bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxygen‐18 isotope effects on 13C NMR signals
Authors: Everett Jeremy R. 
Published: May 2005

AbstractA survey of 18O isotope effects on 13C chemical shifts shows that a linear relationship exists between the magnitude of the one‐bond isotope effect and the chemical shift of the carbon atom for carbonyl groups. No such correlation was found for functional groups in which the oxygen atoms are connected to the carbon atoms via single bonds.
13C NMR of organosulfur compounds the 13C chemical shifts of monocyclic γ‐ and δ‐sultones
Authors: Smith Michael B. , Wolinsky Joseph 
Published: May 2005

AbstractThe 13C NMR spectra of several monocyclic γ‐sultones(1,2‐oxathiolane 2,2‐dioxides) and δ‐sultones(1,2‐oxathiane 2,2‐dioxides) have been determined and are presented herein. The chemical shifts of the ring carbons of these compounds are compared in terms of conformational, electronic and anisotropic differences. Electric field effects may be responsible for the chemical shifts of the C‐α carbon, but do not appear to be important for C‐α. Anisotropic deshielding also appears to be important for the chemical shifts of C‐α, but the effects on C‐α appear to be small. Dipole changes at C‐α and C‐α, induced by back donation of electron density from the ring oxygen to sulfur, may explain the chemical shifts at C‐α. Substituent effects are readily explained in terms of well‐known effects. In general, the carbons closest to the sulfonate group are found to be the most affected, and the carbons of the δ‐sultones proximate to the sulfonate group are found to be more deshielded than those of the γ‐sultones.
13C relaxation times, T1, in six‐coordinate cobalt(III) complexes: Study of the axial CoN (heterocyclic) bond
Authors: Huet Jack , Gaudemer A. 
Published: May 2005

AbstractCarbon‐13 relaxation times, T1, have been measured for ten cobalt(III)–cyclohexanedione dioxime complexes: CH3CH2Co(Niox)2‐p‐R‐pyridine [RH, N(CH3)2, CH3, C2H5, C(CH3)3, Cl, Br, CN and COCH3] and CH3CH2Co(Niox)2‐3‐N‐methylimidazole. The values obtained have been rationalized by making assumptions on the length of the metal—hetrocyclic nitrogen bond. The internal rotation around the axial CoN (heterocyclic) bond is faster for the 3‐N‐methylimidazole ligand than for the pyridine ligands. Correlations of the T1 values with the σ‐donor and π‐acceptor character of the pyridine ligands were attempted. The interpretation of the results suggests the existence of π‐back‐bonding from the metal to the N‐1 pyridine nitrogen atom, in agreement with the results of other workers. This conclusion, however, was not supported by the use of the para‐C chemical shift as a criterion for back‐bonding in pyridine–transition metal complexes.
13C NMR spectra of benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives
Authors: Al‐Showiman Salim S. , Al‐Najjar Ibrahim M. , Amin Hassan B. 
Published: May 2005

AbstractCarbon‐13 chemical shift assignments are reported for benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives, where X=CH(OAc)CH3 substituted at positions 2‐7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C‐3, arising from the peri interaction of H‐3 and the 4‐ethyl acetate substituent. Carbon‐13 relaxation times (T1) and nuclear Overhauser enhancements (η) have been measured for benzo[b]thiophene and its derivatives, and the contributions of dipolar, TDD1, and spin rotation, TSR1, relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin‐lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T1, and can form the basis for spectral assignments, as in 1‐phenylethyl acetate. Long‐range 13C1H coupling constants were observed both between ring carbons and between ring carbons with ring side‐chain hydrogens. These results have been used for the structure determination of the title compounds.
Carbon‐13 nuclear magnetic resonance spectra of exo‐ and endo‐2‐norbornyltrimethyl‐stannanes: Corrected assignments
Authors: Kitching William 
Published: May 2005

