bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR studies of reduced porphyrin compounds. Aromatic delocalization pathways
Authors: Harel Yaacov , Manassen Joost 
Published: May 2005

Abstract13C NMR spectra of ms‐tetraphenylchlorins, new aminoalkyl‐ and hydroxy‐pyrroline substituted ms‐tetra‐phenylchlorins, and ms‐tetraphenylisobacteriochlorins are presented and discussed. Significant changes in the chemical shifts of the α‐pyrrole, α‐pyrroline and meso skeletal carbons are found in chlorins and isobacteriochlorins in comparison to porphyrins. In contrast, the chemical shifts of the β‐pyrrole carbons are almost unaffected by the structural modifications in chlorin and isobacteriochlorin. The chemical shifts of the α‐pyrrole carbons in the various chlorins and isobacteriochlorins are strongly affected by the substitutents of the pyrroline ring, or by the introduction of an additional pyrroline ring in isobacteriochlorins. The results show that most of the electron density is concentrated in the unreduced part of the molecule, i.e. in the pyrrole rings and, especially, on the α‐pyrrole carbons and is transferred or removed through the aromatic pathway by substituents on the pyrroline ring. These observations are supporting evidence that the α‐pyrrole, α‐pyrroline and meso‐carbons are in the aromatic pathway and favour the proposal of a 16 atom dianion as the preferred delocalization pathway in chlorins and isobacteriochlorins.
The assignment of signals in the nitrogen NMR spectra of polycyclic diazines
Authors: Witanowski M. , Stefaniak L. , Webb G. A. 
Published: May 2005

Abstract15N Nitrogen screening data are reported for some polycyclic azines and compared with previous results where available. INDO/S parameterized screening calculations for cinnoline and quinazoline help to decide between alternative nitrogen assignments. Nitrogen solvent shifts of several ppm are reported for all of the molecules studied.
High field nuclear magnetic resonance spectra of hydroxyl protons of aldoses and ketoses
Authors: Gillet Brigitte , Nicole Daniel , Delpuech Jean‐Jacques , Gross Bernard 
Published: May 2005

AbstractThe hydroxyl protons of 23 monosaccharides in their pyranoid from (α or β) are examined by proton NMR at 250 MHz in DMSO‐d6 solutions. Intramolecular hydrogen bonding in sugar anions seems to be the major factor in accounting for the lack of parallelism between the pK values and the chemical shifts of the anomeric protons. Another important factor is the possibility of steric hindrance to the solvation of the acidic hydroxyls by the basic DMSO solvent molecules. Equatorial hydroxyls have, as a general rule, lower field chemical shifts (with some exceptions) and larger vicinal HOCH coupling constants, 3J, than axial hydroxyls. Moreover, equatorial hydroxyls are sensitive to the equatorial or axial position of their neighbours, in sharp contrast with axial hydroxyls. Long‐range 4J couplings are observed whenever a zig‐zag arrangement but a necessary condition is a simultaneous axial position of the OH and CH bonds in the above fragment. In this case, the combined use of vicinal (Karplus‐type equation) and long‐range coupling constants allows the description of the stereochemistry of the OH bond in a semiquantitative fashion.
Structure determination from the spin–lattice relaxation behaviour of quaternary carbons. Effects of deuterium substitution
Authors: Norton Raymond S. 
Published: May 2005

AbstractThe use of quaternary carbon relaxation data, including the effects of deuteration thereon, to obtain information about chemical structures is considered. It is shown that a simple qualitative analysis of the effects of deuteration is subject to a number of potential errors. Structural inferences should be based only on a rigorous quantitative analysis of the data. The effects of deuterium substitution on the relaxation behaviour of benzamide in solution have been measured. The data are accounted for satisfactorily by treating the molecule as an axially symmetric ellipsoid. Furthermore, it is found that deuteration has no significant effect on the rotational diffusion of benzamide in solution.
Application of 1H NMREu(fod)3shifted spectra for the determination of the enantiomeric composition and absolute configuration of secondary alcohols, using (−)‐ω‐camphanic esters
Authors: Jurczak Janusz , Konował Andrzej , Krawczyk Zbigniew , Ejchart Andrzej 
Published: May 2005

