bluuebunny/crossref_metadata_2025 huggingface dataset:
Selenium‐77 magnetic resonance in SSe and SeSe isosteres of phenanthrene
Authors: Baiwir Marcel , Llabrès Gabriel , Piette Jean‐Louis , Christiaens LÉOn
Published: May 2005

Selenium‐77 magnetic resonance spectra of sulphur‐selenium and selenium‐selenium isosteres of phenanthrene and some of their 2‐substituted derivatives have been recorded and 48 77Se chemical shifts are presented. The two isomers of the studied compounds could be differentiated because the Se nucleus is always more shielded in the ‘trans’ than in the ‘cis’ isomer, the difference varying between 10 and 40 ppm. CNDO calculations have been performed; they allow an electronic model to be proposed which accounts, at least qualitatively, for the NMR results. They also provide an electronic interpretation of the ring opening of the Se‐containing ‘cis’ isomers when treated with alkyllithium.
The carbon‐13 NMR spectrum of dimethoxybilirubin dimethyl ester
Authors: Kaplan Doron , Navon Gil
Published: May 2005

The 13C NMR spectrum of dimethoxybilirubin dimethyl ester (1) is reported. Methoxyvinylneoxanthobilirubinic acid methyl ester, a compound containing one endo‐vinylpyrromethene unit, was prepared and used in the assignment of the spectrum of 1.
Nitrogen inversion in 3,6‐dihydro‐1,2‐oxazines
Authors: Labaziewicz Henryk , Riddell Frank G.
Published: May 2005

The nitrogen inversion barriers of nine 3,6‐dihydro‐1,2‐oxazines are discussed. Polar solvents were found to increase the nitrogen inversion barriers which, in turn, decrease with increasing size of the N‐substituent.
Cyclic oxonium salts: 13C magnetic resonance spectroscopy. The correlation of chemical shifts with the calculated charge density
Authors: Bégué J. P. , Bonnet‐Delpon D.
Published: May 2005

The 13C chemical shifts of several bicyclic and monocyclic oxonium salts are reported and, in the case of 5‐membered ring unsaturated oxonium salts, compared with ab initio and CNDO calculated charges. A prime dependence of the 13C shielding on the π charge delocalization effects induced by the Y group is established for the Y‐substituted C‐α carbon; a good correlation of δC‐α vs qπ is obtained, using π bond‐order terms. However, contradictory information arises from NMR and theoretical calculations for the C‐ω carbon, which is distant from the Y group. The results are discussed.
14N nuclear quadrupole resonance study of substituted anilines and prediction of in vitro activity of sulfanilamides
Authors: Greenbaum S. G. , Subbarao S. N. , Bray P. J. , Oja T.
Published: May 2005

14N nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines are reported and analyzed in the framework of the Townes and Dailey theory. Satisfactory correlations of the NQR data with both the Hammett σ parameters and the in vitro biological activities of the corresponding sulfanilamides have been found. The results obtained suggest that the nitrogen lone‐pair orbital is more sensitive than the nitrogen–carbon sigma orbital is to substituent effects.
Studies of substituent effects by carbon‐13 NMR spectroscopy. Thiophene and furan chalcone analogues
Authors: Musumarra Giuseppe , Ballistreri Francesco P.
Published: May 2005

13C NMR spectra of 39 thiophene and furan chalcone analogues in CDCl3 solutions are reported. The effect of substituents on the 13C chemical shifts in the phenyl and in the 5‐membered rings is discussed. 13C NMR shifts are correlated with Hammett parameters and with experimental shifts in the chalcone series.
Conformational studies of 3‐amino‐3‐phosphonatopropionic acid. 1H31P coupling constants
Authors: Siatecki Zdzisław , Kozłowski Henryk
Published: May 2005

The 1H and 31P NMR spectra of 3‐amino‐3‐phosphonatopropionic acid, a phosphonic derivative of aspartic acid, have been measured and completely analysed for 14 pH values. The vicinal coupling constants, 3J(HH) and 3J(HP), were used to obtain information on the rotational isomerism of the amino acid. The most stable conformer is the one where the phosphonic and β‐carboxyl groups are in trans position to each other.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. 15N19F coupling constants in fluoropyridines and fluoroanilines
Authors: Sibi Mukund P. , Lichter Robert L.
Published: May 2005

Two‐to five‐bond 15N19F coupling constants have been determined for fluoropyridines, 8‐fluoroquinoline, fluoroanilines and fluoroaniline derivatives. Only in 2‐fluoropyridine is J(NF) large, and this is associated with a lone pair mediated enhancement of the coupling. Values in fluoroanilines and derivatives are <2Hz. Except for the fluoroanilines themselves, J(NF) decreases inversely with the number of intervening bonds. In the anilines, only 5J(NF) is observable. Possible influences of lone pair interaction and hydrogen bonding are discussed.
Inhibition and enhancement of resonance as studied by 13C nuclear magnetic resonance spectroscopy
Authors: Kitching William , Jonge Ian De , Adcock William , Abeywickrema Anil N.
Published: May 2005

13C chemical shifts are reported for a series of 2‐substituted 1,3‐dimethylbenzenes: comparisons of these values with those for the corresponding monosubstituted benzenes reveal, in some cases, large differences in the para‐carbon substituent chemical shifts, which are attributable to steric hindrance of resonance. The questions of steric enhancement of resonance, and methoxy group conformation in certain anisoles are also studied by the 13C NMR technique. Studies of selected 2‐substituted fluorenes are also reported, and substituent chemical shifts at carbon‐7 (traversing eight bonds) of greater than 2ppm are observed. These effects are consistently greater than those reported for the corresponding biphenyl compounds, and are associated with planarity‐enforced enhancement of resonance.
NMR chemical shift substituent effects: 2‐α‐monosubstituted N,N‐diethylacetamides
Authors: Martins Marcos A. P. , Rittner Roberto
Published: May 2005

