resonance effects.
Identification et Etude en Résonance Magnétique Nucléaire du Carbone‐13 des Produits de la Réaction de Quaternisation en Série Thiazolo[3,2‐d]tétrazolique
Authors: Faure R. , Galy J. P. , Vincent E. J. , Elguero J.
Published: May 2005

Nous avons montré que les produits obtenus lors de la quaternisation du thiazolo[3,2‐d]tétrazole, et de deux de ses dérivés, phényl‐3 thiazolo[3,2‐d]tétrazole et tétrazolo[5,1‐b]benzothiazole, sont des sels de tétrazolium. Nous avons discuté des effets dus à la quaternisation en fonction des résultats de la RMN du 13C.
A colour‐coded set of capillaries for improved deuterium locking and shimming of viscous samples
Authors: O'Neill I. K. , Stuart B.
Published: May 2005

Coaxial capillaries containing deuterated materials provide better 2H‐locking and magnet shimming for the 13C and 31P FTNMR observation of viscous samples. A series of capillaries is necessary for the accurate shimming of materials with differing polarities and magnetic susceptibilities.
1H and 13C NMR study of the prototropic tautomerism of 4(5)‐vinyl‐1,2,3‐triazole in dimethylformamide as solvent
Authors: Toppet S. , Wouters G. , Smets G.
Published: May 2005

Carbon‐13 NMR study of 4(5)‐vinyl‐1,2,3‐triazole in dimethylformamide at −55°C allows direct observation of the three separate tautomers. The 13C chemical shift values of the three forms, as well as their percentages in the tautomeric mixture, are given.
NMR spectral studies. XIV. Carbon‐13 nuclear magnetic resonance studies on β‐lactams
Authors: Bose Ajay K. , Srinivasan P. R.
Published: May 2005

Carbon‐13 NMR spectra of a variety of mono‐ and bicyclic β‐lactams have been measured and the chemical shifts of the ring carbon atoms have been assigned unambiguously. Effects of substituents on the chemical shifts of these carbons are also discussed.
The dynamic stereochemistry of dimesityl‐2,4,6‐trimethoxyphenylmethane: A 1H NMR study at 270 MHz
Authors: Willem R. , Hoogzand C.
Published: May 2005

The spectral behaviour of dimesityl‐2,4,6‐trimethoxyphenylmethane (1) was examined by 1H NMR spectroscopy at 270 MHz in order to resolve an isochrony of resonances observed in the low temperature spectra of 1 at 60 MHz. At 270 MHz the spectra of 1 exhibit well resolved o‐methyl resonances at low temperature so that the two‐ring flip mechanism, previously proposed as the threshold mechanism by Mislow et al., receives new independent experimental support.
Characterization of coupling constants to nitrogen. Carbon‐13 chemical shifts and carbon–nitrogen coupling constants of substituted benzaldoximes
Authors: Danoff Ann , Franzen‐Sieveking Marcia , Lichter Robert L. , Fanso‐Free Samuel N. Y.
Published: May 2005

Carbon‐13 chemical shifts and 13C−15N coupling constants of substituted benzaldoximes and of two non‐aromatic oximes have been determined. The coupling constants display little variation as a function of the nature or position of substitution, which suggests that perturbations in the π electron distribution have little effect. The values are compared with the markedly different ones reported for mesitaldoxime, and, in conjunction with the observed solvent effects, are discussed within the Schulman‐Venanzi framework for assessing the role of the lone‐pair.
Determination of hydration equilibrium constants and pKa values of 4‐piperidones in buffered water solutions
Authors: Van Luppen J. J. , Lepoivre J. A. , Dommisse R. A. , Alderweireldt F. C.
Published: May 2005

1H and 13C chemical shift parameters are given for 4‐piperidones and their derivatives in buffered aqueous solution. The 13C shift increments of methyl substituents on the nitrogen atom are discussed. The pH‐shift dependence is studied in detail and pKa values are given for ketone forms and hydration products. The hydration equilibria are measured as a function of pH and temperature.
13C NMR spectra of polymethoxy‐ and methylenedioxyflavonols
Authors: Calvert D. J. , Cambie R. C. , Davis B. R.
Published: May 2005

The 13C NMR spectra of 20 polymethoxy‐ and/or methylenedioxyflavonols are reported. In key cases assignments have been made by examination of fully coupled spectra.
Substituent group effects on the NQR frequency of Cl in certain chloromethane derivatives
Authors: Ramanamurti D. V. , Venkatacharyulu P. , Premaswarup D.
Published: May 2005

An empirical method is suggested for estimating the NQR frequencies of substituted chloromethanes. The frequencies are given by the equation νCl = νo + ∑imi, where the parameters mi are characteristic of the substituent groups, with additive properties in the case of multiple substitution for substituted chloromethanes. The calculations reveal that (i) as in chlorobenzenes, the effect of substituent groups on the NQR frequencies is additive to a first order of approximation, (ii)the effect is much larger in chloromethanes than in chlorobenzenes, (iii) the relative effects of different substituent groups are similar in the two sets, (iv) where there is more than one substituent group their mutual interaction is of the same order of magnitude as the crystal field effects.
15N nuclear magnetic resonance studies of [1‐15N]nicotinamide adenine dinucleotides
Authors: Oppenheimer Norman J. , Davidson Robert M.
Published: May 2005

