bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substituent and ring size dependence of the coupling constant
Authors: Collins M. J. , Hatton P. M. , Sternhell S. , Tansey C. W. 
Published: May 2005

AbstractThe magnitude of the 4J proton‐proton coupling constant across the fragment CH3CCH (a probe of the bond order between the central sp2‐sp2 hybridized carbon atoms) has been found to be essentially independent of substitution on a toluene fragment and on the size of the ring containing the ortho‐allylic fragment. The coupling constant is sensitive to direct substitution on the ortho‐allylic fragment, especially where the substituent is placed α to the methyl group.
13C NMR spectra of some 2′‐nitromethane‐and N‐(methylsulphonyl)‐2′‐nitromethane‐sulphonanilides
Authors: Hasan Misbah Uul , Badar Yasmeen , Qureshi Ikram 
Published: May 2005

AbstractThe 13C chemical shifts in several 2′‐nitromethanesulphonanilides and N‐(methylsulphonyl) ‐ 2′ ‐ nitromethanesulphonanilides are reported. Analysis of the 13C shifts provides an insight into the electronic and steric interactions in these compounds. A comparison of the 2′‐nitromethanesulphonanilides with the corresponding anilines reveals that substitution of a methylsulphonyl group causes an upfield shift of 10–13 pprn for C‐1 while the ortho carbons, C‐2 and C‐6, are deshielded by 4‐6 and 1‐3 ppm, respectively. The unequal shielding of the two ortho carbons is noteworthy. Substitution of a second methylsulphonyl group on nitrogen causes similar changes in the chemical shifts but their magnitude is different. In several compounds the effect of para substituents is not equal at the two ortho or meta carbons.
Conformational correlation of purine nucleosides by high‐field carbon‐13 NMR data
Authors: Nair Vasu , Young David A. 
Published: May 2005

AbstractCorrelation of the nucleic acid base conformation in 43 purine nucleosides with high‐field 13C NMR data is described. A key to the correlation is the chemical shift difference between C‐2′ and C‐3′.
The complete, unambiguous assignment of the 13C NMR spectrum of erythromycin A*
Authors: Ager David J. , Sood Cynthia K. 
Published: May 2005

AbstractThe 13C NMR spectrum of erythromycin A (1) has been unambiguously assigned by use of the 2D INADEQUATE technique in conjunction with DEPT. Previously reported assignments were found to be in error. The effect of solvent, which semms to be negligible on the conformation, was also investigated.
1H, 13C, 15N, 17O and 77Se NMR of selenenamides
Authors: Paulmier Claude , Lerouge Patrice , Outurquin Francis , Chapelle Stella , Granger Pierre 
Published: May 2005

AbstractNumerous areneselenenamides derived from ammonia, primary and secondary amines and two N,N‐bis(arylseleno)alkylamines have been studied. The selenenamides bearing an electron‐withdrawing substituent on the aromatic moiety are stable. The 1H, 13C and 77Se chemical shifts and some coupling constants are reported.For N.N‐dialkyl‐o‐nitrobenzeneselenenamides, the 77Se NMR and the 17O NMR give evidence of an Se‐O interaction. In N‐alkyl derivatives, a hydrogen bond between the amine group and the ortho‐substituent is proposed to explain the deshielding of the selenium nucleus.
13C NMR spectral data of some N‐vanillyl‐, N‐piperonyl‐ and N‐veratryl‐alkylaminoalkylamides
Authors: Baldessari Alicia , Gros Eduardo G. 
Published: May 2005

Abstract13C NMR spectra for 66 N‐vanillyl‐and‐piperonyl‐ and N‐veratryl‐chloralkyl‐and‐alkylaminoalkyl‐amides are reported. Relative substituent effects are discussed.
Experimental methodology for high‐resolution solid‐state NMR of heavy‐metal spin‐1½ nuclei
Authors: Harris Robin K. , Sebald Angelika 
Published: May 2005

