bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen‐15 nuclear magnetic resonance spectroscopy. NH proton exchange reactions of urea and substituted ureas
Authors: Yavari Issa , Roberts John D.
Published: May 2005

Proton‐coupled nitrogen‐15 NMR spectra of urea, N‐methylurea, N,‐N′‐dimethylurea, N‐methyl‐N′‐benzylurea and N‐phenylurea have been obtained at natural abundance level in neutral, basic and acidic solutions at 25°C. Base‐catalyzed NH proton exchange of the NH2 group of N‐methylurea in water was found to be 1.5 times faster than that for the ‐NH‐ group, while the corresponding acid‐catalyzed exchange is 7.5 times faster. Comparison of urea and N,‐N′‐dimethylurea in water shows urea to be 10 times faster in base but 2 times slower in acid. The ratio of the base‐catalyzed NH proton exchanges of the two ‐NH‐ groups of N‐methyl‐N′‐benzylurea in dimethyl sulfoxide is close to unity, whereas the CH3NH‐ group exchanges 4 times faster in acid. Similarly, the C6H5NH‐ group of N‐methyl‐N′‐phenylurea exchanges 50 times faster than the CH3NH‐ group in base and about 3 orders of magnitude slower in acid. The results are rationalized by consideration of steric and electronic effects.
A ‘shiftless’ relaxation reagent for metal nuclide and nitrogen‐15 magnetic resonance in aqueous solution
Authors: Gansow Otto A. , Triplett Kelly M. , Peterson Timothy T. , Botto Robert E. , Roberts John D.
Published: May 2005

Addition of small amounts of [Gd(2 : 2 : 1)]3+ cryptate to aqueous solutions containing 111Cd2+ or formamide decreases metal nuclide or nitrogen‐15 spin‐lattice (T1) relaxation times without affecting cadmium or nitrogen chemical shifts. This cryptate is thereby demonstrated to have substantial promise for greatly decreasing the time necessary to obtain natural abundance metal nuclide or 15N NMR spectra with satisfactory signal‐to‐noise ratios for many compounds with long metal or 15N relaxation times.
Determination of the configuration of new 8,13‐diazasteroids by means of 13C NMR
Authors: Verchère Catherine , Rousselle Dominique , Viel Claude
Published: May 2005

One methyldecahydroisoquinoline and some octahydro‐ and decahydro‐isoquinolone derivatives were studied by 13C NMR. The configuration of these products was deduced by comparison of the experimental chemical shifts and the calculated values. Conclusions could thus be reached on the configuration of related 8,13‐diazasteroids in the 19‐norandrostane series.
Dynamic NMR study of chair–chair interconversion in N,N ‐dimethylpiperidinium iodide in aqueous solution using 13C T1p measurements
Authors: Doddrell David M. , Barron Peter F. , Field James
Published: May 2005

13C T1ρ values measured for N,N‐dimethylpiperidinium iodide yield activation parameters (ΔH≠ and ΔG values of 43.7 and 41.6 kJ mol−1) for the chair‐chair interconversion in aqueous solution similar to those measured for 1,1‐dimethylcyclohexane. The potential of 13C T1ρ values for studying dynamic processes in aqueous solutions is illustrated.
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

Alterations 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

Two 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

Solvent 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

Determination 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

The 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

A 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

Geminal 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

17O 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

The 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

13C, 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

The 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.
13C NMR Spectra of Δ 24(28) Phytosterols
Authors: McInnes A. G. , Walter J. A. , Wright J. L. C.
Published: May 2005

The effect of structure and stereochemistry on the 13C chemical shifts for 24‐methylenecholesterol, fucosterol and isofucosterol has been determined.
31P chemical shifts in N‐aryliminotriphenylphosphoranes
Authors: Briggs Elizabeth M. , Brown Geoffrey W. , Cairns Peter M. , Jiricny Josef , Meidine Mohamed F.
Published: May 2005

31P 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

Reaction 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

Carbon‐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

13C 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

Direct 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.
Semi‐empirical calculations of dihydropyran conformations
Authors: Jankowski K.
Published: May 2005

Semi‐empirical calculations of dihydropyran conformations have been performed using a Karplus‐type equation with the sum of chemical shifts as a correction parameter. A graphical method has been proposed to evaluate the conformational state of the molecules.
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