The synthesis of [1‐15N]nicotinamide adenine dinucleotide is described. Chemical shift data from 15N NMR studies are presented for the pyridine ring nitrogen of labeled NAD and related compounds. The results indicate a 15N label in the N‐1 position to be highly sensitive to the redox‐state of the pyridine moiety, with an upfield shift of over 100 ppm observed upon reduction of NAD+ to NADH. The feasibility of conducting 15N NMR studies of pyridine nucleotide binding to dehydrogenases is discussed.
Carbon‐13 nuclear magnetic resonance studies of creatine, creatinine and some of their analogs
Authors: Dietrich Robert F. , Marletta Michael A. , Kenyon George L.
Published: May 2005

Creatine (N‐methyl‐N‐amidinoglycine), creatinine (1‐methyl‐2‐aminoimidazolin‐4‐one) and a series of 38 of their close structural analogs have been examined using natural abundance 13C NMR spectroscopy at 25.16 MHz. Both proton‐coupled and proton noise‐decoupled spectra were recorded. Unequivocal assignments of the carbon resonances could be made in the vast majority of cases. Both 13C NMR chemical shifts and 1J(CH) values can be used to characterize and to differentiate readily between analogs of creatine and analogs of creatinine. For example, the 1J(CH) coupling constants for the α‐carbons of the acyclic creatine analogs were all in the 140–142 Hz range, whereas the corresponding coupling constants for the related, cyclized creatinine analogs were all in the 150–152 Hz range.
Assignment and sign determination of (C, H) and (H, H) coupling constants in N‐acetylimidazole with selective population inversion experiments
Authors: Pachler K. G. R. , Wessels P. L.
Published: May 2005

The assignment of the (C, H) couplings in N‐acetylimidazole and the determination of the relative signs of all (C, H) and (H, H) couplings with SPI experiments are described. All coupling constants are of the same, positive, sign as the directly‐bonded (C, H) coupling constants. Some advantageous features of the SPI technique, such as selectivity and increased sensitivity, are discussed in comparison to conventional double irradiation methods.
Hindered rotation in the N(2,2,2‐trichlorocarboethoxy)nortropanes. An NMR study
Authors: Scheiber P.
Published: May 2005

A rarely occurring type of hindered rotation was observed by 1H NMR in some N‒(2,2,2‒trichlorocarboethoxy)nortropanes. A complete lineshape analysis gave the activation energy Ea = 56.9 kJ mol‒1 for the rotation around the CH2OCO bond.
1H NMR study of some substituted acyclic silaethanes, 2‐silapropanes and 2‐methyl‐2‐silapropanes and their rotameric populations around the SiC bond
Authors: Carleer Robert , Anteunis Marc J. O.
Published: May 2005

Three series of substituted silaalkanes, (i) SiH3CH2X, (ii) MeSiH2CH2X and (III) Me2SiHCH2X, have been prepared (X=Cl, Br, I, NMe2, OMe, SMe), and the shifts and coupling constants extracted from their1H NMR spectra. Coefficients averaged over three rotameric states can be obtained from the first series which are used for the correction of coupling constants resulting from the presence of the electronegative substituents X. With the aid of the Karplus‐Conroy angular dependence of the interproton coupling constants in silaethane† fragments, corrected for electronegative substitution, approximate rotameric populations in series ii and iii were obtained. Except for X=NMe2, there is always a preference for asynclinalX/CH3relationship, even for sandwiched situations (series III).
The stereochemistry of the 6‐membered ring of cedranone
Authors: Rodríguez Mario , Bertrán José Fernández
Published: May 2005

Evidence from the coupling constants and solvent shifts of the protons in cedranone rules out the boat and chair conformations of the cyclohexanone ring. Linear correlation of the solvent shifts of the C‐15 methyl protons of cedranone with those of the α‐methyl groups of fenchone indicates a nearly planar conformation of the cedranone ring. Site factor analysis of the ASIS effect of the methyl protons of cedranone provides conclusive evidence of a quasi‐chair conformation of the 6‐membered ring.
Ligand conformation in lanthanide complexes by NMR paramagnetic shifts: L‐proline and L‐valine
Authors: Mossoyan J. , Asso M. , Benlian D.
Published: May 2005

A fitting procedure is descdribede to establish the conformation and molecular dynamics of flexible molecules co‐ordinated to lanthanide cations from NMR paramagnetic shift data of 1H and 13C resonances. The results from L‐proline and L‐valine in aqueous solution at low pH values are consistent with peak assignments given by independent methods. A free rotation of the pyrrolidine ring is proposed in the case of L‐proline, and a rigid lock in the case of L‐valine, and angle and distance values are given for the cation and ligand positions in the complex.
Aromatic imine stereochemistry as studied by 13C and 1H NMR of 15N‐enriched materials
Authors: Buchanan Gerald W. , Dawson Brian A.
Published: May 2005

A series of thirteen 15N‐enriched N‐aryl imines derived from benzaldehydes and acetophenones have been prepared and examined by 13C and 1H NMR. Preferred conformations of the C‐arvl and N‐aryl rings have been deduced from 13C chemical shifts and 13C‐15N couplings. Evidence for steric inhibition of resonance in O‐alkylated materials is presented. Relative signs of 1J(CN) and 2J(CCN) have been determined in some compounds. An E: Z interconversion barrier of 21.6 kcal mol−1 has been obtained from 1H NMR coalescence data.
Comparative conformational studies of cyclic derivatives by 13C NMR spectroscopy
Authors: Casanova Joseph , Zahra Jean‐Pierre , Waegell Bernard
Published: May 2005