1H NMR chemical shifts for some α‐hetero‐substituted N,N‐diethylacetamides were recorded. The resonance assignments for the syn‐ and anti‐methylene and ‐methyl protons have been made unambiguously through their aromatic solvent induced shifts and are opposed to the literture assignments for the N‐methylene protons. An empirical relationship between the Charton polar (σL) and steric (V) parameters and the α‐methylene proton resonances was found. The N‐methylene proton chemical shifts also showed a qualitative dependence on the α‐substituent electronegativity, while the N‐ethyl methyl proton chemical shifts were related to the α‐substituent steric effects. The Paulsen and Todt anisotropic model and the more populated rotamers proposed seem to explain the results very well.
Nitrogen‐15 coupling constants: Geminal coupling, 2J(15NH), in cis‐ and trans‐aldonitrones and vicinal coupling, 3J(15NH), in cis‐and trans‐ketimines, oxaziridines and nitrones
Authors: Boyd Derek R. , Stubbs Michael E. , Thompson N. J. , Yeh Herman J. C. , Jerina Donald M. , Wasylishen Roderick E.
Published: May 2005

Nitrogen‐15‐hydrogen 2J(15NH), 15N, 13C 1J(15N13C) and 13C, H 1J(13CH) coupling constants have been measured and their signs determined for cis‐and trans‐[9‐anthryl(13C)methylene](2H3)methylamine (15N)‐oxide. Values of 2J(15NH) were of similar magnitude (∼2 Hz) but were of opposite sign. The results are compared and contrasted with those reported for related imino and quaternary imino systems. Vicinal 3J(15NH) coupling constants have been measured in cis‐ and trans‐15N‐[1‐(α‐naphthyl)ethylidene]benzylamine and 15N‐[1‐(p‐nitrophenyl)ethylidene]‐t‐butylamine and were found to be larger when the imino methyl group was cis to the nitrogen lone pair. The corresponding cis and trans ketonitrones formed by photoisomerization of the derived oxaziridines had 3J(15NH) values of c. 3.3 Hz. A study of the signs and magnitudes of observed and calculated 15N,H coupling constants for all of the 15N labelled imines, oxaziridines, imine N‐oxides (nitrones) and similar model systems which were synthesized is described.
13C NMR spectra of some spiro cyclic glycidic esters
Authors: Hügel H. M. , Porter Q. N.
Published: May 2005

The 13C NMR of fourteen spiro cyclic glycidic esters and two amides have been investigated.
The fixed conformation of the leucyl side‐chain in a tripeptide
Authors: Abraham Raymond J. , Jackson J. Timothy , Thomas W. Anthony
Published: May 2005

The complete analysis of the 1H NMR spectrum of the leucyl side‐chain of a tripeptide allows the deduction of the conformation of this side‐chain. In the peptide, in contrast to the free amino acid, the side‐chain is in a single fixed conformation.
Proton and carbon‐13 nuclear magnetic resonance studies of substituted pyrimidines. V13C, 1H coupling contsants for some methyl‐ and aminopyrimidines
Authors: Riand Jacques , Chenon Marie‐Thérèse
Published: May 2005

J(13C1H) coupling constants for some methyl‐ and aminopyrimidines have been determined by 13C NMR. Both the one‐bond and long‐bond and long‐range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the 3J(C‐i,H) coupling constants between a ring carbon C‐i and the ring protons are larger than the 2J(C‐i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: 3J(C,Me). These general rules are very useful for the assignment of resonances in complex 13C spectra of pyrimidines and seem to be valid for other 6‐membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on 1J (CH) for monosubstituted pyrimidines allows the estimation of 1J (CH) for polysubstituted pyrimidines with a very good accuracy.
1H dynamic nuclear magnetic resonance study of hindered internal rotation in N‐aroyl‐ and N‐thioaroyl‐N′‐ piperonylpiperazines
Authors: Benassi Rois , Taddei Ferdinando , Leonardi Amedeo , Nardi Dante
Published: May 2005

The NMR variable temperature behaviour of N‐aroyl‐ and N‐thioaroyl‐N′‐piperonylpiperazines was investigated. The largest chemical shift separation between the exchanging methylene groups, and the highest energy barrier, is found for the thioamide compounds. Results from semi‐empirical calculations are qualitatively in line with the experimental findings, revealing that the higher barrier in the thiocarbonyl compounds compared with the carbonyl compounds is mainly connected with differences in the energies of ground states, rather than in those of transition states, of these molecules. The effect of the nature of the heterocyclic ring containing the amidic nitrogen atom on the barrier height is also discussed.
Nuclear magnetic resonance of psychotherapeutic agents. IV—conformational analysis of 2,3‐dihydro‐1H‐1,4‐benzodiazepines
Authors: Romeo G. , Aversa M. C. , Giannetto P. , Ficarra P. , Vigorita M. G.
Published: May 2005

The lanthanide shift reagent (LSR)/1H NMR study of some 7‐chloro‐5‐phenyl‐2,3‐dihydro‐1 H‐1, 4‐benzodiazepines shows that these compounds exist in CDCI3 solution as two pseudo‐boat conformers, rapidly interconverting at room temperature. Computer simulated lanthanide induced shifts (LIS) are consistent with LSR complexation by the imine nitrogen atom. The lanthanide shifts the conformational equilibrium towards conformer (a), with a pseudoequatorial 1‐substituent: this effect may be the result of the greater basicity of 4‐N when the 1‐N lone pair is pseudoaxially directed, thus permitting an extended electron delocalization from 1‐ to 4‐N through the fused benzene ring. The detection of H‐9/1‐Me through space spin‐spin coupling in medazepam (7‐chloro‐1‐methyl‐5‐phenyl‐2,3‐dihydro‐1H‐1,4‐benzodiazepine) supports the observed higher availability of conformer (a) to LSR. A LIS computer calculation to predict the population ratio results in reasonable agreement with the conformational changes based on the response of 3J(HH) to lanthanide addition. The electronic and steric effects which determine the greater stability of conformer (a) may be effective in the drug‐receptor interaction.
1H and 13C NMR study of dihydro derivatives of methylphenobarbital
Authors: Rautio Marjatta , Rahkamaa Erkki
Published: May 2005

