bluuebunny/crossref_metadata_2025_split huggingface dataset:
1H and 31P NMR spectra of the phenyl ester of dichlorophosphoric acid in a nematic phase
Authors: Hansen J. , Jacobsen J. P. 
Published: May 2005

AbstractThe 1H and 31P NMR spectra of the phenyl ester of dichlorophosphoric acid dissolved in Merck nematic phase IV have been recorded and analysed. The values of the dipole dipole couplings have been discussed in terms of several different geometric models. Non‐planarity of C‐1, O, P and the phenyl ring must be assumed in order to account for the results; a twist angle of 49° was found.
The relationship between proton–proton NMR coupling constants and substituent electronegativities. II—conformational analysis of the sugar ring in nucleosides and nucleotides in solution using a generalized Karplus equation
Authors: Haasnoot C. A. G. , de Leeuw F. A. A. M. , de Leeuw H. P. M. , Altona C. 
Published: May 2005

AbstractThe relationship between vicinal NMR proton–proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on 3J(HH); second, empirical correlations between the parameters governing the conformation of β‐D‐furanosides (taken from an analysis of 178 crystal structures) were used to define proton–proton torsion angles as a function of the pseudorotation parameters P and Φm; and, third an iterative least‐squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′‐cyclic nucleotides, a base‐stacked ribonucleotide, 2′‐anhydroarabinonucleosides, α‐D‐2′,2‐O‐cyclouridine, 2′‐ and 3′‐aminosubstituted ribonucleosides, 2′‐ and 3′‐deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.
1H and 13C nuclear magnetic resonance study of (D3)‐trishomocuban‐4‐ol and (D3)‐trishomocubanone
Authors: Dekker Theodor G. , Oliver Douglas W. , Pachler Klaus G. R. , Wessels Philippus L. , Woudenberg Marianne 
Published: May 2005

AbstractThe complete assignments of the 1H and 13C NMR spectra for (D3)‐trishomocuban‐4‐ol (3) and (D3)‐trishomocubanone (4) are reported. The difference between the 1H and 13C chemical shifts of 3 and 4 and those of the hydrocarbon (D3)‐trishomocubane, and the substituent effect of the hydroxy group, can be adequately explained by the unique stereochemistry of these compounds.
Prediction of ortho(β) 13C chemical shifts in conjugated systems
Authors: Craik D. J. , Ternai B. 
Published: May 2005

AbstractAn equation has been developed which relates ortho or C‐β 13C substituent chemical shifts (SCS) to the ortho proton–proton coupling constant in the unsubstituted member of a conjugated series. This method is an extension of previous equations which have been used to predict ortho 1H SCS values, and has its origin in a relationship between bond order and SCS values. The equation was derived from ortho 13C data in 2‐naphthalenes and monosubstituted benzenes and its application to other unsaturated series is discussed.
Effect of lanthanide shift reagents on conformational equilibria
Authors: Dixon J. R. , McIntyre P. S. , Morris I. G. , Williams D. L. 
Published: May 2005

AbstractThe conformational equilibrium constants for a series of 1‐alkyl substituted cyclohexanols have been determined using a lanthanide shift reagent, and the results compared with other methods. In comparison to other technique greater preference is shown by the hydroxyl group for the equatorial position. This is rationalized by the effect on the equilibrium of the bulky shift reagent.
Correlation of nitrogen‐14 nuclear quadrupole resonance data in sulfanilamides with the in vitro activities
Authors: Subbarao S. N. , Bray P. J. 
Published: May 2005

AbstractSeveral sulfanilamide‐type compounds in their solid state have been investigated by the 14N nuclear quadrupole resonance (NQR) technique. The electron distributions at the sites of the nitrogen atoms, calculated by the Townes and Dailey theory, indicate a significant correlation between the quadrupole coupling constant for the primary amino nitrogen (N4), which is a measure of the (π‐σ) electron density at N4, and the in vitro bacteriostatic activity of the sulfanilamides.
The 1H and 13C chemical shifts for some tetrakis(para‐substituted phenyl)ethylenes
Authors: Smith William B. 
Published: May 2005

AbstractThe proton and carbon chemical shifts for a series of tetrakis(p‐substituted phenyl)ethylenes are described. Assignments followed routine substituent chemical shift trends. Both proton and carbon chemical shifts ortho to the varying substituent follow the empirical parameter, Q. The ethylene carbon chemical shifts are proportional to those at the position para to the varying substituent.
The configuration and conformation of the tricyclo[4.4.1.12,5]dodecan‐11‐ols determined by 1H NMR spectroscopy using the shift reagent Eu(fod)3
Authors: Mason Timothy J. 
Published: May 2005

