bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of the INDO parameterization on the indirect spin–spin coupling constants as calculated by the FPT INDO method
Authors: Contreras R. H. , Engelmann A. R. , Scuseria G. E. , Facelli J. C. 
Published: May 2005

AbstractAlterations have been introduced in the semi‐empirical INDO parameters in order to study their influence on the Fermi contact term of the indirect spin–spin coupling constants as calculated by the finite perturbation theory (FPT). For this purpose a set of molecules containing hydrogen, carbon and/or fluorine has been selected. In general, most coupling constants are found to be much more sensitive than other molecular properties to small changes in the INDO parameters. This sensitivity depends strongly on the particular calculated coupling constant. In most cases the uncertainty in the INDO parameters leads to uncertainties in the coupling constants which are much greater than their experimental errors.
NQR investigations in crystalline 2,6‐dichlorobenzamide
Authors: Murti D. V. Ramana , Venkatacharyulu P. , Premaswarup D. 
Published: May 2005

AbstractTwo resonance lines were observed in 2,6‐dichlorobenzamide, both in liquid nitrogen and at room temperatures, using a self quenched super‐regenerative NQR spectrometer. Analysis of the Zeeman effect on the two lines using an uncut crystal grown from solution reveals: (1) the crystal belongs to the orthorhombic system; (2) there are two crystallographically equivalent but physically non‐equivalent directions for the principal field gradient making an angle of 71° for the low frequency line, and four such directions for the high frequency line; (3) the directions of the crystalline axes a, b and c are tentatively fixed as (90°, 90°), (90°, 90°) and (0°,—); (4) from morphological studies a: b: c are estimated as 0.959 ± 0.005: 1:1,402 ± 0.005 and, from the estimated density (1.440 gms/cc) of the crystal, the absolute values a, b, c are calculated, on the basis of four molecules per unit cell, as a = 8.33 Å, b = 8.68 Å and c = 12.18 Å; (5) there are a mininium of four molecules per unit cell; the four molecules lie in four different planes which are, however, connected by symmetry operations. There is an inplane bending by 6.5° between the two CCl bonds away from one another and (6) the ionic, single bond and double bond characters for both chlorines are almost equal and are in the ratio 25:72:3.
Proton magnetic resonance studies of compounds with bridgehead nitrogen. 38—solvent effects in the 1H NMR spectra of nitrogen heterocyclic systems containing a 1,3‐arrangement of heteroatoms
Authors: Crabb Trevor A. , Jupp Philip A. 
Published: May 2005

AbstractSolvent effects on the 1H NMR parameters of perhydro‐oxazolo[3,4‒a]pyridine, perhydropyrido[1,2‒c]‒[1,3]oxazine and perhydrothiazolo[3,4‒a]pyridine derivatives are described. Particularly marked are changes in the proton‐proton geminal coupling constants of the NCH2O and NCH2S methylene protons with solvent and these are attributed to reaction field and solvation effects rather than to changes in the position of conformational equilibria.
Stereochemistry of organophosphorus compounds. XVI—configuration and conformations of 2‐substituted 2‐oxo‐(thio)‒3‒phenyl‒5‒methyl‒1,3,2‒oxazaphospholidines. Applications of 1H NMR Eu(dpm)3 shifts and LCAO MO EHM calculations for stereochemical study. Modified Karplus type function for 3J(HH′) in heteroatomic moieties
Authors: Samitov Yu. Yu , Musina A. A. , Aminova R. M. , Pudovik M. A. , Khayarov A. I. , Medvedeva M. D. 
Published: May 2005

