bluuebunny/crossref_metadata_2025_split huggingface dataset:
A quantitative empirical treatment of 13C NMR chemical shift variations on successive substitution of methane by halogen atoms
Authors: Gasteiger Johann , Suryanarayana Iragavarapu 
Published: May 2005

AbstractThe 13C NMR chemical shifts of halogen‐substituted methanes are reproduced by a linear two‐parameter equation. The parameters consist of the charge on the carbon atom, as calculated by iterative partial equalization of orbital electronegativity, and the square of the mean molecular polarizability.
Substituent effects on 13C chemical shifts of 1‐arylsulphonyl‐2‐arylaziridines
Authors: Knipe A. C. , Khandelwal Y. , McAuley I. E. , Brown N. M. D. 
Published: May 2005

AbstractCarbon‐13 chemical shifts of 1‐phenylsulphonyl‐2‐phenylaziridine and several of its m‐ and p‐substituted derivatives have been determined. The substituent chemical shift (SCS) effects on the benzylic carbon C‐2, and on the methylene carbon C‐3 have been satisfactorily correlated with Hammett substituent parameters (δ) for variation of the C‐2‐aryl ring substituent (with a fixed arylsulphonyl ring), and for analogous variation of the arylsulphonyl ring (with a given C‐2‐aryl ring). The results reveal an inverse C‐2‐aryl SCS effect on C‐2, whereas the effect on C‐3 is normal; substituents on the arylsulphonyl ring have a normal effect on both C‐2 and C‐3, for which the SCS is to higher frequency with increasing electron‐withdrawing power of the substituent.
Investigation of Benzimidazoles. 5—transmission of the substituent effects in 2‐substituted 5(6)‐nitrobenzimidazoles studied by 1H, 13C and 15N NMR spectroscopy
Authors: Lopyrev V. A. , Larina L. I. , Vakul'skaya T. I. , Larin M. F. , Shibanova E. F. , Titova I. A. , Voronkov M. G. , Liepin'sh E. E. 
Published: May 2005

AbstractThe influence of substituents on the 1H, 13C and 15N NMR chemical shifts of 2‐substituted 5(6)‐nitrobenzimidazoles and their analogues labelled with 15N in the nitro group was investigated. It was found that the substituent effects are transmitted to the carbon and hydrogen nuclei in positions 4–7 mainly by the resonance mechanism, but to the nitro‐nitrogen atom with approximately equal contributions from the resonance and inductive components. Comparison of the transmission of substituent effects in nitro‐benzimidazoles with para and meta derivatives of nitrobenzene showed that the nitro group seems to be more tightly conjugated with the benzimidazole fragment than with the benzene ring.
An equation utilizing empirically derived substituent constants for the prediction of vicinal coupling constants in substituted ethanes
Authors: Colucci William J. , Jungk Steven J. , Gandour Richard D. 
Published: May 2005

AbstractA simple equation has been developed for the prediction of vicinal coupling constants in HCCH fragments:

The equation is a cosine series in θ, the torsion angle between vicinal hydrogens. The feature which distinguishes this equation from similar equations is the inclusion of δSi terms, which describe the magnitude of each substituent's effect. These substituent constants have been defined from experimental data. An orientation effect which is dependent on the torsion angle(s) between substituent(s) and a vicinal hydrogen is included. Substituent constants have been defined for 39 groups, of which 15 have been experimentally determined herein. The parameters for the equation have been defined from 49 torsion angles in 19 conformationally rigid compounds. The torsion angles have been determined from x‐ray crystal structure data and molecular mechanics calculations. The multiplicity of structures used to determine the substituent constants should allow for the application of this equation to a wide variety of structures.
1H NMR and IR spectra of antitumour anthracyclines: Effect of the substitution pattern on the chemical shift values of the phenolic protons and on IR absorptions of the quinone system
Authors: Vigevani Aristide , Ballabio Marzia , Gandini Elena , Penco Sergio 
Published: May 2005

