bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of 13C NMR spectra of 13C‐enriched cycloartenol biosynthesized from [1‐13C]‐, [2‐13C]‐and [1,2‐13C2]‐acetate. Revised 13C NMR spectral assignments of cycloartenol and cycloartanol and 13C NMR spectral support for the generally accepted skeleton formation mechanism of cycloartenol
Authors: Kamisak Wasuke , Honda Chie , Suwa Kiyoko , Isoi Koichiro 
Published: May 2005

AbstractPreviously proposed 13C NMR spectral assignments of cycloartenol (9,19‐cyclolanost‐24‐en‐3β‐ol) (1) and cycloartanol (9,19‐cyclolanostan‐3β‐3‐ol) (2) were re‐examined by means of 13C‐enrichment experiments and LIS measurement of 13C chemical shifts. Revised signal assignments are proposed for C‐7, C‐11, C‐16, C‐18, C‐21 and C‐28 of 1 and C‐7, C‐11, C‐12, C‐15 and C‐16 of 2. Experimental proof for the skeleton formation mechanism of 1 based on 13C NMR spectral findings is presented.
13C NMR study of the structures of open‐chain bis‐reissert analogues and their salts
Authors: Iyer Radhakrishnan P. , Ratnam Rakesh K. , Kulkarni Subodh P. , Zubair M. A. , Coutinho Evans C. , Sonaseth Mariam S. , Gopalan Balasubramanian 
Published: May 2005

AbstractThe structures of open‐chain bis‐Reissert analogues and their salts were investigated using 13C NMR spectroscopy. Evidence is presented to show that the former exists in the acyclic form in solution. Detailed structural studies and the 13C NMR data clearly show that, in solution, the open‐chain bis‐Reissert salt analogues exist predominantly as the amino tautomer.
Carbon‐13 spectra of some heterocyclic analogues of biphenylene
Authors: MacBride J. A. Hugh , Leow Mei Ling , Wright (the late) Peter M. , Kilcoyne John P. , Wakefield Basil J. 
Published: May 2005

AbstractThe 13C chemical shifts for 2,7‐, 1,8‐ and 1,6‐diazabiphenylenes are reported, together with some coupling constants and the 13C chemical shifts of a benzothiophene analogue of biphenylene. The results can be explained by the existence of a paramagnetic ring current in the four‐membered ring of the nitrogen‐containing compounds which is absent in the case of the benzothiophene. A possible explanation is offered.
Long‐range 13C1H spin—spin coupling constants in the conformational analysis of formyl derivatives of furan and thiophene
Authors: Benassi Rois , Folli Ugo , Mucci Adele , Schenetti Luisa , Taddei Ferdinando 
Published: May 2005

AbstractLong‐range coupling constants, nJ(C, H), involving the formyl proton or carbon and the carbons or protons of the heterocyclc ring, were measured in the two isomeric formyl‐furans and ‐thiophenes by employing coupled 13C NMR spectra. In furan‐2‐carboxaldehyde these coupling constants, obtained in solutions of different polarity, show conformational dependence and quantitatively reproduce the trend of conformer populations obtained from proton‐proton coupling constants. Even in thiophene‐2‐carboxaldehyde, 3J(C, H), where H is the formyl proton, shows that the very biased equilibrium is further shifted toward the S,O‐cis form in polar media. For the 3‐formyl derivatives the changes of nJ(C, H) in different solvents are small, at the limit of experimental error; even so, comparison with the values measured for 4‐iodofuran‐ and 4‐iodothiophene‐3‐carboxaldehyde, which show an equilibrium significantly dependent on solvent polarity, enables one to verify that in these derivatives the X,O‐trans form, prevailing in the equilibrium mixture, increases with increasing solvent polarity. From a least‐squares analysis of the experimental values, the conformer populations in the different solvents and the coupling constants of the separate conformers were estimated. The coupling constants obtained show the effectiveness of each nJ(C, H) in the conformational analysis of these compounds. Larger changes, as a function of conformer populations, are expected for 3J(C, H) relative to the formyl proton, and this proves to be the observable quantity which best demonstrates small changes in the conformational equilibrium. The thermodynamic aspects of the equilibrium for the 3‐formyl derivatives are discussed and, by employing classical reaction‐field theory, it is tentatively shown that the increase of the less polar X,O‐trans form in polar media should be due to the fact that quadrupolar contributions prevail over dipolar effects.
Aromatic ring currents in benzotriptycenes, studied by high‐resolution deuterium NMR at high fields
Authors: Bastiaan E. W. , Wegman M. A. M. , MacLean C. 
Published: May 2005