AbstractDetermination of the configuration and preferable conformations of a series of 2‒substituted 2‒oxo(thio)‒3‒phenyl‒5‒methyl‒1,3,2‒oxazaphospholidines by 1H NMR, 1H{31P} double resonance NMR and 1H{31P} {CH3} triple resonance NMR is discussed in detail. As the first step for configurational assignment Eu(dpm)3 paramagnetic shift values are used. The study of the temperature dependence of the 3J(PNCH) coupling constants shows that compounds of the cis series adopt the semi‐chair conformation, but those of the trans series show considerable contributions from alternative conformations. Detailed analysis of the proton‐proton vicinal coupling constants in the heteroatomic moieties have been carried out. Modified Karplus type functions for the 3J(HH′) coupling constants have been found. These functions take into account the electronegativity and orientation of the α‐atoms. It is shown that the semi‐chair conformation of compounds of the cis series is characterized by a cyclic torsion angle ψ = 30° in accordance with both the experimental data and LCAO MO EHM calculations.
Lanthanide induced shifts as a conformational probe for o,o,o′,o′‐tetrasubstituted diphenyls
Authors: Díaz E. , Guzmán A. , Cruz M. , Mares J. , Ramírez D. J. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe 1H NMR spectra of several symmetrical diphenyls, having two unlike substituents on the ortho positions of each aromatic ring, were determined in the presence of Eu(fod)3 and of Pr(fod)3. The lanthanide induced shifts were used to establish the more probable conformation of the molecules, as deduced from computer calculations assuming pseudocontact interactions. It was found that the two like groups are in opposite conformation and that the inter‐ring angles are in the order of 15–35°.
Nitrogen‐15 NMR evidence for the structures of N‐9‐H‐Xanthen‐9‐yl‐ and N,N′‐Di‐9 H‐xanthen‐9‐yl‐ureas
Authors: Coxon Bruce , Fatiadi Alexander J. , Cohen Alex , Hertz Harry S. , Schaffer Robert 
Published: May 2005

AbstractA new monoxanthen‒9‒yl derivative of urea has been synthesized and the structure of this product (N‒9 H‒xanthen‒9‒ylurea) and that of the previously known N,N′‒di‒9 H‒xanthen‒9‒ylurea have been proved by 15N NMR and other spectroscopic techniques. A series of 13C and 15N labeled urea derivatives has been prepared and the utility of their 13C and 15N chemical shifts and coupling constants in the structural analysis of urea derivatives has been investigated.
13C NMR: The stereochemical dependence of 15N13C coupling constants in pyrazoles
Authors: Axenrod T. , Mangiaracina P. , Watnick C. M. , Wieder M. J. , Bulusu S. 
Published: May 2005

AbstractGeminal 15N13C coupling constants have been measured in a series of 15N‐enriched 1‒phenyl‒3,5‒dialkyl‐substituted pyrazoles. The importance of the orientation of the nitrogen lone‐pair in determining the magnitude of 2J(15N13C) values is reflected in the enhanced coupling observed for those carbon atoms lying close in space to the lone‐pair electrons.
17O nuclear magnetic resonance studies of some amino acids at natural abundance
Authors: Valentine B. , Amour T. St , Walter R. , Fiat D. 
Published: May 2005

Abstract17O chemical shifts of four amino acids at natural abundance have been obtained. Sensitivity was enhanced by accumulating a large number of scans or employing high concentrations at elevated temperature. Routine memory overflow was avoided by using a combination of solvent suppression and phase alternating pulse sequences.
Carbon‐13 nuclear magnetic resonance spectra of methyl 2‐pyronecarboxylates
Authors: Imagawa Takeshi , Haneda Akira , Kawanisi Mituyosi 
Published: May 2005

AbstractThe 13C NMR spectra of methyl 2‐pyrone‐3‐, 4‐, 5‐ and 6‐carboxylates were studied and the substituent effects on the 2‐pyrone ring were compared with those of some model compounds. 1H NMR spectra were also recorded and discussed. The long range 13C, 1H coupling constants were obtained, discussed and proved useful in signal assignments.
Carbon‐13, 1H spin–spin coupling VI—biphenylene
Authors: Runsink Jan , Günther Harald 
Published: May 2005

Abstract13C, 1H coupling constants for biphenylene have been obtained from the analysis of the 13C NMR spectrum of the natural abundance α‐13C‐ and β‐13C‐isotopomers. The various mechanisms responsible for the observed results are discussed.
Determination of the methyl group rotation energy barrier in some substituted tricyclo [3.1.0.02,6]hexanes by carbon‐13 spinlattice relaxation
Authors: Mellink W. A. , Kaptein R. 
Published: May 2005

