bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 NMR spectral studies on some labdane diterpenoids
Authors: Patra Amarendra , Mitra Alok K. , Biswas Swapna , Gupta Chitra Das , Basak Ajoy , Barua A. K. 
Published: May 2005

AbstractCarbon‐13 NMR signal assignments of the labdane diterpenoids andrographolide and 14‐deoxyandrographolide, along with their acetates, and isodeoxyandrographolide have been made. This study indicates that the C‐6 and C‐11 resonance assignments of isovirescenol‐B, made earlier, should be interchanged.
Carbon‐13 spin–lattice relaxation in some polyfluoroaromatic compounds
Authors: Hamza M'Hamed Ali , Serratrice Guy , Delpuech Jean‐Jacques 
Published: May 2005

AbstractCarbon‐13 chemical shifts, spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T1 values for the para‐carbon of monosubstituted fluorobenzenes is clearly shorter than the T1 values for the ortho‐ and meta‐carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C2 in‐plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.
Improved methods for assignment of multiplicity in 13C NMR spectroscopy with application to the analysis of mixtures
Authors: Cookson David J. , Smith Brian E. 
Published: May 2005

AbstractImproved methods for the assignment of resonance multiplicity in 13C NMR spectra are described. Assignments are achieved either by direct observation of resonance intensity modulations resulting from gated spin echo (GASPE) experiments, or from the derivation of ‘selected multiplet’ spectra containing only C, CH, CH2 or CH3 carbon resonances. The methods are time‐efficient and, by comparison with the single frequency off‐resonance decoupling assignment technique, show improved spectral resolution. Chemical mixtures are used to illustrate the procedures. Possible application to materials deriving from fossil fuel sources is considered.
Linear and angular annelation effects on the 13C NMR spectra of tricyclic aromatic ketones. 1—annelated indanones
Authors: Buchanan G. W. , Isabelle M. E. , Wightman R. H. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts are reported for nine tricyclic aromatic ketones formally derived from indanone. The influences of remote ring size, as well as linear, angular exo and angular endo ketone orientation are examined. Results are compared with available 1H NMR data. For indanone itself, based on selective 1H decoupling experiments, a recently reported CIDNP derived 13C signal assignment is shown to be in error.
The tetramethylammonium ion (TMA+) versus the hydronium ion (H3O+) as internal reference for 1H NMR measurements in superacid media. Solute–solvent interactions
Authors: Rimmelin Paul , Schwartz Sylvie , Sommer Jean 
Published: May 2005

AbstractIt is shown that the chemical shift of the generally utilized internal reference for 1H NMR measurements in superacid media, namely, tetramethylammonium bromide, which is normally fixed at 3.10 ppm from external TMS, changes with the composition of the acid mixture (HF or HSO3F:SbF5). This is attributed to solute–solvent interactions. The use of both the tetramethylammonium ion or the hydronium ion as internal references is discussed, as the hydronium ion appears to be only slightly influenced by these interactions.
Conformational analysis by 13C spin–lattice relaxation times. Evidence for an intramolecular CH …︁ N hydrogen‐bond in a 4H‐1,2,4‐triazole derivative
Authors: Houssin Raymond , Hénichart Jean‐Pierre 
Published: May 2005

AbstractThe modification of the 13C spin–lattice relaxation time values for the C atoms in the side‐chain of 4‐(morpholinoethyl)‐1,2,4‐triazole has been found to be characteristic of the structure variation caused by different solvents, and evidence for the formation of an intramolecular hydrogen bonding in an apolar medium has been provided.
13C NMR spectra of natural products. 1—guaianolides
Authors: Da Silva Antonio J. R. , Garcia Marcos , Baker Paul M. , Rabi Jaime A. 
Published: May 2005

