bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preferred conformations of pilocarpine, pilocarpine.HCl and isopilocarpine.HCl in solution, deduced from 200 MHz 1H NMR spectra
Authors: Maat L. , Peters J. A. , Aboul‐Enein Hassan Y. 
Published: May 2005

AbstractThe 200 MHz 1H NMR spectra of pilocarpine, pilocarpine.HCl and isopilocarpine.HCl have been studied. Evidence is presented for the preferred conformations of the compounds in aqueous solution, with the methylimidazolyl moiety antiperiplanar with respect to the α‐carbon of the butanolide ring.
Complexation of hydroxylated ent‐kaurane diterpenoids with boric acid as an aid to the assignment of the 13C NMR spectra
Authors: Fernández‐Gadea Francisco , Jimeno María L. , Rodríguez Benjamín 
Published: May 2005

AbstractThe 13C NMR spectra of some hydroxylated ent‐kaurane diterpenoids were measured in CDCl3‐Py‐d5 (1:1) solution and also after addition of boric acid. Complexation of ent‐3β,18‐, ent‐7α,15β‐, ent‐7α,15α‐, ent‐15β,16β‐ and ent‐16β,17‐dihydroxy derivatives with boric acid produced considerable chemical shift changes and marked broadening of the signals of the hydroxy‐bearing and neighbouring carbon atoms. This behaviour provides a useful and reliable method for assigning the 13C NMR spectra of these compounds.
Electron spin resonance study of some polycyclic nitrogen heterocyclic radical anions
Authors: Sevenster Arjen J. L. , Tabner Brian J. 
Published: May 2005

AbstractIn dimethylformamide the ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine both exhibit line broadening due to slow molecular tumbling over a wide temperature range. Similar effects are also observed in the spectra of the radical anions of quinoxaline and phenazine. The ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine have been interpreted by computer reconstruction and the hyperfine splitting constants assigned with the aid of Hückel unpaired electron density calculations.
Configurations and conformations of cis‐ and trans‐N‐methyl‐ and ‐N‐benzyl‐4,5‐ and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines
Authors: Sohár P. , Fülöp F. , Bernáth G. 
Published: May 2005

AbstractThe configurations and conformations of cis‐ and trans‐N‐methyl‐ and ‐N‐benzyl‐4,5‐ and ‐5,6‐tetramethylenetetrahydro‐1,3‐oxazines were determined by 1H and 13C NMR spectroscopy. The cis isomers are conformationally homogeneous, having the hetero atom attached to the cyclohexyl ring, in the axial and equatorial positions, respectively, in the 5,6‐ and 4,5‐tetramethylene compounds, similar to the case of the 2‐p‐nitrophenyl‐substituted analogues investigated previously.
Assignment of proton NMR spectra and conformational analysis by two‐dimensional heteronuclear relayed correlation NMR spectroscopy
Authors: Turner Christopher J. 
Published: May 2005

AbstractThe method of two‐dimensional heteronuclear relayed correlation spectroscopy was used to establish the assignment of the severely overcrowded part of the proton spectrum of menthol by relating it to the previously assigned carbon spectrum. Extrapolation of the signal‐to‐noise ratio obtained with overnight data accumulation on a 10 mM solution suggests that this experiment should be feasible on as little as 10 mg of a moderate‐sized organic compound.
1H and 13C NMR studies on N‐(cyclohex‐2‐en‐1‐ylidene)amines
Authors: Kilger Ralf , Margaretha Paul 
Published: May 2005

Abstract1H and 13C NMR spectroscopy allow the identification of diastereomeric Z‐ and E‐N‐(cyclohex‐2‐en‐l‐ylidene)amines and the assignment of their configuration.
Solvent dependence of the molecular structure of hydrogen cyanide determined by NMR of partially oriented molecules
Authors: Dombi G. , Diehl P. , Lounila J. , Wasser R. 
Published: May 2005