AbstractThe choice of standard compounds for setting up CP MAS NMR experiments on the nuclei 77Se, 119Sn, 195Pt, 199Hg and 207Pb in organometallic compounds is discussed. Spectra of suitable compounds are presented, together with the relevant optimum acquisition parameters (contact times, recycle delays).
Conformational dependence of 17O chemical shifts in 1,3‐dioxa‐2‐silacyclooctanes: Anomeric effect
Authors: Kupče Ē. , Liepiņš E. , Zicmane I. , Lukevics E. 
Published: May 2005

Abstract17O NMR spectra of 1,3‐dioxa‐2‐silacyclooctanes have been studied. The 17O NMR signal of derivatives existing in the crown conformation is shifted downfield by 7–10 ppm relative to derivatives existing predominantly in conformations belonging to the boat–chair family. This shift is assumed to be due to the anomeric effect in 1,3‐dioxa‐2‐silacyclooctanes.
17O NMR studies on substituted N‐arylacetamides and aryl acetates: Torsion angle and electronic effects
Authors: Boykin David W. , Deadwyler Gina H. , Baumstark A. L. 
Published: May 2005

Abstract17O NMR spectroscopic data at natural abundance in acetonitrile at 75°C were obtained for sixteen N‐arylacetamides, three N‐methyl‐N‐arylacetamides and seven aryl acetates. The 17O chemical shifts of the N‐arylacetamides are significantly influenced by both electronic and steric factors. A Hammett plot of the data for 4‐substituted N‐arylacetamides gives a slope of 22 ppm. Ortho substituents result in significant shielding effects, in contrast to previously reported results for conjugated ketnoes. A quantitative relationship between 17O chemical shift data and torsion angle was found for the sterically hindered arylacetamides. Electronic effects on the aryl acetate 17O chemical shifts are, in comparison, greatly reduced. Steric factors for aryl acetates show even smaller effects on the 17O chemical shifts.
Elimination of direct responses and one‐bond modulations in long‐range heteronuclear chemical shift correlation spectra through the use of low‐pass J filters and BIRD pulses
Authors: Salazar Miguel , Zektzer Andrew S. , Martin Gary E. 
Published: May 2005

AbstractModified long‐range heteronuclear chemical shift correlation pulse sequences which incorporate both BIRD pulses midway through the Δ2 magnetization transfer delay and low‐pass J filters are described. The BIRD pulse provides the means of decoupling one‐bond modulations of response intensity when magnetization is transferred to protonated carbons. The one‐ and three‐step low‐pass J filters utilized eliminate responses due to directly attached protons over a range of one‐bond coupling constants.Results obtained by long‐range optimization of the conventional heteronuclear chemical shift correlation pulse sequence, the previously reported pulse sequence containing only the BIRD pulse midway through Δ2 and the two new pulse sequences described in this work are compared using 2,3‐dihydrofuran as a model compound.The low‐pass J filters have no adverse effects on the ability of the BIRD pulse to decouple one‐bond modulations. Modulation decoupling in the modified pulse sequences was confirmed using the 3J(C‐3, H‐1) coupling pathway of the simple alkaloid norharmane. The response intensities, however, were up to 10% lower with a one‐step low‐pass J filter when compared with the simpler pulse sequence containing only the BIRD pulse midway through Δ2.
Two‐dimensional NMR analysis of himachalol and its correlation with other sesquiterpenoids of the himachalane series
Authors: Prakash Om , Roy Raja , Kulshreshtha D. K. 
Published: May 2005