AbstractThe 13C NMR spectra of 18 guaianolides have been measured and the chemical shifts assigned. The compounds investigated include the naturally occurring eremanthin (1), dehydrocostus lactone, eregoyazin, eregoyazidin and other semisynthetic lactones derived from 1. Qualitative analysis of the data suggests that the predominant conformation in almost all compounds so far studied is a distorted chair‐like form.
13C NMR spectra of natural products. 2—eudesmanolides
Authors: da Silva Antonio J. R. , Garcia Marcos , Baker Paul M. , Rabi Jaime A. 
Published: May 2005

AbstractThe 13C NMR spectra of eight eudesmanolides have been measured and the chemical shifts assigned. Among the compounds studied are the naturally occurring α‐cyclocostunolide, santamarin, arbsculin A and reynosin.
Investigation of benzimidazoles: II—the influence of substituents and solvents on the 1H and 13C NMR chemical shifts of 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates
Authors: Larina L. I. , Vakul'skaya T. I. , Filatov A. V. , Istomin B. I. , Shibanova E. F. , Lopyrev V. A. , Voronkov M. G. 
Published: May 2005

AbstractThe influence of substituents on 1H and 13C NMR chemical shifts of 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates in different solvents has been investigated. It has been shown that the transmission of the electronic effects of the substituents in benzimidazoles and their quaternary salts are almost the same. The nature of the solvent influences only the intensity of the transmission of the electronic effects of substituents in 2‐substituted 1,3‐dimethylbenzimidazolium perchlorates.
13C NMR and ESR spectroscopic investigations on tert‐butyl‐substituted cyclopentadienones
Authors: Kalinowski Hans‐Otto , Franz Lothar H. , Maier Günther 
Published: May 2005

Abstract13C NMR spectra of 11 di‐, tri‐ and tetra‐tert‐butyl‐substituted cyclopentadienones are discussed with respect to charge distribution and substituent effects. The chemical shifts of the unsubstituted cyclopentadienone, calculated from substituent increments, are in good agreement with published CNDO calculations and can be rationalized by the inductive effect of the carbonyl group. In addition, the ESR signals shown by some of the cyclopentadienones are described, and possible reasons for their appearance are discussed.
The effect of phosphorylation of the histidyl residue in the tetrapeptide Gly‐Gly‐His‐Ala. Changes of chemical shift and pK values in 1H‐ and 31P‐NMR spectra
Authors: Kalbitzer Hans Robert , Rösch Paul 
Published: May 2005

AbstractPhosphorylation of the tetrapeptide Gly‐Gly‐His‐Ala by phosphoamidate provides a model peptide for proteins which, in the course of their reaction, bind a phosphoryl group to an imidazole ring. 31P‐ and 1H‐NMR data, including chemical shift and pK values, for this peptide and its three phospho‐derivatives are presented. These data show that it is possible, by NMR studies, to decide whether or not a peptide or a protein is phosphorylated at the N‐1 or at the N‐3 position of an imidazole ring, and how this information can be achieved.
13C NMR study of psilostachyinolides from some ambrosia species
Authors: Borges‐del‐Castillo J. , Manresa‐Ferrero M. T. , Rodríguez‐Luis F. , Vázquez‐Bueno P. , Joseph‐Nathan P. 
Published: May 2005

Abstract13C NMR data are presented for the psilostachyinolides, psilostachyin C, psilostachyin, canambrin, psilostachyin B, altamisin, paulitin and isopaulitin, obtained from Ambrosia cumanensis H.B.K., Ambrosia psilostachya D.C. and Ambrosia canescens (Gray).
Carbon‐13 NMR parameters of phenyltin halogenides and phenyltin chalcogenides
Authors: Mathiasch B. 
Published: May 2005

AbstractThe 13C NMR shift parameters and couplings to tin are reported for nine phenyltin halogenides and seven phenyltin chalcogenides, as well as the T1 results for Ph2SnTe. A pronounced linear dependence of all coupling constants on the para‐carbon shift is discussed.
13C NMR spectra of 1‐stearoyl‐2‐linoleyl‐sn‐glycero‐3‐phosphorylcholine and 1‐stearoyl‐2‐arachidonoyl‐sn‐glycero‐3‐phosphorylcholine in CDCl3 solution and in sonicated dispersions in 2H2O
Authors: Santarén Juan F. , Rico M. , Guilleme J. , Ribera A. 
Published: May 2005