AbstractThe chemical shifts and the direct and indirect spin–spin coupling constants of HCN have been measured in various liquid crystal solvents. The sign of the indirect coupling constant J(15NH) is found to be negative. The 13C shift anisotropy is 334±20 ppm. The molecular structure apparently varies considerably with the solvent used. These solvent effects, which can be attributed to a correlation between vibration and rotation of the molecule, are corrected.
A carbon‐13 nuclear magnetic resonance study of the 1,4‐diene analogues of steroid hormones and related steroids
Authors: Gonzalez Mario D. , Burton Gerardo 
Published: May 2005

AbstractThe 13C NMR spectra of sixteen 4‐ene‐3‐keto‐ and 1,4‐diene‐3‐keto corticosteroids are described. Substituent shifts and the effect of added methanol‐d4 are reported, and conformational distortions and intramolecular hydrogen bonding are analysed based on these data.
Large lanthanide‐induced chemical shifts in cobalt complexes of enethials (α,β‐unsaturated thioaldehydes)
Authors: Dittmer Donald C. , Parker Edward Joseph , Bodwell James R. 
Published: May 2005

AbstractEu(fod)3‐, Yb(fod)3‐ and Pr(fod)3‐induced chemical shifts of the ‘thioaldehydic’ protons in enethial ligands complexed to a cobalt cyclopentadienyl group are unusually large and in the same direction (10–30 ppm downfield per mole of shift reagent per mole of substrate). The shifts of the protons induced by Eu(fod)3 and Pr(fod)3 in the enethial ligands show an alternation in sign on proceeding away from the sulfur atom. In contrast to the results with the fod reagents, the ytterbium and lanthanum shift reagents Yb(thd)3 and La(thd)3 caused only small shifts of protons in the 2‐phenylpropenethial ligand. No induced shifts with the Eu or Pr reagents were observed for a cyclopentadienyl cobalt complex of dithioglyoxal. The induced shifts in these enethial complexes may be caused by varying blends of complex formation, contact and pseudocontact shifts. Caution is advised in assigning origins to lanthanide induced shifts in such organometallic systems.
The conformational energy difference for δ‐valerolactone
Authors: Lambert Joseph B. , TeVrucht Mollie L. E. 
Published: May 2005

AbstractThe temperatuure dependence of the vicinal OCH2CH2 coupling constant in the six‐membered ring δ‐valerolactone suggests the presence of at least two conformers of unequal energy. Analysis of this temperature dependence by the Wood‐Fickett‐Kirkwood method in six solvents produces free energy differences in the narrow range 0.8–1.4 kcal mol−1, with a mean of 1.0 kcal mol−1 and no apparent dependence on solvent polarity. Thus the two conformers, probably the half‐chair and the classic boat, have similar polarities. The analogous four‐ and five‐membered lactones show little or no temperature dependence for their analogous coupling constants, in agreement with the presence of a single conformation for these rings.
1H and 13C NMR study of phosphopeptides: 2—Ac–PSer–Gly, Ala–PSer–Gly and Gly–PSer–Phe
Authors: Pogliani L. , Ziessow D. 
Published: May 2005

Abstract1H and 13C NMR spectra of AC–PSer–Gly, Ala–PSer–Gly and Gly–PSer–Phe have been measured and analysed as a function of pD. The NMR parameters of the PSeryl side chain are a function of the sequence. The second titration step of the phosphate group (pK2 = 5.7) is much more difficult to detect in Ac–PSer–Gly and Ala–PSer–Gly than in Gly–PSer–Phe. The conformation in which H‐αC‐αC‐βOP forms a planar W‐type arrangement predominates only for Ala–PSer–Gly. In the other two phosphopeptides the gauche conformations contribute increasingly, in particular for Gly–PSer–Phe.
Proximity effect in the 13C NMR spectra of alkylpyridines: An aid in structure elucidation
Authors: Holík Miroslav , Turečková Milena , Vymětal Jan 
Published: May 2005