The 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

Carbon‐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

Carbon‐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

The 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

The 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

1H 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

13C, 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

The 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

Natural 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

The 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

‘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

The 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

A 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

13C 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

Carbon‐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

Sum‐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

The 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.
13C and 1H NMR investigation of the structure of N″‐sulphonyl‐N‐alkylideneformamidrazones
Authors: Jakobsen P. , Treppendahl S.
Published: May 2005

The 13C and 1H NMR spectra of N″‐sulphonyl‐N‐alkylideneformamidrazones have been recorded and the chemical shifts assigned. The tautomeric structure proved to be an N2‐ alkylidenehydrazide sulphonylimide. The barrier to rotation around the CN1 bond was estimated from variable from temperature 1H NMR measurements, and the Z/E ratio and its solvent dependence was investigated.
Investigation of substituent effects on the 1H NMR spectra of chalcones
Authors: Solčániová E. , Toma S.
Published: May 2005

1H NMR spectra of 26 substituted chalcones (3‐aryl‐1 phenyl‐2‐propene‐1‐ones and 1‐aryl‐3‐phenyl‐2‐propene‐1‐ones) have been studied. The chemical shifts of the α and β protons to the carbonyl group were correlated with Hammett s̀ parameters. To gain information on the effect of the transmission of the resonance and inductive contributions of the substituents on the chemical shifts of H‐α and H‐β, two parameter correlations with 𝒻 and 𝓇 parameters were also perfomed. The chemical shifts of the aromatic protons of the para‐disubstituted benzene ring correlated with the ai substituent increments.
Carbon‐13 nuclear magnetic resonance spectra of ceveratrum alkaloids
Authors: Carey Francis A. , Hutton William C. , Schmidt James C.
Published: May 2005

The 13C NMR spectra were determined and signals assigned to the various carbons of the alkamines veracevine, germine and zygacine derived from steroidal alkaloids of the ceveratrum class. Assignment of signals was aided by analysis of the partially relaxed spectrum of cervagenine 9,12,14‐orthoacetate‐3, 16‐diacetate.
Configurational assignment by 13C NMR of stereoisomeric epoxyspirocyclohexanes derived from 4‐tert‐butylcyclohexanone
Authors: Bottin‐Strzalko T. , Roux‐Schmitt M. C.
Published: May 2005

The equatorial or axial configurational assignment of stereisomeric epoxyspirocyclohexanes, derived from the reaction of 4‐tert‐butylcyclohexanone with the anion of 2‐chloropropionitrile, has been determined by comparing the 13C chemical shifts of these compounds with those of the parent compounds, of known configuration, and resulting from the condensation of the anion of chloracetonitrile with 4‐tert‐butylcyclohexanone. A high field shift is observed for the cyclohexane ring carbons on going from the equatorial to the axial epoxide.
The effect of solvents on the 13C NMR chemical shifts of the carbonyl carbon and the rotational barriers of N,N‐dimethylbenzamide
Authors: Fong C. W. , Grant H. G.
Published: May 2005

The 13C solvent induced chemical shifts (SICS) of the carbonyl carbon and the thermodynamic barriers to rotation about the CN bond of N,N‐dimethylbenzamide are linearly related to the solvent parameter, ET(30). A multi‐parametric solvent parameter approach indicates that the SICS are influenced equally by polar effects and hydrogen‐bond donor effects. Rotational barriers for N,N‐dimethylbenzamide may, in principle, be determined by measurement of the 13C chemical shift of the carbonyl carbon in a particular solvent.
1H and 13C NMR studies of 7‐azaindole and related compounds
Authors: Cox R. H. , Sankar S.
Published: May 2005

The 1H and 13C chemical shifts, proton‐proton coupling constants, and one‐bond carbon‐hydrogen coupling constants have been obtained for 7‐azaindole, 1‐methyl‐7‐azaindole, their corresponding methyl iodide salts, and the related compound 7‐methyl‐7H‐pyrrolo [2,3‐b]pyridine. are different from those of either 7‐azaindole or 1‐methyl‐7‐azaindole.
Unusual carbonyl carbon chemical shifts in the 13C nuclear magnetic resonance spectra of cyclic ketones
Authors: Yates Peter , Auksi Hillar , Gosbee J. A. , Langford G. E. , Maclachlan F. N.
Published: May 2005