AbstractIn order to study the aromatic ring currents in triptycene and tribenzotriptycene, the magnetic susceptibility anisotropies of these molecules have been determined by the NMR analogue of the Cotton‐Mouton effect: Δ χ(triptycene) = 24.0 x 10‐34 m3 (1.91 x 10‐28 emu), Δ χ(tribenzotriptycene) = 44.5 x 10‐34 m3 (3.54 x 10‐28 emu). These values are well predicted from a model of independent fragment molecules, showing that the ring currents in the rings of triptycene and tribenzotriptycene are essentially the same as in planar aromatic molecules.
Rate of degenerate rearrangement of the 2‐methyl‐2‐norbornyl cation studied by 13C selective pulse transfer and two‐dimensional NOESY spectroscopy
Authors: Baine Peter , Domenick Robert L. , Servis Kenneth L. 
Published: May 2005

AbstractThe rate of the degenerate 6,1‐hydride shift and rearrangement of the 2‐methyl‐2‐norbornyl cation has been determined using selective pulse transfer experiments and 2D NOESY experiments over the temperature range 200–220 K. Least‐squares analysis of the data gives a free energy of activation of 11.3 kcal mol−1. The results are compatible with the presence of σ‐delocalization in the 2‐methyl‐2‐norbornyl cation.
2D NMR studies of the phenyldichloroarsine—british anti—lewisite adduct
Authors: Dill Kilian , Adams Earle R. , O'Connor Richard J. , McGown Evelyn L. 
Published: May 2005

AbstractOne‐ and two‐dimensional NMR spectroscopy was used to determine the structure of the phenyldichloroarsine‐British anti‐lewisite adduct. The major component had the hydroxymethyl group in the anti orientation with respect to the phenyl ring on the arsenous atom. This structure was based on the chemical shifts of the 1H and 13C resonances and on the respective homonuclear coupling constants.
Structure elucidation of a hexahydrocannabinol derivative via 13C13C homonuclear correlation and 1H13C heteronuclear correlation with proton detection
Authors: Zetta Lucia , De Marco Antonio , Anklin Clemens , Cornia Mara , Casiraghi Giovanni 
Published: May 2005

AbstractTwo‐dimensional carbon‐carbon correlated spectra (2D‐INADEQUATE) and proton‐carbon correlated spectra obtained with proton detection have been used to determine the absolute configuration and conformation of a hexahydrocannabinol derivative obtained with highly stereocontrolled synthesis. From the proton‐proton coupling constants the junction between rings B and C was found to be trans and the relative stereodisposition of C‐10a, C‐9 and C‐6a was deduced to be R.
13C NMR of diterpenes: Use of the C‐19 methyl group as a probe for locating a tetrasubstituted double bond
Authors: Taran Martine , Miguel Bernadette Arreguy‐San , Delmond Bernard , Petraud Michel , Barbe Bernard 
Published: May 2005