AbstractThe resonances in the 13C NMR spectra of 1,2,5,6‐tetramethyl‐3,4‐dimethylenetricyclo[3.1.0.02,6]hexane and the corresponding enone and dione have been assigned. The rotation energy barriers of the methyl groups have been determined from 13C spin‐lattice relaxation time measurements; barriers of 6.7–10.9 kJ mol−1 have been found. Since X‐ray data have shown that the skeleton bonds are bent away from the CCH3 axis by angles of over 120°, only minor interactions occur between adjacent methyl groups. Therefore, these barriers are mainly governed by interactions with the CC skeleton bonds.
31P chemical shifts in N‐aryliminotriphenylphosphoranes
Authors: Briggs Elizabeth M. , Brown Geoffrey W. , Cairns Peter M. , Jiricny Josef , Meidine Mohamed F. 
Published: May 2005

Abstract31P chemical shifts in N‐aryliminotriphenylphosphoranes and the corresponding N‐methylated phosphonium salts are presented. They can be correlated with those theories of the bonding in phosphorus‐nitrogen ylides which involve partial double bonding as a result of pπ–dπ overlap.
Differentiation of isomeric 1,2‐dihydroisoquinolin‐4(3H)‐ones by proton magnetic resonance of their 4‐benzyl derivatives
Authors: Waigh Roger D. 
Published: May 2005

AbstractReaction of a 3,3‐dimethyl‐1,2‐dihydroisoquinolin‐4(3H)‐one with a benzyl Grignard reagent gives a 4‐benzyltetrahydroisoquinoline in which the signal of a 6‐methoxy group suffers a large upfield shift in the 1H NMR spectrum, whereas a 7‐methoxy group is relatively unaffected. This effect can be used to determine whether an RO‐substituent is in the 6‐ or 7‐position and, in particular, to distinguish isomeric derivatives with different RO‐groups in the 6‐ and 7‐positions. The method will allow the mechanism of cyclization of 3,4‐dimethoxybenzylaminoacetonitriles to be more fully elucidated.
Carbon‐13 NMR spectra of solid bicyclo[3. 3. 1]nonan‐9‐one. Conformational studies in the solid state
Authors: Wasylishen Roderick E. , Friesen Kenneth J. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of solid polycrystalline bicyclo[3.3.1]nonan‐9‐one and adamantanone have been measured at 315K. The relatively narrow 13C linewidths observed for these solids, together with measured spin‐lattice relaxation times, indicate that both these solids are orientationally disordered. Observed 13C chemical shifts of solid bicyclo[3.3.1]nonan‐9‐one indicate a twin‐chair conformation for the two cyclohexanone rings.
Carbon‐13 NMR spectroscopy of kawa‐pyrones
Authors: Banerji A. , Siddhanta A. K. , Acharyya A. K. , Dutta C. P. 
Published: May 2005

Abstract13C NMR spectra of six kawa‐pyrones (styryl α‐pyrones) have been assigned. The assignments are based on the splitting pattern in the coupled spectra, comparison of the chemical shifts with those of model compounds and by application of additivity relationships. The 13C NMR of styrene was also reinvestigated.
13C1H spin–spin couplings in cyclic α,β‐unsaturated enones and their protonated derivatives. Measurements and quantum chemical calculations
Authors: Schreurs J. , Van Noorden‐Mudde C. A. H. , van de Ven L. J. M. , de Haan J. W. 
Published: May 2005

AbstractDirect and long‐range 13C1H coupling constants are presented for the enone moieties of cyclopent‐2‐enone, cyclohex‐2‐enone and their protonated derivatives. A correlation is given between the experimental values and the results of quantum chemical calculations (CNDO/2, INDO). The existing calculations are modified in order to improve the relationship between the calculated and experimental results.
The 13C,H coupling constants in structural and conformational analysis. IV–The rotational dependence of the long‐range CH couplings of the aldehyde and hydroxyl protons in salicylaldehyde
Authors: Äyräs Pertti , Laatikainen Reino , Lötjönen Simo 
Published: May 2005