The 13C chemical shift of the substituted or functionalized carbon of various medium and large rings is plotted against ring size (6–15 carbons). The curves thus obtained allow a conformational analysis of the corresponding derivatives.
Additive of substituent effects on the chemical shift of the formyl proton in disubstituted benzaldehydes
Authors: Castañeda H. O. , Contreras R. H. , de Kowalewski D. G.
Published: May 2005

An additivity relationship of substituent effects on the formyl proton chemical shift has been tested with ten disubstituted benzaldehydes. In most cases it is found that the formyl proton chemical shift, extrapolated to infinite dilution in nitromethane, is in good agreement with that calculated using the additivity relationship.
Prediction of anti and gauche vicinal proton‐proton coupling constants in carbohydrates: A simple additivity rule for pyranose rings
Authors: Altona Cornelis , Haasnoot Cornelis A. G.
Published: May 2005

The effect of the relative orientation and electronegativity of substituents on the magnitude of 3J(aa), 3J(ae) and 3J(ee) is well predicated by a simple set of additivity constants, valid for pyranose rings in carbohydrates. The proposed set of parameters is used to calculate 327 coupling constants [3J(HH)] in a variety of pyranosides and related compounds. A comparison with experimental values taken from the literature shows that couplings in molecules which are conformationally pure and underformed can be predicted with a surprising accuracy. An overall root‐mean‐square agreement of 0.29 Hz is attained for a selected group of 305 coupling values. A statistical breakdown of ΔJ(aa) and ΔJ(ae) [ΔJ=J(exp)‐J(calc)] along each carbon‐carbon bond in the pyranose systems reveals an unexpected degree of geometrical homogeneity.
The molecular structure of allenes and ketenes. XIV—semi‐empirical descriptions of 13C chemical shifts of ketene imines and deduced from the effects of isoelectronic substitutions in allenes
Authors: Runge Wolfgang
Published: May 2005

An essentially algebraic model for semi‐empirical calculations of 13C chemical shicts of ketene imines and ketenes is presented which utilizes geometrical and non‐geometrical aspects of symmetry. In particular, emphasizing isoelectronic substitution as a generalized symmetry principle, it is shown that approximation functions for the description of 13C chemical shifts of ketene imines and ketenes can be deduced from those used for the allenes, and that the parameters which are necessary for the calculations of the carbon resonances of the heterocumulenes are simply related to those used for the allenes. A comparison between calculated and experimental 13C chemical shifts of complex ketene imines and ketenes demonstrates the relevance of the suggested model.
Vitamin B6 and derivatives. II—13C NMR study of systems formed by pyridoxal phosphate or pyridoxal with octopamine
Authors: Haran Raymond , Laurent Jean‐Pierre , Massol Michel , Nepveu‐Juras Francoise
Published: May 2005

Schiff base formation by condensation of pyridoxal phosphate or pyridoxal with octopamine in aqueous or methanolic medium was investigated by 13C NMR. Enolimine forms are favoured in methanolic solution, whereas in aqueous solution the predominant ketoenamine forms show a hydrogen bond between the iminium proton and the C‐3‐O− phenolate anion of the pyridoxal phosphate. The addition of Cu++ ions is consistent with the hypothesis of chelation of Cu++ by the nitrogen of the aldimine function and the phenolate function of pyridoxal phosphate.
The configuration of β‐halogenoenamines. The use of a new procedure for NOE measurements
Authors: Granger Pierre , Chapelle Stella , Poirier Jean‐Marie
Published: May 2005

The configurations of 16 different β‐halogenoenamines have been determined using the proton NOE effect, and the same results were obtained as when the 2J(CH) coupling constants were used. A new procedure called the ‘repetitive shift frequency’ is presented for the NOE determinations which allows better reproducibility and improves the precision.
13C NMR Studies: Effect of steric compression on chemical shifts of carbons in diastereoisomers
Authors: Prashad Mahavir , Seth M. , Bhaduri A. P. , Banerji Avijit
Published: May 2005

13C NMR of diastereoisomeric pairs of 2,3‐diaryl‐2‐methylbutyronitriles revealed a difference in the chemical shift of the carbon atoms between the diastereoisomers and the observed shifts were greatly influenced by the presence of an ortho substituent in the 3‐phenyl ring.
11B13C coupling constant in LiB(CH3)4
Authors: Yanagisawa Masaru , Yamamoto Osamu
Published: May 2005

Coupling constants between 11B and 13C, 13C and 1H, and 11B and 1H were obtained for LiB(CH3)4 in 1,2‐dimethoxyethane, in which the anion B(CH3) is belived to exist as a separate ion pair. The correlations of the coupling constants with the effective nuclear charge of boron, and with the s character of the BC bond, are discussed.
The conformation of (1R,2S,4R,5S)‐2,4‐dimethoxybicyclo[3.3.1]nonan‐9‐one and some related compounds
Authors: Camps P. , Jaime C.
Published: May 2005

A mixture of stereoisomers of 2,4‐dimethoxybicyclo[3.3.1]nonan‐9‐one was prepared, separated by column chromatography and characterized by 60 MHz 1H NMR spectroscopy using Eu(fod)3. A double chair conformation with axial methoxyl groups is established for (1R,2S,4R,5S)‐2,4‐dimethoxybicyclo[3.3.1]‐nonan‐9‐one on the basis of the J(12), J(2,H‐3 exo) and J(2,3 endo) values and the chemical shifts for H‐2(4). The conformation of some related compounds is subsequently inferred.
15N NMR spectroscopy 24—chemical shifts and coupling constants of α‐amino acid N‐carboxyanhydrides and related heterocycles
Authors: Kricheldorf Hans R.
Published: May 2005

