bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon‐13 NMR data of some 4H‐imidazo[2,1‐c][1,4]benzoxazines
Authors: Rao K. Vara Prasad , Reddy P. S. N. , Sundaramurthy V. 
Published: May 2005

AbstractCarbon‐13 chemical shifts of twelve 4H‐imidazo[2,1‐c][1,4]‐benzoxazine derivatives and three 4‐alkyl‐2H‐1,4‐benzoxazin‐3‐ones are reported.
The 1H and 13C NMR spectra of some furanoid norditerpenes
Authors: Lentini A. , Webster J. , Ternai B. , Komori T. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of Diosbulbin A, B, D and G have been studied. The proton spectra were analysed with the aid of nuclear, magnetic double resonance and comparison with reference compounds. The assignments of the carbon shifts have been obtained by means of proton noise decoupling, single frequency off‐resonance decoupling, the attached proton test and by comparison with reference compounds.
13C NMR determination of the configuration of methyl‐substituted double bonds in medium‐ and large‐ring terpenoids
Authors: Lange Gordon L. , Lee Moses 
Published: May 2005

Abstract13C NMR spectroscopy can be used to determine the configuration of methyl‐substituted double bonds in medium‐ and large‐ring terpenoid natural products. A number of examples from our investigations in the germacranolide field are presented, and clearly show that if the resonance for the vinylic methyl group appears at a value greater than 20 ppm the double bond has a (Z)‐configuration whereas if the value is less than 20 ppm an (E)‐configuration is present. Literature examples of other classes of compounds are also cited to illustrate the generality of this method.
Deuterium isotope effects on silicon‐29 chemical shifts
Authors: Berchier Fabienne , Pai Yi‐Ming , Weber William P. , Servis Kenneth L. 
Published: May 2005

AbstractThe deuterium isotope effects on the 29Si chemical shifts in several organosilanes and siloxanes have been determined. For silanes, the one‐bond effects are approximately −0.2 ppm per deuterium and follow an additivity relationship. The two‐bond effect is small.
Characterization of P—AU—N bonds in the solid state by 15N NMR
Authors: Berners‐Price S. J. , Morden K. , Opella S. J. , Sadler P. J. 
Published: May 2005

AbstractThe high‐resolution solid‐state and solution 15N NMR spectrum of Et3PAu(phthalimide‐15N) are compared. Both spectra exhibit a remarkably well resolved doublet attributable to the scalar two‐bond31P–15N coupling (41 Hz). The absence of substantial quadrupolar effects due to 197Au is discussed.
NMR studies of methylenebispyridinium derivatives
Authors: Munavalli S. , Szafraniec L. L. , Beaudry W. , Poziomek E. J. 
Published: May 2005

AbstractThe methylene proton chemical shifts of the magnified image system appear to be affected by the synergistic interactions of a combination of various effects. Although it is difficult to single out the origin, transmission and magnitude of these effects, the synergistic interactions pervade the molecule, causing a net displacement of the chemical shifts. The substituent‐produced chemical shifts show a clear trend in their dependence on the nature of the substituents and the Hammett parameters. Strong through‐conjugation between the aromatic nitrogen and resonance donor substituents in the para‐position is observed.
Carbon–carbon coupling constants of 1‐phenylazo‐2‐naphthol and 2‐phenylazo‐1‐naphthol obtained by the SEMINA‐1 technique
Authors: Hansen Poul Erik , Lyčka Antonín 
Published: May 2005