AbstractThe 13C NMR spectra of diterpenic derivatives having pimarane, isopimarane and the (13S) rosane skeleton have been recorded. This analysis has shown that the chemical shift of the 19‐CH3 group depends on the position of the tetrasubstituted double bond in these skeletons. The C‐19 methyl group can be used as a probe for distinguishing the isopimarane from the rosane skeleton.
Unequivocal assignment of the position of sulphonation in DL‐camphor by 1H and 13C NMR spectroscopy
Authors: Stanley P. D. , Cremlyn R. J. , Nangle J. , Swinbourne F. J. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of a sulphamoyl derivative of DL‐camphor have been examined. The unequivocal assignment of the position of substitution has been achieved by the attached proton test, 2D correlation spectroscopy and NOE difference spectroscopy.
13C NMR spectra of substituted pyridine N‐oxides. Substituent and hydrogen bonding effects
Authors: Brycki B. , Nowak‐Wydra B. , Szafran M. 
Published: May 2005

AbstractAromatic 13C chemical shifts of 4‐ and 3‐substituted pyridine N‐oxides in aprotic and protic solvents are reported and discussed. Changes in chemical shifts caused by hydrogen bonding and protonation are much smaller than those induced by a substituent, and are not related to the pKa values of N‐oxides. Since the effect of hydrogen bonding is not in the same direction as that due to the substituent effect, the estimation of proton transfer from measured chemical shifts is not possible in complexes of pyridine N‐oxides with trifluoroacetic acid. A linear correlation is obtained between the ipso carbon substituent chemical shifts of 4‐ and 3‐substituted pyridine N‐oxides and mono‐substituted benzenes, which supports the suggestion that electronic factors other than Δq are more important for the ipso carbon.
Distinction of 15N resonances based on differences in small 15N, 1H coupling constants. An application of 1H‐decoupled INEPT experiments
Authors: Glemarec C. , Remaud G. , Chattopadhyaya J. 
Published: May 2005

AbstractA modified 1H‐decoupled INEPT pulse sequence has been used for assigning 15N resonances, based on differences in small 15N, 1H coupling constants (1–12 Hz). Both enhancement and distinction of the 15N lines are achieved. The usefulness of this method is demonstrated for wyosine triacetate and caffeine.
NMR spectra of the porphyrins. 34—Determination of the conformational equilibria of monosubstituted piperidines at room temperature using cobalt(III) porphyrin shift reagents
Authors: Abraham Raymond J. , Medforth Craig J. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of piperidine and eight monosubstituted piperidines and their spectra with cobalt(III) mesotetraphenylporphyrin chloride (CoTPPCl) and cobalt(III) octaethylporphyrin chloride (CoOEPCl) were assigned using a range of NMR techniques. When complexed to the porphyrin shift reagent the axial and equatorial conformers were in slow exchange at room temperature, allowing the determination of conformational equilibria and substituent chemical shifts (SCS).Conformational free energy differences (−ΔG°, kcal mol−1) obtained for 4‐substituted piperidines using CoOEPCl at 298 K were 0.5 (X = Br), 0.7 (X = OH), 0.8 (X = carbethoxy), 1.8 (X = Me) and > 1.6 (X = Ph). These were in good agreement with literature values. For CoTPPCl the corresponding values were −0.2 (axial conformation favoured), 0.3, 0.7, 1.4 and > 1.6, indicating that an axial orientation of the 4‐substituent was more favoured than with CoOEPCl. This difference was rationalized in terms of steric and electrostatic interactions between the piperidine substituent and the phenyl rings of CoTPPCl. In both cases proton and 13C SCS values were in good agreement with those in the literature.With 1‐, 2‐ and 3‐methylpiperidines unusual results were obtained for both porphyrins. For 3‐methylpiperidine −ΔG° was only 0.8 kcal mol−1 compared with a literature value of 1.6 kcal mol−1, whilst for 1‐ and 2‐ methylpiperidine reduction of the shift reagent to cobalt(II) occurred. With 1‐methylpiperidine the reduction was complete and no complexation was observed, but only some of the shift reagent was reduced by 2‐methylpiperidine and the remaining shift reagent complexed to the amine.
Structure and conformation of α‐bromobutyrolactones in the solid state and solution
Authors: Gharbi‐Benarous Josyane , Dana Gilbert , Philoche‐Levisalles Michele , Bois Claudette 
Published: May 2005