Abstract1H NMR and IR data of numerous natural and synthetic analogues of daunorubicin and doxorubicin, anthracycline antibiotics successfully used in the clinical treatment of human tumours, have been recorded. The chemical shift values of the phenolic protons of approximately 130 compounds are reviewed and discussed with the aim of establishing a relationship between δ values and structural features. The IR absorptions of the quinone system in the region 1560–1680 cm−1 are also examined.
Increments for calculation of the 13C NMR shifts of acetylated polyphenols considering steric interactions
Authors: Wegner‐Hambloch S. , Glombitza K.‐W. 
Published: May 2005

AbstractConsiderable deviations in the values obtained are an inherent deficiency in the calculation of 13C NMR chemical shifts of the polyphenolic phlorotannins from brown algae when using increments for monosubstituted aromatic substances. In order to account for steric interactions within this class of compounds, special increments have been developed by the use of multiple linear regression with dummy variables. With these 13C NMR chemical shift increments, the occurrence of known and of hitherto unknown substitution patterns can be predicted.
NMR Spectral Analysis of Tetrahydro‐2‐( 3,4 ‐dimethoxyphenyl)‐4‐[(3,4‐dimethoxyphenyl)methyl]‐3‐furanmethanol, a Dimethyl Ether of Lariciresinol, from Monechma ciliaturn
Authors: Maat L. , Peters J. A. , Linders J. T. M. , Hussein Ayoub S. M. 
Published: May 2005

AbstractTetrahydro‐2‐(3,4 ‐dimethoxyphenyl)‐4‐[(3,4‐dimethoxyphenyl)methyl]‐3‐furanmethanol has been isolated from Monechrna ciliaturn. Its structure was deduced from the 200 MHz 1H NMR spectrum.
Carbon‐13 NMR studies of oxazolidines, N‐borane‐oxazolidines and oxazolidinium salts derived from pseudoephedrine: Steric effect of the BH3 and CH3 groups on the chemical shifts
Authors: Paz‐Sandoval M. A. , Santiesteban F. , Contreras R. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts in various oxazolidines derived from pseudoephedrine and their corresponding N‐borane adducts and oxazolidinium salts are examined. The observed shifts can be rationalized on the basis of steric factors, owing to the similarity between the borane adducts and the oxazolidinium salts, i.e., BH3 and CH3 appear to have the same substituent effects.
Aryl carbon chemical shifts of methylbenzoic acids and methylbenzoate anions
Authors: Guilleme Joaquin , Diez Ernesto , Bermejo Francisco J. 
Published: May 2005

AbstractThe aryl carbon chemical shifts of methylbenzoic acids in CDCl3 and methylbenzoate anions in aqueous NaOH solutions have been assigned. The shifts have been interpreted by means of a model based on the additivity of substituents which is similar to that previously developed for the analysis of the methyl chemical shifts. Corrective parameters included to take into account the interactions of adjacent substituents are found to be related to both the twist angle, θ, of the carboxyl or carboxylate substituents and the conformation of the methyl groups. The derived values of the twist angle are in closer agreement with x‐ray data than those estimated from UV spectra or from Cl‐PPP computations.
13C NMR spectra of plucheinol and its ester derivatives
Authors: Arriaga F. J. , Borges‐Delcastillo J. 
Published: May 2005

Abstract13C NMR data are presented for plucheinol and its ester derivatives obtained from Pluchea odorata (L) Cass. A comparison with the data reported for cuauhtemone derivatives was carried out. An unexpected deshielding for C‐4 in diester derivatives was observed.
Conformational analysis of N‐acylazabicyclooctanes
Authors: Sohár P. , Pelczer I. , Váczi I. , Tombor A. , Matolcsy G. 
Published: May 2005

AbstractN‐Acyl derivatives of 1,3,3‐trimethyl‐6‐azabicyclo[3.2.1]octane were synthesized as compounds with potential pesticidal activity. The conformation of the starting compound and the substituent dependence of the amide rotamers of the acyl derivatives were studied by 1 and 13C NMR spectroscopy, making use of solvent effects (ASIS) and DR, DNOE and DEPT measurements.
Halogenated epoxides 8—13C NMR data of ring halogenated oxiranes
Authors: Spraul M. , Keul H. , Pfeffer B. , Hähnle J. , Griesbaum K. 
Published: May 2005