AbstractThe isomeric tricyclo[4.4.1.12,5]dodecan‐11‐ols have been synthesized from the (6+4) cycloaddition product of tropone with cyclopentadiene. The configuration and conformation of each isomer was determined from the proton shift gradients induced in the olefinic proton signals in the 1H NMR spectra of intermediate compounds by Eu(fod)3.
Carbon‐13 NMR characterization of the bispyridinium oximes, toxogonin, HS‐3, HS‐6 and HI‐6
Authors: Waysbort D. , Balderman D. , Amitai G. 
Published: May 2005

AbstractThe structure of the bispyridinium oximes, toxogonin, HS‐3, HS‐6 and HI‐6, used as antidotes in organophosphorus poisoning, is confirmed by 13C NMR spectroscopy. The 13C NMR spectra of the corresponding monopyridinium precursors substantiate the signal assignment in the bispyridinium oxime spectra. In all oximes studied the hydroxyiminomethyl group (CHNOH) exists in the syn configuration. The 13C signal differences also readily allow analysis of binary mixtures of the oximes and provide an easy method for monitoring their stability.
Anionic lanthanide shift reagents. Application to the assignment of NH peaks of amidinium ions
Authors: Perrin Charles L. 
Published: May 2005

AbstractAnionic EDTA complexes of Pr(III) and Eu(III) produce downfield and upfield shifts, respectively, of the NH resonances of amidinium ions, RC(NH2)2+. These LnEDTA− ‐induced shifts arise through the formation of weak ion pairs. Results for the acetamidinium ion show that Hz, the high field NH, experiences a greater shift than HE. This result confirms the expectation that in the ion pair the anionic shift reagent approaches closer to Hz. Thus LnEDTA−‐induced shifts can be used to assign NH peaks of amidinium ions. Such shifts are then used to assign the low field NH peak of the benzamidinium ion to HE, whereas the low field NH peaks of the azoisobutyramidinium ion and formamidinesulfinic acid are assigned as Hz.
13C NMR spectroscopy of the withanolides and other highly oxygenated C28 steroids
Authors: Gottlied Hugo E. , Kirson I. 
Published: May 2005

AbstractThe 13C NMR spectra of 29 highly oxygenated C, steroids with the withanolide skeleton, 24 of which are naturally occurring substances or acetates thereof, were recorded and the carbon signals fully assigned. The shifts of the heavily functionalized A/B ring system can serve as a ‘fingerprint’ for the different substitution patterns. A study of the effects of hydroxyl substitution in the ring D/side chain part of the molecules leads to conformational information, including preferred rotamers around the 17—20 and 20—22 bonds. Systems with both 17α‐ and 17β‐oriented side chains are thus analysed.
Configuration and 13C NMR spectra of 1‐pyrazolines
Authors: Touillaux R. , Tinant B. , Van Meerssche M. , Dereppe J. M. , Leroy G. , Weiler J. 
Published: May 2005

AbstractA comparative study of the 13C spectra of 13 1‐pyrazolines is reported. The results show that the chemical shifts of some carbons are very sensitive to the relative positions of substituents on the 3,4 and 4,5 bonds.
13C NMR spectroscopy of cyclopropane derivatives. 1—monocyclic compounds
Authors: Rol N. C. , Clague A. D. H. 
Published: May 2005

AbstractThe 13C NMR data of an appreciable number of cyclopropane derivatives have been collected. Most of the spectra were recorded by ourselvesand some were taken from the Literature. With a view to furthering the useof 13C NMR spectroscopy as a diagnostic tool in this field, we havemeasured not only the chemical shifts,δ, but also the coupling constants 1J(CH). It is shown that both embody valuable structural information.
Additive NMR chemical shift parameters for deshielded methine protons
Authors: Bell Harold M. , Bowles Deborah B. , Senese Fred 
Published: May 2005

AbstractThe use of additive parameters for the prediction of NMR chemical shifts is widely practised. However, no correlations are available for highly deshielded methine protons. In this work, methine chemical shifts have been studied using both multiple linear regression analysis and Simplex function minimization in an effort to determine under what limiting circumstances the additivity of shift parameters can be expected to apply. As expected, it was not possible to explain satisfactorily all methine shifts with a single set of substituent parameters. However, if only the deshielded cases were considered (H—CXYZ, where at least two of the three groups X, Y, and Z are electron‐withdrawing), a much better set of parameters could be determined. Using a data set of 440 of these deshielded methine shifts, involving 31 different substituents, a standard error of estimate of 0.20 ppm is found for protons spread between 3.0 and 7.5 ppm.
An experimental study of some NMR methods for the measurement of slow exchange rates
Authors: Baine P. , Gerig J. T. , Stock A. D. 
Published: May 2005