Sodium borohydride reduction of methylphenobarbital leads to the formation of two different dihydroderivatives, reduced either in position 4 or position 6. The structures of the derivatives have been determined through analysis of the 1H and 13C NMR spectra of phenobarbital, methylphenobarbital and their derivatives. Detailed interpretation of the spectra and the resulting spectral parameters indicate conformations where the hydroxyl groups are axial and trans to the ethyl group. In these configurations the phenyl ring becomes equatorial. The results also allow an unambiguous assignment of the resonances of the phenyl carbons 2′(6′) and 3′(5′) of phenobarbital and the carbonyl carbons 4 and 6 of methylphenobarbital, differing interpretations having been previously advanced in the literature.
13C chemical shifts and conformational analysis of S‐methylthiolanium cations
Authors: Barbarella G. , Dembech P.
Published: May 2005

The 13C NMR spectra of all cations obtained by methylation at sulphur of the mono‐and dimethylthiolanes are reported. The methyl substituent on sulphur affects the shieldings of the adjacent carbons in a manner which allows easy identification of the cis and trans isomers. For most compounds the 13C pattern is consistent with a half‐chair ring conformation with maximum staggering at C‐3, C‐4. Only with methyl groups at the 1,2‐or 1,2,3‐positions is the half‐chair appreciably deformed. It is suggested that in these cases the preferred conformation is a quasi‐envelope with C‐3 at the top.
8 and 16‐Membered ring phosphorus compounds. Ring size dependence of the NMR parameters
Authors: Martin J. , Robert J. B.
Published: May 2005

The 1H NMR spectral analysis of four 8‐membered rings, 2‐thioxo‐ (or 2‐oxo‐) 2‐R‐1,3,6,2‐ trithiaphocane, is reported. The stereochemistry of the 8‐membered ring is discussed. The 31P NMR spectral parameters [δ31P, 1J(PC)] obtained on several cyclic 1,3,2‐dithiaphospha compounds of variable size (5, 6, 8, 12 and 16‐membered rings) are discussed as a function of the ring size and of the geometry of the molecule.
15N and 13C satellites in proton spectra of nitromethane oriented in a lyotropic solvent
Authors: Diehl P. , Bjorholm T. , Amrein J.
Published: May 2005

15N and 13C satellites in the Proton spectrum of nitromethane oriented in a lyotropic solvent have been observed. Indirect as well as direct (13CH) and (15NH) couplings have been measured and the molecular structure has been derived.
15N NMR substituent effects in pyridines and pyrimidines
Authors: Städeli W. , von Philipsborn W.
Published: May 2005

15N chemical shifts of 32 substituted pyridines and 19 substituted pyrimidines, together with additional data from the literature, are used to evalute substituent increments, Ai and Aik, in the respective series. Differential chemical shifts, Δδ(N), correlate with corresponding Δδ(C) values whereby, on the ppm scale, nitrogen shifts are approximately three times more sensitive towards substituents than carbon shifts. The 15N increments have proven additive and useful for assignment purposes.
Some quantum chemical aspects of solvent effects on NMR parameters
Authors: Ando I. , Webb G. A.
Published: May 2005

The non‐bonded interactions which occur between solute and solvent molecules are discussed and the various models which describe the interactions are presented. The models are employed, within a quantum chemical framework, to estimate the extent of medium effects on chemical shifts and spin‐spin couplings. Comparison between the calculated and available experimental data is provided for some first row nuclei.
Dynamic NMR study of hindered rotation around the CN bond in thiopiperidides
Authors: Ciureanu Mariana , Sahini Victor E. , Cornea Felicia , Cercasov Cornelia , Contineanu Mihai
Published: May 2005

The barriers to internal rotation about the CN bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG‡) increases in the series cinnamoylthiopiperidide<thiobenzoylpiperidide<phenylthioacetylpiperidide. This trend was discussed in terms of the electronic structure, using HMO calculations. For m‐and p‐substituted cinnamoylthiopiperidides the barriers were shown to increase with the electron withdrawing character of the substituent in the aromatic ring.
Examination of the aspirin acetylation site of human serum albumin by 13C NMR spectroscopy
Authors: Gerig J. T. , Katz K. E. , Reinheimer J. D. , Sullivan Glenn R. , Roberts John D.
Published: May 2005

Human serum albumin has been specifically acetylated using aspirin in which the methyl carbon of the acetyl group was enriched to 90% 13C. A single resonance at 23.13 ppm downfield from tetramethylsilane was observed in 13C differences spectra obtained at both 25.2 and 45.3 MHz. Chemical shift studies of several model compounds suggest that this is the resonance position to be expected for an acetamide group exposed to solvent. The line width observed for the enriched methyl resonance is consistent with free rotation of the methyl group.
Fast searching for identical 13C NMR spectra via inverted files
Authors: Bremser W. , Wagner H. , Franke B.
Published: May 2005

Inverted files of spectral features should be employed when searching for identical or similar spectra. The efficiency of interescting the entries for chemical shifts with a small deviation is very high for larger molecules and incomplete spectra. A novel spectral code describing the spectral appearance in hierarchical order (SAHO) facilitates the search for complete spectra with a relatively high tolerance of the chemical shifts. A vailable information on the chemical composition of the molecule, as well as the incusion of SFOR‐multiplicities, will further narrow down the number of suitable reference compounds.
Diastereomeric non‐equivalence of (−)‐ω‐camphanic esters of chiral secondary alcohols in 13C NMR spectroscopy
Authors: Jurczak Janusz , Konowal Andrzej , Krawczyk Zbigniew , Ejchart Andrzej
Published: May 2005