AbstractX‐ray diffraction of a single crystal of 4β‐phenyl(or mesityl)‐3β‐methyl‐2α(or 2β)‐bromobutyrolactone confirmed the envelope conformation of the butyrolactone unit. In both cases the aryl group is equatorial and the methyl group is axial; the 2α‐bromine is axial and the 2β‐bromine is equatorial. The coupling constants observed by 1H NMR for a series of α‐bromobutyrolactones show two types: with a mesityl group at C‐4 there is always a pure conformation with an equatorial mesityl group; with a phenyl group at C‐4 the two reverse envelope forms are possible, the favoured effects being equatorial Ar > axial Br > equatorial Me. In the generalized Karplus equation a strong influence of the relative orientation of the bromine and the carbonyl on the corresponding electronegativity parameters was observed. These parameters were evaluated by means of the electronegativity group concept and weighted by a stereochemistry‐dependent coefficient (cis or trans).
ESR and ENDOR investigations of phenanthrenesemiquinones
Authors: Stegmann Hartmut B. , Dao‐Ba Hoang , Mäurer Manfred , Scheffler Klaus , Buchner Hans , Hartmann Erwin , Mannschreck Albrecht 
Published: May 2005

AbstractA series of phenanthrenesemiquinone–diphenylthallium complexes were prepared in solution from the corresponding quinones. ESR, ENDOR and TRIPLE spectra provided the proton coupling constants and the unambiguous assignment to distinct molecular positions. The thallium splitting becomes considerably less negative if the semiquinones are twisted by steric hindrance in the 4‐ and 5‐positions. On the other hand, substitution in the 1‐ and 8‐positions renders aTI more negative. These results are interpreted in terms of steric hindrance of the ion‐pair solvation.
Unambiguous assignment of the 13C NMR spectra of methylindoles
Authors: Morales‐Ríos M. S. , Del Río R. E. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe 13C NMR spectra of all possible indoles substituted with one, two or three methyl groups on the pyrrole ring were assigned from heteronuclear two‐dimensional 13C/1H contour plots and homonuclear hydrogen‐hydrogen decoupling experiments at a specific concentration of 0.83 M in CDCl3 and in DMSO‐d6. The results confirm controversial assignments for some compounds, and provide the assignments for those compounds not previously studied by this technique. In addition, deuterium/hydrogen NMR isotope effect on 13C chemical shifts (DHIECS) for indoles, wherein the labile NH was partially exchanged to ND, are reported. In this way DHIECS values over two, three, four and five bonds were measured. The results in each solvent are discussed in terms of the number of bonds between the exchanged hydrogen and the observed carbon, and also according to their geometric dependence. This provides some evidence of the vibrational origin of the DHIECS.
13C NMR assignment of dammarane triterpenes and dendropanoxide: Application of 2D long‐range 13C1H correlation spectra
Authors: Tori Motoo , Matsuda Reiko , Sono Masakazu , Asakawa Yoshinori 
Published: May 2005

AbstractThe 13C NMR chemical shifts of some dammarane‐type triterpenes, produced by oxidation of dammaran‐20(S)‐ol and 20(S)‐hydroxydammaran‐3β‐yl acetate with m‐chloroperbenzoic acid, were assigned by complete analysis of these compounds using 2D long‐range 13C1H correlation spectra and 2D INADEQUATE; it was found necessary to revise previous assignments. The 13C NMR signals of dendropanoxide were also analysed by 2D techniques including HHC relayed 13C1H correlation spectra.
13C NMR and 1H NMR chemical shifts of bis(1,1‐dimethylethyl) disulfide and bis(1,1‐dimethylethyl) trisulfide and their oxide derivatives
Authors: Freeman Fillmore , Lee Choonsun 
Published: May 2005