AbstractThe 13C NMR data of 42 ring‐halogenated oxiranes containing fluorine, chlorine, bromine and, in one case, iodine as substituents are reported and discussed with respect to the influence of the halogen and of other substituents on the chemical shifts of the ring carbon atoms. For monocyclic mono‐ and dichlorooxiranes increments have been determined which allow the calculation of the chemical shifts of the ring carbon atoms. Comparison of the 13C NMR data of substituted 1,2‐dihaloethylenes with those of the corresponding epoxides showed that the signals of the ring carbon atoms of the halogenated oxiranes always appeared at considerably higher field than those of the sp2 hybridized vinylic carbons in the respective precursors.
Simplified measurement of lanthanide‐induced shifts
Authors: Raber Douglas J. , Peters Joop A. 
Published: May 2005

AbstractA simplified procedure is presented for the determination of accurate lanthanide‐induced shifts. Experimental and simulated data are used to show that bound shifts for both 1:1 and 1:2 complexes with shift reagent can be obtained with as few as six or seven different lanthanide: substrate concentration ratios. This represents a substantial saving in experimental effort over the 25 different concentration ratios that were used previously for this method. The modified procedure affords accurate results if care is taken to minimize experimental errors, and if data are obtained over a wide range in the fraction of substrate that is complexed.
NMR Spectroscopy of platinum(II)‐8‐substituted quinoline complexes. nJ(PtH) Coupling Constants and Pt…︁HC Interactions
Authors: Anklin C. G. , Pregosin P. S. 
Published: May 2005

AbstractA series of complexes of composition trans‐[PtCl2L(PEt3)], where L is an 8‐substituted quinoline, have been studied by 1H and 31P NMR spectroscopic methods [substitnent = CHO, CH3, HC(CH3)2, CHBr2]. The protons of the substitnent at the 8‐position couple to 195Pt with values for nJ(195Pt1H) which are too large for five‐bond coupling constants, thereby suggesting a Pt…︁HC interaction. Two‐dimensional 1H NMR methods were used for purposes of assignment and also for defining a chemical exchange process. The shape of the 195Pt satellite lines in the 1H spectra vary with the magnetic field strength owing to CSA relaxation of the 195Pt.
Residually coupled attached proton test in the 13C NMR assignment of natural products
Authors: Crews Phillip , Naylor Steve , Myers Barbara L. , Loo James , Manes Lawrence V. 
Published: May 2005

AbstractAttached proton test (APT) spectra acquired with residual coupling (termed RECAPT) can be advantageous in assigning 13C NMR spectra of complex natural products. RECAPT was applied to the analysis of the 13C NMR spectra of two terpene marine natural products to illustrate its advantages over APT in situations where peaks are accidentally degenerate, or where large J(CH) values give misleading phase APT peaks.
Electron–nuclear double resonance (ENDOR) studies of neutral odd–alternate aromatic hydrocarbon free radicals formed by thermal dissociation
Authors: Lewis I. C. , Singer L. S. 
Published: May 2005

AbstractElectron–nuclear double resonance (ENDOR) spectra are presented for the odd‐alternate aromatic hydrocarbon neutral radicals phenalenyl, [2H5]phenylphenalenyl and for the benzo[c,d]pyrenyl and benz[d,e]anthracenyl radicals formed by thermal dissociative processes in solution. Proton hyperfine coupling constants were determined from the ENDOR spectra and were shown to give an excellent linear correlation with McLachlan spin densities with Q = −26.5 G.
An investigation of the tautomeric equilibria of some 3‐hydroxyindazole derivatives by 15N NMR spectroscopy
Authors: Schilf W. , Stefaniak L. , Witanowski M. , Webb G. A. 
Published: May 2005