AbstractThe structures of seven polysubstituted alkylpyridines, recently isolated from coal tar, were elucidated using their 13C NMR spectra. For tri‐ and tetra‐substituted derivatives the correct isomeric structure was found from their conformity with the proximity effect, i.e. the deviations from additivity when calculating chemical shifts from substituent increments (SCS) for sterically crowded molecules. This effect manifests itself both on the ring and on the alkyl carbon signals, and in most cases shifts their position upfield.
Reversal of order of chemical shifts. Differential solvent effects in the hydrogen shifts of toluene, m‐xylene and o‐xylene as determined by 320 MHz tritium NMR spectroscopy
Authors: Long Mervyn A. , Saunders John K. , Williams Philip G. , Odell Allan L. , Martin R. Wayne 
Published: May 2005

AbstractChemical shifts for the aromatic tritons of toluene decrease in the order meta>para>ortho for pure toluene, but in the order meta>ortho>para for dilute solutions of toluene in carbon tetrachloride, chloroform, cyclohexane and dimethyl sulphoxide; m‐xylene shifts are 5>4,6>2 in the pure state and 5>2>4,6 in carbon tetrachloride and dimethyl sulphoxide; o‐xylene shifts are 4,5>3,6 in the pure state and reversed in carbon tetrachloride.
A natural abundance 15N NMR investigation of bilirubin IX‐α
Authors: Hansen Poul E. , Jakobsen Hans J. 
Published: May 2005

AbstractNatural abundance 15N NMR spectra have been obtained for bilirubin IX‐α using polarization transfer via the INEPT and SINEPT‐2 techniques. The resonances for all four nitrogens are clearly resolved. 15N chemical shifts and 15N1H coupling constants over one and three bonds are reported. Heteronuclear chemical shift correlation between 15N and 1H for the four NH groups has been established by means of the SINEPT‐2 pulse sequence.
The use of two nematic solvents in the determination of molecular structure of systems providing deceptively simple spectra
Authors: Khetrapal C. L. , Kunwar A. C. , Arumugam S. 
Published: May 2005

AbstractThe use of two liquid crystals as solvents in the determination of molecular structure has been demonstrated for systems which do not provide structural information from studies in a single solvent owing to the fact that the spectra are deceptively simple, with the result that all the spectral parameters cannot be derived with reasonable precision. The specific system studied was 2‐(p‐bromophenyl)‐4,6‐dichloropyrimidine, for which relative inter‐proton discances have been determined from the proton NMR spectra in two nematic solvents.
Configurational analysis of diastereomeric open‐chain and cyclic nitro‐substituted diols by NMR spectroscopy
Authors: Sohár P. , Mikite Gy. , Pelczer I. , Kovács Á. , Kis‐Tamás A. 
Published: May 2005

AbstractNitro‐substituted 1,3‐dioxanes and pyrans with potential biological activity were synthesized. The relative configurations of the threo and erythro isomers of 2‐nitro‐1‐phenylpropane‐1,3‐diol (the starting materials) and of 5‐nitro‐2,4‐diphenyl‐1,3‐dioxane, the products formed with benzaldehyde, were determined by 1H and 13C NMR spectroscopy. Cinnamaldehyde and nitroethanol give a homologue of nitrophenylpropanediol, which exists as a mixture of two diastereomeric cyclic hemiacetals. After dissolving in CDCl3, the ratio of these components changes from approximately 10:1 to 3:2 in a few days. The ethyl acetal of the hemiacetal is stereohomogeneous, and the ethoxy group is axial to the pyran ring owing to the anomeric effect. This configuration was proved by two‐dimensional NMR measurement, permitting separate observation of the originally overlapping multiplets and direct reading of the H,H coupling constants.
13C NMR studies on trifluoroacetyl derivatives of 2‐acetamido‐2‐deoxyhexoses
Authors: Ranganathan M. , Balaram P. 
Published: May 2005

AbstractThe effect of trifluoroacetylation on the 13C chemical shifts of 2‐acetamido‐2‐deoxyhexoses was examined. Studies of the 2‐acetamido derivatives of glucose, galactose and mannose established that no regular trend in the 13C shifts occurred on trifluoroacetylation. This was in marked contrast to the results obtained for the 1H chemical shifts.
Substituent dependence of stable conformations in triazolobenzothiazines
Authors: Sohár P. , Fodor L. , Szabó J. , Bernáth G. 
Published: May 2005