The chemical shifts of amino acid N‐carboxyanhydrides (NCAs) and cyclic or linear urethanes are less sensitive to solvent effects than those of amides and lactams. The values of the one‐bond 15N1H coupling constants depend on the solvent and are 5‐8 Hz larger than those of ureas and amides. The 15N13C coupling constant of the NCO group is also unusually high, while that of the N—CH group lies within the range known for N‐acylated aliphatic amines. The one‐bond 15N13C coupling constant was found to be insensitive to conformational changes.
Stereochemical studies—XXXVII: Saturated heterocycles—XIII Configuration and conformation of Z‐ and E‐N‐methyl‐ and ‐N‐ benzyl‐2‐p‐nitrophenyl‐4,5‐ and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines
Authors: Sohár P. , Gera L. , Bernáth G.
Published: May 2005

The configuration and conformation of Z‐ and E‐N‐methyl‐ and ‐N‐benzyl‐2‐p‐nitrophenyl‐4,5‐, and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines were determined by 1H and 13C NMR spectroscopy. The Z isomers were proved to be conformationally homogeneous, having the heteroatom in axial and equatorial position, respectively, in the case of the 5,6‐ and 4,5‐tetramethylene compounds. Consequently, the p‐nitrophenyl group and the anellated cyclohexyl ring are all‐cis arranged in the Z‐5,6‐tetramethylene compounds while in the case of the Z‐4,5‐tetramethylene isomers the p‐nitrophenyl group and the cyclohexyl ring are trans arranged to the hetero ring.
Determination of the isotope distribution in partially deuterated compounds by NMR difference spectroscopy
Authors: Roth K. , Melzer P. , Kurreck H.
Published: May 2005

The position and the isotope distribution within labelled compounds can be determined by NMR by analysing the difference spectrum, and its integral, of the labelled and the corresponding parent compound. The method is applied to m‐terphenyl and it 4–4″‐dideutero derivative.
The structure and ring‐puckering vibration of thietane as studied by 1H and 13C NMR spectra of the oriented molecule
Authors: Jokisaari J. , Kuonanoja J. , Häkkinen A.‐M.
Published: May 2005

The 1H and 13C NMR spectra of partially oriented thietane have been recorded and analysed. The molecular structure was determined assuming the molecule to be planar and rigid. Because of the unsatisfactory fit of the dipolar coupling constants, a model which also takes into account the ring‐puckering vibration was applied. This model leads to a better fit, but also to long CH distances. Consequently, it seems that the one‐dimensional ring‐puckering model does not on its own explain the differences between the experimental and calculated coupling constants.
Proton magnetic resonance spectra of substituted adamantane‐2,4‐diones. Determination of the C‐6 and C‐9 stereochemistry
Authors: Ahmed S. Asghari , Hickmott Peter W. , Cooper Maurice W. , Stenhouse Ian A.
Published: May 2005

The 220 MHz 1H NMR spectra of 6‐hydroxy‐7‐methyl‐6‐phenyladamantane‐2,4‐dione, 6‐hydroxy‐5,7‐dimethyl‐6‐phenyladamantane‐2,4‐dione, and 6‐hydroxy‐7,9‐dimethyl‐6‐phenyladamantane‐2,4‐dione have been determined and complete proton assignments carried out with the aid of multiple irradiation. The stereochemistry of the C‐6 and C‐9 chiral centres have been determined and some of the factors affecting the magnitude of the geminal, vicinal and W coupling constants are discussed.
Carbon‐13 NMR studies on some 5‐substituted quinoxalines
Authors: Hollstein Ulrich , Krisov Galen E.
Published: May 2005

Eleven 5‐substituted quinoxalines (NO2, NH2, COOH, OCH3, CH3, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their 13C NMR spectra have been measured in DMSO‐d6 and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1‐substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1‐substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5‐Fluoroquinoxaline was also measured in CDCl3, CD3COCD3, CD3CN, CD3OD, C6D6 and CD3COOD. In all solvents an abnormally low 2J(CF) (∼ 12 Hz) was found for C‐4a and no CF spin‐spin splitting could be detected for the three‐bond coupling of C‐8a. Similar abnormalities were found in 2‐fluoroaniline and 2‐fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C‐8 (‘para’ position) and the Hammett σp parameter of the substituent.
A carbon‐13 nuclear magnetic resonance study of compounds substituted by a perfluoroalkyl chain
Authors: Tordeux M. , Leroy J. , Wakselman C.
Published: May 2005

The 13C NMR spectra of alkanes, alkanones and cyclohexanones substituted by perfluoroalkyl groups, RF, have been studied. The influence of the perfluoroalkyl group on the chemical shifts of other carbons of the molecules is the same regardless of the RF chain length.
1H and 13C NMR of substituted chromium tricarbonyl complexes; substituent effects and Cr(CO3) conformation
Authors: Solladié‐Cavallo A. , Suffert J.
Published: May 2005

It is shown that 13C NMR is not suitable for determining the conformation of the Cr(CO)3 group in monosubstituted chromium tricarbonyl complexes. However,. 1H NMR can be used for such determinations if one takes substituent effects into account, whn necessary, and an appropriate relationship is proposed. The populations, xA, of the eclipsed conformer so obtained for various substituents increase with the π donor ability of the substituent. These results are consistent with X‐ray results and with Carter and Hoffmann's models.
Carbon‐13 nuclear magnetic resonance studies of leonurine hydrochloride and its analogues
Authors: Langford Gordon E. , Yates Peter , Yeung Hin Wing , Cheng Kin Fai
Published: May 2005