AbstractThe 13C NMR spectra of pure exo‐2‐norbornyltrimethylstannane and a mixture of the exo‐ and endo‐isomers have been recorded. 1H–13C polarization transfer spectra have been obtained and require the previously reported assignments for C‐3 and C‐4 in the exo‐isomer to be reversed. The reported assignments for the endo‐isomer are correct. The new assignment for C‐4‐exo [with J(119Sn,13C) vic=12 Hz, instead of the previously assigned J(vic)=23 Hz], has a very minor effect on the nature of the Karplus curve [for 3J(119Sn,13C)] generated previously.
Application of NMR spectroscopy of chiral association complexes. 13—electron donor–acceptor complexes between racemic carbazolo[3,4‐c]carbazoles and an optically active acceptor
Authors: İçli Siddik , Burgemeister Thomas , Mannschreck Albrecht , Zander Maximilian 
Published: May 2005

AbstractStrong electron donor–acceptor (EDA) association between carbazolo[3,4‐c]carbazoles and an optically active tetranitrofluorenone derivative was detected by UV–visible spectroscopy and by 1H NMR shifts. 1H NMR splittings at low temperatures are due to diastereomeric association complexes and, thus, prove the chirality of carbazolocarbazoles.
Electron spin resonance studies of several anion radicals of nitro‐substituted thioacylpiperidines and morpholines
Authors: Cercasov C. , Cornea F. , Ciureanu M. , Hillebrand M. , Sahini V. E. , Volanschi E. 
Published: May 2005

AbstractThe radical anions of m‐ and p‐ nitro‐substituted derivatives of several classes of N‐(thioacyl)‐piperidines and ‐morpholines have been studied by ESR spectroscopy. The anion radicals were found to be centred on the nitro group, and the distribution of the unpaired electron was found to be dependent on the extent of conjugation between the thiocarbonyl group and the aromatic moiety of the molecule. The hfs constants were discussed in terms of the spin densities calculated by the McLachlan procedure.
Structural studies on 6‐methyl‐9‐carbamoyl‐tetrahydro‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones by 1H, 13C and 15N NMR spectroscopy
Authors: Tóth Gábor , de La Cruz Carlos , Bitter István , Hermecz István , Pete Béla , Mészáros Zoltán 
Published: May 2005

AbstractSeveral 6‐methyl‐9‐carbamoyltetrahydro‐4H‐pyrido[1,2‐α]pyrimidin‐4‐ones have been prepared using phosgene iminium chloride. These compounds can exist in equilibrium as the cis (3A) imine ⇌ (3B) enamine ⇌ trans (3C) imine. 1H, 13C and 15N NMR prove that the cis‐ and trans‐imine isomers are predominant in the equilibrium. 1H NMR data reveal that the share of the 3B enamine form is negligible at measurable concentrations. The isomeric ratio 3A:3C is time dependent and can be monitored by measuring the CH3C‐6 and (CH3)2N signals. The 13C NMR data show that doublets in the range 42–45 ppm for C‐9 are only compatible with the imine forms 3A and 3C. The SCS values of the CH3C‐6 and OCN(CH3)2 groups were calculated and used for identification of the cis and trans isomers. 15N NMR data show that the N‐1 chemical shift of the imine is approximately − 140 ppm for compound 3, whereas that of a fixed enamine is around − 267.8. This provides additional support for the predominance of the imine tautomers in the equilibrium 3A ⇌ 3B ⇌ 3C. 15N data allow the stereoisomers 3A and 3C to be distinguished.
Barriers to rotation of the dimethylamino group in some 2‐amino‐4‐(N,N‐dimethylamino)pyrimidines
Authors: Wells C. H. J. 
Published: May 2005

AbstractThe free energy of activation for rotation about the exocyclic CN bond of the dimethylamino group of some 6‐substituted 2‐amino‐4‐(N,N‐dimethylamino)pyrmidines has been determined using 1H NMR line shape analysis. The results are discussed in terms of the relative electron‐withdrawing and electron‐releasing effects of the substituents.
Carbon‐13 NMR of quinone methides
Authors: Benson Mabry , Jurd Leonard 
Published: May 2005