The Ketonic 13C NMR signals of a series of 6‐hydroxy‐5‐oxobicyclo[2.2.2]oct‐7‐ene‐2‐carboxylic acid lactones and of haplophytine and related N‐substituted 3‐piperidinones occur at exceptionally high field; the structural factors which are responsible have been elucidated by comparisons with related compounds.
60, 90 and 250 MHz 1H NMR spectra of sultams and sultones
Authors: Albert K.‐H. , Dürr H. , Doss S. H. , Zahra J. P.
Published: May 2005

The high‐field 1H NMR spectra of 1,3‐propanesultams (2), 2,4‐butanesultams (3) and 2,4‐dimethyl‐1,3‐butadienesultams (6) are reported. Comparison of 2,3 and 6 with 1,3‐propanesultone (1) and 2,4‐dimethyl‐1,3‐butadienesultone (5) reveals that the paramagnetic shift induced by the NH group is smaller than that induced by oxygen. NMR spectra at lower temperature show coupling effects with the NH proton. A half‐chair conformation was deduced for 2,4‐butanesultam from coupling constants and from a conformational analysis based on the R values, but a chair‐chair interconversion could not be detected in the temperature range between 210 and 330 K. An unambiguous assignment was carried out for the methyl signals in the spectrum of 5 by homodecoupling experiments.
A carbon‐13 NMR study of sterically hindered organotin derivatives
Authors: Axelson D. E. , Holloway C. E. , Vuik C. P. J.
Published: May 2005

Proton and 13C NMR has been used to examine a series of organotin derivatives. Anisochronous shifts are reported for chiral derivatives of tin, and 1H and 13C spin coupling constants to 117Sn and 119Sn are discussed. Spin lattice relaxation of 13C in these derivatives has been measured, and is used to indicate the effects of steric crowding on the ligands in terms of their freedom to undergo conformational rerrangements.
A novel assignment method in the 13C NMR spectroscopy of coumarins and furocoumarins
Authors: Duddeck Helmut , Elgamal M. Hanni A. , Elhady Faten K. Abd , Shalaby Nagwa M. M.
Published: May 2005

The signal shifts caused by replacing the carbonyl oxygen by sulphur represent a valuable method of assignment of the 13C NMR signals in coumarins and furocoumarins substituted at the benzoic and furanoic rings.
Modelling of the alkyl environment effects on the 13C chemical shift
Authors: Dubois Jacques‐Emile , Carabedian Michel
Published: May 2005

Using a topological parameter, λR, to characterize the effects of a variable mono or polyalkyl environment, R, on widely varied types of 13C sites gives rise to a homogeneous description of their chemical shifts over the entire range of δ13C variation (220 ppm/TMS). The proposed model, δ13C=ωcλR+ηc expresses the chemical shift in terms of this parameter together with the sensitivity, ωc, of the perturbed 13C site, bonded to a constant environment in a given family, and with ηc as the reference shift. In the case of polyalkyl environments, R=∑ Ri (n ⩽ 4); since the use of λR presupposes that groups Ri coexist in R without interacting, it is expressed as the sum of the intrinsic effects of each of these groups. Thus, this model demonstrates the general character of most of the common alkyl environment effects and the specific behaviour of the various types of 13C atoms. The homogeneity of this description relies on an assessment of the Ri contribution by the DARC/PELCO topological analysis of alkyl sites in a series of reference alkynes. The δ13C values calculated for 138 compounds, belonging to the alkane, alkene, allene, alcohol, amine, epoxide, ester and ketone families, are highly satisfactory (r̄=0.979, s̄=0.98).
High‐resolution NMR spectra of fluorene and its derivatives: VI—1‐methylfluorene, truxene and decacyclene
Authors: Drake J. A. G. , Jones D. W.
Published: May 2005