The diastereomeric differences (Δδ) were measured by 13C NMR spectroscopy for a series of 11 (−)‐ω‐camphanic esters of secondary alcohols of known absolute configuration. This method cannot be used for the determination of the absolute configuration, but it can be applied to the estimation of the enantiomeric purity of chiral alcohols.
Carbon‐13 NMR spectra of 3‐aryl‐2‐thioxo‐4‐imidazolidinones. Conformational isomerism and substituent effects
Authors: Khadim Mohammad A. , Colebrook Lawrence D.
Published: May 2005

A 13C NMR study of a series of 3‐aryl‐2‐thioxo‐4‐imidazolidinones, which are capable of existing as enantiomeric or diastereomeric rotational isomers about the aryl CN bond, shows that rates of internal rotation are slow at the probe temperature. The effects of hetero‐ and aryl‐ring substituents on hetero‐ring carbon atoms have been established.
Conformational preferences of some substituted methyl groups in cyclohexanes as studied by carbon‐13 nuclear magnetic resonance
Authors: Kitching William , Olszowy Henry , Adcock William
Published: May 2005

Low temperature 13C NMR spectra of 80:20 mixtures of cis and trans‐4CH3CH3C6H10CH2X, where C6H10‐is 1, 4‐disubtituted cyclohexyl and X=Br, CN, OH, OCH3, Si(CH3)3, Sn(CH3)3, Pb(CH3)3 and HgOCOCH3 have been recorded. The signals of the trans (e, e) components were assigned from the ambient temperature spectra of C6H11CH2X and the established substituent effects of an equatorial methyl group in cyclohexane. Conformational equilibria of the cis (e, a⇄a, e) components were then computed from the intensities of the (remaining) signals (∼180 K) of the two conformational isomers. From these equilibria A values of CH2X were calculated, assuming additivity of conformational energies of CH3 and CH2X (the counter‐poise approach). In general, these values are very similar to the value of the CH3, although some trends do emerge. This study provides α, β, γ, and δ effects for a wide range of axial and equatorial CH2X groups.
The relationship between 19F and 13C substituent chemical shifts and electron densities. 2—p‐phenylacetyl fluorides
Authors: Brownlee Robert T. C. , Craik David J.
Published: May 2005

The 19F substituent chemical shifts (SCS) of a series of para‐phenylacetyl fluorides (XPhCH2COF) are reported and compared with the related benzoyl fluoride series (XPhCOF). A dual substituent parameter analysis of the results for the new series shows that both inductive and resonance effects are reduced by one third when compared with the benzoyl fluorides. 13C shifts for the side chain carbonyl were also measured and found to follow a reversed trend in substituent effects, consistent with a pi polarization mechanism. SCS values for the fluorine and its adjacent carbon are not directly related. Ab initio (STO‐3G) calculations of the carbon and fluorine electron density for this series have been compared with the appropriate SCS values. From the electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for electron densities and the observation that the fluorine SCS values follow a normal direction, whilst those for the adjacent carbon are reversed, it is concluded that fluorine SCS values (and Δqπ values) result from polarization of the CF pi bond and do not merely monitor changes in electron density of the adjacent carbon.
Studies in tertiary amine oxides. III—carbon‐13 NMR assignment of N‐alkynyl cyclic amines
Authors: Al‐Rawi Jasim M. A. , Khuthier Abdul‐Hussain
Published: May 2005

Carbon‐13 NMR spectra of 24 N‐alkynyl cyclic amines were analysed. The effect of substituting the acetylenic proton by n‐butyl, tert‐butyl and phenyl groups was determined.
Carbon‐13 nuclear magnetic resonance studies of anthraquinones. IV—correlation of substituent effects for 1‐substituted anthraquinones
Authors: Berger Y. , Berger‐Deguée M. , Castonguay A.
Published: May 2005

The spectra of various 1‐substituted and 1,5‐disubstituted anthraquinones have been studied and the chemical shifts of the different carbon nuclei determined. The chemical shifts previously reported for 1‐Me‐anthraquinone have been corrected and reassigned. The C‐1, C‐4 and C‐13 shifts of 1‐substituted derivatives are correlated with the chemical shifts of monosubstituted benzenes. Deviations from the regression lines can be explained by the existence of steric factors and hydrogen bonding. A three‐parameter correlation with Swain and Lupton's ℱ and ℛ and Schaefer's Q provides relationships for the prediction of all chemical shifts of 1‐substituted anthraquinones when the substituents have a cylindrical symmetry.
The use of 13C satellites in proton spectra for a study of the rα structure and of the internal rotation of p‐chlorotoluene partially oriented in nematic phases
Authors: Diehl P. , Moia F.
Published: May 2005

The proton magnetic resonance spectra with natural abundance 13C satellites of p‐chlorotoluene in isotropic as well as in oriented solvents are analyzed. The indirect CH and HH couplings are determined from the isotropic sample and one bond 13C isotope effects on the proton chemical shifts are measured. The direct couplings derived from the oriented samples are corrected for harmonic vibration and used to determine the molecular rα structure with a 6‐fold hindering potential for the methl group. The resulting CH and CC bond lengths have errors which are smaller than 0.002Å. They deviate from the unsubstituted benzene molecule by between −1.1 and −0.5% for the CH and between +0.3 and +0.5% for the CC distances. It is not possible to obtain conclusive information about the hindering potential.
1H NMR spectra of benzo[b]furan, benzo[b]thiophene and benzo[b]selenophene oriented in a lyotropic mesophase
Authors: Bechtold W. E. , Goldstein J. H.
Published: May 2005

The proton nuclear magnetic resonance spectra of benzo[b]‐furan, ‐thiophene and ‐selenophene oriented in a potassium laurate lyotropic liquid crystal have been analyzed. Geometrical information has been obtained and compared to previous thermotropic results and various hypothetical models.
13C nuclear magnetic resonance spectra. XV—the γ‐anti substituent effect and its dependence on substitution at the α‐ and γ‐carbon atom
Authors: Duddeck Helmut , Islam Md. Rabiul
Published: May 2005