Abstract15N NMR shielding data are reported for six 3‐hydroxyindazole derivatives and compared with the results of INDO/S‐SOS shielding calculations which are used for assignments. The position of tautomeric equilibrium was found to be solvent dependent and to be proportional to the Gutmann acceptor number of the solvent employed.
Application of 15N NMR to a quantitative investigation of tautomerism in some thiolopyridines
Authors: Stefaniak L. , Webb G. A. , Brevard C. , Bourdonneau M. , Lejeune R. , Thunus L. , Lapière C. L. 
Published: May 2005

Abstract15N NMR shielding measurements are reported for a series of derivatives of some thiolopyridines. The results obtained are used to provide quantitatively reliable estimates of three tautomeric equilibria involving the pyridine nitrogen atom.
13C nuclear magnetic resonance spectra of amaryllidaceae alkaloids. I—alkaloids with the crinane skeleton
Authors: Frahm August W. , Ali Ahmed A. , Ramadan Mahmoud A. 
Published: May 2005

AbstractThe13C NMR spectra of 15 Amaryllidaceae alkaloids with the crinane skeleton were measured and the chemical shifts unequivocally assigned. From the derived specific shift ranges, it is possible to establish both the complete oxygenation pattern of the 5, 10b‐ethanophenanthridine skeleton and its stereochemical arrangement.
Substituent effects on 1H NMR spectra of 4‐and 4′‐substituted tras‐N‐benzylideneanilines in acidic solution
Authors: Odian George , Yang Nan‐Ioh , Wei Yen 
Published: May 2005

AbstractVarious 4‐ and 4′‐substitued trans‐N‐benlizylidenanilines were synthesized and their 1H NMR spectra recorded at 30 °C in DMSO‐d6, and acidic media (TFA‐d and D2SO4). The effects of substituents on the chemical shifts of H‐α (proton on carbon of imine group) and H‐2′ (protons on benzaldehyde ring ortho to the imine group) were analysed by the Hammett single parameter and Taft dual substituent parameter (DSP) techniques. In the neutral solvent DMSO‐d6, there is transmission of the electronic effects of substituents on the benzaldehyde ring to the H‐α and H‐2′ protons, but no electronic transmission for substituents on the aniline ring. There is a dramatic change in acid media. Protonation of the imine group results in significant electronic transmission from substituents on the aniline ring to the H‐α and H‐2′ protons, as well as an enbancement in electronic transmission from substituents on the benzaldehyde ring. DSP analysis indicates that both inductive and resonance factors are responsible for the observed electronic transmission effects, with resonance being the major factor.
Analysis of the proton, carbon, and nitrogen NMR spectra of cis,cis‐ and cis,trans‐1,3,5‐triaminocyclohexane
Authors: Yu Chin , Dumoulin Charles L. , Levy George C. 
Published: May 2005

AbstractThe proton spectrum of the isomeric mixture of cis,cis‐ and cis,trans‐1,3,5‐triaminocyclohexane was assigned with a 2D COSY experiment. Using Forrest's modified equation and the 2D J spectrum results, the conformations of the two isomers were analysed. The six‐membered ring of the cis,trans isomer is flattened by 1,3‐diaxial interactions between two amino substituents; in the cis,cis isomer, ring pucker is increased owing to non‐bonded interaction between the equatorial amino groups and adjacent methylene protons. The 13C and 15N spin—lattice relaxation of the two isomeric 1,3,5‐triaminocyclohexanes was also measured at different pH values; NHx groups rotate faster with decreasing pH. Rotation/jump rates and barriers are reported, determined from the NT1DD ratios between 15N and 13C nuclei.
Endor studies of cation radicals from pharmacologically active phenothiazines
Authors: Helle N. , Kurreck H. , Bock M. , Kieslich W. 
Published: May 2005