AbstractTwo mixed‐acid lecithins: 1‐stearoyl‐2‐linoleyl‐sn‐glycero‐3‐phosphorylcholine (SLL) and 1‐stearoyl‐2‐arachidonoyl‐sn‐glycero‐3‐phosphorylcholine (SAL) have been synthesized by phospholipase A2 digestion of 1,2‐distearoyl‐sn‐glycero‐3‐phosphorylcholine (DSL), followed by reacylation of the lysolecithin with the desired fatty acid anhydride. 13C (25.2 MHz) NMR spectra of SLL and SAL in CDCl3 solution and in sonicated dispersions in 2H2O have been obtained. Complete spectral assignments are reported for the two molecules in both systems. 13C nuclear spin‐lattice relaxation times (T1) of SLL and SAL in sonicated aqueous dispersions have also been measured. Relaxation rate profiles as a function of the chain segment position are in general agreement with those recently obtained from 2H NMR for similar systems.
Characterization of organic substrates bound to cross‐linked polystyrenes by 13C NMR spectroscopy
Authors: Jones Alan J. , Leznoff Clifford C. , Svirskaya Polina I. 
Published: May 2005

AbstractThe 13C NMR spectra of a wide variety of organic substrates bound to 2% cross‐linked polystyrenes may be obtained routinely, provided the resins can be sufficiently swollen. The 13C chemical shifts of polymer‐bound trityl alcohol, polymer‐bound monotrityl ethers of the symmertrical diols HO (CH2)nOH (n=2, 4, 6, 7, 9 and 10), and some related intermediates in the solid phase synthesis of insect pheromones are presented. 13C shift additivity correlations, differing little from those in free trityl ethers, are drawn.
Structure elucidation with lanthanide‐induced shifts. 13—A critical evaluation of methods for obtaining bound shifts and association constants
Authors: Raber Douglas J. , Hardee Linda E. 
Published: May 2005

AbstractThe use of lanthanide‐induced shifts for rigorous structure analysis requires accurate values corresponding to only one of the complexes that can be formed. A combination of computational and experimental studies have been carried out to evaluate several commonly used procedures for obtaining bound shifts. The results indicate that only two of these methods afford values which are reliably related to the actual bound shifts. In addition, both methods afford values for the association constant. Guidelines are suggested which allow a chemist to anticipate when each methods can be successfully employed.
Polar substituent effects on 13C NMR spectra in ethyl cis‐2‐substituted cyclopropane carboxylates
Authors: Kusuyama Yoshiaki , Inoshita Satoru , Okada Ginjiro , Yanagi Minoru , Tokami Kenjiro , Fuchu Hiroshi , Tsuno Yuho , Mishima Masaaki 
Published: May 2005

Abstract13C FT NMR spectra of ethyl cis‐2‐substituted cyclopropanecarboxylates were obtained in chloroform‐d and the chemical shifts were compared with those of the corresponding trans isomers. In most cases, the resonances for the ring carbons and the carbonyl group carbon appeared further upfield than those of the trans isomers, and were found to be useful for distinguishing the stereoisomeric 1,2‐disubstituted cyclopropanes.
The rα structure of benzonitrile, determined by NMR of the oriented molecule
Authors: Diehl P. , Amrein J. , Veracini C. A. 
Published: May 2005

AbstractThe indirect and direct proton–proton, proton–carbon and proton–nitrogen coupling constants of benzonitrile have been measured from proton spectra with natural abundance satellites, and also from proton and 15N spectra of the molecule enriched in 13C or 15N at the cyano group, both in isotropic as well as in oriented solvents. The rα structure of the entire molecule has subsequently been determined.
1H NMR study of cis‐trans isomerization in two analogs of the thiol form of thiamine
Authors: Chriss Derald , Miller Robert H. , Echols Richard E. , Vessel Ellen 
Published: May 2005