AbstractHigh‐field 1H NMR studies of himachalol (1) have been carried out by two‐dimensional NMR methods. The stereochemical aspects of this molecule were studied through the application of stereospecific coupling constants, the nuclear Overhauser effect and lanthanide‐induced chemical shifts. Complete and unambiguous 13C chemical shift assignments of 1 have been made for the first time by using two‐dimensional heteronuclear (1H13C) correlation NMR spectroscopy, DEPT, broad‐band proton decoupling and selective heteronuclear spin decoupling 13C NMR methods. Complete 13C chemical shift assignments of isocentdarol, centdarol and centdarone have also been made using some of the above techniques and their stereostructures have been corrected.
Utility of 13C NMR spectroscopy in monitoring the course of a complex reaction sequence: Reaction of pyrrole with formaldehyde
Authors: Katritzky Alan R. , Law Kam Wah 
Published: May 2005

AbstractThe complex course of the reaction of pyrrole with formaldehyde has been completely elucidated by quantitative 13C NMR spectroscopy using the inverse‐gated decoupling technique. The final product is 2,5‐bis(hydroxymethyl)pyrrole (with a free 1‐position), but three main intermediates containing 1‐hydroxymethyl groups were identified, and the rise and subsequent fall of their populations followed. The intermediacy of additional compounds (formals) also renders the reaction more complex. The molar fractions of four hydroxy‐methylpyrroles present in the reaction mixtures were calculated from the 13C NMR data and plotted against time. At 45 and 65°C pyrrole reacted completely with formaldehyde in 1 h and in less than 30 min, respectively. This work illustrates the utility of the 13C NMR investigation of an industrially important reaction.
13C and 1H NMR studies of structure and tautomerism in some perimidines
Authors: Woodgate P. D. , Herbert J. M. , Denny W. A. 
Published: May 2005

AbstractThe 13C NMR spectra of some 1‐ and 2‐substituted perimidines and perimidinium salts are discussed and assigned. Although the spectra of most of the 2‐substituted perimidines are comparatively simple, several examples display 13C and 1H spectral characteristics indicative of inhibition of prototropic tautomerism.
1H bridging and terminal hydride T1 values. Comments on classical vs non‐classical hydride identification using T1 criteria
Authors: Ammann C. , Isaia F. , Pregosin P. S. 
Published: May 2005

AbstractHydride 1H T1 values are reported for a selected series of ruthenium, iridium and platinum complexes. These T1 values range from 6.9 to 0.05 s with the shortest value, 0.05 s, assigned to a complex containing both hydride and coordinated molecular hydrogen, i.e. “M(H2)”. There are nuclear Overhauser enhancements arising both from protons on coordinated ligands and other hydride ligands. It is suggested that the molecular weight of the complex and the measurement conditions can be important factors for T1.
High‐power 13C and 1H nuclear magnetic resonance in dry gluten
Authors: Belton P. S. , Duce S. L. , Colquhoun I. J. , Tatham A. S. 
Published: May 2005

AbstractHigh‐resolution, solid‐state 13C NMR spectra of wheat gluten obtained under a variety of acquisition conditions are reported. These spectra are compared with the results from a 1H relaxation study of dry gluten in which the transverse relaxation times, the spin–lattice relaxation times in the rotating frame and the spin–lattice relaxation times in the laboratory frame at three different Larmor frequencies are characterized. It is concluded that 13C experiments, the proton transverse relaxation measurements and the rotating frame results distinguish between protein and lipid motional environments, whilst the laboratory frame proton spin–lattice relaxation results detect two separate protein environments. The relationship between the laboratory frame spin–lattice relaxation time constants and Larmor frequency is consistent with a model of macromolecular motion in which the polymer chains are held between cross‐link points. Observed changes in the various proton relaxation times on removal of lipid or disruption of disulphide cross‐links are interpreted in terms of the frequency and anisotropy of molecular motions in the gluten system.
13—Lanthanide‐induced shift (LIS) investigation of the conformation of aryl sulphones using a novel lanthanide–sulphone complexation model
Authors: Abraham Raymond J. , Haworth Ian S. 
Published: May 2005