AbstractFrom the 1H and 13C NMR spectra of angularly condensed triazolobenzothiazine derivatives it was established that these compounds can be classified into two conformation types, depending on the substituents. The 10‐methyl‐3‐carbethoxy derivatives are cis‐anellated, conformationally flexible systems, where one of the aromatic hydrogens (H‐9) and one of the methoxy substituents (8‐OMe) of the benzothiazine skeleton on the one hand, and the 1‐aryl ring on the other, lie close to each other in the preferred conformer. By assuming this conformation, the molecules avoid the steric hindrance of the 10‐Me and 1‐aryl groups. All compounds unsubstituted on the angular C‐10 atom, and the 3‐aryl‐substituted derivatives of the 10‐Me analogues, occur in a different conformation, containing the 1‐aryl ring well removed from H‐9 and the 8‐OMe group.
Nitrogen‐15 nuclear magnetic resonance spectroscopy as a probe for the study of membrane models
Authors: Tellier Charles , Malnoe Patricia , Poignant Serge 
Published: May 2005

Abstract15N NMR spectroscopy has been used to investigate liposomes from an enriched phospholipid (dipalmitoyl‐phosphatidylcholine). It is shown that this probe can yield interesting information on the dynamics of head groups and on some interactions at the lipid–water interface. Even large multilamellar vesicles give rise to narrow, symmetrical signals, with a maximum nuclear Overhauser effect over the phase transition temperature. The sensitivity of the technique as regards structural changes was demonstrated by a complete study made between 20 and 60°C.
17O NMR studies on polycyclic quinones, hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators
Authors: Chandrasekaran Subramanian , Wilson W. David , Boykin David W. 
Published: May 2005

AbstractThe 17O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex‐2‐enone (1), α‐tetralone (2), anthrone (3), 4H‐pyran‐4‐one (4), 1‐benzopyran‐4(4H)‐one (5), xanth‐9‐enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5‐dihydroxybenzoquinone 5,8‐dihydroxynaphthoquinone and 1,4‐dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused‐ring effect on the carbonyl chemical shift. A single 17O resonance was observed for 2,5‐dihydroxybenzoquinone (358 ppm) and 5,8‐dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4‐dihydroxyanthraquinone gave two discrete 17O signals at 441 and 87 ppm, indicating that in this case proton exchange between oxygen atoms is slow.
Conformational studies of dicyclohexylthallium chloride, bis(4‐methylcyclohexyl)thallium chloride and bis(4‐tert‐butylcyclohexyl)thallium chloride by 1H NMR
Authors: Cheesman Bruce Victor , White Raymond Frederick Martin 
Published: May 2005

AbstractVicinal thallium–hydrogen coupling constants are used to discuss conformations in dicyclohexylthallium chloride, bis(4‐methylcyclohexyl)thallium chloride and bis(4‐tert‐butylcyclohexyl)thallium chloride. Thallium does not have a very strong preference for equatorial positions in dicyclohexylthallium chloride, whereas bis(4‐alkylcyclohexyl)thallium chlorides exist largely in one conformation. Bis(4‐methylcyclohexyl)thallium chloride exists in three isomeric forms; the major product appears to be the cis‐isomer (equatorial methyl, axial thallium), with the other two isomers probably containing thallium trans to the methyl group (axial thallium being preferred). The preference for the cis‐isomer (equatorial tert‐butyl, axial thallium) of bis(4‐tert‐butylcyclohexyl)thallium chloride is such that other isomers are not obtained.
Application of 1H and 13C NMR to the structural elucidation of tetrahydroquinoxalines condensed with five‐membered heterocycles
Authors: Charushin V. N. , Chernyshev A. I. , Sorokin N. N. , Chupakhin O. N. 
Published: May 2005