AbstractThe proton‐coupled 13C NMR spectrum of salicylaldehyde was analysed. The second‐order character of the seven independent sub‐spectra allowed the signs of most of the couplings to be determined. The input values for the analyses were obtained from the known J(CH) values of benzene, phenol and benzaldehyde using the additivity principle. In most instances, very good agreement between the calculated and observed values was obtained. Significant couplings of the ring carbons to both the aldehyde and hydroxyl protons were also observed. The magnitude of these couplings was very dependent on the stereochemical relationships between the coupled nuclei.
Structural examination of some polychlorinated 2‐phenoxyphenols by 1H and 13C nuclear magnetic resonance
Authors: Nordén Bo , Edlund Ulf , Nilsson Carl‐Axel 
Published: May 2005

AbstractCarbon‐13 NMR spectra of some polychlorinated 2‐phenoxyphenols have been obtained. The substituent chemical shifts obtained by varying the chlorine substitution pattern of one ring are very similar to those reported for the corresponding diphenyl ethers. Thus, the replacement of a 2‐chlorine atom by a hydroxyl group only induces minor shielding changes at the adjacent aryl moiety and the 13C chemical shift changes are mainly determined by the preferred conformations governed by the steric demand of the ortho substituents. An 1H NMR/IR study revealed an equilibrium between intermolecular aggregates and intramolecular OH…π species in the concentration interval 2‐0.005 M. Any hydrogen bonding effects on 13C NMR shieldings are, therefore, minor compared to shielding variations caused by steric perturbations.
Ion pairing and the rotational mobility of organic ions in solution
Authors: Levy George C. , TerryBailey J. 
Published: May 2005

AbstractCarbon‐13 dipolar spin‐lattice relaxation times can be used to study microscopic ion mobility in solvent‐separated and contact ion‐pair systems. Two chemically stable ion pairs were studied. Cyclohexylammonium formate observed in a number of solvents allows correlation of relaxation times—and therefore ion rotational mobility—with empirical solvent polarity indices. Estimation of the effective anion radius shows a change of a factor of three in size arising from solvation/ion‐pairing effects. Trimesate trianion (1,3,5‐tricarboxybenzene) with differing cations present in solution is a good probe of changes in the solvation sphere and degree of ion aggregation. Variable temperature studies give an activation energy for overall ionic reorientation of c. 5 kcal/mol.
CIDNP assisted assignment of carbon‐13 NMR lines in α‐tetralone and α‐indanone
Authors: Michael Maurer H. , Bargon Joachim 
Published: May 2005

AbstractThe reversible abstraction of hydrogen from benzene‐1,3,5‐triol by photoexcited α‐tetralone or α‐indanone in solutions of methanol leads to CIDNP in the 13C NMR spectra of these compounds. The information gained from the phase of the polarization in the CIDNP spectra is used to resolve the ambiguities in the assignment of the 13C NMR lines for α‐indanone and α‐tetralone, arising from conflicting literature data. Chemical shifts for both compounds in methanol are reported. 2′‐Methylacetophenone does not exhibit CIDNP in the 13C spectrum under similar conditions.
The role of linear electric field effects in halogen induced 13C chemical shifts in cyclohexanes and methylenecyclohexanes
Authors: Van Dommelen Marianne E. , de Haan Jan W. , Buck Henk M. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of methylenecyclohexane at low temperature are compared with those of 4‐chloro‐ and 4‐bromo‐methylenecyclohexane under the same conditions. It is concluded that the halogen induced shift differences at the double bond are to be ascribed largely to linear electric field (LEF) effects. At the same time, doubt is expressed concerning similar explanations for C‐4 in halo‐substituted cyclohexanes. The large influence of using different values of longitudinal bond polarizabilities is demonstrated. Finally, some remarkable long‐range shift effects on double bonds are described for geranyl chloride and geranyl bromide.
1H NMR studies of proton transfer and σ‐complex formation in the reactions of N‐substituted picramides with oxygen and nitrogen bases
Authors: Crampton Michael R. , Gibson Brenda , Matthews Raymond S. 
Published: May 2005