The 13C NMR spectra of leonurine hydrochloride and thirteen of its analogues in DMSO‐d6 have been analyzed. Changes in the aromatic substituents have no significant effect on the chemical shifts of the side chain methylene carbons indicating that they do not influence the conformation of the latter. Observed deviations from additivity of substituent effects for the methylene carbon chemical shifts suggest that the methylene side chains of these compounds may be more tightly coiled than are the corresponding n‐alkanes. In representative cases no change in conformation is evident in 50% aqueous DMSO‐d6 solutions, indicating that similar considerations may apply in aqueous media.
Structure determination of di‐O‐benzylidene derivatives of L‐iditol by 1H and 13C NMR spectroscopy
Authors: Sohár P. , Fehér G. , Toldy L.
Published: May 2005

The configuration and stable conformation of two dibenzylidene‐L‐iditol isomers formed upon benzalation of L‐iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative—the main product of the benzalation reaction—were determined by 1H and 13C NMR spectroscopy.
The nuclear magnetic resonance spectra of N‐nitroso‐N‐alkyl amino acids
Authors: Chow Yuan L. , Polo Joel
Published: May 2005

Structurally related acyclic and cyclic N‐nitroso‐N‐alkyl amino acids were prepared and their 1H, 13C and 15N NMR spectra were investigated. The changes in the 13C NMR spectra of the N‐nitroso α‐amino acids after dissolving in solvents suggest that they posses the Z‐configuration in the crystalline state; in solution some of them isomerize to mixtures of the Z‐ and E‐isomers whose composition appear to depend on steric factors. The 13C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The 13C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the α‐carbons and shielding on the β‐carbons.
A carbon‐13 NMR study of phenyl‐substituted cyclophosphazenes
Authors: Krishnamurthy S. S. , Ramabrahmam P. , Woods M.
Published: May 2005

The 13C NMR spectra of the cyclotriphosphazenes N3P3CI6−n Phn (n=2, 3, 4, 6) and the tetrameric derivatives 2,2,6,6‐N4P4CI4Ph4 and N4P4Ph8 have been recorded. The carbon chemical shifts can be largely explained on the basis of concomitant mesomeric electron release from the benzene ring and inductive electron withdrawal by phosphorus. The magnitude of 1J(P, C‐1) for the non‐geminal compounds is ≃40 Hz higher than that observed for the geminal compounds. Some aspects of the NMR data are also discussed with reference to the X‐ray crystal structures of several phenyl‐substituted cyclotri‐ and cyclotetra‐phosphazenes.
1H NMR studies on dimeric 2‐methylchromones
Authors: Mahran M. R. , Sidky M. M.
Published: May 2005

A study is presented on the configuration and conformation of 2‐methylchromone‐dimer, as well as on khellin‐dimer, based on 1H NMR spectroscopy.
Coupling of chromatography and NMR. 3—study of flowing gas chromatographic fractions by proton magnetic resonance
Authors: Buddrus Joachim , Herzog Helmut
Published: May 2005

A procedure is described which allows the recording of 1H NMR spectra from gas chromatographic (GC) fractions flowing through the magnetic field with a velocity of c. 0.6 cm/s. The spectra are obtained by the pulse Fourier transform technique; the beginning and the termination of the pulse sequence is timed according to the chromatogram from a thermal conductivity detector. The line width of the signals in the NMR spectra is 2 Hz.
Tritium nuclear magnetic resonance spectroscopy. 14—analysis of tritiated methyl groups
Authors: Bloxsidge James P. , Elvidge John A. , Jones John R. , Evans E. Anthony , Kitcher J. Philip , Warrell David C.
Published: May 2005

The complete analysis of the tritium distribution in tritiated methyl groups in labelled compounds is achieved by a direct method for the first time, through 3H NMR spectroscopy aided by resolution enhancement.
1H and 13C NMR study of 8‐hydroxyquinoline and some of its 5‐substituted analogues
Authors: Kidrič J. , Hadži D. , Kocjan D. , Rutar V.
Published: May 2005

1H and 13C NMR spectra of 8‐hydroxyquinoline (oxine) and its 5‐Me, 5‐F, 5‐Cl, 5‐Br and 5‐NO2 derivatives have been studied in DMSO‐d6 solution. The 1H and 13C chemical shifts and proton–proton, proton–fluorine, carbon–proton and carbon–fluorine coupling constants have been determined. The 1H and 13C chemical shifts have been correlated with the charge densities on the hydrogen and carbon atoms calculated by the CNDO/2 method. The correlation of the 1H and 13C chemical shifts with the total charge densities on the carbon atoms is approximately linear (rH2 = 0.85, rC2 = 0.84). The proton in peri position to the nitro group in 5‐NO2‐oxine is an exception.
Synthesis, 1H NMR spectral properties and conformational preferences of some open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units
Authors: Bottino Francesco , Pappalardo Sebastiano
Published: May 2005