AbstractThe diastereomeric differences (Δδ) were measured for a series of 11 (−)‐ω‐camphanic esters of secondary alcohols of known absolute configuration, using 1H NMR spectroscopy with Eu(fod)3 as shift reagent. This method is convenient and useful for the measurement of enantiomeric compositions, whereas additional assumptions must be applied in determining the absolute configuration related to the signs of the diastereomeric differences.
13C,13C coupling constants from a mixture of isotopomers (13C) of substituted aromatic compounds; 1‐nitronaphthalenes
Authors: Hansen Poul Erik , Albrand Jean‐Pierre 
Published: May 2005

Abstract13C Homonuclear decoupling experiments led to the assignment of the carbon‐carbon coupling constants of 13C‐enriched 1‐nitronaphthalene obtained by nitration of [1‐13C]naphthalene. The effects of substituents on coupling constants can be explained on the basis of the electronegativity of the first atom of the substituent, and the observed substituent effects are shown to be parallel to previous data for oxygen containing substituents.
1H NMR structural study of 2‐phenylthiazolidine
Authors: Térol A. , Subra G. , Fernandez J. P. , Robbe Y. , Chapat J. P. , Granger R. 
Published: May 2005

AbstractDeuteration of 2‐phenylthiazolidine, and its complexation with the shift reagent tris(1,1,1,2,2,3,3‐heptafluoro‐7,7‐dimethyl‐4,6‐octanedionato)europium, have been used to study the signals and conformation of the heterocyclic protons and to interpret the 1H NMR spectrum of this 2‐substituted thiazolidine.
15N NMR spectroscopy 31—preliminary study on the insulin‐a chain (bunte salt form)
Authors: Hull William E. , Büllesbach Erika , Wieneke Hans‐Joachim , Zahn Helmut , Kricheldorf Hans R. 
Published: May 2005

AbstractThe Bunte salt derivative was prepared from bovine insulin‐A isolated from natural sources, and was purified by chromatography. Natural abundance 40.55 MHz 15N NMR spectra were measured in water and dimethyl sulphoxide. The latter solvent gave the best resolution, and 20 of the 22 possible amide nitrogen signals were detected. Several model oligopeptides were also measured and their usefulness for assignments is discussed.
Stereochemical study of hexahydro[1,3]thiazolo[3,2‐a]pyridines by 1H and 13C NMR
Authors: Barbry Didier , Ricart Guy , Couturier Daniel 
Published: May 2005

AbstractConfigurations and preferred conformations of a number of hexahydro[1,3]thiazolo[3,2‐a]pyridines have been assigned on the basis of their 1H and 13C NMR spectra. The conformational preferences of these compounds have been interpreted in terms of the minimization of dipolar type interactions, arising from 1,3 arrangements of the heteroatoms, which are increased by the electron donor induction effect of the alkyl groups. The stereochemistry of the salts of these bases is very different from that of the free compounds. For the gem‐disubstituted compound, an explanation in terms of the ‘gem‐dimethyl effect’ and a slight deformation at the nitrogen atom is proposed.
13C NMR spectra of cassane diterpenoids. The stereochemistry of the caesalpins
Authors: Connolly J. D. , Orsini Fulvia , Pelizzoni Francesca , Ricca Giuliana 
Published: May 2005

AbstractAssignments of the 13C NMR resonances for some cassane diterpenoids have been made. The data have proved to be a useful tool for the stereochemical examination of the caesalpins.
Sterically hindered aromatic compounds. X—molecular distortions and asymmetry in a symmetrically substituted azobenzene
Authors: Barclay L. Ross C. , Dust Julian M. , Brownstein S. , Gabe E. J. 
Published: May 2005