The overlapping spin systems in the 220 MHz 1H spectra of 1‐methylfluorene (1) in carbon disulphide and deuteriated chloroform solutions have been analysed separately and refined by LAOCOON with the aid of methyl‐ and methylene‐decoupled spectra. Ortho‐coupling constants in the 6‐membered rings are similar to each other and to those in fluorene (4). Solvent and concentration shifts suggest loose pairing of solute molecules. 220 MHz 1H spectra of α‐truxene (2) in carbon tetrachloride and deuteriated nitrobenzene, 220 MHz 1H spectra of decacyclene (3) in carbon tetrachloride, and 90 MHz FT 1H spectra of 3 in deuteriated chloroform show steric deshielding; the solvent dependence of shifts also suggests solute pairing in 2. Shifts in 1H decoupled 22.6 MHz 13C spectra of 2 in deuteriated chloroform were assigned with the aid of Cr(acac)3 relaxation agent.
Substituent chemical shift (SCS) correlations for the hydroxyl proton of substituted benzyl alcohols
Authors: Abraham Raymond J. , Bakke Jan M.
Published: May 2005

The hydroxyl proton chemical shift in substituted benzyl alcohols may be used, either at infinite dilution in CCl4, or in dilute solutions in DMSO, as a reliable indicator of substituent effects. The sensitivity of the hydroxyl proton to substituents is much greater than that of the methylene protons, and this is shown to be due to an increased dependence of the hydroxyl proton on the field effect of the substituent. The percent resonance contribution to the OH chemical shifts is identical in benzyl alcohols and phenols.
Application of semi‐empirical calculations of 13C chemical shifts and 1J(CH) coupling constants to the analysis of carbonium ion structures
Authors: Cheremisin A. A. , Schastnev P. V.
Published: May 2005

13C chemical shifts and 13CH coupling constants for classical and non‐classical structures of some typical carbonium ions have been calculated by the method of summation over excited states in the INDO approximation using a special parameterization. Comparison of the data obtained with the experimental values shows that the calculation of the chemical shifts and spin‐spin coupling constants is superior to energy calculations, and provides a useful means for the study of the structure of carbonium ions.
Application of paramagnetic shift reagents to the conformational analysis of isomeric dienones
Authors: Filippova T. M. , Bekker A. R. , Lavrukhin B. D.
Published: May 2005

Paramagnetic NMR shift reagents, Eu(fod)3 and Pr(fod)3, have been applied to study the one‐ene conformations of isomeric dienones. The results obtained using various complex formation models are analysed. The preferred model suggests participation of both carbonyl oxygen Ione pairs in binding with the shift reagents. Criteria for the estimation of errors in the determination of the structure parameters of the substrate‐paramagnetic reagent complexes are suggested. The data obtained using NMR shift reagents are consistent with the existence of dienone α,β‐cis‐isomers as s‐cis‐conformers only, with the carbonyl group lying out of the plane of all the other atoms of the molecule. Both s‐cis and s‐trans conformers occur in dienone α,β‐trans‐isomers.
Nitrogen and carbon NMR of some benzofuroxans
Authors: Witanowski M. , Stefaniak L. , Biernat S. , Webb G. A.
Published: May 2005

15N and 14N NMR spectra show that there is no valence tautomerism involving the nitro group in nitro derivatives of benzofuroxan systems and that the N‐oxide function has a fixed position in the furoxan ring. Carbon chemical shifts of molecules with one, two or three furoxan rings attached to a benzene ring reveal additivity of effects which makes possible a complete and unambiguous assignment of the shifts.
A statistical study of the additivities of substituent effects in the 13C NMR chemical shifts of hydroxy‐ and chloro‐substituted benzenes
Authors: Knuutinen Juha , Laatikainen Reino , Paasivirta Jaakko
Published: May 2005

The 13C NMR spectra of six hydroxybenzenes, all chlorobenzenes, all chlorophenols and eight chlorocatechols are measured and assigned. The additivity of the substituent effects and the usefulness of some corrective parameters are studied with regression analysis. The order of the chemical shifts is most efficiently predicted by the simplest substituent effect model, containing only the direct effects of the substituents, although the 95% confidence limits of the calculated shifts are as high as 5.6 ppm. If the chemical shifts need to be predicted within the measuring errors (approximately 0.05–0.10 ppm, in the present data), the number of necessary corrections is very impractical. The correction parameters are found to be independent of the solvent if no conformational effects are operative. These corrections, or the non‐additivity parameters, are thus theoretically interesting. Approximate 1J(CH) couplings are also reported and the additivity of substitution effects on these parameters are discussed.
Assignment of the 13C chemical shifts of ethidium bromide and analogs in D2O solution
Authors: Griggs Billy G. , Davidson Michael W. , Wilson W. David , Boykin David Withers
Published: May 2005