The conformational preferences in solution of eight new open‐chain and cyclic aromatic sulphides containing pyridine or 1,3,4‐thiadiazole units have been investigated, parallel to those of some structurally related phenyl sulphides, by means of 1H NMR spectroscopy. The results obtained have shown that replacement of phenyl by the pyridyl or the 1,3,4‐thiadiazolyl moieties induces slightly different propeller arrangements, ascribed to the higher conjugative tendency of both electron‐deficient heteroaromatic rings, in all open‐chain mixed sulphides, in opposition to the skew arrangements observed for phenyl sulphide derivatives. No prominent differences have been found for cyclic sulphides, which preferentially adopt the sterically unhindered saddle shape conformation.
NMR study of the structure of the nitration intermediate of furfural
Authors: Gaset A. , Gorrichon J. P.
Published: May 2005

The structure of the intermediate obtained in the come of the nitrationof 2‐furancarboxaldehyde was investigated by means of1H and13C NMR. It was shown unambiguously that this intermediate is 2‐acetoxy‐2‐diacetogymethyl‐5‐nitro‐2,5‐dihydrofuran.
Proton polarization transfer in natural abundance 15N NMR studies of E‐ and Z‐isomers of N‐alkylformamides
Authors: Sørensen O. W. , Scheibye S. , Lawesson S.‐O. , Jakobsen H. J.
Published: May 2005

Proton polarization transfer has been used for the convenient observation of proton coupled natural abundance 15N NMR spectra of the E‐ and Z‐isomers of N‐methylformamide at 10.14 MHz. Second‐order spectral analysis is required to determine the 15NH coupling constants, at least for the E‐isomer of secondary formamides. An useful stereospecificity is observed for both the one‐ and two‐bond 15NH coupling constants.
The assignment of the 1H and the 13C NMR chemical shifts of N‐phenyl‐2,4‐dimethylbuta‐1,3‐diene‐1,4‐sultam
Authors: Radeglia R. , Fanghänel E.
Published: May 2005

The assignment of the signals in the 13C and 1H NMR spectra of N‐phenyl‐2,4‐dimethylbuta‐1,3‐diene‐1,4‐sultam is difficult for the signal pairs C‐2 and C‐4, C‐1 and C‐3, (C‐1)H, (C‐2)CH3 and (C‐4)CH3. The 13C NMR spectrum recorded under gated decoupling conditions provide long‐range couplings which make possible an unambiguous assignment of the 13C NMR signal pairs. Application of the 1H CW off‐resonance decoupling technique in recording the 13C NMR spectra enables the assignment information from the 13C NMR spectrum to be transferred to the 1H NMR spectrum.
Mercury‐199 NMR chemical shifts in substituted diphenylmercury and phenylmercuric chloride
Authors: Wells Peter R. , Hawker Darryl W.
Published: May 2005

The influence of substituents on the 199Hg chemical shifts of some Ar2Hg and ArHgCl species in 1:1 CDCl3: CH2Cl2 and in CDCl3: DMSO solutions is reported. The effects are substantial and are in the direction of electron withdrawal producing increased shielding (i.e. shifts towards higher field).
Dihedral‐angle dependence of the vicinal 15N,13C spin‐coupling constants. A new NMR parameter for the conformational analysis of amino acids and peptides
Authors: Kainosho Masatsune , Tsuji Takashi
Published: May 2005

The first successful observation of the vicinal 15N,13C spin‐coupling constants in a series of amino acids, comprising Val, Ile, Leu and Thr, in which the α‐nitrogens are fully replaced with 15N, is described. A Karplus‐type dihedral‐angle dependence was noted for the coupling constants between the α‐nitrogen and γ‐carbon nuclei which may, in turn, be applied to the conformational analysis of other amino acids and small peptides. The potential usefulness and limitation of this new parameter in such applications is briefly discussed.
Carbon‐13 T1 measurements on glyceryl trivalerate
Authors: Hosur Ramakrishna V. , Govil Girjesh
Published: May 2005

13C spin lattice relaxation times (T1) of glyceryl trivalerate have been measured as a function of concentration in CDCl3 solutions. The T1 values indicate that there is a gradient in the rate of rotational motions around the CC bonds in the hydrocarbon chains, the rate increasing towards the methyl groups. Examination of T1 values as a function of concentration suggests that glyceryl trivalerate does not aggregate in CDCl3 solutions, unlike other lipids with long hydrocarbon chains. It is concluded that the length of the hydrocarbon chain plays a dominant role in determining the aggregation behaviour of lipids in solution.
Carbon‐13 nuclear magnetic resonance study of the motional behaviour of bilirubin and of some of its derivatives
Authors: Kaplan Doron , Navon Gil
Published: May 2005

A comparative study of the spin‐lattice relaxation times (T1) of proton‐bearing carbons in bilirubin and its derivatives is reported. The NT1 values of the backbone carbons indicate that the overall reorientation of the molecule is isotropic. In dimethyl sulphoxide solutions, the segmental motion of the propionic side chains is very limited in bilirubin, bilirubin dimethyl ester and mesobilirubin dimethyl ester, faster in dimethoxybilirubin dimethyl ester and is very fast in the propionic residue of vinylneoxanthobilirubinic acid methyl ester. The relative mobilities of the propionic residues are interpreted on the basis of intramolecular hydrogen bonding in which the solvent participates. The dimeric form of bilirubin dimethyl ester in chloroform solutions is confirmed by the correlation time of tumbling of the backbone. In this solvent the segmental motion of the propionic side chains is rapid, indicating the probable absence of hydrogen‐bonding. In bilirubin, bilirubin dimethyl ester and dimethoxybilirubin dimethyl ester, internal rotation is rapid for the endo‐vinyl group and slow for the exo group, correlating with reported differences in the chemical behaviour of these residues in bile pigments.
The structural dependence of two‐bond 13C13C coupling constants
Authors: Klessinger Martin , Stöcker Michael
Published: May 2005