AbstractThe 13C NMR spectra of four ortho‐ and seven para‐quinone methides were assigned using chemical shift and long‐range carbon‐proton coupling information. The carbonyl shifts are compared with those in ortho‐ and para‐benzoquinones. The chemical shifts of the carbonyls of the p‐quinone methides are observed at δ 186.2–186.4 for the three ortho‐di‐tert‐butyl‐substituted compounds and at δ 180.7–181.5 for the four ortho‐oxy‐substituted compounds. In the three o‐quinone methides with meta, para‐dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o‐quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.
Application of biosynthetic 13C‐enrichment using [1‐13C]‐, [2‐13C]‐ and [1,2‐13C2]‐acetate as precursor for 13C NMR spectral assignment of higher plant metabolites. The assignments of some bryonolic acid derivatives
Authors: Kamisako Wasuke , Suwa Kiyoko , Morimoto Kayoko , Isoi Koichiro 
Published: May 2005

AbstractThe 13C NMR spectra of some derivatives of bryonolic acid (1) (D:C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) were assigned by means of 13C‐enrichment, lanthanide‐induced shifts (LIS) and comparison of chemical shift data between derivatives. The 13C‐enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1‐13C]‐, [2‐13C]‐ or [1,2‐13C2]‐acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl‐3β,29‐diols (3,29‐diacetyl‐D:C‐friedoolean‐8‐en‐β,29‐diol) 5, 5a, 5b and 5c, and 3‐acetyl‐3β,29‐diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their 13C NMR spectra were recorded. The 13C concentration of the 13C‐enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C‐29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D‐ and E‐ring carbons and those of the methyl carbons linked to these rings.
1H NMR study of naphthoflavones with shift reagents
Authors: Joseph‐Nathan P. , Santillan R. L. 
Published: May 2005

AbstractThe complete assignment of the proton NMR spectra of several α‐, β‐ and γ‐ naphthoflavones at 100 MHz using Eu(fod), and double resonance experi‐ ments has been carried out. The compounds were found to associate at the carbonyi oxygen, by analogy with flavones where complete structural assignment can be attained using Pr(fod)3, at 60MHz. The three types of naphthoflavones can be distinguished by observation of the quantitative lanth‐ anide‐induced shifts at H‐3 and/or H‐5, combined with their chemical shift values in the absence of shift reagent.
Methyl carbon chemical shifts of methylbenzoic acids and methylbenzoate anions
Authors: Guilleme Joaquin , Diez Ernesto , Garrigos Lluis , Esteban Angel L. 
Published: May 2005

AbstractMethyl carbon chemical shifts have been assigned for methylbenzoic acids dissolved in CDCl3, and for methylbenzoate anions obtained by dissolving these acids in aqueous NaOH solution. Chemical shifts have been interpreted by means of additive substituent parameters which reflect conformational features existing between adjacent substituents. Barriers to rotation of a methyl group adjacent to a carboxyl or carboxylate group have been estimated to differ by less than 2 kJ mol−1 from the barrier of a methyl group in o‐xylene.
Carbon–proton coupling constants in allenes, ethenes and butatrienes. Application to conformational analysis of allenyl and vinyl alkyl ethers and thioethers
Authors: Koole N. J. , de Bie M. J. A. , Hansen P. E. 
Published: May 2005