AbstractThe rates of interconversion of the cis and trans rotational isomers of N‐trifluoroacetyl‐N‐methylbenzylamine have been determined by a variety of NMR lineshape experiments and by several double resonance methods. Comparison of the results for the slow exchange region suggests that a Fourier transform version of the transfer of saturation method of Forsen and Hoffman, as well as transfer of magnetization after selective 180° inversion of the resonance of one rotamer, give rate constants nearly as reliable as lineshape methods. Use of the rate of signal recovery after saturation of the resonance of one rotamer gave results which were less accurate. The available data produced the following activation parameters for amide rotation in this compound: ΔG‡, 18.9 kcal mol−1; ΔH‡, 22.3 kcal mol−1 and ΔS‡, 9.8 e.u. when the solute was 2 M in 1,1,2,2‐tetrachloroethane‐d2.
1H NMR and 13C NMR spectra of disulfides, thiosulfinates and thiosulfonates
Authors: Freeman Fillmore , Angeletakis Christos N. , Maricich Tom J. 
Published: May 2005

AbstractThe 1H NMR and 13C NMR spectra of neopentyl and benzyl substituted disulfides, thiosulfinates, thiosulfonates, thiols, sulfides, sulfinic acids and sulfonic acids are reported. The deshielding electron withdrawing effects of −SO, −SO2, −SO2−, −SO2H, −SO3−, −SO3H and SO3CH3 on α‐methylene and benzylic protons are observed. The 1H NMR spectra show, except for two dialkylthiosulfinates, that the α'‐protons of thiosulfinates absorb farther downfield than those of the thiosulfonates. Although the 13C NMR spectra show that αSO effects are deshielding and are smaller than the αSO2 effects, the α'SO values are more shielding than the α'SO2 values for some compounds. The effects on 13C NMR spectra which result from substituting a phenyl group for a neopentyl or benzyl group are discussed. The α‐methylene carbon shifts for neopentanesulfinic acid and α‐toluenesulfinic acid are further downfield than those for the corresponding sulfonic acids.
Carbon‐carbon coupling in [3‐13C1]tryptophan
Authors: London R. E. 
Published: May 2005

AbstractCarbon‐carbon coupling constants have been observed in [90% 3‐13C1]tryptophan and used to assign the 13C resonances of the indole ring. The results support a reassignment of C‐5 and C‐6 recently suggested on the basis of the reassigment of the corresponding resonances in indole. Coupling constants are compared with theoretical values obtained using a finite perturbation theory Blizzard‐Santry program, and excellent agreement is obtained for the 1J(CC) values. The calculations predict that the Fermi contact contribution is dominant for all nJ(CC) couplings to C‐3.
Carbon‐13 NMR spectra of some epoxides derived from dicyclopentadiene
Authors: Matoba Yasuhiro , Kagayama Takashi , Ishii Yasutaka , Ogawa Masaya 
Published: May 2005

AbstractThe 13C NMR spectra of a series of epoxides derived from endo‐ and exo‐dicyclopentadiene and their partially hydrogenated compounds were determined to examine the substituent effects arising from the introduction of the oxirane ring in comparison with those found in other ring systems. The 13C signals of some epoxides were assigned by using lanthanide shift reagents. Characteristic substituent effects exerted by an oxirane ring were demonstrated. Marked steric γ‐effects of −8—13 ppm were observed at the bridge carbon signal in the bicyclo[2.2.1]heptane skeleton. Differences were found in the substituent effects between endo‐ and exo‐dicyclopentadiene epoxides, and have been discussed in relation to the molecular geometry.
Substituent effects on carbon‐13 chemical shifts in 2,6‐disubstituted adamantanes
Authors: Majerski Zdenko , Vinković Vladimir , Meić Zlatko 
Published: May 2005

AbstractCarbon‐13 NMR spectral data for a series of symmetrical 2,6‐disubstituted adamantanes (O, CH2, CH3, OH, OCOCH3) are presented. The substituent effects on 13C chemical shifts are additive, except for carbons 2 and 6 in 2,6‐adamantanedione. The non‐additivity of the substituent effect in the diketone can be interpreted in terms of a through‐space interaction of the carbonyl π‐electrons; the additivity in the other derivatives indicates that there is no appreciable interaction between the substituents.
Transmission mechanisms of inter‐proton long‐range couplings in substituted anisoles
Authors: de Kowalewski D. G. , Contreras R. H. , Engelmann A. R. , Facelli J. C. , Durán J. C. 
Published: May 2005