AbstractCarbon‐carbon coupling constants of 1‐phenylazo‐2‐naphthol and 2‐phenylazo‐1‐naphthol have been measured with the SEMINA‐1 pulse sequence. The carbon–carbon couplings provide an unambiguous assignment of the 13C spectra. The magnitudes of the carbon–carbon coupling constants are discussed in relation to the tautomeric nature of the compound. Substituent effects on couplings are also considered.
1H and 13C NMR spectra of tetrahydroquinoxalines condensed with six‐membered heterocycles
Authors: Charushin V. N. , Sorokin N. N. , Chernyshev A. I. , Baklykov V. G. , Ponizovsky M. G. , Chupakhin O. N. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of tetrahydroquinoxalines condensed with pyridazine, pyrazine, oxazine, oxadiazine, thiadiazine or triazine rings have been measured in DMSO‐d6 solution. The effects of six‐membered heterocycles on 1H and 13C chemical shifts and the values of one‐bond 1J(CH) and vicinal 3J(HH) coupling constants for the ring junction fragment are considered. The differences between the 1H and 13C spectral parameters of tetrahydroquinoxalines annelated with five‐ or six‐membered heterocycles with the same set of heteroatoms attached to the ring junction carbons are also discussed.
13C NMR chemical shift assignments for some 1H‐pyrrole‐2‐carboxylic acid derivatives
Authors: Sammes Michael P. , Katritzky Alan R. , Law Kam Wah 
Published: May 2005

AbstractComplete 13C NMR chemical shift assignments are reported for 32 1H‐pyrrole‐2‐carboxylic acid esters and amides, bearing in addition alkyl, phenyl, acetyl, alkoxycarbonyl and diethylamino substituents. The substituent chemical shift effect for the 2‐Ph group on the pyrrole ring carbon atoms is also reported.
1H NMR spectra of carbohydrate‐derived polyhydroxycarboxylates
Authors: Van Duin M. , Peters J. A. , Kieboom A. P. G. , Van Bekkum H. 
Published: May 2005

AbstractAn analysis of the 1H NMR spectra of polyhydroxycarboxylates is presented. Conclusions with regard to the configuration and the conformation are drawn from chemical shifts and vicinal coupling constants.
1H, 13C and 31P NMR studies of the stereochemistry of chiral (4R, 6R)‐2‐substituted‐1,3,2‐dioxaphosphorinanes
Authors: Szalontai G. , Bakos J. , Tóth I. , Heil B. , Pelczer I. , Sohár P. 
Published: May 2005

Abstract13C, 1H and 31P NMR investigations have been carried out to determine the ring stereochemistry and phosphorus configuration for four chiral (4R, 6R)‐2‐substituted‐1,3,2‐dioxaphosphorinane derivatives 1–4 (2‐substituent = Cl, Ph, OMe and O‐t‐Bu, respectively). 1H NMR spectra, double resonance, 2D‐J experiments and spin simulation proved the chair character of the ring. Depending on the position of R, two diastereomers may exist, but in most cases only one predominating form was detected. Dynamic processes were observed for 1 and 2. Saturation transfer experiments proved the existence of ring and/or phosphorus inversions.
Synthesis and high‐resolution 1H NMR spectra of four dimethylaminated dipyridyl ketones
Authors: Jones D. W. , Pakdel H. , Hallas G. , Hepworth J. D. 
Published: May 2005

AbstractFour new dimethylaminated pyridoylpyridine intermediates, bis(3‐dimethylamino‐2‐pyridyl) ketone (1), 6‐dimethylamino‐3‐pyridyl 4‐pyridyl ketone (2), 6‐dimethylamino‐3‐pyridyl 3‐pyridyl ketone (3) and 6‐dimethylamino‐3‐pyridyl 2‐pyridyl ketone (4), have been synthesized and their 100 MHz 1H NMR spectra analysed iteratively as ABC, ABCX and ABXY spin systems. In 2–4 the H‐5 shift ortho to the dimethylamino substituent is unaffected by the orientation of the pyridyl substituent, but H‐4 and H‐2 are increasingly deshielded in the sequence 2–4. In 3, when benzene‐d6 replaces chloroform‐d1 as solvent, H‐5′ and H‐4′ in the unsubstituted pyridyl ring suffer appreciable upfield shifts.
13C NMR studies of the triterpene 3α‐hydroxylup‐20(29)‐en‐23,28‐dioic acid and some derivatives
Authors: Preiss A. , Lischewski M. , Adam G. , Budéšínský M. 
Published: May 2005

AbstractThe 13C NMR assignment of the triterpene 3α‐hydroxylup‐20(29)‐en‐23,28‐dioic acid and some of its derivatives has been carried out. In addition to conventional methods, 2D 1H13C chemical shift correlation, nuclear Overhauser enhancement difference and decoupling difference techniques were used for the assignment.
Heteronuclear Overhauser effect measured with selective proton irradiation. Application of a new method
Authors: Bigler P. , Kamber M. 
Published: May 2005