AbstractExperimental carbon–proton coupling constants are reported for 36 monosubstituted allenes, 20 ethenes and 5 butatrienes. The data for the allenes cover a range of substituents in which either the first atom of the substituent (all Group IV–VII elements of the second and third row are covered) and/or the substitution of that atom is varied. The electronegativity (σI) of the substituent directly attached to the coupled carbon atom is correlated with the 1J(CH) coupling. This is also borne out by the good correlations between 1J(CH) values in the allenes and 1J(CH) values in various other classes of chemical compounds. Theoretically calculated 1J(CH) values correctly reflect the substituent effects on the experimental values in the allenes, ethenes and butatrienes spearately, but fail to give a satisfactory description of the differences in 1J(CH) for these types of compounds. In disubstituted allens and ethenes the substituent effects on 1J(CH) values are additive. The experimental and calculated values differ by less than 1 Hz. Two‐ and three‐bond carbon–proton couplings are also discussed in terms of electronegativity, substituent and hybridization effects and mutual relationships. Large values, up to 6 Hz, are found for 4J(CH) and 5J(CH) in the allenes and butatrienes. These large values are ascribed to σ‐π interactions. For geometrically equivalent couplings a constant ratio of nJ(CH)/nJ(HH) is found in the ethenes (0.65; n = 3) and in the allenes and butatrienes (0.55; n = 4 and 5, respectively). 1J(CH) and 3J(CH) coupling constants are used for the conformational analyses of vinyl, allenyl and butatrienyl ethers and thioethers. At room temperature the methyl and ethyl ethers are predominantly in an s‐cis conformation, whereas the iso‐propyl allenyl ether is a mixture of s‐cis and s‐trans; the tert‐butyl allenyl ether exists mainly in the s‐trans conformation. The thioethers are all in the s‐cis conformation.
Dimers from cyclic α‐diketones. Confirmation of structure by solid‐phase CPMAS 13C NMR spectroscopy
Authors: Macomber Roger S. , Murphy Paul 
Published: May 2005

AbstractThe solid‐phase 13C CPMAS NMR spectra of the crystalline dimers from 10‐, 12‐ and 14‐membered cyclic α‐diketones were found to be in full accord with the symmetrical tricyclic 2,5‐dihydroxycyclohexane‐1,4‐dione structures previously proposed on the basis of molecular formulae and infrared spectroscopy.
Carbon‐13 spin–lattice relaxation of tropane alkaloids. Anisotropic rotational motion of tropine and pseudotropine
Authors: Uusvuori Raimo , Lounasmaa Mauri 
Published: May 2005

AbstractThe 13C spin–lattice relaxation times of tropine and pseudotropine have been measured in CDCl3 as a function of concentration. The same relative increase in concentration serves to increase the relaxation rates much less in the region 0.9–5.0 wt.% than in the region 5.0–14.3 wt.%. The rotational diffusion coefficients have been calculated from the relaxation data using Woessner's anisotropic rotational diffusion model. Reorientation of both molecules is shown to be moderately anisotropic. The principal axes of the rotational diffusion tensor in the symmetry plane of both molecules are rotationally shifted from the principal axes of the moment of inertia tensor of the free molecules, and the main rotational axis is parallel with a line passing through the centre of mass of the molecule and the nitrogen atom.
Carbon‐13 NMR of some organophosphorus compounds. 2—chemical shifts and PC coupling constants of diaryl‐, dialkoxy‐ and diaryloxy‐phosphine amines with general formula Y2PNRR'
Authors: Al‐Rawi Jasim M. A. , Sheat M. A. , Ayed Nacur 
Published: May 2005

AbstractCarbon‐13 chemical shifts and 2J(POC), 3J(POCC), 2J(PNC) and 3J(PNC) coupling constants of 30 compounds containing the amine moiety, with the general formula Y2PNRR' (Y  C6H5, CH3O, CH3CH2O, CH2O; Y2  1,2‐dioxybenzene) have been determined. J(PNC) values have been used to explain the preferred conformation around the PN bond. A comparison between 2J(PNC) and 2J(PNH) was accomplished.
Carbon‐13 NMR spectroscopy of some Strychnos alkaloids. Part 2
Authors: Verpoorte R. , van Beek T. A. , Riegman R. L. M. , Hylands P. J. , Bisset N. G. 
Published: May 2005