AbstractInter‐proton long‐range and ring couplings were measured in o‐anisaldehyde and in seven disubstituted anisoles. In order to investigate the transmission mechanisms of long‐range couplings with the methoxy group, partially restricted molecular orbital (PRMO) calculations were carried out within the FPT‐INDO method on o‐anisaldehyde. σ‐ and π‐electron, and through‐space transmitted components were separated. For the energetically favoured trans‐OMe conformation a through‐space component was found for the couplings of the methyl protons with the ortho‐proton, and it was found that its sign, as well as its magnitude, depends on their relative positions. If free rotation, however, is assumed for the methyl group, the averaged value for this coupling constant is negative.
Carbon‐13 NMR signals of some natural coumarins and their derivatives
Authors: Patra Amarendra , Mitra Alok K. 
Published: May 2005

AbstractThe 13C NMR spectra of the natural coumarins ostruthin, osthol, aegelinol (enantiomer of decursinol), luvangetin, seselin, anomalin, oxypeucedanin (and its enantiomer prangolarin) and oxypeucedanin hydrate and some of their derivatives have been studied. Self‐consistent resonance assignments have been made following chemical shift theory and using simple models. Carbon‐hydrogen coupling constants of some compounds are also reported. The alkoxy group/s at C‐5 and/or C‐8 in linear furocoumarins, as well as in linear pyranocoumarins, have unusually small shielding effects on the ortho‐ and para‐carbons. This study also indicates that the C‐4a and C‐8 resonance assignments of osthol, made earlier, should be reversed.
Carbon‐13proton coupling constants in N‐substituted imidazoles. A 13C NMR study and MO calculations
Authors: Pachler K. G. R. , Pachter R. , Wessels P. L. 
Published: May 2005

AbstractThe 13C NMR data of imidazole, and N‐methyl‐, N‐acetyl‐, N‐trifluoroacetyl‐, N‐heptafluorobutyryl‐ and 2‐methyl‐imidazoles, were obtained from proton‐noise decoupled and single frequency NOE 13C NMR spectra. The considerable changes in the directly‐bonded (C, H) coupling constants upon N‐acetylation of the imidazole ring, which are comparable to those noted when going from the neutral to the cationic form of imidazole, are primarily due to the large π‐electron transfer ability of the N‐acetyl‐ and N‐trifluoroacetyl‐substituents. The differences in magnitude of the three‐bond (C, H) coupling constants along different paths in the imidazole ring may be attributed to the larger π‐contributions across a pyridine‐like nitrogen than along a pyrrole‐like nitrogen.
Deuterium‐induced 13C nuclear magnetic resonance isotope shifts and 13C2H couplings for signal assignments and determination of deuteration site in cyclooctanone
Authors: Milosavljević Slobodan , Jeremić Dragoslav , Mihailović Mihailo Lj. , Wehrli Felix W. 
Published: May 2005

AbstractUnambiguous signal assignments in the 13C spectra of monodeuterated cyclooctanones derived from the lead tetraacetate or silver oxide/bromine oxidations of the corresponding 1‐monodeutero‐alcohols have been obtained from deuterium‐induced 13C isotope shifts and geminal and vicinal 13C2H spin‐spin coupling constants. The label in the ketones is shown to be in position 5.
17O NMR investigation of p,π‐interactions in α,β‐unsaturated and aromatic ethers
Authors: Kalabin G. A. , Kushnarev D. F. , Valeyev R. B. , Trofimov B. A. , Fedotov M. A. 
Published: May 2005

AbstractThe 17O chemical shifts have been measured for 51 α,β‐unsaturated and aromatic ethers. A good linear relationship is found between the 17O chemical shifts in a series of dialkyl and the corresponding alkyl vinyl ethers. Hence, the extent of p,π‐interaction, between the oxygen atom and the vinyl group in the latter series does not, apparently, depend upon branching at the α‐carbon atom in the alkyl moiety of these ethers. The PhOBut ether, however, as compared to the other alkyl phenyl ethers, shows significantly weakened p,π‐interaction, which is apparently related to the steric hindrance of this interaction. The effects of two unsaturated groups upon the 17O chemical shifts in the corresponding ethers are non‐additive. This is undoubtedly a result of ‘rivalry’ between these groups for conjugation with the lone electron pairs on the ethereal oxygen. The 17O chemical shift ranges of substituted methyl and vinyl phenyl ethers are nearly equal (≈30 ppm). An analysis of the 17O shielding for cyclopropyl ethers shows no observable p,σ‐conjugation in these compounds. Excellent correlation (r>0.99) between the values of 17O chemical shifts and the calculated (MO LCAO SCF, CNDO/2) π‐electron charges on the corresponding oxygen atoms look promising for experimental estimations of π‐electron densities on the ethereal oxygen.
Chemistry of 6H‐pyrido [4, 3‐b] carbazoles. Part 10—Carbon‐13 nuclear magnetic resonance spectra of ellipticines and some model compounds
Authors: Sainsbury M. , Watkins D. , Weerasinghe D. K. 
Published: May 2005