AbstractThe 13C NMR and 1H NMR spectra of bis(1,1‐dimethylethyl) disulfide and bis(1,1‐dimethylethyl) trisulfide and their oxygenated derivatives, including sulfinothioic acid S‐esters and sulfonothioic acid S‐esters, have been studied. Deshielding βSO and β effects and shielding γSO and γ effects are observed. The NMR spectra of tert‐butyl polysulfides and the influences of sulfur atoms are also compared and discussed.
Application of two‐dimensional NMR spectroscopy in the determination of solution conformation of nucleic acids
Authors: Hosur R. V. , Govil Girjesh , Miles H. Todd 
Published: May 2005

AbstractTwo‐dimensional NMR has developed into an important tool for the study of solution structures of nucleic acids. The conformational information is generally derived from the three bond coupling constants (J) and interproton distances (r). Strategies have been developed to obtain J values using COSY and J‐resolved spectroscopy. Estimation of interproton distances involves measurement of NOESY build‐up curves as a function of mixing time. This information can be coupled with structural refinement techniques to obtain the three‐dimensional structure of nucleic acids. Here we have described the current status of this important field with particular reference to advancements in applications to DNA structures.
Application of 1H NMR bi‐selective relaxation times to conformational analysis in solution
Authors: Sugiura Makiko , Takao Narao , Fujiwara Hideaki 
Published: May 2005

AbstractThe usefulness of 1H bi‐selective relaxation times (T) and selective relaxation times (T) for structure and conformation determination is emphasized. A pulse sequence has been devised which provides the apparent observed T. The cross‐relaxations (σij) or Fij values are derived from the observed T and T values. The σij values can be correlated with the HH distances (rij) and can be used for conformational analysis or structure determination. The Fij values, which indicate the fractional contribution to the dipolar relaxation of proton i via the interaction with proton j(i ≠ j), can be compared with the NOE values. 2‐Vinylpyridine was chosen as a model compound and three types of T1 values were measured for its protons. Its conformation in CDCl3 solution is discussed based on the correlation between the σij obtained and the rij values. A conformational equilibrium is suggested.
Utility of 1H/2H isotope shifts for the 13C NMR assignments of indole derivatives
Authors: Morales‐Ríos M. S. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe deuterium/hydrogen NMR isotope effects on the 13C chemical shift (DHIECS) of the cycloalkano[b]indoles 1,2,3,4‐tetrahydro‐9H‐carbazole, 3‐tert‐butyl‐1,2,3,4‐tetrahydro‐9H‐carbazole and 1,2,3,4‐tetrahydrocyclopent‐[b]indole, wherein the labile NH was partially exchanged to ND, were measured at a concentration of 0.83 M in CDCI3 and in DMSO‐d6 solutions. The DHIECS values show defined trends that allow definitive 13C NMR assignments. The isotope effects over three and four bonds for the sp3 hybridized carbons are linearly interdependent, even when one of these isotope effects becomes negative.
High‐resolution 1H and 13C NMR spectroscopy of some hydrazo compounds
Authors: Al‐Rawi J. M. A. , Khayat M. A. R. 
Published: May 2005

Abstracto‐Benzenediazonium carboxylates couple with methylene‐active compounds to yield hydrazo derivatives with high purity. The 1H and 13C NMR data of eleven such products are presented and analysed. The predominance of the hydrazo over the azo form is consistent with accepted criteria. Furthermore, evidence for the preference of the carbethoxy group over the acetyl group for intramolecular hydrogen bonding is suggested.
Proton nuclear magnetic resonance studies of dibenzo‐p‐dioxins: Substituent effects
Authors: Ashley David L. , Reddy V. Vikram , Patterson Donald G. 
Published: May 2005