AbstractProton magnetic resonance (1H NMR) was used to study cis‐trans isomerization in N‐methyl‐N‐(1‐methylthio‐2‐propenyl)formamide and N‐benzyl‐N‐(1‐methylthio‐2‐propenyl)formamide, two analogs of the thiol form of thiamine. Benzene dilution studies and shift reagent studies were used to make resonance assignments, which indicate that the predominant isomer for each analog has the CC bond trans to the carbonyl oxygen. Shift reagent studies, using Pr(fod)3 in CCl4 or CDCl3, suggest that the reagent may be bonding to both the nitrogen and oxygen atoms of the substrate. For some of the systems studied, varying ρ at constant temperature had the same spectral effect as varying temperature at constant ρ.
Carbon‐13 NMR studies of Ni(II) porphyrin and chlorin complexes
Authors: Ulman Abraham 
Published: May 2005

AbstractThe 13C NMR spectra of tetraalkyl‐porphyrin and ‐chlorin complexes of nickel(II) were studied. The 13C NMR of (5,10,15,20‐tetramethylchlorinato)nickel(II) supports the model of asymmetric charge distribution in this chlorin, as derived from the structure analysis and from previous proton NMR studies.
Carbon‐13 NMR spectra of isocoumarin, N‐methyl‐1(2H)‐isoquinolinone and related compounds
Authors: Spassov S. L. , Atanassova I. A. , Haimova M. A. 
Published: May 2005

AbstractThe 13C NMR spectra of isocoumarin, N‐methyl‐1(2H)‐isoquinolinone and 14 of their 3‐ and/or 4‐substituted derivatives were measured and assigned with the aid of various spectral techniques. The values of the one‐bond and some of the long‐range 13C‐13C‐1H coupling constants are reported. The effect of substitution on the 13C chemical shifts is discussed.
A 15N NMR investigation of some azolopyridines
Authors: Stefaniak L. , Roberts John D. , Witanowski M. , Hamdi B. T. , Webb G. A. 
Published: May 2005

Abstract15N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S‐SOS calculations of nitrogen shieldings. Previous 14N NMR results for some of these compounds are reinterpreted. The 14N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine‐type nitrogens are more reliably assigned from the 15N spectra combined with the results of the INDO/S‐SOS calculations for individual molecules. A combination of 14N and 15N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments considered.
A 13C and 1H NMR study of diastereomeric α‐methylidene‐β‐hydroxy‐γ‐alkoxy esters
Authors: Banfi Luca , Potenza Donatella , Ricca Giuliana Severini 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of α‐methylidene‐β‐hydroxy‐γ‐alkoxy‐pentanoates and ‐decanoates are presented. These data are consistent with a preferred conformation in which an intramolecular hydrogen bond is present. Very characteristic steric shifts in the 13C and 1H NMR spectra provide an efficient tool for the configurational assignment for this class of compounds.
33S chemical shifts and line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions
Authors: Annunziata Rita , Barbarella Giovanna 
Published: May 2005

AbstractThe 33S chemical shifts, δ, and the line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions were measured at 23.009 MHz. δ increased with decreasing electronic charge on sulphur. The line width varied from 3–10 ppm for sulphones to 400 ppm for sulphonium ions. The higher geometrical flexibility of five‐membered ring sulphones with respect to the six‐membered ring compounds was reflected in the variations of δ with methyl substitution. Open‐chain sulphoximides are shielded with respect to the corresponding sulphones, whereas open‐chain sulphimides are deshielded with respect to the corresponding sulphoximides.
Effect of molecular motion and solvent interactions on nitrogen‐15 relaxation in anilines
Authors: Lambert Joseph B. , Stec Daniel 
Published: May 2005