It is shown that the γα effects of hetero substituents on the 13C chemical shift (γα SCS) are enlarged by +2 to +5 ppm by substituting the α‐hydrogen atom by any group or atom (e.g. CH3, OR, F, Cl, Br). The same is encountered when the axial γ‐hydrogen is replaced by CH3, OH or F. If, however, the substituting atom at the γα‐carbon atom is a higher‐row halogen (Cl or Br), diamagnetic γα SCS for this signal are observed which may even exceed those for unsubstituted γα‐carbon atoms. The removal of a 1,3‐diaxial hydrogen‐hydrogen interaction and the existence of a still unspecified ‘heavy halogen effect’–both diamagnetic contributions to the γγ SCS of hetero substituents–are responsible for these findings. Methyl groups do not behave like hetero substituents with respect to the γα SCS.
Analysis of the 13C NMR spectra of mono‐ and dimethoxy‐β‐methyl‐β‐nitrostyrenes: Spectral assignments and conformational effects
Authors: Bailey Keith , Legault Donald
Published: May 2005

The 13C NMR spectra of β‐methyl‐β‐nitrostyrene and its nine mono‐ and dimethoxy‐derivatives have been determined. Chemical shift data are presented and analysed in a self‐consistent manner which allows most of the signals to be unambiguously assigned. Trends in the data can be interpreted in terms of the conformational properties of the variously‐substituted compounds.
Application of 13C and 15N NMR spectroscopy to structural studies on nitramines
Authors: Bulusu Suryanarayana , Axenrod Theodore , Autera Joseph R.
Published: May 2005

15N and 13C chemical shifts and the 1J(15N15N), 1J(15N13C) and 1J(13CH) coupling constants have been determined for a number of 15N‐enriched cyclic and acyclic secondary nitramines. The results are interpreted in terms of both electronegativity effects and conformational factors.
Solvent effects on the nitrogen screening of some nitroalkanes
Authors: Witanowski M. , Stefaniak L. , Lamphun B. Na , Webb G. A.
Published: May 2005

High precision 14N screening measurements are presented for some nitroalkanes. The screening increases as the dielectric constant of the solvent decreases in all cases considered. The β effect on the nitrogen screening is found to be largely independent of solvent, and is thus an intrinsic property of the nitroalkanes. Good agreement is obtained between the observed solvent effects on nitrogen screening and those calculated by the SOS procedure using INDO/S parameters. It is concluded that the measured nitrogen screening changes monitor the electronic changes which occur in the nitroalkanes as the medium is changed.
Saturated 5‐membered ring conformation. 1—1H NMR study of protonated methyltetrahydrofurans in superacid medium
Authors: Infarnet Y. , Duplan J. C. , Huet J.
Published: May 2005

Several methyltetrahydrofurans have been studied in HSO3FSbF5SO2 solution. O‐Protonation was observed from 1H NMR measurements at low temperature, and the coupling constants between +OH and the CH protons α to oxygen were measured from the CH signals. A conformational interpretation could be carried out from these results.
On the nature of haloform–aromatic complexes
Authors: Fernández Bertrán J. , Rodríguez M.
Published: May 2005

A study of the correlation of haloform proton solvent shifts in 13 aromatichydrocarbons gives clear evidence that the nature of the interactions is predominantly dipole‐induced dipole and not specific acid‐base interactions. The presence of halogen bonding interactions between the halogen atoms and the π electrons are not detected for CHCl3 and CHBr3, and can only be present to a marginal extent for CHI3. The ASIS effect is not related to the molar concentration of the aromatic solvents, and the effect of alkyl substituents is explained in terms of exctuded zones around the aromatic ring.
Preferential site of solvation of the furan ring in acidic solvents
Authors: Bertrán José Fernández , Rodríguez Mario
Published: May 2005

A study of the correlation of solvent effects on the chemical shifts of the methyl protons of sylvan, toluene and α‐picoline led to the conclusion that the preferential site of solvation of the furan ring in acidic solvents is the π‐electron cloud and not the n‐electron orbital of the oxygen atom.
High resolution NMR in solids; A simple and improved ‘magic angle’ probe design for conventional small gap 13C FT spectrometers
Authors: Bayle J. P. , Courtieu J. , Jullien J. , Kan S. K.
Published: May 2005

The mechanical and electronic design of a ‘magic angle’ NMR probe is described. This probe can be incorporated in a conventional small gap 13C FT spectrometer, without any hardware or software change, to obtain high resolution 13C NMR spectra on organic solids. A simple way of tuning the homogeneity and adjusting the angle is also proposed. Illustrative experimental results on various types of molecular crystals with different molecular mobilities, a clathrate compound and a polymer are discussed.
Saturated 5‐membered ring conformations. 2—1H NMR study of protonated N‐methylpyrrolidines
Authors: Infarnet Y. , Duplan J. C. , Huet J.
Published: May 2005

The 1H NMR spectra of the protonated and unprotonated forms of cis‐ and trans‐N‐methylhexahydroisoindoline, of 1,3,3,4,4‐pentamethylpyrrolidine and of 1,3,3‐trimethylpyrrolidine were analyzed. The coupling constants between the NH⊕ and the CH protons α to the nitrogen allowed the study of the conformation of the cyclic systems in pseudorotation.
Non‐empirical calculations of the nuclear magnetic resonance spectra of imidazole and hydrated imidazole
Authors: Prado F. Ribas , Giessner‐Prettre C. , Pullman B.
Published: May 2005

The magnetic shielding constants of the 1H, 13C and 15N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5‐membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin‐spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin‐spin coupling constants are not very sensitive to solvent effects.
13C NMR investigations of phenol–triethylamine complexes: The influence of hydrogen bond interaction on the electronic structure of phenols
Authors: Ilczyszyn Marek , Latajka Zdzisław , Ratajczak Henryk
Published: May 2005