AbstractNo significant steric effects are observed in the proton and carbon resonance spectra of 2,2′,4,4′,6,6′‐hexa‐t‐butylazobenzene, a very distorted molecule in the solid state.
Nitrogen‐15 nuclear magnetic resonance spectra of ketenimines
Authors: Eberl Karl , Roberts John D. 
Published: May 2005

AbstractNitrogen‐15 NMR spectra of 11 ketenimines have been taken both at the natural‐abundance level of 15N and with the aid of 15N‐labeling. The nitrogen chemical shifts are substantially different from those of neutral imines and are upfield, more like those of protonated imines. The results are in accord with significant delocalization of the nitrogen lone‐pair. Furthermore, there is a rough parallelism between the 13C shifts of the terminal carbons and the 15N shifts.
Selective population transfer in 15N and 13C NMR: Signs of 15NH and 15N13C coupling constants in secondary amide and iminium salts
Authors: Martineau H. , Trierweiler M. , Martin M. L. 
Published: May 2005

AbstractThe selective population transfer method has been applied to the study of a secondary amide and of the corresponding iminium salt. Important signal‐to‐noise enhancements were accessible in both fully coupled and proton decoupled 15N and 13C spectra. Moreover, the resolving power of the method was exploited for the accurate determination of long range 15N1H coupling constants. Experiments in which the selective inversion of transitions pertaining to the 15N satellite spectrum of multiplets which themselves constitute the 13C satellite spectrum of the main proton resonances could be carried out. The influence of a change from the amide to the iminium structure on the magnitudes and the signs of various 15N1H and 15N13C coupling constants is discussed.
NMR studies of actinomycins varying at the proline sites
Authors: Mauger A. B. , Thomas W. A. 
Published: May 2005

AbstractThe proton NMR spectra of 14 actinomycins and the 13C NMR data for four of these compounds were compared with those of actinomycin D. These compounds differ from actinmycin D by the replacement of one or both proline residues by sarcosine, azetidine‐2‐carboxylic acid, 4‐ketoproline, or cis or trans isomers of 4‐hydroxy‐, 4‐chloro‐ or 4‐methylproline. In those (aniso) compounds in which one proline residue is replaced, the possibility of isomerism was considered, since replacement could be located in either the α‐ or β‐peptide. Except for the sarcosine case, for which both isomers have been isolated, the aniso‐actinomycins gave spectra in which the presence of a second isomer was undetectable. Attempts to utilize the NMR data to determine which peptide contained proline, and which its congener, produced the tentative conclusion that in these compounds there is a biosynthetic preference for replacement of the β‐peptide proline residue. In comparing conformationally dependent NMR parameters for the various actinomycins, the most obvious variations appeared in the proline congener α‐proton splittings. Some of these (for cis isomers of 4‐chloroproline and 4‐methylproline) reflected different pyrrolidine ring geometries to that of proline, while others (for the corresponding trans isomers) did not. Only minor differences were apparent in the conformations of other regions of the peptide moieties.
Deuterium nuclear magnetic resonance spectroscopy. II—distribution of deuterium in some labelled nitrogen heterocyclic compounds
Authors: Al‐Rawi Jasim M. A. , Behnam George Q. , Taha Nihad I. 
Published: May 2005

AbstractPyridine, methylpyridines, quinoline and isoquinoline have been labelled with deuterium using pre‐reduced platinum dioxide (PtO2·2H2O) and heavy water. Their 2H chemical shifts from monodeuteriated TMS have been assigned. The extent of the labelling has been determined directly by 2H NMR spectroscopy.
1H and 13C NMR study of tri‐L‐serine in aqueous solution
Authors: Pogliani L. , Ziessow D. 
Published: May 2005