AbstractDipolar relaxation of 15N in anilines and anilinium ions is influenced by overall motion of the molecule, by rotation about the aryl–‐nitrogen bond, by inversion of the aniline nitrogen and by interactions of the NH2 or NH3+ group with the solvent. These factors are assessed by comparison of the 13C and 15N dipolar relaxation times as a function of para‐substitution on the aryl ring. In the anilines (solvent CDCl3), electron withdrawal brings about faster relative motion of the amine side‐chain, contrary to expectation from consideration of CN rotation but in agreement with the effects from nitrogen inversion. The 15N dipolar relaxation time correlates with the Hammett σp. For the anilinium ions (solvent Me2SO‐d6), there is no correlation with σp and no qualitative relationship with either CN rotation or N inversion. Nitrogen‐15 relaxation, corrected for overall motion as judged by ring 13C relaxation, correlates with the inductive parameter σI. Electron withdrawal through induction reduces hydrogen bonding and increases side‐chain mobility. For most of the anilines and for all of the anilinium ions, solvent interactions cause the nitrogen side‐chain to be less mobile than the aryl ring. Under these circumstances, the Woessner approach cannot be used to calculate barriers. The hydrogen bond donor properties of the anilines are reduced in the absence of electron‐donating substituents, and the first barriers to NH2 rotation/inversion were calculated by this procedure: aniline in CDCl3 3.5 kcal/mol, p‐chloroaniline in CDCl3 3.4 kcal/mol and p‐nitroaniline in acetone 3.8 kcal/mol.
Two‐dimensional NMR studies of cyperene
Authors: Joseph‐Nathan P. , Martińez E. , Santillan R. L. , Wesener J. R. , Günther H. 
Published: May 2005

AbstractCombined utilization of 1H1H homonuclear and 1H13C heteronuclear NMR chemical shift correlations, two‐dimensional J‐resolved 1H NMR measurements and homonuclear 1H double resonance experiments allowed specific assignments for both 1H and 13C NMR frequencies to be made for the tricyclic sesquiterpene cyperene. The results also provided information on the conformation of the six‐membered ring of this natural product, which was recognized as a distorted chair.
13C and 1H NMR spectral studies of N‐alkylmethylquinolinium salts
Authors: Jaroszewska Jolanta , Wawer Iwona , Oszczapowicz Janusz 
Published: May 2005

Abstract13C and 1H chemical shifts of fourteen N‐alkylmethylquinolinium salts in DMSO‐d6 are reported, and compared with those of the eleven corresponding methylquinoline bases. The influence of ring substitution by methyl groups in the salts and substitution at the nitrogen atom and the effect of the anion are discussed.
Luminescent metal complexes. 4—13C NMR spectra of the tris chelates of substituted 2,2′‐bipyridyls and 1,10‐phenanthrolines with ruthenium(II) and osmium(II)
Authors: Cook Michael J. , Lewis Anthony P. , McAuliffe Glenn S. G. 
Published: May 2005

Abstract13C Chemical shifts are reported for the ruthenium(II) tris complexes of thirteen 2,2′‐bipyridyls and three 1,10‐phenanthrolines and for the osmium(II) tris complexes of five 2,2′‐bipyridyls. Chelation induced shifts (δcomplex – δligand) are discussed in terms of models for π back‐bonding. 13C NMR is shown to be a convenient tool for the direct observation of the geometrical isomerism of complexes formed from monosubstituted ligands.
Glucosidation shifts of allylic and benzylic alcohols in 13C NMR spectroscopy
Authors: Horibe Isao , Seo Shujiro , Yoshimura Yohko , Tori Kazuo 
Published: May 2005