Abstract13C NMR data for a series of natural and semi‐synthetic ar‐hydroxy‐ and ‐methoxy‐substituted Strychnos alkaloids are presented and are used to determine substituent‐induced chemical shift (SCS) values for the various substitution patterns.
13C NMR spectroscopic study of lupinine and epilupinine salts and amine oxides
Authors: Podkowinska Halina , Skolik Jerzy 
Published: May 2005

AbstractThe 13C NMR spectra of the isomeric alkaloids lupinine and epilupinine and their perchlorates, methiodides and N‐oxides are discussed. Chemical shift changes due to protonation, quaternization and N‐oxidation are analysed. The trans‐quinolizidine ring fusion is proved for epilupinine salts and for the N‐oxide. Lupinine also exists predominantly with the trans ring fusion, but the cis ring fusion is found in the methiodide. An equilibrium of two stereoisomers, one with trans‐ and the other with cis‐ring fusion, has been established for lupinine perchlorate in D2O solution. Lupinine N‐oxides isolated in the crystalline state are shown to have both trans‐ and the cis‐ring fusion.
Conformation of a diastereoisomeric pair of enkephalin analogues: A 400 MHz 1H NMR study
Authors: Bajusz S. , Casy A. F. 
Published: May 2005

Abstract1H NMR spectra recorded at 400 MHz of the enkephalin analogues Tyr‐D‐NIe‐Gly‐Phe‐D(and L)‐NIeS and the dipeptide Ac‐Phe‐D‐NIeS as solutes in DMSO‐d6 are reported and assigned. A preferred conformation of the D2L5 peptide is proposed, based on evidence of an intramolecular hydrogen bond between Phe4 NH and Tyr1 CO and NH/a‐CH coupling constants. The possibility of conformational differences between the isomeric peptides accounting for differences in their ability to bind to δ‐opiate receptors is discussed.
1H NMR separation of epimeric mixtures by lanthanide shift reagents: Analysis of some isoxazolidine derivatives
Authors: Bucci P. , Chidichimo G. , Liguori A. , Menniti G. , Uccella N. 
Published: May 2005

AbstractEpimeric mixtures of isoxazolidine derivatives were investigated by 1H NMR spectra obtained in the presence of lanthanide shift reagents. The NMR signals of all the components contained in a mixture of 2,3‐diphenyl‐5‐carboxymethylisoxazolidines were identified and the LISCA computer program enabled the stereochemistry of the different isomers to be established.
The study of longifolene by two‐dimensional NMR spectroscopy
Authors: Joseph‐Nathan P. , Santillan R. L. , Schmitt P. , Günther H. 
Published: May 2005

AbstractThe complete assignment of the 13C NMR spectrum of longifolene was achieved from double quantum coherence measurements, while combined evaluation of a 1H13C heteronuclear chemical shift correlation diagram and a homonuclear 1H J‐resolved diagram provided all proton chemical shifts. Conformational information on the seven‐membered ring of the tricyclic sesquiterpene was obtained from proton chemical shift considerations.
Selenium‐77 NMR chemical shifts of five‐membered selenium and sulphur heterocycles with CSe, CS, and CO groups
Authors: Poleschner Helmut , Radeglia Reiner , Meyer Hinrich 
Published: May 2005

AbstractThis paper reports the 77Se NMR chemical shifts of 1,3‐dithiole‐, 1,3‐thiaselenole‐ and 1,3‐diselenole‐2‐ones, ‐thiones and ‐selones, of the corresponding saturated compounds 1,3‐diselenolane‐2‐one, ‐thione and ‐selone, and the 1,3‐thiaselenolium tetrafluoroborates, either unsubstituted or substituted by morpholino, ethylthio or ethylseleno groups in the 2‐position. The 77Se chemical shift values of the ring selenium and the CSe groups are compared with the 13C chemical shift values of neighbouring carbon atoms. The relationships between the 77Se chemical shifts of the CSe groups and the wavelengths of their n→* absorption in the UV‐visible spectrum are discussed with respect to the significance of the δE term in the contribution of the paramagnetic screening and the electron density distribution.
13C NMR spectroscopic evidence for the existence of the monocation of pyropheophytin a
Authors: Lötjönen Simo , Hynninen Paavo H. 
Published: May 2005