AbstractA variety of substituted phenothiazine cation radicals, including those from pharmacologically active derivatives, e.g. chlorpromazine, alimemazine and laevomepromazine, have been studied by means of ENDOR and TRIPLE resonance spectroscopy. These techniques allowed accurate determinations of hyperfine coupling constants, including their signs. Conclusions concerning molecular structure (e.g. twist angles) could be drawn, supporting previous investigations of the interrelationship of molecular conformations with the pharmacological potential, i.e. neuroleptic, antihistaminic or anti‐Parkinsonian.
Measurement of long‐range heteronuclear selective 13{1H} NOE enhancements: 4‐ (α‐arylethylidene)‐2‐phenyl‐5(4H)‐oxazolones
Authors: Cativiela Carlos , Sánchez‐Ferrando Francisco 
Published: May 2005

AbstractThe technique previously described as two‐bond heteronuclear selective NOE difference was improved to yield quantitative data on NOE enhancement factors by recording separately the unperturbed and the perturbed FIDs. In this way the E and Z stereoisomers of 4(α‐arylethylidene)‐2‐phenyl‐5(4H)‐oxazolones were easily distinguished. The latter showed positive NOE ehancements on quaternary carbons placed two, three and four bonds away from the irradiated methyl protons, as well as a negative NOE on a nearby protonated carbon.
Computer‐assisted analysis of the 1H NMR spectra of peracetylated galactose‐containing oligosaccharides
Authors: Jimeno M. Luisa , Martin‐Lomas Manuel , Alemany Antonio 
Published: May 2005

AbstractThe computer‐assisted analysis data of t1H NMR spectra of peracetylated α‐and β‐1 →3‐ and ‐1 → 4‐linked D‐gal‐actopyranosyl‐D‐galactopyranoses and several tetraacetylatedO‐methyl derivatives of D‐galactopyranose are reported.
NMR investigations on benzheteroazoles. 2—NMR investigations of N‐acylated 2‐aminobenzimidazoles
Authors: Gründemann E. , Graubaum H. , Martin D. , Schiewald E. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of 74 N‐acylated 2‐aminobenzimidazoles were determined and assigned. The chemical shifts are discussed as a function of electronic and spatial substituent effects. Line broadening for certain C signals are traced to prototropy at N‐1 and N‐3, and N‐3 and Nexo.
Relaxation studies of carbonyl rhenium clusters. Part 2—relaxation mechanisms and estimation of the 13C chemical shielding anisotropy in the [Re3(μ‐H)4(CO)10]− anion at low temperature
Authors: Beringhelli Tiziana , D'Alfonso Giuseppe , Molinari Henriette 
Published: May 2005

AbstractApplication of the non‐selective inversion recovery technique to 13C spectra of moderately enriched [Re3(μ‐H)4(CO)10]− indicates that relaxation times, at low temperatures, are strongly field dependent and decrease with increasing field strength. Measurements performed at 183 K and at 20.15, 50.31 and 67.88 MHz indicate that chemical shielding anisotropy is dominant at higher fields, which differs from the behaviour previously observed at room temperature where the main relaxation pathway is scalar coupling with the quadrupolar rhenium isotopes. The 13C chemical shielding anisotropy was estimated to be in the range 476±40 ppm. Interactions with quadrupolar rhenium also affect the hydrogen spin‐spin relaxation times.
NMR spectra and stereochemistry of 2‐(piperidin‐2‐ylmethyl)cycloalkanols
Authors: Begley Michael J. , Crabb Trevor A. , Roch Olive G. 
Published: May 2005

Abstract2‐(Piperidin‐2‐ylmethyl)cycloalkanols have been synthesized by the reaction between 2‐picolyllithium and cycloalkene oxides, followed by catalytic hydrogenation of the resulting 2‐(pyridin‐2‐ylmethyl)cycloalkanols. The configurations of the 2‐(piperidin‐2‐yl‐methyl)cycloalkanols were assigned by comparing their 13C and 1H NMR parameters with those of 2‐(piperidin‐2‐ylmethyl)cyclohexanols of known (x‐ray) configuration.
The study of sipholanes by two‐dimensional NMR spectroscopy
Authors: Carmely S. , Kashman Y. 
Published: May 2005