AbstractA new method for the measurement of partial heteronuclear NOE effects is proposed, and its application to the elucidation of unknown structures is demonstrated. In contrast to the basic experiment with simultaneous irradiation of all proton multiplet lines with a relatively high decoupler power, the individual lines are irradiated successively several times using a very low decoupler power. An improved selectivity in the proton domain combined with higher sensitivity in the carbon domain are the main attributes of this powerful technique.
Line widths, sensitivity and artifacts in 33S NMR Spectra: The case of aqueous sulphides
Authors: Belton P. S. , Cox I. J. , Harris R. K. 
Published: May 2005

AbstractThe factors giving rise to artifacts in the NMR spectra of 33S and other quadrupolar nuclei of low magnetogyric ratio are examined and some tests for their detection are proposed. The effects of line width and probe ring‐down time on the observed signal intensity are considered and a quantitative relationship is described. Sulphur‐33 NMR spectra of sodium sulphide solutions are reported which differ substantially from those recently published. The reasons for these and other differences between reported spectra are explained in terms of experimental artifacts of the types described.
Complete assignment of the 13C NMR spectra of the ring forms of digitoxose by DEPT spectrum editing and two‐dimensional proton chemical shift correlation spectroscopy
Authors: Coxon Bruce 
Published: May 2005

AbstractThe 13C chemical shifts of the four isomeric ring forms of D‐digitoxose in dimethyl sulfoxide‐d6 solution have been assigned completely by DEPT 13C NMR spectrum editing and two‐dimensional carbon–proton chemical shift correlation spectroscopy. The 13C chemical shifts are discussed in terms of their dependence on ring size and on anomeric configuration. The equilibrated mixture of four ring forms of D‐digitoxose in dimethyl sulfoxide‐d6 solution has been analysed quantitatively by 13C NMR spectroscopy, and the results compared with those obtained previously by 1H NMR.
13C chemical shifts of chlorinated biphenyls
Authors: Yanagisawa Masaru , Hayamizu Kikuko , Yamamoto Osamu 
Published: May 2005

AbstractThe 13C NMR spectra of 48 chlorinated biphenyls are presented. The 13C shifts of the individual carbons are interpreted by the additive contributions from the substituent effect of a chlorine atom, and by the repulsive interaction of chlorine atoms substituted in a crowded relationship on the biphenyl ring.
Compounds with bridgehead nitrogen. 50—1H NMR spectra and structures of the products derived from the reaction between trans‐3‐aminotetralin‐2‐ol and formaldehyde
Authors: Crabb Trevor A. , Roch Olive G. , Robinson Paul 
Published: May 2005

AbstractIn contrast to the reported reaction between trans‐1‐aminotetralin‐2‐ol and formaldehyde, which gives r‐6a, c‐9a,t‐15a,t‐18a‐5,6,6a,9a,14,15,15a,18a‐octahydro‐9,18‐methanodinaphtho[1,2‐d:1′,2′‐i][1,6,3,8]dioxadiazecine, an examination of the δ 4.0–5.0 region of the 1H NMR spectra of the products of the reaction between trans‐3‐aminotetralin‐2‐ol and formaldehyde showed these to be a 50:50 mixture of r‐5a,t‐8a,c‐14a,t‐17a‐ and r‐5a,c‐8a,t‐14a,t‐17a‐5,5a,8a,9,14,14a,17a,18‐octahydro‐8,17‐methanodinaphtho[2,3‐d:2′,3′‐i] [1,6,3,8]dioxa‐diazecine. In a similar way, the reaction between trans‐2‐aminocyclohexanol and formaldehyde was re‐examined and found to produce initially a ca 80:20 mixture of r‐4a,t‐7a,c‐11a,t‐14a‐ and r‐4a,c‐7a,t‐11a,t‐14a‐7,14‐methanoperhydrodibenzo[d,i][1,6,3,8]dioxandiazecines.
Sulphur‐33 nuclear magnetic resonance of oxidized petroleum asphaltene
Authors: McIntyre Deane D. , Strausz Otto P. 
Published: May 2005