Abstract1H and 13C NMR spectral data for 21 N‐methyltetrahydroquinoxalines annelated with furan, pyrrole, imidazole or thiazole rings are reported. Unambiguous assignments of the ring junction 13C resonances were made on the basis of selective decoupling experiments and with the aid of one‐bond and long‐range 13C–1H coupling constants. The effects of five‐membered heterocycles on the 1H and 13C chemical shifts of the ring junction hydrogen and carbon atoms are considered. Values of one‐bond 1J(CH) and vicinal 3J(HH) coupling constants between the ring junction protons are also discussed as a diagnostic means for structural elucidation of tetrahydroquinoxalines condensed with five‐membered heterocycles.
Unusually large deuterium isotope effects on one‐bond 13C, 1H coupling constants in trans‐stilbene challenged
Authors: Ernst Ludger 
Published: May 2005

AbstractThe reported apparent large decrease in 1J(C‐α, H‐α) by 1.75±0.20 Hz on replacement of one of the olefinic protons by deuterium in trans‐stilbene is due to improper first‐order analysis of the 1H‐coupled 13C spectrum of the parent compound. Consequently, the implied conformational difference between trans‐stilbene and α‐deuterio‐trans‐stilbene, which was used to explain the result, is not substantiated.
13C NMR spectra of some N‐substituted 1,2‐dihydro‐3,1‐benzoxazin‐4‐ones
Authors: Aversa Maria C. , Ferlazzo Alida , Giannetto Placido 
Published: May 2005

AbstractThe natural abundance 13C NMR spectra of a series of hitherto unknown l‐atyl‐methyl‐1,2‐dihydro‐3,1‐benzoxazin‐4‐ones have been recorded. The assignments of the various resonances have been made from chemical shift arguments, by the analysis of the fine splittings caused by one‐bond and long‐range couplings and also by comparison with model compounds.
The effect of the internal reference on ASIS correlations: 1—Formyl protons of p‐X‐benzaldehydes
Authors: Bertrán J. Fernández , Rodríguez Mario 
Published: May 2005

AbstractThe correlation of the ASIS of the formyl protons of benzaldehyde and six of its p‐X‐derivatives in 12 aromatic solvents show marked deviations. Evidence is presented that these deviations are caused by variations in the shielding of the internal reference protons caused by aromatic solvents. Equations are developed which gauge the effect of TMS on the linear correlations of proton ASIS.
Studies of Erythrina alkaloids: VII—13C NMR spectral studies of some Erythina alkaloids
Authors: Chawla A. S. , Chunchatprasert S. , Jackson A. H. 
Published: May 2005

AbstractA variety of alkaloids have been isolated from the seeds of a range of Erythrina species, including dienoid, alkenoid and lactonic derivatives. The 13C NMR spectra of these compounds have been assigned by internal comparisons within this series of related compounds and also by the use of model compounds.
Application of the INEPT technique to 13C NMR assignments in polynuclear aromatic nitrogeneous heterocycles; 6H‐pyrido[4,3‐b]‐5,11‐dimethylcarbazole (ellipticine)
Authors: Mansour T. S. , Wong T. C. , Kaiser E. M. 
Published: May 2005

AbstractThe 13C NMR spectrum of 6H‐pyrido[4,3‐b]‐5,11‐dimethylcarbazole has been re‐examined to confirm the assignments using normal decoupled and coupled INEPT techniques. The results indicate that there were several errors in previous assignments. J(13C, 1H) for the seven methine carbons have also been obtained.
Carbon‐13 chemical shift assignment of some organophosphorus compounds: 1—Dialkyl and diaryl (alkylamido)phosphates with general formula Y2P(X)NHR
Authors: Al‐Rawi Jasim M. A. , Behnam George Q. , Ayed Naceur 
Published: May 2005

AbstractCarbon‐13 chemical shifts and the POC, POCC, PNC and PNCC coupling constants of 18 compounds containing the amine moiety, and with the general formula Y2P(X)NHR [Y=C2H5O, C6H5O, CH2O, Y2=1,2‐dioxybenzene; X = O or S; R = H, CH3, C2H5, PhCH2CH2, (CH3)2CH, C(CH3)3, C6H11, C6H5, C6H5NH] have been determined. The Y2P(X) group shows a sterically induced effect on the amine moiety; the 13C chemical shift of the Y group is, however, almost unaffected on replacing P(O) by a P(S) group.
Chemistry of heterocycles 6—13C NMR study of 7,8‐dihydro‐6H‐3‐methyl‐5,7‐diarylisoxazolo‐[4,5‐B]azepines
Authors: Rao C. Jankiram , Krishnamurthy A. , Shoolery James N. 
Published: May 2005