AbstractHigh‐resolution proton nuclear magnetic resonance through heptachlorinated dibenzo‐p‐dioxins are presented. Chemical shifts from dioxins that were synthesized separately are used to assign congeners formed in mixtures. Linear multiple regression analysis was applied to the chemical shift results and the model yielded excellent shift predictability once substituent interactions had been included in the analysis. The average deviation from experimental values was 0.004 ppm. The intra‐ring substituent effects can be explained by a combination of through‐space and ring current effects. Inter‐ring substituent effects showed a dependence on distance, but the reason for this trend is not clear. These measurements demonstrate a reproducible chemical shift effect over nine bonds.
Phosphorus–nitrogen compounds. Part 59. Aromatic carbon‐13 NMR spectra of phenyl‐substituted cyclotriphosphazatrienes. Second‐order effects with phosphorus‐31 nuclei
Authors: Deutsch W. Francis , Parkes Harold G. , Shaw Robert A. 
Published: May 2005

AbstractThe 13C NMR spectra were obtained for the geminal series N3P3Cl6−nPhn (n = 2, 4, 6) and for the mono spiro series N3P3Ph2[X(CH2)n Y]Cl2 (X = Y = O, n = 2, 3, 4; X = Y = NH, n = 2, 3, 4; X = Y = NMe, n = 2, 3; X = O, Y = NH, n = 3, 4; X = NH, Y = NMe, n = 2, 3; X = O, Y = NMe, n = 2). Multiplet structures were observed in the 13C NMR spectra of N3P3Ph2[HN(CH2)3NH]Cl2 at 0°C. The complexity of these resonances could be altered by a change in temperature. These observations have been rationalized in terms of second‐order interactions with remote phosphorus nuclei, which can be systematically altered with temperature. Inductive and resonance substituent coefficients have been calculated using the dual substituent parameter method from the relative shelding of the meta (C‐3) and para (C‐4) nuclei in the phenyl ring.
NMR study of backbone rearrangements in gibberellins
Authors: Avent Anthony G. , Hanson James R. , d'Oliveira Bras H. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of the rearrangement product of gibberellic acid obtained in concentrated sulphuric acid confirm the structure which had previously been assigned by chemical degradation. The triene produced from methyl gibberellate by the action of methanolic hydrogen chloride is shown to possess the 5α, 6β‐H stereochemistry. The incorporation of deuterium into the latter is described.
Epoxidation‐induced shifts in the carbon‐13 NMR spectra of steroids: Lanostane derivatives
Authors: Martynow Jacek , Paryzek Zdzisław 
Published: May 2005

AbstractThe 13C chemical shifts of triterpenoidal olefins and epoxides related to lanosterol are described and discussed. The epoxide function located in the central part of the tetracyclic steroidal skeleton allows the evaluation of epoxidation‐induced shifts (EIS) for several carbons. The most characteristic and valuable for stereochemical assignments are the EIS values for γ‐carbons C‐1, C‐5, C‐12, C‐19 and C‐28 in 8α,9α‐epoxides, and C‐1 and C‐19 in 9α,11α‐epoxides. The C‐α effect (EIS −55 to −79 ppm) is found to be susceptible to minor conformational distortions of the molecular framework. Characteristic signals are discussed in terms of their predictive value for each group of analysed compounds.
2H NMR study of the behaviour of water in a reversed micellar system. Hydrogen bond breaking and clathrate formation by an inhalation anaesthetic
Authors: Yoshino Akihiro , Yoshida Tadayoshi , Takahashi Kensuke 
Published: May 2005

AbstractThe behaviour of water in the reversed micelles of the glycerol α‐monooleate (GMO)–decane‐2H2O system was investigated by deuteron nuclear magnetic resonance. The chemical shifts (δ) and the spin–lattice relaxation times (T1) of heavy water were found to be dependent on temperature. The temperature dependence of the T1 and δ values reveals that the structural change in heavy water induced by the inhalation anaesthetic enflurane is very different below and above ca. 300 K. Below ca. 300 K a cage of a water polyhedron builds up around an enflurane molecule. Above ca. 300 K there is no water polyhedron cage because of the cleavage of the hydrogen bonds in the polyhedron water, and some of the water molecules are tightly adsorbed on the enflurane molecules.