Abstract270 MHz1H and 22.6 MHz13C NMR spectra of the tripeptide (L‐Ser)3 dissolved in D2O have been measured and completely analysed as a function of pD in the region from 1.1 to 10. The pK(NH2)=7.0 is distinctly lower than common values for N‐terminal residues. The chemical shifts for the peptide seryl residue change little with pD, with the H‐β1 and H‐β2 resonances being differently affected by the ionization of the COOH and NH2 groups. The 13C‐α chemical shift in the peptide seryl residue exhibits a sequence effect which is considerably larger than expected on the basis of recently reported mean shifts. Rotational isomerism about the C‐αC‐β bond is studied for the three different Ser residues on the basis of vicinal coupling constants 3J(H‐α, H‐β), and it is found that the population pb (‐OH gauche to ‐CO‐, and trans to ‐NH‐) in the N‐ and p‐Ser residues is notably larger than pb in Ser and Acetyl‐Ser. In. C‐Ser, In. C‐Ser, pb is comparable to pb in Ser, but is twice as large as pb in AcSer.
Dependence of the γ carbon‐13 shielding effect on the dihedral angle
Authors: Lambert Joseph B. , Vagenas Adelia R. 
Published: May 2005

AbstractThe γ effects on 13C shielding have been examined for a series of rigid molecules containing the substituents CH3, OH, NH2, F, Cl, Br or I. Plots of the γ effect vs the CC‐αC‐βX dihedral angle are well scattered if the plots do not distinguish modes of substitution. For the series in which the resonating carbon is CH2, however, fairly linear correlations are observed for XCH3, OH, NH2, Cl and Br. It is concluded that within a structurally defined and substitutionally homogeneous series, there is a reasonably linear stereochemical dependence. Although substitution at C‐α does not seriously alter the linear relationship, hybridization of the intermediate carbons may be important. The slopes of the plots for the γ effect vs dihedral angle are remarkably similar. Neither a strictly steric (van der Waals) nor a strictly polar source can be the cause of the linear relationship, since our series of substituents ranges widely with respect to both size and electronegativity. The only two factors that are constant within the series are the removal of the hydrogen atom (CCCH to CCCX) and the addition of the bonding and nonbonding orbitals on X that were not present on H.
Natural abundance proton‐coupled 15N NMR spectra of pyridines observed from proton polarization transfer experiments
Authors: Jakobsen Hans J. , Yang P.‐I. , Brey Wallace S. 
Published: May 2005

AbstractNatural abundance proton‐coupled 15N NMR spectra have been observed for pyridine and a series of mono‐ and disubstituted pyridines using polarization transfer achieved by the selective population transfer method. The magnitudes and signs of the 15N1H spin‐spin coupling constants between the ring‐nitrogen and ring‐protons are determined from complete iterative spectral analysis and/or selective population transfer experiments. Substituent effects on the 15N1H coupling constants are discussed and compared with those for 13C1H couplings in substituted benzenes.
Carbon‐13 NMR spectra of some labdane diterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Biswas Swapna , Gupta Chitra Das , Chatterjee Tapan K. , Basu K. , Barua A. K. 
Published: May 2005

AbstractCarbon‐13 signal assignments of the labdane diterpenoids phlogantholide‐A, its diacetate and isophlogantholide‐A are reported. The assignments of the 13C NMR signals of 14‐deoxyandrographolide and its diacetate, made earlier, have now been confirmed by lanthanide shift studies on the former and also by 13C spectral studies on anhydroandrographolide diacetate and 14‐deoxy‐11,12‐didehydroandrographolide diacetate.
Spectral analysis of the high‐resolution proton‐coupled carbon‐13 NMR spectra of 1,3,2‐dithiarsolanes
Authors: Aksnes D. W. , Holak T. A. 
Published: May 2005