Two‐bond 13C13C coupling constants are discussed on the basis of INDO‐SCPT calculations. The dependence of 2J(CC) on bond angle variation and on methyl substitution is evaluated, and it is shown that 2J(CC) depends linearly on the bond orbital s‐character product of the terminal carbon atoms, whereas no systematic relationship with the hybridization of the central carbon atom was obtained. Alkyl group substituent effects are found to be additive. The coupling constants of a number of cyclobutane derivatives are discussed on the basis of these structural relationships; it is shown that the experimental findings can be interpreted quite consistently by assuming a dual‐pathway coupling mechanism.
1H and 13C NMR study of the effects exerted by an oxirane ring in the epoxybicyclo‐[2.2.2]octane series
Authors: Christol H. , Laffite C. , Plénat F. , Renard G.
Published: May 2005

The 1H and 13C NMR spectra of 2,3‐disubstituted exo‐5,6‐ and endo‐5,6‐bicyclo[2.2.2]octanes, and the corresponding alkanes, have been investigated to determine the effects exerted by an oxirane ring. The 1H NMR study showed that the anti protons, H‐7a and H‐8a, are significantly shielded and the syn protons, H‐7s and H‐8s, are deshielded, although to a smaller extent, by the exo‐oxirane. An endo‐oxirane has practically no effect on the same protons. The stereochemistry of epoxybicyclo[2.2.2]octanes is, thus, easily deduced from 1H NMR data. The 13C NMR study of the epoxy compounds provided an estimate of the value of α, β, γ syn and γ anti effects (to the epoxide oxygen) of an oxirane ring. In these rigid bicyclic molecules, of known geometry, the γ syn and the γ anti effects are of the same value, even though the dihedral angles are very different (0° and 120°).
ESR studies of nitroxide radicals formed in the low temperature photolysis of N‐nitrosamines
Authors: Joshi Avinash , Yang George C.
Published: May 2005

Various N‐nitrosamines were photolyzed in toluene solution in the temperature range −100°C to −30°C to yield dialkyl nitroxides. The nitrosamines studied were N‐nitrosodimethylamine, N‐nitrosodiethylamine, N‐nitrosodipropylamine, N‐nitrosodibutylamine and N‐nitrosodicyclohexylamine. Subsequent nitroxide side products were also detected by ESR, and a mechanism for their formation is proposed. Temperature dependent hyperfine couplings of the methylene protons were observed for a few radicals of the type R1CH2NO˙R2.
The effect of iodine on the carbon‐13 relaxation times of pyridine
Authors: Smith William B.
Published: May 2005

The addition of iodine to pyridine not only causes appreciable changes in the 13C chemical shifts but also a marked reduction in spin‐lattice relaxation times. The effect at the γ‐carbon is larger than at the α‐ and β‐carbons. This is consistent with the formation of a pyridine‐iodine complex with a preferential tumbling about the C‐γNI axis. Elementary theory is applied to approximate the tumbling ratio.
Carbon‐13 resonance assignments of some friedelanes and taraxasteranes
Authors: Patra Amarendra , Mukhopadhyay Apurba K. , Mitra Alok K.
Published: May 2005

Carbon‐13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol and epi‐friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revision.
13C nuclear magnetic resonance spectra of several hydroxy diterpene derivatives
Authors: Delmond Bernard , Taran Martine , Valade Jacques , Petraud Michel , Barbe Bernard
Published: May 2005

13C NMR spectra of several hydroxy diterpene derivatives having a pimarane, isopimarane and (13S, 8α)rosane skeleton have been recorded. The most significant effects caused by the introduction of hydroxyl groups in such a skeleton are demonstrated. The magnitudes of the γ‐ and δ‐effects are large enough to allow their use in sterochemical assignments.
1H NMR studies of 3,8‐dioxatricyclo‐[3.2.1.02,4]octane derivatives
Authors: Marfisi Claude , Cossu Michèle , Aycard Jean‐Pierre
Published: May 2005

A series of 6‐X‐3,8‐dioxatricyclo[3.2.1.02,4]octanes (XCO2CH3, CN, Cl and CN) are studied by NMR, after their syntheses by epoxidation of the corresponding 7‐oxabicyclo[2.2.1]heptenes. The NMR parameters (J, δ) are determined, and also the anisotropy effects of methyl groups at the 1,5 bridgehead positions. The results allow an unambiguous identification of the diastereo‐isomers having a gem‐chlorocyano group in the 6 position.
13C chemical shifts of symmetrically substituted biphenyls: Unambiguous signal assignment for the carbons ortho and para to an aryl group
Authors: Fuji Karou , Yamada Toshihide , Fujita Eiichi
Published: May 2005

The natural abundance 13C NMR spectra of 2,2′‐dimethyl‐, 2,2′‐dimethoxy‐ and 2,2′‐dihydroxybiphenyls, and a series of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls were recorded. Unambiguous signal assignments of the carbons ortho and para to an aryl ring in biphenyls were made by selective deuteration and/or the graphical method for 1H single frequency off‐resonance decoupled spectra. Contrary to the reported assignments, it was shown that the signal for C‐6 in 2,2′‐dimethylbiphenyl clearly appears at lower field than that for C‐4. The signals for the ortho carbons (C‐6) of 2,2′‐dimethoxy‐5,5′‐disubstituted biphenyls generally appeared at lower fields than those for the para carbons (C‐4). The validity of applying deuterium isotope shifts to the assignments of 13C chemical shifts of di‐ and tetra‐substituted biphenyls is also discussed.
Carbon‐13 NMR spin‐lattice relaxation in dithiarsolanes. Correlation between molecular motions and structural properties
Authors: Aksnes D. W. , Holak T. A.
Published: May 2005