AbstractA 33S NMR spectrum has been obtained from an asphaltene sample for the first time. Asphaltene from the Athabasca tar sands bitumen, Alberta, Canada, was oxidized with RuVIII, which selectively converts sulphide sulphur into the corresponding sulphone. The 33S NMR spectrum of this sample at 30.7 MHz featured a broad signal centred at 320 ppm downfield from CS2. The width of this signal was too broad, owing to the quadrupole relaxation of the nuclei in the solution and/or the many types of sulphone molecules, to permit the assignment to any particular sulphone types. This situation was not improved by the use of proton broad band decoupling at elevated temperatures. Nevertheless, the mere presence of the aliphatic sulphones provides the first unambiguous evidence for the presence of aliphatic sulphides in a petroleum asphaltene. Similar results were obtained from sulphones prepared by peroxide oxidation of high molecular weight sulphides isolated from bitumen from the Wabasca, Alberta deposit.
1H NMR additive shielding coefficients (Z) for organoseleno groups in vinyl selenides
Authors: Ferraz Helena M. C. , Comasseto Jaão V. , Brandt Carlos A. 
Published: May 2005

AbstractAdditive shielding parameters for the phenylseleno group (ZPhSe‐gem = 1.36; ZPhSe‐cis = 0.31; ZPhSe‐trans = 0.29) have been estimated. Examples of the calculation of chemical shifts for olefinic protons in vinylic selenides by means of these increments are given. A comparison with 2‐pyridylseleno and methylseleno substituents has been made. The standard deviations of the Z values are 0.06 for ZPhSe‐gem, 0.10 for ZPhSe‐cis and 0.05 for ZPhSe‐trans.
Complete 13C NMR spectra of the axial forms of methyl‐, ethyl‐ and isopropylcyclohexane
Authors: Squillacote Michael E. , Neth Joann M. 
Published: May 2005

AbstractLow‐temperature 13C NMR spectral data have been obtained for equatorial and axial methyl‐, ethyl‐ and isopropylcyclohexane using a high‐temperature cryogenic trapping technique. 13C chemical shift differences between major and minor conformations of each compound are discussed in terms of chemical shift theories. A convenient synthesis of deuteriated dichlorofluoro‐ and difluorochloromethane, which are excellent low‐temperature NMR solvents, is also presented.
14N nuclear quadrupole resonance study of the protonation of thiourea
Authors: Murgich Juan , Magaly Santana R. , Abanero Jose A. 
Published: May 2005

Abstract14N NQR frequencies of thiourea complexes with HCIO4, HCI and H2SO4 obtained at 77 K are reported. Comparison of NQR data previously obtained in hexamethylenetetramine‐2thiourea showed that the perchloric acid complex was a hydrogen‐bonded complex. A similar comparison with uronium salts showed that the other complexes were thiouronium salts. The protonation site in thiouronium salts was shown to be the S atom. S protonation produced decreases of the N non‐bonding orbital occupation number and increases in those of the NN and NC sigma bonds. Changes in the N non‐bonding orbital produced by protonation were larger in thiourea than in urea.
High‐resolution 13C NMR studies of proanthocyanidin polymers (condensed tannins)
Authors: Newman Roger H. , Porter Lawrence J. , Foo L. Yeap , Johns Stanley R. , Willing Richard I. 
Published: May 2005

AbstractHigh‐resolution 13C NMR spectra of some proanthocyanidin polymers are presented. They were measured in acetone‐d6‐water (1:1, v/v) solution at 30 °C and at 62.5 MHz. The chemical shifts of selected resonances in these spectra were compared with those of structurally related monomers and oligomers. These comparisons enable certain deductions to be made regarding the stereochemistry and mode of linkage of the constituent flavanoid monomer units of these polymers.
Optimized detection of small spin–spin couplings in two‐dimensional chemical shift correlation experimentsCOSY and DEPT
Authors: Batta Gy. , Kövér Katalin E. 
Published: May 2005