AbstractThe high‐resolution proton‐coupled 13C NMR spectra of 2‐chloro‐ and 2‐phenyl‐4‐methyl‐1,3,2‐dithiarsolane and 2‐chloro‐ and 2‐phenyl‐1,3,2‐dithiarsolane have been obtained and completely analysed. The spectral analysis has provided all the 13C chemical shifts and 13C1H coupling constants, including their relative signs. The results of this work are adequately interpreted in terms of two rapidly equilibrating half‐chair conformers with the 4‐methyl pseudo‐axial or pseudo‐equatorial. The cis isomers appear to be conformationally biased towards the form with the 4‐methyl pseudo‐equatorial. The two one‐bond 13C1H coupling constants of the methylene group are distinctly different. For both the cis and trans isomers, the largest one‐bond coupling always involves the methylene proton situated syn to the substituent at arsenic. The observed variation in the geminal and vicinal 13C1H coupling constants are discussed in terms of a stereospecific inductive effect of the sulphur hetero‐atoms and conformational factors.
NMR studies of the chalcogen analogues of benzofuran. IV—Proton, carbon‐13 and selenium‐77 magnetic resonance in nitrobenzo[b]selenophenes
Authors: Baiwir Marcel , Llabrès Gabriel , Christiaens Léon , Piette Jean‐Louis 
Published: May 2005

AbstractThe 1H, 13C and 77Se chemical shifts have been measured for mononitrobenzo[b]selenophenes. For the homocyclic nuclei, the observed 1H‐ and 13C‐values calculated from the empirical increments of nitrobenzene. Anomalous effects are observed in the 2‐ and 3‐substituted derivatives and the nature of the SeNO2 interactions in the former is discussed. 77Se chemical shifts of the 4‐, 5‐ and 7‐nitro derivatives are approximately correlated with the CNDO calculated electron densities; they also compare well with those of selenoanisoles and other phenyl alkyl selenides. The chemical shifts are also compared with the corresponding values in other heterocycles containing a selenophene moiety.
High resolution 1H NMR spectra of 2,2′‐biquinoline
Authors: Drake J. A. G. , Jones D. W. 
Published: May 2005

AbstractFrom analysis and refinement by the LAOCOON III program of the 220 MHz 1H spectrum of 2,2′‐biquinoline, recorded as a saturated solution in carbon disulphide, most derived chemical shifts and coupling constants are close to corresponding values in quinoline. However, H‐3 is at 1.5 ppm lower field in 2,2′‐biquinoline than in quinoline and the ortho‐coupling 3J(34) in the heterocyclic ring is 0.5 Hz larger in 2,2′‐biquinoline than in quinoline; fairly free rotation about the 2,2′ bond is inferred.
Carbon‐13 NMR of polycyclic aromatic compounds. 1—Methoxybenz[a]anthracene‐7, 12‐diones
Authors: Wilbur David , Manning Wayne B. , Hilton Bruce D. , Muschik Gary M. 
Published: May 2005

AbstractBenz[a]anthracene‐7, 12‐dione, eight monomethoxybenz[a]anthracene‐7, 12‐diones and two dimethoxybenz[a]anthracene‐7, 12‐diones were analyzed by 13C and 1H NMR. All 13C and 1H resonances have been assigned. Substituent effects on the 13C chemical shifts are discussed.
Signs of proximate 31P, 19F and 19F, 19F spin–spin coupling constants in 2‐trifluoromethylphenyldifluorophosphine
Authors: Schaefer Ted , Marat Kirk , Lemire Alberta , Janzen Alexander F. 
Published: May 2005

AbstractIn 2‐trifluoromethylphenyldifluorophosphine the proximate couplings 4J(19F31P) and 5J(19F19F) are + 68.3 and + 8.3 Hz, respectively. 1J(13C31P) is −57.0 Hz, 2J(13C‐1, 10F) is + 9.9 Hz and 2J(13C‐6, 13C‐6, 31P) is + 10.1 Hz. The trifluoromethyl substituent induces substantial changes in some coupling constants, particularly those between the 31P and ring 13C nuclei.
Studies in tertiary amine oxides. Part V—carbon‐13 nuclear magnetic resonance spectra of some N‐aryl tertiary amines, the corresponding N‐oxides and the meisenheimer rearrangement products
Authors: Khuthier Abdul‐Hussain , Al‐Rawi Jasim M. A. , Al‐Kazzaz Abdul K. , Al‐Iraqi Mohammed A. 
Published: May 2005