The influence of hydrogen bond formation on the screening at the C‐1 carbon of phenols is investigated, both experimentally and theoretically. Qualitatively good agreement between experimental and predicted data, obtained by means of calculations based on the CNDO/2 method and the Karplus–Pople theory, is observed. The main factors determining the chemical shift changes in the series of complexes are discussed.
13C13C vicinal coupling constants of sulphonium cations
Authors: Barbarella G. , Dembech P.
Published: May 2005

The 13C13C vicinal coupling constants of cyclic sulphonium cations, with the labelled carbon bound to the positively charged sulphur atom, cannotbe related to the dihedral angle ϕ by a Karplus type correlation.
1H NMR studies of solvent effects on hydrogen bonding in some pyridine trifluoroacetates
Authors: Dega‐Szafran Zofia , Dulewicz Ewa
Published: May 2005

The chemical shifts of hydrogen bonded protons in complexes of 11 substituted pyridines with trifluoroacetic acid were examined, in five dry solvents of different activity, with respect to proton transfer and aggregation effects. The results were correlated with ΔpKa, the Kirkwood function and E T parameters. The solvent effect on the intersection point obtained from the plot of the chemical shift of the hydrogen bonded protons against ΔpKa can be used, similar to an isotopic effect, to differentiate strong hydrogen bonds. The aggregation of acid–base complexes can lead to downfield or upfield shifts; the variation of chemical shift with aggregation depends on the position of the proton in the hydrogen bridge.
350 MHz 1H NMR spectra, dipole moments and preferred conformation of 8,9‐epoxy‐6,7‐dihydro‐5H‐benzocyclohepten‐5‐ones
Authors: Huet Jean , Kotkowska‐Machnik Zofia , Zakrzewski Janusz
Published: May 2005

350 MHz 1H NMR spectra and dipole moments showed that in the preferred conformation of 8,9‐epoxy‐6,7‐dihydro‐5H‐benzocyclohepten‐5‐one and its 1,4‐dimethoxy derivative the oxirane ring takes a pseudo‐axial position.
Carbon‐13 spectra of 2‐hetera[3](1,1′)ferrocenophanes
Authors: Piórko A. , Ratajczak A. , Dominiak M.
Published: May 2005

The analysis of the 13C FT NMR spectra of 2‐hetera[3](1,1′)ferrocenophanes containing an oxygen, sulphur, selenium atom, phenyl‐substituted nitrogen or a methylene group in the 2‐position of the bridge has been carried out. The electronegativity of this fragment affects both chemical shifts and coupling constants, but no simple relationship was found.
Solvent effects on 13C and 17O chemical shifts of polar molecules. Comparison between experiment and theory
Authors: Tiffon Bernard , Ancian Bernard
Published: May 2005

Experimental solvent effects on 13C and 17O chemical shifts of acetone, and 13C chemical shifts of acetonitrile are compared with theoretical calculations by Jallali‐Heravi and Webb (solvaton model). Calculated values are, generally, in agreement with experimental results for atoms belonging to polar groups, but not for methyl carbons for which van der Waals interaction effects are predominant.
Synthesis and carbon‐13 nuclear magnetic resonance spectroscopy of 5,6‐dihydro‐2‐methyl‐1,4‐oxathiin, trans‐tetrahydro‐1,4‐benzoxathiin, 1,4‐tetrahydro‐[9,10]benzoxathiin, the 4‐oxides, 4,4‐dioxides and related acyclic compounds
Authors: Rooney Robert P. , Dyer John C. , Evans Slayton A.
Published: May 2005

The results of a 13C NMR spectral investigation involving 5,6‐dihydro‐1,4‐oxathiins, 1,4‐tetrahydro[9,10]benzoxathiin, trans‐tetrahydro‐1,4‐benzoxathiin, and the corresponding sulfoxides and sulfones are reported. An interpretation involving a dipolar structure with (2p→2p)π conjugation as opposed to (2p→3d)π interactions with the vinyloxy sulfides seems consistent with trends in the 13C NMR shifts. For the sulfoxides and sulfones, the substitutent‐induced chemical shift (SCS) effects at the β vinylic carbons (βSO and βSO2 effects) are considerably less than those at sp3 carbons. The γSO and γSO2 values at the sp2γ carbons indicate deshielding, in contrast to the shielding at the sp3 carbons.
13C NMR specta of 4‐quinolones and related compounds
Authors: Katritzky Alan R. , Ellison Joan , Frank Judit , Rákóczy Piroska , Radics Lajos , Gács‐Baitz Eszter
Published: May 2005

Complete assignments are made for 23 4‐quinolones and related compounds. Literature data are used to calculate chemical shifts for 17 of these compounds: calculated and experimental shifts are in excellent agreement—all within 5 ppm for nine of the compounds and a maximum discrepancy of 7.6 ppm.
Complete assignment of the carbon‐13 NMR spectrum of chlorophyl a
Authors: Lötjönen Simo , Hynninen Paavo H.
Published: May 2005

The 13C NMR spectrum (at natural abundance) of monomeric chlorophyll α in acetone‐d6 has been recorded to re‐examine the assignments of the low field (aromatic‐olefinic) region of the spectrum. The assignments, made by the examination of the fully coupled spectrum and by the use of long‐range selective 1H decoupling (LSPD) with low‐power irradiation, were compared with those of the previous reports. The results of the present work clarify the ambiguities previously encountered in the assignment of the 10a‐ester, 7c‐propionyl, P‐2‐phytyl, 2b‐vinyl, γ‐ and β‐methine carbon atoms, as well as the β‐pyrrolic carbon‐6 and α‐pyrrolic carbons −16 and −17 of chlorophyll α. Reassignment of the three last carbons was found necessary. Knowledge of the chemical shifts of these carbon atoms was considered to be particularly valuable, as it yields relevant information on the delocalized π electron system which is crucial for the function of chlorophyll in photosynthesis.
Observation of steric hindrance in heteraferrocenophanes by carbon‐13 NMR
Authors: Piórko A. , Ratajczak A.
Published: May 2005