AbstractThe conformation of diphenyl sulphone and 3,4′‐dichlorodiphenyl sulphone has been studied by the lanthanide‐induced shift (LIS) technique. The lanthanide–sulphone complexation model was established using the conformationally rigid dibenzothiophene sulphone molecule. Several models were tried, including both monodentate and bidentate coordination of oxygen to lanthanide. Poor results were obtained for the bidentate models, but three different monodentate models (one‐, two‐ and three‐site) all gave reasonable solutions. The binding position in the three‐site model was established using the program LIRAS4, an adaptation of LIRAS3, with an LnO geometry having R and ϕ values of 2.8 Å and 150° being suggested. Site populations were 16%, 42% and 42% in sites 1, 2 and 3, respectively.Diphenyl sulphone has insufficient data (ΔM values) for a complete analysis, but the more extensive data set for 3,4′‐dichlorodiphenyl sulphone allowed a full analysis which indicated a preferred twist angle of the phenyl rings (θ) of 90°, using all the monodentate models. However, the three‐site model produced significantly lower errors in the predicted shifts and also suggested an identical lanthanide position to that found for dibenzothiophene sulphone. Site populations were 0%, 50% and 50% in sites 1, 2 and 3, respectively, the zero occupancy of site 1 being rationalized in terms of steric interactions with the H‐1 protons. Preferential binding of the shift reagent to the SO bond trans to the meta‐chlorine atom (65%) was observed.
Long‐range protoncarbon‐13 coupling constants of monosaccharides by selective heteronuclear 2D‐J NMR spectroscopy
Authors: Morat Claude , Taravel François R. , Vignon Michel R. 
Published: May 2005

AbstractLong‐range J(CH) values were measured for six glycoside derivatives by a selective 2D‐J heteronuclear sequence. The values obtained are discussed in terms of conformational effects and constitute a valuable contribution to 2J and 3J comprehension.
Assignment of the NMR spectra of benzo[b]triphenyleno[1,2‐d]thiophene through the application of zero quantum proton—proton correlation combined with proton‐detected long‐range multiple quantum heteronuclear chemical shift correlation
Authors: Zektzer Andrew S. , Sims L. D. , Castle Raymond N. , Martin Gary E. 
Published: May 2005

AbstractAssignment of the congested proton and carbon NMR spectra of heterocyclic benzo[b]triphenyleno[1,2‐d]thiophene was accomplished through the concerted application of several two‐dimensional NMR experiments. The inherent insensitivity of homonuclear zero quantum coherence to magnetic field inhomogeneity was used to advantage in disentangling the heavily overlapped proton NMR spectrum. Direct heteronuclear pairings were established using heteronuclear correlation with broad band homonuclear vicinal proton decoupling. Limited sample availability and solubility precluded complete establishment of long‐range heteronuclear correlations by conventional means. Proton‐detected long‐range heteronuclear multiple quantum coherence did, however, provide sufficient long‐range heteronuclear correlations to complete the assignment.A comparison of the data obtained from COSY and zero quantum experiments is presented; the ability of each to establish proton connectivities is discussed. Sensitivity limitations inherent in the conventional long‐range optimized heteronuclear chemical shift correlation experiment are contrasted with the advantages of the proton‐detected long‐range heteronuclear multiple quantum correlation experiment. Practical limitations of the latter are considered.
Long‐range CH correlation 2D NMR spectroscopy 2—effect of TANGO and BIRD pulses
Authors: Krishnamurthy V. V. , Casida John E. 
Published: May 2005

AbstractThe basic CH correlation sequence, with the delays lengthened to facilitate long‐range correlations, was modified by using TANGO and BIRD pulses (both basic and composite) to facilitate both the suppression of one‐bond cross‐peaks and the decoupling of long‐range cross‐peak intensity modulations due to one‐bond coupling. The relative effectiveness of these modifications is illustrated with nicotinamide as a model compound. The use of a combination of the basic TANGO pulse and the basic BIRD pulse achieves both of these aims. The composite TANGO pulse can replace the basic TANGO pulse when more effective suppression of one‐bond cross‐peaks is needed. The use of the composite BIRD pulse during refocusing increases F1 noise and artifacts and is therefore not recommended.
Stereochemistry of crown ethers. I. Conformational and dynamic behaviour of N‐tosyl‐substituted diaza crown ethers
Authors: Kleinpeter E. , Gäbler M. , Schroth W. 
Published: May 2005