AbstractTwo‐dimensional chemical shift correlation experiments (COSY and DEPT) may be applied to the detection of small spin‐spin couplings. To increase the sensitivity of these techniques, careful optimization of the experimental parameters is required. Equations applicable to AX spin systems are given for the optimal choice of delay periods in the pulse sequences. Practical applications have been demonstrated for oligosaccharide sequencing.
Conformational analysis part. 8—A lanthanide‐induced shift NMR investigation of the conformation of amiodarone derivatives
Authors: Abraham Raymond J. , Smith Paul E. , Deleuze Colette , Gatto Vincent Lo 
Published: May 2005

AbstractA LIS investigation of analogues of amiodarone containing the 3‐benzoyl‐2‐butylbenzofuran system has been performed, utilizing the pseudo‐contact shifts of all the proton and carbon nuclei in the molecules. The 13C diamagnetic shifts were removed by use of La(fod)3 and the pseudo‐contact shifts were analysed to obtain the conformations in solution of these molecules.In 3‐(2,6‐dibromobenzoyl)‐2‐butylbenzofuran (1), the ortho bromo substituents produce sufficient steric hindrance so as to enable the separate O‐trans and O‐cis conformers to be observed at room temperature.Thus the LIS analysis was performed on both conformers separately. In each case good solutions (Rx <5%) were obtained for the conformations in which the benzofuran and carbonyl groups are coplanar and the phenyl group orthogonal to this plane. This was achieved using an unsymmetrical model of the lanthanide complexation to the carbonyl group in which the different spatial environment of the oxygen lone pairs is allowed for in the refinement procedure.In 3‐(3,5‐diiodobenzoyl)‐2‐butylbenzofuran (2), in which there is no evidence of conformation isomerism in the NMR spectrum down to ‐100 °C, the analysis of the LIS data on the basis of a rapidly interconverting mixture of conformers analogous to those of 1 did not produce a satisfactory result. In contrast, analysis on the basis of a single conformation in which the phenyl group is coplanar with the carbonyl group and the benzofuran moiety is twisted out of this plane gave a satisfactory solution for an angle of twist of ca 90°. Owing to the long time scale of the NMR experiment, the LIS results are also consistent with a rapidly interconverting equilibrium between two non‐planar conformations in which the average angle of twist of the benzofuran group is ca 90°. This intriguing result can be rationalized by steric considerations and molecular mechanics calculations which indicate that, in the absence of any abutting ortho substituents on the phenyl group, coplanarity of the carbonyl group and the 2‐alkylbenzofuran moiety is less favoured energetically than coplanarity of the carbonyl and the phenyl groups. The slightly greater intrinsic torsional barrier of the carbonyl and benzofuran parts is more than compensated for by the increased steric interactions of the carbonyl with the 2‐alkyl and 4‐hydrogen groups of the benzofuran in the planar form.
Cyclodextrins as chiral complexing agents in water, and their application to optical purity measurements
Authors: Greatbanks David , Pickford Roderick 
Published: May 2005

AbstractThe interaction of β‐cyclodextrin with propanolol hydrochloride was shown by NMR to produce diastereomeric pairs observable in D2O solution at 400 MHz. By addition of racemate to pure (–)‐isomer, the usefulness of this novel technique in being able to measure optical purity in water down to the 1% level was demonstrated. Using changes in chemical shifts and NOE effects, a possible structure for the inclusion complex is proposed. γ‐Cyclodextrin induced larger shifts in the spectrum than the β‐equivalent, whereas α‐cyclodextrin had no effect.
Chiral phenyl‐substituted chalcone epoxides. I—Correlative determination of absolute configuration by 1H NMR lanthanide‐induced shifts
Authors: Langin‐Lantéri Marie‐Thérèse , Fonbonne Catherine , Huet Jean , Petit‐Ramel Michèle 
Published: May 2005

AbstractThe absolute configuration of an unknown 2′‐ or 4‐ and (or) 4′ phenyl‐substituted chalcone oxide can be predicted from the chemical shift behaviour of the 1H NMR spectrum of the substrate in the presence of the lanthanide chiral complex Eu(hfbc)3.
Interactions between 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate and nucleoside 5′‐monophosphates in aqueous solution
Authors: Sagan Barbara L. , Walmsley Judith A. 
Published: May 2005