Abstract1H NMR measurements of N‐substituted picramides in dimethyl sulphoxide‐methanol containing sodium methoxide show that the two major modes of 1:1 interaction involve transfer of an amino proton to give the conjugate base or methoxide attack at the 3‐position to give a σ‐adduct. The proportion of parent reacting by the latter pathway increases as the proportion of methanol in the solvent increases. Some comparative measurements in isopropanol‐dimethyl sulphoxide show that relative to methoxide the isopropoxide ion has a greater propensity for proton abstraction than for base addition. Reaction of the substrates with amide ions derived from piperidine or from benzylamine gives σ‐complexes by attack at unsubstituted ring positions. In the benzylamide adducts spin coupling is observed between the amino proton and the adjacent ring and methylene protons.
13C, 1H spin coupling constants of dimethylacetylene
Authors: Hayamizu Kikuko , Yamamoto Osamu 
Published: May 2005

Abstract13C, 1H spin coupling constants of dimethylacetylene have been determined by the complete analysis of the proton coupled 13C NMR spectrum. For the methyl carbon 1J(CH) = + 130.64 Hz and 4J(CH) = + 1.58 Hz, and for the acetylenic carbon 2J(CH) = − 10.34 Hz and 3J(CH) = +4.30 Hz. The 5J(HH) long‐range coupling constant (+2.79 Hz) between the methyl protons was also determined.
The 13C NMR spectrum of 5‐ O‐β‐D‐primeverosyl genkwanine
Authors: García‐Granados A. , de Buruaga J. M. Sáenz 
Published: May 2005

AbstractThe 13C NMR spectra of 5‐O‐β‐D‐primeverosyl genkwanine and its acetate are studied and assignments are proposed.
13C nuclear magnetic resonance of organophosphorus compounds XII—phospholes and dibenzophospholes
Authors: Gray George A. , Nelson John H. 
Published: May 2005

AbstractNatural abundance 13C NMR studies have been carried out on a series of phospholes and dibenzophospholes. The systems were analyzed with respect to ring conformation and substituent orientation. Assignments of all chemical shifts have been made by investigating partially relaxed inversion‐recovery spectra and by investigating the field dependence of the spectra. A nonplanar (6‐membered central ring) tricyclic phosphine was also examined. Here, the value of the two bond coupling constant 2J(PC) allowed determination of the orientation (axial) of the phosphorus‐substituted phenyl ring. Conclusions regarding cyclic conjugation in phospholes are presented.
Structure elucidation with lanthanide induced shifts. 6—solvent effects on bound shifts and association constants
Authors: Raber Douglas J. , Johnston Milton D. , Janks Christopher M. , Perry Joseph W. , Jackson George F. 
Published: May 2005

AbstractThe NMR spectra of acetone, adamantanone and 1‐adamantanecarbonitrile have been studied in the presence of Eu(fod)3 in various solvents. A substantial solvent dependence is found for the association constants between shift reagent and substrate. The magnitude of the association constants is correlated with solvent polarity, and a tenfold decrease in K1 is observed upon changing from carbon tetrachloride to the more polar dichloromethane. Only a very small solvent dependence is observed for the bound shifts. The relative bound shifts (and therefore the structures of the LS complexes) are found to be solvent independent. The small solvent dependence of the absolute magnitude of the bound shifts for the LS complexes is suggested to result from experimental errors.
Unexpected second‐order effects in proton‐coupled 13C NMR spectra
Authors: Douglas Alan W. , Shapiro Michael 
Published: May 2005