AbstractThe 13C FT NMR spectra of β‐D‐glucopyranosides (including their tetraacetates) of several secondary allylic and benzylic alcohols were compared with those of methyl β‐D‐glucopyranoside and the corresponding parent alcohols. The characeristic glucosidation shifts observed for these alcohols may be applicable to the determination of the absolute configuration of the hydroxy group in these alcohols.
1H, 13C and 15N NMR spectra of [1,2‐15N2]pyrazole derivatives
Authors: Fruchier Alain , Pellegrin Valdo , Claramunt Rosa Maria , Elguero Jose 
Published: May 2005

AbstractThe chemical shifts and coupling constants of [1,2‐15N2]pyrazole, 2‐(1‐[1,2‐ 15N2]pyrazolyl)‐2‐[l,3‐2H6]propanol, 1‐nitro[1,215N2] and 3‐nitro[1,2‐15N2]pyrazole are reported.
Magnetic resonance study of diastereomeric interactions of nitroaromatic sulfxides with alcohols in solution
Authors: Sweeting Linda M. , Anet Frank A. L. 
Published: May 2005

AbstractThe synthesis of optically active (1R,2R)‐ and (1S,2R)‐2‐deuterio‐2,3‐dihydro‐2‐methyl‐6‐nitrobenzothiophene‐1‐oxide (3 and 4) is described. Several racemic aryl methyl carbinols in the presence of 3 or 4 give different chemical shifts for enantiomeric CH, CH3 and OH protons. These chemical shift differences are larger than those observed in analogous sulfoxide–alcohol pairs without nitro groups. Quinine and cinchonidine cause observable non‐equivalence of methylene and aromatic protons in racemic 4. The magnitude of the diastereomeric shift difference is sensitive to temperature, solvent, concentration, nature of the π system and steric effects.
Stereochemical study of hindered α‐glycols by 1H and 13C NMR spectroscopy
Authors: Pascal Y. , Convert O. , Berthelot J. , Fournier F. 
Published: May 2005

AbstractSterically hindered α‐glycols, obtained from electrochemical hydrodimerization of polycyclic ketones (indanone, tetralone, chromanone, flavanone, xanthone and fluorenone), were studied by 1H and 13C NMR. Evidence of conformational hindrance was deduced from the 1H spectra; meso or racemic configurations and the conformational stereochemistry of these molecules in solution were assigned.
Stereostructure of condensed‐skeleton cis‐ and trans‐dihydro‐1,3‐thiazines and 1‐thia‐3‐azaspiroalkenes
Authors: Sohár P. , Simon L. , Bernáth G. 
Published: May 2005

AbstractThe stereostructures of some condensed‐skeleton cis‐ and trans‐dihydro‐1,3‐thiazines and 1‐thia‐2‐phenyl‐3‐azaspiro[4n + 1]alk‐2‐enes (n = 3–6) were established by 1H and 13C NMR spectroscopy. A comparative study indicated that the cis‐thiazines have greater conformational mobility than the corresponding oxazines, although the preferred conformer of the two types of cis compounds is the same, with the sulphur axial and the 4‐methylene group equatorial relative to the rings.
13C NMR spectra of 3‐substituted phlorophenone compounds
Authors: Dekker Theodor G. , Fourie Theunis G. , Snyckers Friedrich O. , van der Schyf Cornelis J. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of 3‐allyl‐, 3‐prenyl‐ and 3‐benzyl‐phlorophenone compounds are reported. Relative substituent effects are discussed.
Determination of the conformation of diethylmethyl‐2‐[p‐(o‐propoxybenzamido)benzoyloxy]ethylammonium bromide in solution by measurement of selective proton spin–lattice relaxation rates
Authors: Sega Alessandro , Ghelardoni Mario , Pestellini Vittorio , Pogliani Lionello , Valensin Gianni 
Published: May 2005

AbstractThe relative conformation of the aromatic rings and the amide bridge of diethylmethyl‐2‐[p‐(o‐propoxybenzamido)benzoyloxy]ethylammonium bromide has been established by a combined analysis of non‐selective, single‐selective and double‐selective pulse experiments using, as a basis of comparison, the Dreiding molecular model of the compound.