AbstractHydrophobic binding of 2,2‐dimethyl‐2‐silapentane‐5‐sulfonate (DSS) to guanosine 5′‐monophosphate (5′‐GMP) and cytidine 5′‐monophosphate (5′‐CMP) results in an upfield shift of the 1H NMR trimethylsilyl resonances with respect to an internal reference tetramethy lammonium ion. The nature of the nucleotide‐DSS interaction and the stability of the resulting complexes have been studied. The magntiude of the effect is dependent on the nature and extent of the self‐association of the nucleotide and the nucleotide concentration. For nucleotides which self‐associate non‐cooperatively to form disordered base stacks, such as Li2(5′‐GMP) and M2(5′‐CMP), where M = Li+, Na+, K+ and Rb+, the formation of 2 : 1 complexes (nucleotide to DSS molar ratio) has been proposed. Apparent equilibrium constants for the 2 : 1 complexes are 0.44 M−2 for Li2(5′‐GMP) at 2 °C and an average value of 0.30 M‐2 for M2(5′‐CMP) at 1 °C. For the Na+ and Rb+ salts of 5′‐GMP, which form strongly associated, ordered self‐aggregates, the interaction between DSS and 5′‐GMP is considerably reduced owing to the inability of DSS to compete effectively with the self‐aggregation process.
1H and 13C NMR investigation of conformational isomerism in amiodarone and derivatives
Authors: Deleuze C. , Nisato D. , Gatto V. Lo , Chatelain P. , Gubin J. 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of amiodarone and several derivatives are reported and assigned. The hypothesis of an O‐trans to O‐cis conformational equilibrium in most of these molecules has been investigated by examining the 1H and 13C chemical shifts, and by NOE and LIS experiments, variable‐temperature NMR and IR spectroscopy.The assumed O‐trans/O‐cis equilibrium would be fast on the NMR time scale for amiodarone, which has no ortho substituents on the C‐3 benzoyl substituent. However, in the 2′,6′‐dibromobenzoyl derivatives, separate O‐trans and O‐cis conformers are observed at room temperature in the NMR spectrum in the ratio of ca 60:40, favouring the O‐trans conformer. The coalescence temperatures and activation energies (ΔG) of the 2′,6′‐disubstituted compounds are obtained; the activation energy increases with the size of the ortho substituents but the conformer ratio remains unchanged. In contrast, removal of the C‐2 butyl substituent on the benzofuran ring gives 100% of the O‐trans conformation.
NMR and theoretical (MNDO and Ab Initio) studies of lone‐pair electron‐π‐electron interactions: The conformation of 9‐methoxyfluorene
Authors: Bakke Jan M. , Rønneberg Hanne , Chadwick Derek J. 
Published: May 2005

AbstractThe results of NMR investigations based on the heteronuclear 3J(CH3, H‐9) coupling constant, the methyl group chemical shift, lanthanide‐induced shifts and MNDO calculations indicate that 9‐methoxyfluorene exists predominantly in the trans conformation in which the methyl group is oriented in an antiperiplanar relationship with respect to H‐9. Previous experimental work on the 9‐hydroxy analogue demonstrated a similar conformational preference, which is also indicated by the results of MNDO and ab initio calculations presented here. The origin of the preference probably lies in a repulsive interaction between the electrons of the aromatic π‐systems and the lone‐pair electrons of the hydroxyl or methoxyl oxygen.
Structural effects on 17O NMR shifts of cyclic phosphine oxides
Authors: Quin Louis D. , Szewczyk Jerzy , Linehan Kathleen , Harris David L. 
Published: May 2005

AbstractThe 17O NMR chemical shifts of a variety of cyclic phosphine oxides were recorded at natural abundance. The shifts proved to be extremely sensitive to structural effects such as ring size and the presence of γ‐interactions. Values were found to cover a 70 ppm range. The most unusual effect was discovered with phosphine oxide groups in the 7‐position of the norbornene framework. When the oxygen was anti to the double bond, exceptionally strong deshielding (by as much as 60 ppm) occurred relative to the isomer with syn oxygen. 17O NMR clearly has value as a structural diagnostic technique with phosphine oxides.