The 13C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8‐diamino‐5‐methylphenanthridinium chloride (3) in D2O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°‐τ‐90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the 13C chemical shifts of 1 and 3.
Rotational barriers in bisadducts of 1‐cyano‐1‐methylethyl radicals with nitrones and nitroso compounds
Authors: Iwamura Michiko , Katoh Morimatsu , Iwamura Hiizu
Published: May 2005

The temperature‐dependent 1H NMR spectra have been measured for the bisadducts 2a and 3 of 1‐cyano‐1‐methylethyl radicals with α‐phenyl‐N‐benzylnitrone [N‐(benzylidene)benzylamine N‐oxide] and nitrosobenzene, respectively. A free energy of activation of ΔG≠ = 62.8 ∼ 64.4 kJ mol−1 (15.0 ∼ 15.4 kcal/mol) at 24 ∼ 45 °C has been obtained for 2a by applying the Eyring equation to the rate constants at the coalescence points of the methyl signals. The line shapes due to four methyl signals exchanging between two sites of equal population have been simulated by the theoretical calculation to give an activation enthalpy of 52.3 kJ mol−1 (12.5 kcal/mol) and the corresponding entropy of −39.3 J K−1 mol−1 for 3. As the inversion barriers at pyramidal nitrogens of hydroxylamine derivatives should be lowered in N‐phenyl derivatives because of conjugation, the rate process which is responsible for the observed temperature dependent NMR spectra can be assigned to restricted rotation around one of the skeletal CNOC bonds. The relevance of the results to the conformations of nitroxides derived from the spin trapping method using α‐phenyl‐N‐t‐butylnitrone [N‐(benzylidene)‐t‐butylamine N‐oxide] and nitroso spin traps is discussed.
Interproton coupling over dual vicinal and homoallylic paths in 4‐membered rings
Authors: Barfield Michael , Abia Augustine A.
Published: May 2005

A study is presented of cis and trans HH coupling over dual vicinal (HCCH) and homoallylic/interbenzylic/interbenzylic (HCCCCH) paths in the series of molecules cyclobutene and benzocyclobutanes, and a series of dihydrocyclobutacenaphthylenes. Both the experimental and calculated molecular orbital results for these molecules increase in magnitude as the π‐bond order of the homoallylic (interbenzylic) path decreases. These trends appear to be consistent only with homoallylic (interbenzylic) coupling contributions of negative sign. At least qualitatively, these trends can be rationalized in terms of the increase in positive contributions associated with the π→π* transitions as the energy denominators decrease in the series.
13C nuclear magnetic resonance spectra of some naturally occurring friedelanones
Authors: Gunatilaka A. A. Leslie , Nanayakkara N. P. Dhammika , Sultanbawa M. Uvais S. , Wazeer Mohammed I. M.
Published: May 2005

13C NMR spectra of friedelan, friedelan‐21‐one, friedelan‐6‐one, friedelane‐321‐dione, friedelane‐3,6‐dione and friedelane‐3,6,21‐trione have been recorded and signals assigned using off‐resonance decoupling, inversion recovery and lanthanide induced shift techniques.
The use of chiral shift reagents in an NMR study of 2,2′,6,6′‐tetrasubstituted biphenyls
Authors: Diaz E. , Rojas‐Dávila E. , Guzmán A. , Joseph‐Nathan P.
Published: May 2005

The determination of the enantiomeric composition of 2,2′,6′6′‐tetrasubstituted biphenyls using 1H NMR spectroscopy, in combination with chiral lanthanide shift reagents, has been studied. In general, the S compounds give largeer induced shifts than the correspondind R isomers when d‐camphor derived shift reagents are used.
13C NMR spectra of some amides and imides. Effect of inductive and mesomeric interactions, cyclization and hydrogen bonding on 13C NMR chemical shifts
Authors: Hasan Misbah Ul
Published: May 2005