AbstractThe complete assignment of the 13C and 1H NMR spectra of sipholenol‐A and sipholenone‐A, two new triterpenes isolated from a marine sponge, were achieved from 1H‐13C shift correlation diagrams.
Swinholide‐A, a new marine macrolide. Complete assignment of 1H and 13C spectra by 2D NMR techniques
Authors: Carmely Shmuel , Rotem Michal , Kashman Yoel 
Published: May 2005

Abstract1H and 13C NMR spectra of the novel marine macrolide swinholide‐A, which provide the basis for its structure elucidation, have been completely assigned by parallel use of 1D and homo‐ and hetero‐nuclear 2D NMR techniques. Swinholide‐A (1) probably a polyketide, is a 22‐membered macrolide embodying a dihydropyran ring and a 10‐carbon side‐chain ending with a substituted tetrahydropyran ring. The high degree of overlap of eleven CH—O and nine CH2 signals in the 1D proton NMR spectrum of 1 necessitated the structure elucidation of swinholide‐A tetraformate (2) by 2D homo‐ (up to 6J with formyl groups) and hetero‐nuclear NMR correlations. Formyl groups can be good structural probes in complex polyalcohols, as shown by the observed 5J and 6J formate couplings in 2.
13C NMR spectra of some o‐carbonyl derivatives of naphthols
Authors: Rażniewska‐Lazȩcka G. , Da̧mbska A. , Janowski A. 
Published: May 2005

AbstractAll the signals in the 13C NMR spectra of o‐carbonyl naphthol derivatives (i.e. o‐hydroxy aldehydes, o‐hydroxy methyl ketones and methyl esters of o‐hydroxy acids) are assigned on the basis of the additivity rule of substituent‐induced shifts and selective 13C{1H} hetero‐decoupling experiments [sometimes in the presence of Yb(fod)3]. The differences between the experimental chemical shifts and the values calculated on the basis of the additivity of substituent‐induced shifts are also given; these may be regarded as ‘intramolecular hydrogen bond‐induced shifts’.
15N and 13C NMR spectroscopy of 1,2,6‐thiadiazine 1,1‐dioxide derivatives and fused systems
Authors: Goya Pilar , Ochoa Carmen , Rozas Isabel , Alemany Antonio , Jimeno M. Luisa 
Published: May 2005

AbstractThe natural abundance 15N NMR spectra of sulphamide, sixteen 1,2,6‐thiadiazine and two 1,2,4,6‐thiatriazine derivatives, phenylbutazone and antipyrine have been recorded for the first time. The influence of substituents on nitrogen chemical shifts and the effect of intercalation of SO2 and CO groups between two nitrogen atoms are discussed. Prototropic tautomerism was also studied. 13C NMR data for some of the 1,2,6‐thiadiazine and thiatriazine derivatives are reported.
1H and 13C NMR studies of substituted nitropyridines and nitrobenzenes
Authors: Nudelman N. S. , Cerdeira S. B. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 3‐nitro‐, 5‐nitro‐ and 3,5‐dinitro‐2‐methoxypyridines have been determined. The results show the preferred cis conformation for the 2‐methoxy group, and the importance of steric repulsion between the oxygen atom of this group and those of the o‐nitro group which hinders conjugation in the 3‐nitro‐substituted derivatives. Similar steric inhibition of resonance is observable with 2‐N‐butylamine‐, 2‐N‐cyclohexylamine‐ and 2‐(N‐piperidyl)‐substituted nitropyridines, whose 1H and 13C NMR spectra were also determined. In the case of the secondary amines, a hydrogen bond between the amino proton and the 3‐nitro group was clearly detected. 1H and 13C NMR spectra of 2,6‐dinitro‐, 2,4‐dinitro‐ and 2,4,6‐trinitro‐2‐R‐benzenes (R = OCH3, NHC4H9, NH‐cyclo‐C6H11, NC5H10) were also recorded and compared with those of the pyridine derivatives. The electronic aza and nitro group effects are comparable if conjugation of the nitro group is not hindered.