13C NMR spin‐lattice relaxation times (T1) and nuclear Overhauser enhancements (η) were measured for dithiarsolanes. The contributions of dipolar (T) and spin‐rotation (T) mechanisms were determined. The T1 data were analysed to obtain information on the relative order of magnitude of the internal motion rates. The calculations were based on the isotropic, with internal rotation about the AsPh bond, model of reorientation. In cis, trans‐2‐phenyl‐4‐methyl‐1,3,2‐dithiarsolane, the internal rotation of the phenyl ring is c. three times faster than overall molecular reorientation. The internal motion of the arsolane ring is slightly slower than the phenyl ring rotation. The rotation of the methyl groups in the compounds appears to be considerably hindered, with rotation energy barriers of c. 10 kJ mol−1. In contrast to the situation in the 4‐methyldithiarsolane, the internal motion of the arsolane ring is twice as fast as the internal rotation of the phenyl ring for the methyl‐unsubstituted analogue, 2‐phenyl‐1,3,2‐dithiarsolane.
NMR studies in the heterocyclic series XXIV—1H, 13C and 15N study of 15N labelled indazoles
Authors: Fruchier Alain , Pellegrin Valdo , Schimpf Rémy , Elguero José
Published: May 2005

The 15N chemical shifts and 1H15N and 13C15N coupling constants of nine monolabelled indazoles were measured and assigned. The experimental values are discussed in terms of the indazolic and iso‐indazolic structures, and compared with literature data for other related heterocycles. All the results are consistent with an N‐1(H) tautomeric structure for indazole in DMSO‐d6.
29Si NMR spectra of methylphenylcyclotri‐and ‐tetrasilazanes
Authors: Lavrukhin B. D. , Astapov B. A. , Zhdanov A. A. , Engelhardt G. , Jancke H.
Published: May 2005

29Si NMR spectra of various methylphenyl‐substituted cyclotri‐ and ‐tetrasilazanes, composed of different combinations of the unitsd= Me2SiNH,dph= MePhSiNH andd= Ph2SiNH, have been investigated. For most of the compounds having more than one asymmetric centre, the spectra of both the individual isomers and their mixtures have been studied, and the signals of the individual isomers have been assigned. The effect of a different arrangement of phenyl groups in the rings, and the influence of the stereochemistry of the isomers on the29Si chemical shifts in cyclotri‐ and ‐tetrasilazanes have been studied. The29Si chemical shifts in cyclotrisilazanes are additive and can be represented as the sum of increments corresponding to the number and positions of the phenyl groups in the rings. In these compounds, the spatial structure of the isomers does not exert any noticeable effect on the spectra. On the contrary, chemical shifts are not simply additive in cyclotetrasilazanes: a pronounced stereochemical dependence is apparent.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. NH proton exchange reactions of urea, thiourea, acetamide and thioacetamide
Authors: Chun Yu , Yavari Issa , Roberts John D.
Published: May 2005

Measurements are reported of NH exchange rates of urea, thiourea, acetamide and thioacetamide, using line‐shape analysis with natural‐abundance 15N NMR spectra. Base‐catalyzed NH‐proton exchange of thiourea is 30–40 times faster than for urea, while the corresponding acid‐catalyzed exchange is 150 times slower. The base‐catalyzed proton exchange for thioacetamide is about 1000 times faster than that of acetamide at 25°C, while the corresponding acid‐catalyzed exchange is some 260 times slower.
Application of the nuclear overhauser effect difference experiment: Assignment of the configuration of carboprostacyclin
Authors: Kotovych G. , Aarts G. H. M.
Published: May 2005

Nuclear Overhauser effect difference experiments, together with difference decoupling and inversion recovery measurements, have allowed the complete assignment of the proton magnetic resonance spectrum of carboprostacyclin. The nuclear Overhauser effect measurements prove the 5E configuration at C‐5 for carboprostacyclin. Protons H‐2,2*, H‐3,3*, and H‐4,4* are observed to be nonequivalent due to the asymmetric nature of this molecule.
Stereochemical aspects of proton chemical shifts. X—The slow exchange 1H NMR spectrum of cis‐transoid‐cis‐perhydroanthracene and of cis‐decalin
Authors: Tavernier D. , Anteunis M. J. O.
Published: May 2005

The slow exchange 360 MHz 1H NMR spectra of cis‐transoid‐cis‐perhydroanthracene and of cis‐decalin have been assigned. Shift increments due to the cis‐annelation of a tetramethylene bridge to cyclohexane are presented.
Assignment and analysis of the 500 MHz 1H NMR spectra of somatostatin and the acyclic precursor (S3,14‐Acm)‐somatostatin in dimethyl sulphoxide
Authors: Deleuze C. , Hull W. E.
Published: May 2005

The 500 MHz 1H NMR spectra of somatostatin and the precursor, di‐S3,14‐acetamidomethyl dihydrosomatostatin, in dimethyl sulphoxide solution have been assigned. Chemical shifts, coupling constants and NH shifts vs temperature coefficients are tabulated. The data are consistent with a stable β‐turn/β‐sheet conformation for the precurso, while somatostatin itself appears to be more conformationally mobile, with an average conformation significantly different from that in aqueous solution.