AbstractThe 13C NMR spectrum of ellipticine has been re‐interpreted by reference to model compounds, and correlated with the spectra of a number of new ellipticine derivatives.
The assignment of 13C NMR shift data in clerodanes and related structures
Authors: Luteijn J. M. , Van Veldhuizen A. , De Groot A. 
Published: May 2005

AbstractThe 13C NMR spectra of a number of partial clerodane structures and analogous compounds were recorded. The information thus obtained enabled the assignment of the 13C NMR shifts in a number of naturally occurring clerodanes.
σ‐Correlations and steric effects
Authors: Balasubrahmanyam S. N. , Mallick I. M. 
Published: May 2005

AbstractCarbon‐1 shifts in 1‐dimethylimino‐3‐dimethylamino‐1‐(4‐substituted)phenylprop‐2‐ene perchlorates show high correlation and negative dependence v. a σ set having high f character, similar to α and carbonyl carbon shifts in 4‐substituted styrenes and N,N‐dimethylbezamides, respectively. In sharp contrast with the β‐carbons of the styrenes and the 15N absorptions of benzamides, whose shifts show high positive correlations with specific ratios of f and R characters, the C‐2 shifts remain invariant. In the correlation of the barriers about the N‐CO bond in N,N‐dimethylbenzamides v. f/R, the R effect has been reported to increase dramatically for the meta‐series when values determined in acetonitrile are exchanged with those determined in chloroform and, in the para series, to be higher than (normal) in both solvents. α‐Carbon shifts in tris‐para‐substituted triphenylcarbonium ions correlate with a σ set having exceptionally high R character (c. 98 %). Explanations, based mainly on the likely action of steric factors, are suggested.
Deuterium isotope effects on one‐bond carbon, hydrogen coupling constants
Authors: Everett Jeremy R. 
Published: May 2005

AbstractSmall, negative deuterium isotope effects on 1J(CH) have been found for a variety of simple organic molecules. These new experimental data support theoretical calculations and suggestions based on previous imprecise experimental measurements. The deuterium isotope effects upon the 13C chemical shifts were also measured with high precision.
13C NMR spectroscopy of coumarin derivatives
Authors: Duddeck Helmut , Kaiser Manfred 
Published: May 2005

AbstractThe 13C chemical shifts of 209 naturally occurring and synthetic coumarin derivatives are listed and a number of methods for signal assignments are explained. Substituent effects on 13C chemical shifts (SCS) in monosubstituted coumarins and non‐additivities of SCS in coumarins with more than one substituent are discussed in detail.
Oxazepines and thiazepines. XIII—conformational analysis of 2,3‐dihydrobenzothiazepine derivatives
Authors: Tóth Gábor , Szöllösy Áron , Lévai Albert , Duddeck Helmut 
Published: May 2005

AbstractThe conformation and relative configuration of various condensed heterocycles possessing a 2,3‐dihydro‐1,5‐benzothiazepine moiety and their synthetic intermediates were determined by 1H and 13C NMR spectroscopy. It was found that epimerization takes place during the ring closure reaction.
Conformational preference in thiophene‐2‐carbaldehyde
Authors: Salman Salman R. 
Published: May 2005

AbstractThe 100 MHz 1H NMR spectra of thiophene‐2‐carbaldehyde have been obtained in different solvents and analysed. It was found that the SO‐cis conformation is more stable in all solvents, and that the proportion of the SO‐trans population increases with decreasing polarity of the solvent. CNDO/2 calculations predict that the SO‐cis is more stable than the SO‐trans conformation. The aldehyde coupling to the ring was calculated by the CNDO/2 method and compared with the experimental value.
Comparative NMR study of rhamnobioses—applications
Authors: Dutton G. G. S. , Merrifield E. H. , Laffite C. , Pratviel‐Sosa F. , Wylde R. 
Published: May 2005

Abstract1H and 13C NMR chemical shifts are reported for several rhamnobioses and their acetylated derivatives. The effect of substitution on the rhamnose unit has been determined with respect to the anomeric carbons and linked carbons. These effects have been rationalized and have allowed the assignment of the structure of xanthorhamnin.