The 13C NMR spectra of stereoisomeric trans‐ and cis‐1,3‐dimethyl‐2‐oxa[3](1, 1′)ferrocenophanes, 1,2,3‐trithia[3](1, 1′)ferrocenophane and 1,3‐dithia[3](1, 1′)ferrocenophane have been recorded and analysed. The presence of steric hindrance in some of these compounds was confirmed and the conformations of the molecules were determined.
Self‐consistent perturbation‐INDO calculations of nuclear magnetic resonance carbon–carbon coupling constants for methylcycloalkanes
Authors: Stöcker Michael
Published: May 2005

One bond 13C,13C coupling constants have been calculated for some methylcycloalkanes, as well as for 2‐methylbutane, using the self‐consistent perturbation theory as formulated by Blizzard and Santry at the INDO (intermediate neglect of differential overlap) level of approximation. Together with previously published experimental data, the results can be interpreted satisfactorily on the basis of the Walsh model for cyclopropane and the known s character relationship 1J(13C13C) = 575·s(i)· s(j).
The 13C NMR of olefins complexed with a binuclear Ag(I)–Yb(III) chelate
Authors: Smith William B.
Published: May 2005

The effect of silver ion complexation on the 13C NMR of several rigid olefin structures has been determined. The silver ion induced chemical shifts (AgIS) are not amenable to easy interpretation. Addition of Yb(fod)3 forms binuclear Ag–Yb complexes with the olefin. Lanthanide induced shifts (LIS) fall off rationally with distance from the site of complexation and the averaged position of the lanthanide. The complexes may be used as probes of olefin stereochemistry.
Carbon‐13 nuclear magnetic resonance studies of thiocarbamates, S‐oxides and S,S‐dioxides
Authors: Tseng C. K. , Bowler D. J.
Published: May 2005

The 13C NMR spectra of four thiocarbamates and their corresponding S‐oxides and S, S‐dioxides are reported. Both βSO and β effects are deshielding and range from 20.44 to 21.68 ppm. The βSO′ effects are slightly deshielding (0.20 ∼ 0.0.77 ppm). The β′ effects, on the contrary, are shielding and range from −6.54 to −6.98 ppm. The γ′, δ′, ξ′, and ζ′ effects are also discussed.
13C NMR spectroscopy of new amino protective groups
Authors: Fuchs Wolfram , Kalbacher Hubert , Voelter Wolfgang
Published: May 2005

The 13C data of several new amino protecting groups of the urethane structure are reported. The speeds of acidolytic cleavage are correlated with the 13C parameters.
Determination of one‐bond 14N13C coupling constants in amines using 13C T1ρ measurements
Authors: Mlynárik V.
Published: May 2005

13C T1ρ values measured for isobutylamine, diethylamine, pyrrolidine, piperidine and triethylamine yield one‐bond 14N13C coupling constants and 14N spin‐lattice relaxation times. A decrease of 1J(14N13C) was observed in sterically hindered secondary amines.
Strained cyclobutane compounds: 1H NMR analysis of a new 1‐substituted benzobicyclo[3.1.1]heptene system
Authors: Escale R. , Khayat A. , Girard J. P. , Rossi J. C. , Chapat J. P.
Published: May 2005

The 1H NMR spectra of a number of new derivatives of benzobicyclo[3.1.1]heptene were examined and interpreted by using a single set of coupling constants. All the compounds belonging to this system are in a γ‐shaped configuration. Surprisingly, two different proton‐proton spin‐spin coupling constants (4J=5.5 to 6 Hz and 8.5 Hz) were obtained for the cyclobutane ring.
1H and 13C NMR studies of some aromatic dilactones (precursors of paracyclophanes)
Authors: Solladié‐Cavallo Arlette , Hilbert Marcel
Published: May 2005

Carbon‐13 and proton NMR data of macrocyclic diaromatic dilactones are presented. The observed behaviour of the spectra as a function of temperature shows that the energy barrier for the re‐orientation of the side chains is lower than 49 kJ mol−1 (12 kcal mol−1) and that the energy barrier for the rotation of the aromatic rings is larger than 99 kJ mol−1 (24 kcal mol−1). Hence, chiral substituted dilactones of this type will be resolvable, and the enantiomers can be easily handled at room temperature.
Molecular structure and the indirect spin–spin coupling constants in azulene—a proton NMR study in the nematic phase
Authors: Arumugam S. , Kunwar A. C. , Khetrapal C. L.
Published: May 2005

The proton NMR spectrum of azulene has been investigated in the nematic phase of a liquid crystal. Spectral analysis provided the direct dipole‐dipole coupling constants which were used to derive the structural information. It was found that the relative proton‐proton distances in the 7‐ and 5‐membered rings deviate significantly from those for regular heptagons and pentagons. Indirect spin‐spin couplings were also obtained. Many of the inter‐ring and long‐range couplings have magnitudes between 0.2–0.8 Hz.
Dependence of the γ carbon‐13 shielding effect on electronegativity
Authors: Lambert Joseph B. , Vagenas Adelia R.
Published: May 2005

Three γ effects on 13C shielding in 3,3‐dimethylheteracyclohexanes as a function of the hetero‐atom X have been examined. The γ‐anti effect on the equatorial 3‐methyl group is small in absolute magnitude but strongly dependent on the polar properties of X. The plot of the 13C shielding of this carbon vs the electronegativity of X is linear, with a slope of −5.8 ppm/electronegativity unit. The γ‐gauche effects on the axial 3‐methyl group and on the 4‐carbon are large in absolute magnitude but have quite different dependences on the polar properties of X. Whereas the shielding of the 4‐carbon exhibits a linear dependence on electronegativity (slope −3.5), the axial 3‐methyl group shows little dependence (slope crudely −0.7), even though the geometric relationship between X and either carbon is almost the same. Neither gauche carbon shielding appears to be related to the steric properties of X. The polar component of both the γ‐anti effect and the γ‐gauche effect is interpreted as arising from overlap of appropriately positioned parallel orbitals. For the anti case, the pathway is the familiar zigzag arrangement of bonds. For the gauche case, the pathway may be either through space (the orbitals would be only on X and C‐α; for the 4‐carbon, this interaction would be through the center of the ring) or through bonds (there are parallel axial orbitals on all four atoms). The absence of a significant polar effect for the axial 3‐methyl group suggests that the gauche interaction requires a rigid pathway. The polar component of the general γ‐gauche effect is superimposed upon a larger contribution that is essentially independent of the nature of X and may be associated with the removal of the hydrogen on the β‐carbon and replacement with the γ‐X group.
A tropisomerism: Racemization barrier of 13‐substituted oxyprotoberberines
Authors: Solladié‐Cavallo A. , Stambach J. F. , Jung L.
Published: May 2005