AbstractThe variable‐temperature 1H and 13C NMR spectra of some N‐tosyl diaza crown ethers have been obtained. They are discussed with respect to the preferred conformers of the crowns and the free energies of activation of the interconversional process of the large ring. Both the preferred conformers and the ring interconversional barriers have been found to be strongly dependent on the structure and the ring size of the studied compounds.
13C Nuclear magnetic resonance spectroscopy of 4‐methylcoumarins (4‐methyl‐2H‐1‐benzopyran‐2‐ones)
Authors: Parmar V. S. , Singh S. , Boll P. M. 
Published: May 2005

AbstractThe 13C NMR spectra of 36 differently substituted 4‐methylcoumarins (4‐methyl‐2H‐1‐benzopyran‐2‐ones) have been recorded. The effects of an alkyl side‐chain at C‐3 on the chemical shift values and that of a methoxy or an acetoxy group in place of a hydroxy group have been observed and rationalized. This study may be helpful in the structure elucidation of new and natural 4‐methylcoumarins.
13C NMR spectra of some trichothecene mycotoxins and derivatives
Authors: Avent Anthony G. , Grove John Frederick , Hanson James R. 
Published: May 2005

AbstractA general strategy, using well established techniques, is outlined for the assignment of signals in the 13C NMR spectra of the trichothecene mycotoxins and some related rearrangement products. Heteronuclear NOE difference spectra were employed to assign resonances from quaternary carbons. An example of the use of spin–echo J modulation is given.
Pseudohalogen chemistry. VIII—Substituent constants (Z) for the thiocyanato group in the estimation of the chemical shifts of vinyl protons in α,β‐unsaturated thiocyanates
Authors: Guy Robert G. 
Published: May 2005

AbstractSubstituent constants for the thiocyanato group (Z = 0.94, Z = 0.45 and Z= 0.41) have been derived by an additivity procedure, and shown to reproduce the chemical shifts of vinyl protons in a wide variety of α,β‐unsaturated thiocyanates with an accuracy of ±0.30 ppm in 94% of the cases studied. Deviations due to tBu and COR groups are discussed in terms of steric and field effects.
Assignment of proton and carbon NMR signals of didemnin A in solution
Authors: Kessler H. , Will M. , Sheldrick G. M. , Antel J. 
Published: May 2005

AbstractSeveral one‐ and two‐dimensional techniques have been used to assign the 1H and 13C NMR spectra of the cyclic heptadepsipeptide didemnin A in DMSO. The composition and sequence of the amino acid residues was known beforehand and could be confirmed by heteronuclear proton–carbon long‐range couplings using the COLOC experiment and a recently proposed new inverse technique using Gaussian‐shaped pulses. The aliphatic methyl resonances of the isostatin, hydroxyisovalerylpropionyl, N‐methylleucine and leucine residues were assigned by means of the TOCSY and NOESY techniques. Aliphatic carbon assignment was performed by inverse correlation via heteronuclear double quantum coherence.
15N CP‐MAS NMR study of azo–hydrazone tautomerism of some Azo dyes
Authors: Lyčka Antonín , Jirman Josef , Schneider Bohdan , Straka Jaroslav 
Published: May 2005