AbstractPyropheophytin a, which is an unsymmetric porphyrin, has been titrated with trifluoroacetic acid (TFA) in tetrahydrofuran, the protonation reaction being followed by 13C NMR spectroscopy. TFA was added in small increments to a 0.28 M solution of pyropheophytin a in tetrahydrofuran, and the chemical shift changes of the macrocyclic carbons were determined as a function of the TFA increments. On the addition of TFA the signals of the α‐carbons of ring II experienced a large upfield change, whereas the signals of all other macrocyclic carbons moved only slightly downfield or remained constant. These observations were interpreted as indicating the formation of a monocation in which the proton is attached to the nitrogen of ring II. The 13C protonation shifts of pyropheophytin a were compared with those previously reported for symmetric porphyrins. On the basis of this comparison, the basicity of the macrocyclic nitrogen atoms, the N–H tautomerism and the electron delocalization in structurally different porphyrin macrocycles are discussed.
Conformation changes induced in 2‐spiro‐substituted cephalosporin sulphoxides by the configuration of the spiro bond: A combined 1H and 13C NMR study
Authors: Erdödiné‐Kövér Katalin , Jászberényi J. Cs. 
Published: May 2005

Abstract1,3‐Dipolar cycloadditions of diazomethane and diphenyldiazomethane to exo‐2‐methylenecephalosporins are described. A structural study of the products shows that the initially formed 2‐spiropyrazolinocephems form cyclopropanes by the spontaneous loss of nitrogen. ASIS and NOE measurements reveal that the products with different C‐2 configurations are in two different conformations.
13C NMR chemical shifts of N‐unsubstituted‐ and N‐methyl‐pyrazole derivatives
Authors: Cabildo Pilar , Claramunt Rosa Maria , Elguero Jose 
Published: May 2005

Abstract13C shielding data for 100 derivatives of pyrazole are reported. These include methyl, ethyl, n‐propyl, tert‐butyl, phenyl, hydroxymethyl, carboxyl, ethoxycarbonyl, cyano, amino, hydrazino, nitro, azido, chloro, bromo and iodo groups as substituents on the ring carbon atoms.
The solvent effect on the isotropic hyperfine interaction in some aliphatic polyamine copper(II) complexes
Authors: Pisipati V. G. K. M. , Rao N. V. S. , Muralikrishna V. , Murthy V. S. , Kesavan T. 
Published: May 2005

AbstractESR and optical absorption studies are described for a number of copper(II) chelates with aliphatic polyamines, exhibiting both square pyramidal and square bipyramidal coordination around the copper ion. The complexes studied were bis(N,N′‐dimethylethylenediamine)copper(II) sulphate tetrahydrate, bis(N,N′‐diethylethylenediamine)copper(II) nitrate, diaquosulphato(N,N,N′,N′‐tetramethylethylenediamine)copper(II) hydrate, dinitrato(N,N,N′,N′‐tetramethylethylenediamine)copper(II), dichloro(N,N,N′,N′‐tetramethylethylenediamine)copper(II) and dithiocyanato(N,N,N′,N′‐tetramethylethylenediamine)copper(II). The ESR measurements were carried out in methanol, dimethyl sulphoxide, dimethylformamide and pyridine, at room and liquid nitrogen temperatures. The molecular orbital coefficients were estimated assuming an axial symmetry. The parameter χ proportional to the hyperfine constants shows a variation with the solvent for all these complexes. The χ values in solution are lower than the corresponding average χ values reported in the solid state for each complex. The solvent effect and the influence of 4s character in the ground state are discussed. The χ values, either calculated or reported, for a number of copper complexes for [4O], [3O, N], [2O, 2N], [O, 3N] and [4N] environments around copper(II) are presented.