Carbon‐13 NMR chemical shifts in various amides and imides are examined. The compounds include mono‐ and diamides, acyclic imides and cyclic 5‐ and 6‐membered ring imides. The observed shifts can be satisfactorily rationalized on the basis of various electronic and steric factors which contribute to the chemical shifts in these systems. The 13C shifts in amides and imides are further compared with the shifts in corresponding oxygen analogues, i.e. esters and anhydrides. The saturated and α, β‐unsaturated amide carbonyls absorb in the range of 173–178 ppm and 167–170 ppm, respectively. These shifts are downfield by 2–3 ppm in comparison with the corresponding esters. The carbonyl shifts in cyclic imides appear in the range 170–180 ppm. In comparison with the corresponding anhydrides and amides, these shifts are downfield by 5–7 ppm and 3–4 ppm, respectively. These differences are discussed in terms of electronic interactions and steric effects.
13C NMR studies of some lupane and taraxerane triterpenes
Authors: Carpenter Roshan C. , Sotheeswaran Subramaniam , Sultanbawa M. Uvais S. , Ternai B.
Published: May 2005

The 13C NMR spectra of eight triterpenes are recorded and all carbon shifts have been assigned. The data are in agreement with the structures assigned to the rare lupanediol, lup‐20(29)‐ene‐3α,23‐diol, and other lupane triterpenes isolated from the Sri Lankan Glochidion species (Euphorbiaceae). The 13C NMR data of some triterpenes, aleuritolic acid derivatives and taraxerane derivatives are compared.
Linear electric field (LEF) effects in 13C NMR. Some model calculations on 5‐chloro‐1‐pentene
Authors: Van Dommelen Marianne E. , De Haan Jan W. , Buck Henk M.
Published: May 2005

The usefulness and some of the limitations of the linear electric field (LEF) effect in 13C NMR are illustrated by means of model calculations on the 13C NMR chemical shifts of C‐1 and C‐2 in 5‐chloro‐1‐pentene in nine different conformations. Two different concepts are used in order to calculate the electric fields near C‐1 and C‐2 caused by the C‐5Cl dipole. It is also demonstrated that, when using charges calculated by CNDO/2, the influences of the hydrogen atoms at C‐5 cannot be neglected. The use of the dipole–dipole interaction formula is advocated. The consequences of taking into account the additional contributions of the vinylic bonds to the accumulated charges at C‐1 and C‐2 are described. The results with the dipole–dipole formula show that the same signs and similar magnitudes of the LEF effects are calculated in seven out of nine conformations of 5‐chloro‐1‐pentene. This reduces the LEF to a means of confirming, rather than deducing, conformational equilibria in acylic flexible compounds. The usefulness of some recently published applications of the LEF concept to explain some short range substituent effects is critically discussed, mainly in view of the inhomogeneities of the calculated electric fields.
Low temperature 13C NMR study of 1‐(3‐pentyloxyphenylcarbamoyloxy)‐2‐dialkyl‐ aminocyclohexanes
Authors: Mlynárik V. , Beneš L.
Published: May 2005

Cyclohexane and piperidine ring reversal in 1‐(3‐pentyloxyphenylcarbamoyloxy)‐2‐dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol−1 and activation parameters ΔG≠218 = 43.8 ± 0.4 kJ mol−1, ΔH≠ = 48.9 ± 2.5 kJ mol−1 and ΔS≠ = 23 ± 9 J mol−1 K−1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans‐pyrrolidinyl derivative. In the trans‐piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol−1, ΔH≠ = 55.7 ± 6.3 kJ mol−1 and ΔS≠ = 51 ± 21 J mol−1 K−1 was found for the piperidine ring reversal from the non‐equivalence of the α‐carbons.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Natural abundance nitrogen‐15 spectra of the cis and trans isomers of secondary alkylformamides
Authors: Nakanishi Hiroshi , Roberts John D.
Published: May 2005

The 15NMR chemical shifts were measured of a number of N‐substituted formamides and acetamides at the natural abundance level. The ratios of the cis and trans isomers for several N‐alkylformamides were also determined. Substituent effects on the 15N chemical shifts of formamides are compared with those of some other nitrogen‐containing compounds. There is a consistent pattern of behavior of the one bond spin–spin coupling constants [1J(15NH)] wherein the trans isomers of N‐alkylformamides are larger than those of the cis isomers.