AbstractThe 20.28 MHz 15N CP‐MAS NMR spectra of 15N doubly labelled 3‐methyl‐1‐phenylpyrazole‐4,5‐dione 4‐phenylhydrazone (1), 4‐hydroxyazobenzene (2), 2‐hydroxy‐5‐tert‐butylazobenzene (3) and 1‐phenylazo‐2‐naphthol (4) were measured and the temperature dependence of δ(15N) was followed. For 4, representing a mixture of the azo and hydrazone forms, the hydrazone content was calculated from the 15N chemical shifts of both nitrogen atoms at various temperatures. The two calculations gave identical results. In comparison with measurements in solution, the hydrazone content in 4 is slightly higher in the solid state. Thermodynamic data were calculated using the temperature dependence of In K (K = [hydrazone form]/[azo form]). Some hydrazone content was found in 2 in the solid state, in contrast to the measurements in solution.
Selective heteronuclear NOE enhancements in benzoheterocycles. Effect of ring size on indirect three‐spin effects
Authors: Redondo Jordi , Sánchez‐Ferrando Francisco , Valls Montserrat , Virgili Albert 
Published: May 2005

AbstractThe 80 MHz 1H NMR and 20 MHz 13C NMR spectra of five 4‐methylcoumarins, six 4‐methyl‐2(1H)‐quinolones and nine 3‐methylbenzo[b]furans, including six new compounds, were fully assigned. Homonuclear 1H{1H} NOEs and selective heteronuclear 13C{1H} NOEs were measured after low‐power pre‐saturation of the methyl protons. Indirect, negative heteronuclear NOE enhancements were found in suitable three‐spin systems of the 13C1H{1H} type, and their magnitude was found to be dependent on ring size. The first examples of indirect, heteronuclear NOE enhancements on non‐protonated carbons are described.
Two‐dimensional NMR spectra of sesquiterpenes. II—Noesy study of some sesquiterpene lactones with pseudoguaianolide, 3,4‐seco‐pseudoguaianolide and guaianolide skeletons
Authors: Aljančić‐Šolaja Ivana , Milosavljević Slobodan , Djermanović Miodrag , Stefanović Milutin , Macura Slobodan 
Published: May 2005

AbstractThe application of phase‐sensitive 2D 1H NOE NMR spectroscopy (PS NOESY) in the stereochemical assignment of sesquiterpene lactones such as 4‐oxo‐3,4‐seco‐ambrosan‐6,12‐olide‐3‐oic acid methyl ester, 4‐oxo‐6‐hydroxypseudoguai‐11(13)‐en‐8,12‐olide and 8‐angeloyloxy‐10‐acetoxyguai‐3‐en‐6‐,12‐olide is reported.
High‐resolution 13C NMR study of free and metal‐complexed ionophores in the solid state: Conformation and dynamics of the macrocyclic ring and the effect of intermolecular short contact of methyl groups on spin–lattice relaxation times and displacements of chemical shifts
Authors: Saitô Hazime , Tabeta Ryoko , Yokoi Motoko 
Published: May 2005

AbstractHigh‐resolution 13C NMR spectra of 15 samples of uncomplexed and metal‐complexed tetranactin and nonactin were recorded in the solid state, revealing characteristic displacements of peaks due to complex formation and the effect of crystalline packing on the 13C chemical shifts and spin–lattice relaxation times of the methyl groups. The C‐1 13C chemical shifts of uncomplexed and complexed tetranaction and nonactin are well related to the variation of nearby torsion angles characteristic of the macrocyclic conformation, as determined by x‐ray diffraction. The existence of short intermolecular contact of methyl groups (<3.8 Å) at the surface of the molecules results in either prolonged 13C spin–lattice relaxation times in the laboratory frame (T1C) or substantial upfield displacement of peaks (up to 6 ppm). In addition, significantly reduced T1C values in uncomplexed nonactin (one order of magnitude smaller than those of other compounds) was ascribed to the presence of a puckering motion of the tetrahydrofuran ring and fluctuation of the macrocyclic ring in the solid state (with a time scale of 10−8 s). Finally, how the conformations of these compounds in the solid are retained in chloroform solution was examined in view of the differences in the 13C chemical shifts between the solid and solution.