AbstractThe carbon‐13 NMR spectra of some N‐(2‐ or 4‐nitrophenyl) tertiary amines and their corresponding N‐oxides have been analysed. These N‐oxides undergo thermal rearrangement to O‐arylhydroxylamines, for which the 13C NMR spectral assignments were also carried out. The N‐oxidation effect on the aromatic and aliphatic fragments is calculated.
A 15N nuclear magnetic resonance study of the base‐catalyzed NH2 exchange reactions of acetamide and thioacetamide
Authors: Nee Michael , Chun Yu , Squillacote Michael E. , Roberts John D. 
Published: May 2005

AbstractThe base‐catalyzed NH2 exchange reactions of acetamide and thioacetamide were studied by 15N nuclear magnetic resonance spectroscopy by the use of line‐shape analysis. The 15N NMR spectra of these primary amides at intermediate exchange rates were broad doublets, which indicated that the two amide protons were exchanging at different rates. The line‐shape analysis indicated that the ratio of exchange rates was 6±1 for acetamide and 3±1 for thioacetamide.
13C NMR spectra of benzodiazepinones: Application to isomeric structure determination
Authors: Bernardini A. , Viallefont Ph. , Essassi E. M. , Zniber R. 
Published: May 2005

AbstractA 13C NMR study of a number of substituted 1,5‐benzodiazepin‐2‐ones has been carried out, and shows that this technique is one of the rare spectroscopic methods which allows an unambiguous identification of the number and nature of the isomers formed in the condensation of a β‐ketoester with a substituted O‐phenylenediamine.
Configurational assignment by 13C NMR of stereoisomeric 3‐bromo‐3‐acyl derivatives of 5α‐ and 5β‐ androstane
Authors: Bégué J. P. , Bonnet‐Delpon D. 
Published: May 2005

AbstractThe configurational assignment of stereoisomeric 3‐bromo‐3‐acyl derivatives of steroids in both the 5α and 5β series has been carried out by comparing the 13C chemical shifts of C‐3. A downfield shift is observed for C‐3, bearing a bromine and an acyl group, on going from the isomer with an equatorial bromine to that with an axial bromine. This rule has been established by comparison of the 13C chemical shifts of model compounds in 4‐tert‐butylcyclohexanes of known configuration.
1H NMR spectroscopic determination of the isomeric ratios of bisphenol‐F diglycidyl ethers
Authors: Domke Wolf‐Dieter 
Published: May 2005

Abstract1H NMR spectroscopy was used as a rapid method of determining the amount of the three possible isomeric forms of bisphenol‐F diglycidyl ether, one of the basic materials of epoxy resins for industrial applications. The complete spectral analysis of the glycidyl group, with respect to chemical shifts, coupling constants and magnetic anisotropy, made it possible to separate the overlapping signal regions by computational spectral simulation. Partial separation could also be obtained by application of the ‘Aromatic Solvent Induced Shift’ effect. A combination of both methods has been used successfully for the quantitative determination of the isomeric ratios of commercially available bisphenol‐F diglycidyl ethers.
Proton NMR spectroscopy of asymmetric benzylamines. The long‐range effects of an asymmetric environment
Authors: Jagur‐Grodzinski Joseph 
Published: May 2005

Abstract1H NMR Spectra of the asymmetric benzylamines N‐benzyl‐N‐butyl‐2‐hydroxy‐1,3‐propandiamine, N‐benzyl‐N‐(2‐ethylhexyl)‐2‐hydroxy‐1,3‐propandiamine, N‐benzyl‐N‐butyl‐2,3‐epoxypropanamine and N‐benzyl‐N‐(2‐ethylhexyl)‐2,3‐epoxypropanamine, were analysed. A pronounced non‐equivalance of the benzylic hydrogens is induced by asymmetric carbons in γ position with respect to the benzylic group. [Δδ=0.2–0.3 ppm; J(AB)∼13.5 Hz]. Two sets of AB patterns were observed when two asymmetric carbons were present in the same molecule. RS+SR Diastereomers can thus be distinguished from the RR+SS enantiomers.