Abstract‘Unexpected’ second‐order effects encountered in proton‐coupled 13C NMR spectra where relative proton shifts are large compared to proton‐proton coupling constants are illustrated. The observed phenomenon is explained, with reference to the ABX spin system as a model, as being due to the near equality of the relative proton shift, in frequency units, to the difference between one‐bond and long‐range 13CH couplings. The effect may be removed by a change in operating field strength or addition of a shift reagent.
Deformation of methylenecyclopropane in solution: NMR study in the nematic phase at 240 and 400 MHz
Authors: Courtieu J. , Gounelle Y. , Jullien J. , Balavoine G. , Fan M. 
Published: May 2005

AbstractThe NMR spectrum of methylenecyclopropane oriented in two nematic phases has been measured at 240 and 400 MHz. Ratios of the proton‐proton distances have been obtained. These values are compared with those deduced from the structure of the molecule in the gaseous state; they suggest an increase of the ethylenic magnified image angle in the nematic phase.
The conformational dependence of vicinal 13C13C spin–spin coupling constants in alicyclic compounds
Authors: Berger Stefan 
Published: May 2005

AbstractA series of alicyclic compounds with dihedral angles of 0°, 60°, 90°, 120° and 180° between a 13C‐labelled carbon atom and a carbon atom separated by three bonds from the label has been synthesized. The vicinal 13C13C spin coupling constants were measured, and from the results a Karplus‐type relationship between 13C13C spin coupling and dihedral angle is proposed.
13C NMR study of substituted nitronaphthalenes
Authors: Mechin Bernard , Richer Jean Claude , Odiot Simone 
Published: May 2005

Abstract13C chemical shifts for a series of substituted nitronaphthalenes have been obtained by several assignment techniques. Deviations from additivity are mainly observed in the ortho‐disubstituted compounds and are due, in part, to the variations of the anisotropic terms for the substituents studied.
Carbon‐13 NMR studies of the biologically active nor‐diterpenoid dilactones from Podocarpus plants
Authors: Hayashi Yuji , Matsumoto Takeshi , Uemura Motokazu , Koreeda Masato 
Published: May 2005

AbstractCarbon‐13 NMR signals of the biologically active norditerpenoid dilactones from Podocarpus plants were fully assigned by using selective 1H decoupling, coupling constants (2JCH), spin‐lattice relaxation times (T1) and correlation of the spectra of more than thirty dilactone congeners. The spectra of five nagilactones, B, C, D, E and F, which constitute representative members of three major structural types of the dilactones: (A) 8:14, 9:11‐dienolide (α‐pyrone) type, (B) 7α:8α‐epoxy‐9:11‐enolide type, and (C) 7:8,9:11‐dienolide type, were extensively analysed. Some characteristic steric interactions for the substituents on the ring system can be demonstrated from the spectral properties.
Some calculations of solvent effects on 17O and 19F chemical shifts
Authors: Jallali‐Heravi M. , Lamphun B. Na , Webb G. A. , Ando I. , Kondo M. , Watanabe S. 
Published: May 2005

AbstractSum‐over‐states perturbation and finite perturbation calculations, within the ‘Solvaton’ model, are presented for the variation of some 17O and 19F chemical shifts as a function of the dielectric constant of the medium. In general, the nuclear screening and charge are predicted to increase as the dielectric constant increases. The effects of hydrogen bonding are included by means of minimum energy dimer models in some of the sum‐over‐states calculations.
Benzazoles XIII—determination of the E and Z configuration of isomeric 2‐(2‐benzimidazolyl)‐di‐ and ‐tetra‐hydrothiophenes by IR, 1H and 13C NMR spectroscopy
Authors: Sohár P. , Mányai Gy. , Hideg K. , Hankovszky H. O. , Lex L. 
Published: May 2005

AbstractThe configuration of the diastereomeric pairs of 2‐(3‐hydroxy‐3‐methyl‐5‐phenyl‐2,3‐dihydrothiophen‐2‐yl)benzimidazole (1a,1b) and 2‐(3‐hydroxy‐3‐methyltetrahydrothiophen‐2‐yl)benzimidazole (2a, 2b), as well as that of the acyl and diacyl derivatives of 2a and 2b, and the structure of the dehydrated products formed by heating 1a or 1b, and 2a or 2b, were determined by IR, 1H and 13C NMR spectroscopy.