The two possible conformations of 13‐R‐substituted oxyprotoberberines are enantiomeric. The racemization barriers are determined for three of these compounds (R=OMe, OCOMe, OCOPh) using variable temperature 1H NMR. It was found that ΔG = 39.0 kJ mol−1 when R = OMe, ΔG = 63.5 kJ mol−1 when R = OCOMe and ΔG = 63.7 kJ mol−1 when R = OCOPh. When R = H, however, the barrier is well below 35 kJ mol−1, suggesting that one of the factors influencing these racemization barriers (as in 2,2′‐bridged biphenyl systems) is steric in origin. Such low barriers to racemization do not allow easy handling of the enantiomers after resolution, but could allow better complexation of the one desired enantiomer to the receptor.
Conformational study of anticholinesterase carbamates in the furylbenzene series by 1H and 13C NMR spectroscopy
Authors: Platzer N. , Ronzani N. , Lang C. , Lange C.
Published: May 2005

The structural analysis of carbamates derived from 2‐(α‐furyl)benzaldoximes and 2‐(α‐furyl)benzyl alcohols was carried out by 1H and 13C NMR spectroscopy. The conjugative and steric effects of alkyl substituents introduced on the benzene rings were found to modify the relative orientation of the aromatic and furan rings. The existence of a close relationship between the stereochemistry of the studied compounds and their anticholinesterase activity has been proposed.
The rα‐structure of partially oriented phthalonitrile determined from its proton spectrum with natural abundance 13C‐ and 15N‐satellites
Authors: Diehl P. , Amrein J. , Bösiger H. , Moia F.
Published: May 2005

The proton spectra of phthalonitrile, including 13C‐ and 15N‐satellites at natural abundance in isotropic and oriented solvents, have been analysed. The entire rα‐structure is derived from the direct couplings. The AISEFT method has been used for obtaining the pure satellite information.
13C NMR and force field investigations of hydrindane conformations
Authors: Schneider Hans‐Jörg , Nguyen‐ba Nghe
Published: May 2005

13C NMR shifts of trans‐ and cis‐annelated bicyclo[4.3.0]nonanes with substituents R in position 8 (R  H, OH, Cl, Br) and 1‐hydroxy derivatives were analysed on the basis of force field calculated torsional angles using Allinger's MM1 program. Shielding increments for the 6 membered ring agree with corresponding cyclohexane values within ± 0.8 ppm maximal deviation. 13C NMR line shape analysis with cis‐hydrindane between 148 and 180 K yielded ΔH* = 37.0 ± 0.4 kJ mol−1 and ΔS* = 28 J mol−1 K−1 for the topomerization. The force field calculated reaction profile showed ΔH* = 37 kJ mol−1, in close agreement.
Assignment of the 13C nuclear magnetic resonance spectra of three 27‐hydroxyfriedelanes
Authors: Gunatilaka A. A. Leslie , Nanayakkara N. P. Dhammika , Sultanbawa M. Uvais S. , Wazeer Mohamed I. M.
Published: May 2005

13C NMR spectra of 27‐hydroxyfriedelane, kokoonol (27‐hydroxyfriedelan‐3‐one) and kokoononol (27‐hydroxyfriedelan‐3,21‐dione) have been recorded and signals assigned using the off‐resonance decoupling, inversion recovery and lanthanide induced shift techniques.
Substituent effects on 13C and 1H chemical shifts in 3‐benzylidene‐2,4‐pentanediones
Authors: Solčániova E. , Hrnčiar P. , Liptaj T.
Published: May 2005

Substituent effects on the 13C and 1H chemical shifts have been studied for derivatives of 3‐benzylidene‐2, 4‐pentanedione. A significant correlation has been found between chemical shifts of the Z carbonyl group (C‐2) and Hammett constants, while no correlation has been found for the E carbonyl group (C‐4). Attempts have been made to determine the structural factors which influence these effects. The conformation of 3‐benzylidene‐2, 4‐pentanediones has been determined by 13C and 1H NMR spectroscopy.
Deuterium isotope effects on 13C nuclear shielding as a measure of tautomeric equilibria
Authors: Hansen Poul Erik , Duus Fritz , Schmitt Peter
Published: May 2005

Large deuterium isotope effects of both signs have been observed on the 13C nuclear shielding in proton‐chelating tautomeric forms of β‐thioxoketones, and small isotope effects of both signs have been found in related forms of Schiff's bases of salicylaldehydes. These effects are interpreted in terms of shifts in the tautomeric equilibria on deuterium substitution of the enolic proton. The observation of deuterium isotope effects is suggested as a useful method for the detection of fast tautomeric equilibria in systems of the following type.
magnified image.
13C NMR spectra of diazastilbenes. II—Torsion angles of trans‐pyridinalanilines and trans‐benzylideneaminopyridines
Authors: Denecke Egon , Müller Klaus , Bluhm Thorsten
Published: May 2005

The torsion angles of trans‐pyridinalanilines and trans‐benzylideneanilines were derived from the chemical shifts of the para‐carbon atoms. The N‐torsion angle is between 33 and 59°. For the C‐torsion angle, a value of approximately 10° is obtained for the benzylideneaminopyridines and the C‐torsion angle for the pyridinalalines is estimated to be in the same range.