AbstractThe 13C NMR data of six 7,8‐hydro‐6H‐3‐methyl‐5,7‐diarylisoxazolo[4,5‐b]‐azepines have been studied. The studies have been confirmed by a new technique called the ‘attached proton test’.
Stereochemistry of diastereoisomeric propionyl esters of 4‐(2‐furyl)‐3‐methyl‐1‐phenethyl‐piperidin‐4‐ols and the analgesic ether derived from their acid‐catalysed ethanolysis
Authors: Casy A. F. , Dewar G. H. , Pascoe R. A. 
Published: May 2005

AbstractThe stereochemistry of diastereoisomeric propionyl esters of 4‐(2‐furyl)‐3‐methyl‐1‐phenethylpiperidin‐4‐ols has been established by 13C NMR analysis. Both isomers, after acid‐catalysed ethanolysis, are converted to the corresponding 4‐ethoxy derivative of configuration (t‐3‐Me, r‐4‐OEt) that correlates with its analgesic properties.
NMR studies on aromatic compounds: VI—13C NMR spectra of some mono‐ and disulphonato‐substituted hydroxynaphthoic acids in DMSO‐d6–water solution
Authors: ruotsalainen heikki , lajunen marja , h. j. lajunen lauri 
Published: May 2005

AbstractCarbon‐13 NMR spectra of sulphonatosubstituted hydroxynaphthoic acids were recorded with and without proton noise decoupling in DMSO‐d6–water (2:1 v/v). The 13C chemical shifts were assigned by using substituted naphthalenes as reference compounds. The additivity law of the substituent effects is discussed for the naphthalenesulphonic acids studied.
13C13C spin coupling constants in tetrahydronaphthylene, hexahydrobenzanthracene and benzo[a]pyrene derivatives
Authors: Cox Richard H. , Levy Louis A. 
Published: May 2005

AbstractThe 13C13C spin coupling constants have been determined in substituted [1‐13C]tetrahydronaphthylenes, [5‐13C]hexahydrobenzanthracenes and [5‐13C]benzanthracene. In addition, the 13C13C spin coupling constants for 7‐hydroxy[7‐13C]benzopyrene, trans‐7,8‐dihydro[7‐13C]benzopyrene‐7,8‐diol and trans‐7,8‐dihydro[10‐13C]benzopyrene‐7,8‐diol are reported, together with the one‐bond carbon‐carbon coupling constants between C‐4 and C‐5 in selected 4,5‐disubstituted benzopyrenes. Values for the directly bonded coupling constants and long‐range coupling constants are similar to those reported previously for other aromatic and aliphatic systems. Substituent effects on carbon‐carbon coupling are compared for similarly substituted cyclic and acyclic systems.
Enantiomeric excess determination of new classes of chiral sulphur compounds by the use of europium shift reagents
Authors: Annunziata R. , Cinquini M. , Cozzi F. 
Published: May 2005

AbstractThe enantiomeric composition of derivatives of new classes of optically active sulphur compounds (variously substituted sulphoxides, sulphoximes, sulphilimines) has been readily determined with the aid of chiral europium shift reagents.
NMR spin–lattice relaxation time measurements in organochalcogen compounds
Authors: Abel E. W. , Orrell K. G. , Platt A. W. G. 
Published: May 2005

Abstract1H and 77Se spin‐lattice relaxation times have been measured for the series of organochalcogen compounds MeE(CH2)nEMe (E=S, Se, n=0–3; E = O, n = 1, 2). The methyl and methylene proton T1 values decreased with increasing mass/size of the chalcogen and with increasing methylene chain length. The values are primarily due to intra‐ and inter‐molecular dipole‐dipole relaxation with proton‐proton cross‐relaxation effects playing a significant role. 77Se T1 values are dominated by spin rotation and chemical shielding anisotropy mechanisms, their relative importance depending on the size of the molecule and temperature of measurement.